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14-Mar-2018 Dear Dr Song: Thank you for sending the revised version of this paper (Incongruent cladistics reveal a new hydrozoan genus (Cnidaria: Sertularellidae) endemic to the eastern and western coasts of the North Pacific Ocean) and for dealing so thoroughly with the referees' comments. I have now had the opportunity to examine your revised manuscript and I am pleased to accept it for publication in Invertebrate Systematics. You will hear in due course from the Production Editor regarding the copyedited manuscript, page proofs, etc. From what I can see, your figure(s) are acceptable in the format you have supplied, but you may be asked for different file formats if needed. Thank you for your excellent contribution. On behalf of the Editors of Invertebrate Systematics, we look forward to your continued contributions to the Journal. Sincerely, Dr Allen Collins Associate Editor, Invertebrate Systematics [email protected]
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Incongruent cladistics reveal a new hydrozoan genus (Cnidaria: Sertularellidae) endemic to the eastern and western coasts of the North Pacific Ocean
Complete List of Authors:
Date Submitted by the Author:
Song, Xikun; Xiamen University, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences; Institute of Oceanology, Chinese Academy of Sciences; University of the Chinese Academy of Sciences Gravili, Cinzia; Universita del Salento; CoNISMa, Consorzio Nazionale Interuniversitario per le Scienze del Mare Bernhard, Ruthensteiner; Zoologische Staatssammlung Munchen Lü, Mingxin; Xiamen University, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences Wang, Jianjun; Third Institute of Oceanography, State Oceanic Administration
Cnidaria, mitochondrial DNA, molecular phyogenetics
Note: The following files were submitted by the author for peer review, but cannot be converted to PDF. You must view these files (e.g. movies) online. Supplementary material 6.nxs Supplementary material 7.nxs
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Incongruent cladistics reveal a new hydrozoan genus (Cnidaria: Sertularellidae)
endemic to the eastern and western coasts of the North Pacific Ocean
Xikun Song A, B, C, H, Cinzia Gravili D, E, Bernhard Ruthensteiner F, Mingxin Lyu
Xiamen University, South Xiang'an Road, Xiamen 361102, China
Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China
University of Chinese Academy of Sciences, Beijing 100049, China
Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, 73100
CoNISMa, Consorzio Nazionale Interuniversitario per le Scienze del Mare, Rome, Italy
Zoologische Staatssammlung München, Münchhausenstr. 21, 81247 München, Germany
Third Institute of Oceanography, State Oceanic Administration, 178 Daxue Road, 361005 Xiamen,
Running title: New hydrozoan genus Xingyurella
State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences,
Corresponding author. Email: [email protected]
; ORCID: 0000-0002-3335-0029
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Table of Contents (TOC) Abstract. Molecular phylogenetics sometimes is inconsistent
with morphological data, notably within the phylum Cnidaria. An integrative approach to a
case of incongruence in hydrozoans results in improved systematics with the designation of
a new genus with divergent origin, endemic to the eastern and western coasts of the North
Pacific Ocean. This suggests that incongruence in molecular and morphological inferences
may be of great systematic significance.
Abstract. Molecular phylogenetics provides objective references for zoological systematics
which sometimes are inconsistent with morphological data. This particularly counts for
some primitive phyla such as Cnidaria. The marine hydrozoan Symplectoscyphus turgidus
(Sertularellidae) is a recent questionable case reported to occupy an unexpected
phylogenetic position and suggested to be assigned to a new genus. However, its position
based on a single Californian specimen seemed doubtful. Here we contributed 16S, 18S and
28S rRNA data of another morphologically related species from the Yellow Sea, forming a
monophyletic clade with the Californian sample, confirming the clade stability. Further
integrative analyses support designating this clade as the new genus Xingyurella gen. nov.,
and lead to a taxonomic revision of species characterized by three hydrothecal marginal
teeth and strong gonothecal spines. This resulted in a new species and three new
combinations: Xingyurella xingyuarum sp. nov., X. gotoi comb. nov., X. pedrensis comb. nov.
and X. turgida comb. nov. Future investigations are required to understand the evolution and
speciation involved in the transoceanic distribution pattern of Xingyurella. The approach
used herein for dealing with non-monophylic conditions may be indicative for further
studies by integrating tropho- and gonosome traits for Sertularellidae and other hydrozoans.
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Additional keywords: Cnidaria, hydroid, lectotype designation, molecular phylogenetics,
new species, taxonomic revision, fine systematics
ZooBank Registration: This article is registered in ZooBank under
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As a substantial component of integrative taxonomy, molecular phylogenetics provides
objective references for systematics of a wide range of biological organisms. However,
inconsistency or incongruence of morphological characters and non-monophyly frequently
challenge traditional taxonomy (Padial et al. 2010; Yeates et al. 2011; Fontaneto et al. 2015;
Sheth and Thaker 2017). This also happens in the early diverging animal phyla such as
Cnidaria, with few stable morphological characters for diagnoses. For example, the family
Sertulariidae Lamouroux, 1812, referring to a traditional taxonomic concept adopted by
Cornelius (1995) and Bouillon et al. (2006), represents very common hydroid forms
attached to hard substrata throughout oceans. Recent molecular data indicate that the family
Sertulariidae Lamouroux is paraphyletic (Moura et al. 2008; Leclère et al. 2009; Peña
Cantero et al. 2010; Maronna et al. 2016; Song et al. 2016b). Several very large genera of
this family were reported to be paraphyletic (Moura et al. 2011; Song et al. 2016a).
Although the family Sertulariidae Lamouroux is a derived group within the Medusozoa
tree (Cartwright and Nawrocki 2010), bearing well-developed chitinous structures
surrounding the trophosome and gonosome of very diversified shape (Bouillon et al. 2006),
its fine systematics is far from fully resolved, partially due to the lack of molecular data and
fine morphological generic diagnoses (Song 2016). Generally, only a few trophosome
characters are selected for generic diagnoses (e.g. Cornelius 1995; Bouillon et al. 2006). For
example, the characters of the number of hydrothecal marginal cusps and operculum valves
could simply distinguish the two largest genera, Sertularella Gary, 1848 (136 species) and
Symplectoscyphus Marktanner-Turneretscher, 1890 (105 species): Sertularella has four
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marginal cusps and four opercular valves, while the number of the latter is three (Cornelius
1995; Bouillon et al. 2006). It seems odd that the gonosome characters are rarely used,
except for the character "with gonotheca origin from within the hydrothecal cavity" listed by
Song et al. (2016b). Maronna et al. (2016) proposed a new concept by raising the family Sertulariidae
Lamouroux to a new suborder Sertulariida and raised its four monophyletic clades as new
families: Staurothecidae, Symplectoscyphidae, Sertularellidae, and Sertulariidae sensu
stricto Maronna et al. 2016. This further increases the requirements for diagnostic characters
for the newly proposed families (Song 2016). In the new system proposed by Maronna et al.
(2016), and adopted by the present study, Sertularella plus a single Symplectoscyphus
species, Symplectoscyphus turgidus (Trask, 1857) (as Xingyurella turgida comb. nov. in this
study) were restricted to the new family Sertularellidae.
Obviously, the phylogenetic position of Symplectoscyphus turgidus is peculiar and
seems to be inconsistent with morphological data. Symplectoscyphus turgidus has three
hydrothecal marginal teeth and three opercular valves just like other species of the genera
Antarctoscyphus Peña Cantero, García Carrascosa and Vervoort, 1997 and Symplectoscyphus,
which were assigned to Symplectoscyphidae Maronna et al., 2016. However, it clusters with
the genus Sertularella instead of any genera of the Symplectoscyphidae (Leclère et al. 2009;
Moura et al. 2011; Maronna et al. 2016; Song et al. 2016b). Moura et al. (2011) thought that
S. turgidus should be moved to the genus Sertularella or even perhaps to a new genus.
Nevertheless, Maronna et al. (2016) and Song et al. (2016b) still provisionally treated S.
turgidus as a questionable taxon, because the peculiar position was only based on a single
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sequenced Californian specimen of one species. Maronna et al. (2016) addressed the need of
additional data of further samples to clarify the position of S. turgidus. In the present study, we contributed new 16S, 18S and 28S rRNA data of a species
morphologically related to Symplectoscyphus turgidus from the Yellow Sea. This turns out to
form a monophyletic clade with Symplectoscyphus turgidus. This confirms the stability of
this "unexpected" phylogenetic position. A further integrative review and additional analyses
provide persuasive evidence to propose this clade with peculiar morphological and
molecular traits as a new genus Xingyurella gen. nov., describe a new species Xingyurella
xingyuarum sp. nov., and make three new taxonomic combinations. Related type material
was examined if available. In addition, some species representing potential candidates for
intermediate morphological condition between Sertularella and Xingyurella are discussed.
Material and methods
The specimens investigated were mainly collected during the First Chinese National
Comprehensive Oceanographic Survey (1958–1960) and recent Shared Research Cruises on
Yellow Sea & East China Sea supported by the National Natural Science Foundation of
China (NSFC, 2010–2013). These specimens were mainly stored in the Marine Biological
Museum of Chinese Academy of Sciences, Institute of Oceanology, CAS (used with
registration prefix MBM). Type material of Sertularella gotoi Stechow, 1913 (as Xingyurella
gotoi comb. nov. in this study) deposited in the Zoologische Staatssammlung München
(ZSM) was re-examined. Some related Californian and Oregon material deposited in the
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Muséum d'histoire naturelle de la Ville de Genève (MHNG) or the Department of
Invertebrate Zoology and Geology, California Academy of Sciences (CASIZ) was examined
with the assistance of P. Schuchert and Z. Mora Vallín, respectively. See full collecting
details in Supplementary material 1.
Morphological and molecular analyses
In general, morphological and molecular data were obtained and analyzed as given by Song
et al. (2016b). The origin of some morphological data is given in the “Integrative analyses
and review” (see below). The amplification and molecular cloning of the partial sequences
of the 16S rRNA, 18S rRNA, 28S rRNA and COI genes were conducted for all recent
ethanol material of Xingyurella xingyuarum sp. nov. using the primers summarized by Song
et al. (2016b), but only picked up nine 16S rRNA clones (631 bp) and two COI clones (899
MF135580–MF135582, MF491516–MF491518) from three specimens and two COI
haplotypes (MF135583–MF135584) from one specimen (Table 2, Supplementary material
Nearly the full length of the 18S and 28S rRNA genes (Genbank accession numbers:
MG763076–MG763080) could be successfully obtained using new primers designed in the
present study (Table 1). This design was inspired by the molecular examination of some
Mollusks (Giribet et al. 2006) amplifying shorter overlapping fragments (530–970 bp) than
used with the previous primer pairs (Song et al. 2016b) which result in longer fragments
(about 1800 bp). The new primers were picked up within the conservative regions with
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reference to published primers (Hillis and Dixon 1991; Giribet et al. 2006; Leclère et al.
2009; Song et al. 2016b). These primers were successfully tested in several species of
Leptothecata (Sertulariidae and Campanulariidae) and Anthoathecata (Tubulariidae)
collected 3–7 years ago and fixed in 70%–100% ethanol. The expected length of the 18S and
28S rRNA after assembling is about 1700 bp and 3400 bp, respectively. These new primers
(Table 1) may be used as alternative primers for some difficult museum-deposited
hydrozoan specimens possibly due to the partial degradation of genomic DNA.
The intra- and inter-species genetic distance (Table 2, 3) of Xingyurella was calculated.
Maximum-likelihood phylogenetic and Bayesian analyses were conducted for the 16S rRNA
dataset (Fig. 1, Supplementary material 2, 6) as well as for the concatenated dataset of the
16S, 18S and 28S rRNA genes (Fig. 2, Supplementary material 2, 7). Some published
hydrozoan 16S, 18S and 28S rRNA sequences (Govindarajan et al. 2006; Cartwright et al.
2008; Moura et al. 2008, 2011; Leclère et al. 2009; Maronna et al. 2016; Peña Cantero et al.
2010; Song et al. 2016b) and some directly submitted sequences by C. W. Cunningham and
P. Schuchert were obtained from GenBank to conduct phylogenetic analyses
(Supplementary material 2). All published 16S rRNA sequences of the genus Sertularella
and type species or species that emerged on representative clades of related trees (Leclère et
al. 2009; Peña Cantero et al. 2010; Moura et al. 2011; Maronna et al. 2016) were selected
for the 16S rRNA tree (Fig. 1).
In some preliminary phylogenetic analyses (not shown), all the 16S haplotypes of
Xingyurella xingyuarum clustered together, so only three genetic divergent haplotypes from
the paratype MBM280254 were shown in the final 16S tree (Fig. 1) to compress its length.
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The COI sequences were not selected for phylogenetic analyses because only few relevant
reference sequences were available from GenBank. Clytia hemisphaerica (Linnaeus, 1767)
was chosen as outgroup for both trees (Figs 1, 2). TIM2+I+G and GTR+I+G (Akaike
information criterion) were chosen as the optimal probabilistic evolution model for the 16S
tree (Fig. 1) and concatenated 16S+18S+28S tree (Fig. 2), respectively.
Integrative analyses and review
Before the integrative analyses, the accuracy of the molecular data of Xingyurella turgida and
X. xingyuarum and their phylogenetic positions were evaluated by the topology of the present
trees (Figs 1, 2) as well as other trees (Leclère et al. 2009; Moura et al. 2011; Maronna et al.
2016; Song 2016; Song et al. 2016b).
With the guidelines of molecular data, integrative analyses were conducted to track some
potential morphological diagnoses to distinguish the main molecular clades in Figure 1 and
Figure 2. At first, the hydrothecae and gonothecae of the samples identified to species rank
were redrawn and visualized directly on the phylogenetic tree (Figs 1, 2). Then the
gonothecae of 25 species selected were redrawn and shown separately for further
morphological examination (Fig. 3). Most line drawings were based on specimens or original
data of the authors (Gravili et al. 2015; Song 2016; Song et al. 2016a, 2016b), some were
with reference to published data, but modified or simplified to present the interested
morphological structure. Additionally, 23 morphological characters of 23 related species of
the family Sertulariidae Lamouroux and Thyroscyphidae Stechow, 1920 were extracted from
published literature for comparative analyses (Supplementary material 3). For the above
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species selected (Figs 1–3, Supplementary material 3), some related species examined by the
authors were given priority. Some other species without molecular data but with typical or
divergent morphological characters of the colony or gonotheca were also included, e.g.
Calamphora parvula Allman, 1888, Sertularella inabai Stechow, 1913, S. mirabilis
Jäderholm, 1896, and S. spirifera Stechow, 1931 (Fig. 3, Supplementary material 3). Detailed
data resources are listed in related figure legends and Supplementary material 3. Finally, a literature survey and review of the original descriptions and illustrations of
nominal species of the family Sertulariidae Lamouroux listed by Bouillon et al. (2006) and
Schuchert (2015) were conducted to detect other potential Xingyurella species, according to
the potential diagnoses of the Xingyurella clade extracted in the present study. Related type
material or specimens from type localities were examined if available.
Lectotype and neotype designations
To provide an objective standard of reference for the identity, a neotype was designated for
Sertularia turgida Trask, 1857 (as Xingyurella turgida in this study) deposited in MHNG,
lectotypes were designated in syntype material in the ZSM for Sertularella gotoi (as
Xingyurella gotoi in this study).
It is doubted that any type material was designated for Sertularia turgida in 1857 (D.
Calder, pers. comm.). According to Stearns (1908), Trask served in the California Academy of
Sciences as one of the eight illustrious founders. Stearns (1908) listed all species nominated
by Trask (including Sertularia turgida) but did not mention any information on type material.
Also, no type material of this species could be found in CASIZ where it should most likely
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have been located (C. Piotrowski, pers. comm.). So, we designated the only published
material (MHNG-INVE-29467) with molecular data (Leclère et al. 2009) as a neotype of S.
turgida. This fertile material was collected from Los Angeles, California, not far from its type
locality San Francisco, California (Supplementary material 1). Its morphology (Figs 4H–L) is
consistent with the original description by Trask (1857).
The largest fertile colony of Sertularella gotoi now deposited in ethanol was selected
(ZSM20050746–ZSM20050752) were selected as paralectotypes. The details of the
specimens are provided in the Systematic account and Supplementary material 2.
Genetic distance. The genetic distance of partial sequences of the 16S, 18S and 28S rRNA
genes of two species of Xingyurella is listed in Table 2 and Table 3. The genetic distance of
X. xingyuarum and X. turgida is 0.014–0.016 (16S), 0.052–0.053 (18S), 0.090 (28S),
respectively. It is much higher than the genetic distance of different haplotypes of X.
xingyuarum (16S, 0.002–0.003, 18S, 0.001). The distance of two clones of partial sequences
of the COI gene (899 bp) of X. xingyuarum is 0.003.
Evaluation of sequence accuracy of Xingyurella. Although only six 16S haplotypes were
obtained in three specimens of X. xingyuarum, sequence polymorphism, haplotype replicates
and shared haplotypes between specimens were detected (Table 2). Firstly, two and four
different 16S haplotypes were picked up in the specimens MBM280232 and MBM280254,
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respectively. This reveals that slight sequence polymorphism exists in the single hydroid
fragment that was used for molecular analyses (sequence distance 0.002–0.003, Table 2).
Secondly, haplotype replicates were picked up in the above two specimens. Thirdly,
although these two specimens were collected in different years, one in November 20th, 2010,
the other in November 5th, 2011, with a geographic distance up to about 400 km, they shared
the same haplotype MF135580 (Table 2, Supplementary material 2). The 18S and 28S rRNA
data also reveal similar results (Table 3, Supplementary material 2). All these provide solid
evidence of the sequence accuracy of the molecular data of X. xingyuarum obtained by the
molecular clone method.
The sequences of Xingyurella turgida and X. xingyuarum form the same monophyletic
clade on both ML and Bayesian analyses (Figs 1, 2). This further increases confidence in the
accuracy of the 16S, 18S and 28S sequences of both species that originated from both
Eastern and Western coasts of the North Pacific Ocean. It rules out the possibilities of DNA
contamination, e.g., by other Sertularella species, during molecular experiments. The COI
sequences of X. xingyuarum were not selected for phylogenetic analyses because only a few
relevant reference sequences were available from GenBank. Nevertheless, their accuracy can
be inferred based on their position in the unpublished COI tree with limited taxa constructed
by Song (2016).
Main molecular clades. The Bayesian analysis of the 16S rRNA results is almost the same
topology as the ML tree, only several sequences emerge in slightly different positions (Fig.
1), whereas the topology of the different analyses for the concatenated 16S+18S+28S tree is
exactly the same (Fig. 2). The present trees concur with the new classification proposed by
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Maronna et al. (2016). The clades on the concatenated tree are similar with the 16S tree,
except for the absence of some taxa. So only the related clades on the 16S rRNA tree were
used and analyzed in the following. Even only with 16S rRNA sequences of 14 identified Sertularella and Xingyurella
species, the paraphyletic clades of the Sertularellidae could be manually divided into six
sub-clades annotated as C1 to C6 (Fig. 1). These clades are also presented on the
concatenated tree except clade C3 (Fig. 2). The first clade, C1 includes Sertularella
mediterranea Hartlaub, 1901, S. ornata Broch, 1933, S. polyzonias (Linnaeus, 1758) (type
species of Sertularella), S. ellisii (Deshayes & Milne Edwards, 1836), S. africana Stechow,
1919 and several unidentified sequences. Then Clade 4 to Clade 6 cover several other
Sertularella species, including Sertularella gayi (Lamouroux, 1821), S. robusta Coughtrey,
1876 (C4), S. sanmatiasensis EI Beshbeeshy, 2011, S. rugosa (Linnaeus, 1758) (C5) and S.
diaphana (Allman, 1885) (C6).
The Xingyurella clade (Fig. 1: C2) clusters together with Sertularella simplex (Hutton,
1873) (C3), but not with clades of the genera Antarctoscyphus, Fraseroscyphus Boero &
Bouillon, 1993 and Symplectoscyphus which also have three hydrothecal cusps and three
opercular valves. On the 16S tree, the non-parametric bootstrapping of ML analysis and
posterior probability of Bayesian analysis of this clade (C2 + C3) are 73 and 0.98,
respectively (Fig. 1). On the concatenated tree, the ML and Bayesian values are 95 and 1
(Fig. 2), respectively. Both trees show relatively high stability of the Xingyurella clade. This
result is generally consistent with other trees of different data sets containing Xingyurella
turgida (as Symplectoscyphus turgidus, Leclère et al. 2009; Moura et al. 2011; Maronna et al.
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2016; Song 2016; Song et al. 2016b). This suggests that Xingyurella turgida should not be
treated as a questionable taxon and overlooked only due to its “peculiar” position. It seems
appropriate to test these findings from molecular phylogenetics by integrating morphological
Integrative analyses and review
Species with molecular data. It is striking that all species of the Sertularellidae and
Thyroscyphidae clades with hydrothecae bear four marginal teeth and four opercular valves
except for the Xingyurella clade (Fig. 1: C2). Although the Xingyurella clade and the
Symplectoscyphidae clade occupy distant phylogenetic positions, they share the same
hydrothecal characters with three marginal teeth and three opercular valves (Fig. 1).
The gonothecal structures of the Sertularellidae clades are relatively complex. They
could be manually divided into three morphological types. The first type (Fig. 1: C1, C3, C4,
C5), including the type species of Sertularella, S. polyzonias, shares the following characters:
surface with transverse grooves, without spines, with several apical cusps (Figs 1–2,
Supplementary material 3). The Xingyurella clade (Fig. 1: C2) represents the second type:
with surface spines, and several apical cusps (Figs 1, 2H, 3, 6 and Supplementary material 3).
It is different from the genera of Symplectoscyphidae that do not have any gonothecal spines
(Figs 3X–Z). The female gonotheca of Staurotheca antarctica Hartlaub, 1904 also has
similar surface spines, but is distinguished from Xingyurella by two basal digitiform
projections (Fig. 3AB). Sertularella diaphana (Fig. 1: C6) represent the third type, with
several longitudinal ridges and a gonothecal operculum composed of two equal valves,
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without neck and apical cusps (Fig. 3N). The gonotheca of the Thyroscyphidae clade is
completely different from the above three types: surface smooth, without gonothecal neck or
apical cusps (Fig. 3W, Supplementary material 3). The different morphological types of gonothecae described above are generally in
accordance with different molecular clades. This indicates that the morphology of
gonothecae is valuable for the systematics of Sertularellidae.
Typical species without molecular data. The gonothecae of some other Sertularella species
without molecular data are much more typical and diversified. Six species of them should be
noticed (Fig. 3): Sertularella acutidentata Billard, 1919 and S. quadridens (Bale, 1884) are
similar with S. diaphana, but have different numbers of apical cusps and gonothecal
opercular valves (Figs 3O, T); Sertularella albida Kirchenpauer, 1884 and S. mirabilis do
not have apical cusps (Figs 3P, S); Sertularella inabai is similar with Xingyurella, but have
several longitudinal ribs (Figs 3Q–R); Sertularella spirifera has several spines around the
gonothecal neck, but does not have apical cusps (Fig. 3U).
Integrative analyses for taxonomic diagnoses. Further comparative analyses of 23
morphological characters of 23 related species of the family Sertulariidae Lamouroux and
Thyroscyphidae are listed in Supplementary material 3. Some family or generic diagnoses
could be easily extracted, e.g. Thyroscyphidae is characteristic of pedicellate hydrothecae
(Supplementary material 3: column D1), Calamphora parvula has unique stolonal colonies
(A1), Sertularella mirabilis forms net-like colonies (A2).
Moreover, the gonothecal characters listed in the Supplementary material 3 seem to be
relatively stable and permit the recognition of some main clades in Sertularellidae (see
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above). This does not yet count for the presence or absence of the gonothecal acrocyst
(Supplementary material 3: column E8) because little acrocyst data are available at present.
Some hydrothecal characters, such as hydrothecal arrangement pattern on hydrocladium
(D2), hydrotheca free or partially adnate (D3), hydrothecal surface smooth or with grooves
(D4), and the numbers of hydrothecal internal teeth (D7), also contribute little valuable
information for generic diagnoses. The characters related to branching pattern, e.g.
hydrocladium with or without branching apophysis (C2), with or without the axillary
hydrotheca (C3), with or without repeated dichotomously branchlets (C4) might be useful
for diagnoses at genera or species level. However, it is difficult to judge their taxonomic
values at present because they were usually ignored by earlier taxonomists.
Proposal for the new genus. The systematics of the Sertularellidae becomes much more
complicated if species without molecular sequences are included. Nevertheless, Xingyurella
is the most reasonable and persuasive monophyletic clade to be proposed as a new genus at
least according to its unique hydrothecal and gonothecal characters. These characters include
hydrothecae with three marginal teeth and three opercular valves, as well as gonothecal
surface with strong spines.
Integrative review and revision. A subsequent review of the nominal species of the family
Sertulariidae Lamouroux supports the assignment of Sertularella gotoi and Sertularella
pedrensis Torrey, 1904 to Xingyurella according to similar morphological characters. All
these lead us to propose three new taxonomic combinations including Xingyurella gotoi, X.
pedrensis and X. turgida, and a new species Xingyurella xingyuarum sp. nov. See detailed
descriptions and diagnoses in the Systematic account.
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Systematics Class Hydrozoa Owen, 1843
Subclass Hydroidolina Collins, 2000
Superorder Leptothecata Cornelius, 1992
Order Macrocolonia Leclère, Schuchert, Cruaud, Couloux & Manuel, 2009
Suborder Sertulariida Maronna, Miranda, Peña Cantero, Barbeitos & Marques, 2016
Family Sertularellidae Maronna, Miranda, Peña Cantero, Barbeitos & Marques, 2016
Genus Xingyurella gen. nov.
Etymology. xingyu is derived from two Chinese characters in the given names of the first
author’s wife “xing” and daughter “yu”, meaning "meteor shower" in Chinese. Its gender is
Type species. Xingyurella xingyuarum sp. nov.
Diagnosis. Colony with or without distinct hydrocauli. When hydrocauli branched, with
axillary hydrotheca, the axillary apophysis absent; the basal internode of each branchlet is
discernibly longer than other internodes, sometimes with a pedicle at the base. Hydrocauli
and hydrocladia with regular and oblique internodes, each internode bearing a hydrotheca.
Hydrothecae alternately arranged in two longitudinal rows in one plane; hydrotheca tubular,
partly adnate, smooth or with grooves, with three marginal cusps, one adcauline and two
lateral abcauline, and three opercular valves forming a pyramid, with or without internal
tooth; retracted hydranth with abcauline caecum. Gonotheca ovate, growing directly from
hydrocaulus or hydrocladium, pedicellate, with strong spines partly or entirely covering the
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Remarks. When branched, the absence of an axillary apophysis is characteristic in
Xingyurella. Generally, an axillary apophysis is present in the genera Antarctoscyphus and
Symplectoscyphus (Song et al. 2016b). The basal internode of the hydrocladium in
Xingyurella is distinctly longer and thinner than other internodes growing towards the distal
end. Sometimes a basal pedicle is present on this internode. This kind of pedicle is observed
in X. turgida (Fig. 4E) where the hydrocladium arises. The pedicle in Xingyurella is fairly
similar but still differs from the axillary apophysis in the genera Antarctoscyphus and
Symplectoscyphus, which belongs to one of the two extended processes of the hydrocaulus.
Gonothecal spines also exist in some other genera of the family Sertulariidae
Lamouroux, but they are mostly located in different positions or arranged in different
patterns. Some species of the genus Sertularia (including the type species, Sertularia
argentea Linnaeus, 1758) have only several apical spines or horns. Some species of the
genus Diphasia L. Agassiz, 1862, Staurotheca Allman, 1888 (Figs 3AA–AB) and
Tamarisca Kudelin, 1914, also have a lot of spines like Xingyurella, but they are arranged
and positioned in different arrays, with the exception of Diphasia digitalis Busk, 1852.
Diphasia digitalis also has spines throughout the gonothecal surface, but it does not have
apical cusps (Nutting 1904; Song 2016). Molecular data suggest that Diphasia, Sertularia
and Staurotheca occupy different phylogentic positions remote to Xingyurella (Figs 1, 2).
The position of Tamarisca is still unknown; nevertheless, it seems to have little
morphological affinity with Xingyurella.
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A key (see below) and a comparative table (Table 5) for the morphology of Xingyurella
and the doubtful species Sertularella nodulosa Calkins, 1899 are given in the present study.
See discussion of S. nodulosa in the Remarks of X. turgida.
Key to species of Xingyurella and the doubtful species Sertularella nodulosa
1 Matured gonotheca with spines only on the upper part of the surface ................................ 2
– Matured gonotheca with spines throughout the surface ...................................................... 3
2 Hydrotheca turgid, hydrocaulus not branched, if rarely abnormally branched, without an
axillary hydrotheca .................................................................................................... X. turgida
– Hydrotheca not turgid, hydrocaulus branched, an axillary hydrotheca present at the
branching place..................................................................................... Sertularella nodulosa
3 Hydrotheca much more tapering towards the distal end, surface almost smooth, with
hydrothecal internal teeth ..............................................................................................X. gotoi
– Hydrotheca slightly tapering towards the distal end, surface with obvious transverse
grooves, without internal teeth ............................................................................................... 4
4 Colony stout, hydrocaulus not branched or rarely branched, hydrotheca 1/3–1/2 adnate,
grooves only located on the middle part of hydrothecal surface ........................... X. pedrensis
– Colony slender, hydrocaulus always branched, branches with repeatedly dichotomous
ramifications, hydrotheca almost free, strong grooves throughout the hydrothecal surface .. X.
Xingyurella turgida (Trask, 1857) comb. nov.
(Figs 4, 8)
Sertularia turgida Trask, 1857: 113, pl. 4, fig. 1.
Sertularella turgida – Clark, 1877: 259–260, pl. 38, figs 4–5; Hartlaub, 1901a: 360, pl. 21,
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figs 5–6; Hartlaub, 1901b: 67, pl. 2, fig. 30, pl. 3, figs 21–22; Torrey, 1902: 64–65, pl. 7,
figs 59–62, pl. 8, figs 63–69; Nutting, 1904: 95, pl. 22, figs 2–5.
Symplectoscyphus turgidus – Stechow, 1923b: 173.
Not Sertularella turgida – Calkins, 1899: 359–360, pl.4, figs 22, 22A–B [ = Sertularella
conica Allman, 1877]; 360–361, pl.5, figs 29, 29A [ = Sertularella nodulosa Calkins,
? Sertularella turgida – Fraser, 1911: 71; 1914: 193; 1935: 145; 1936: 126; 1937: 160, pl. 36, figs 192a–b; Stechow, 1913b: 133, fig. 105.
? Diphasia sp. – Inaba, 1890: 296, figs 32–33.
? Symplectoscyphus turgidus – Stechow, 1923c: 12; Yamada, 1959: 58; Hirohito, 1983: 56,
fig. 26; 1995: 225–228, figs 77a–c; Park, 1998: 63, fig.3.
Type locality. Bay of San Francisco, Monterey, Tomales Point, attached on mollusca and algae (Trask 1857).
Type material. The type material of this species could not be found in the invertebrate
collections of the Department of Invertebrate Zoology and Geology, California Academy of
Neotype. MHNG-INVE-29467 (Figs 4H–L), with 16S, 18S and 28S rRNA data (Leclère et
al. 2009; Supplementary material 2). See collecting information in Supplementary material 1
and measurements in Table 4.
Description. Trophosome. Colony erect, unbranched (Figs 4A–C) or rarely branched (Fig.
4E, I); rare abnormal branchlets only emerging on the upper part of hydrocauli, without the
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axillary hydrotheca and the axillary apophysis; the basal internode of every branchlet with a
relatively long pedicle (Fig. 4E). With regular and oblique internodes, contracted at both
ends of each internode; each internode bearing a hydrotheca. Hydrothecae arranging tightly,
alternately in two longitudinal rows in one plane; hydrotheca turgid, half of the adcauline
part adnate, becoming shrunk and narrow towards the distal end (Figs 4E, J), margin with
three cusps, one adcauline and two lateral abcauline, three intrathecal teeth observed (Figs
4J–K); operculum composed of three valves forming a pyramid, retracted hydranth with
poorly developed abcauline caecum (Fig. 4J).
Gonosome. Gonotheca ovate, pedicellate, growing directly from lower part of
hydrocaulus (Figs 4H–I). The upper part of the gonothecal surface with upward strong
spines, the lower part with transverse grooves (Figs 4D, F–G, L).
Distribution. Coast of California, USA (Fig. 8), shallow waters no more than 30 m deep.
Remarks. Hartlaub (1901b) treated Sertularella conica Allman, 1877 and Sertularella
nodulosa as synonyms of X. turgida (as Sertularella turgida), which was accepted by Torrey
(1902), Nutting (1904) and Hirohito (1995). However, after a review of the original
descriptions of S. conica and S. nodulosa, we find that they are different species than X.
turgida. Nutting (1904) mentioned that Sertularella conica has four marginal cusps. This
means that it belongs to the genus Sertularella, but it differs from X. turgida. The other
nominal species, S. nodulosa exhibits characters of hydrotheca (with three marginal cusps)
and gonotheca (with strong spines) that are typical for the newly proposed genus Xingyurella.
This suggests that S. nodulosa may be an additional species that could be moved to
Xingyurella. Sertularella nodulosa is different from X. turgida by its well-developed
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branching pattern (with secondary branchlets and an axillary hydrotheca present, Table 5). It
is also different from other Xingyurella species (X. gotoi, X. pedrensis and X. xingyuarum)
by the coverage rate of gonothecal spines (Table 5). Its gonothecal spines only cover the
distal half of the gonothecal surface (Calkins 1899), while the spines of the above three
Xingyurella species cover the entire gonothecal surface (Table 5). Diphasia sp. recorded by Inaba (1890) from Japan is very similar to X. turgida
according to the illustrations. It shares the same simple branching pattern, the same coverage
rate of spines on gonothecal surface, and the same number and arrangement pattern of
hydrotheca internal teeth (Table 5). Three main differences could be found from the
illustration Figure 33 (Inaba 1890: 296): the hydrotheca is much longer, its surface is smooth,
and it does not suddenly shrink towards the distal end (Table 5).
The records of Symplectoscyphus turgidus by Hirohito (1983, 1995) from Sagami Bay
and Park (1998) from Jeju Island are doubtful. These records represent a morphological type
that differs from X. turgida, X. gotoi and X. xingyuarum. The latter species are simply
branched, similar to X. turgida. However, the hydrotheca is much narrower and longer, its
surface is smooth, and the spines are covering the entire gonothecal surface (Hirohito 1983,
1995; Park 1998). Hirohito (1983, 1995) noticed the morphological differences of X. turgida
(as Symplectoscyphus turgidus) and X. gotoi (as Sertularella gotoi), but he still treated
Sertularella gotoi as a synonym of Symplectoscyphus turgidus. He mentioned that both
nominal species may be very variable in the morphological characters of hydrotheca and
gonotheca, but he thought the differences of these characters had no importance for
identification (Hirohito 1995). He mentioned that he found intermediate forms in the
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developmental degree of spines of gonothecae in the Sagami Bay samples of S. turgidus
(Hirohito 1983), but he did not clearly describe in the text or draw convincing illustrations
showing the intermediate gonothecal form that are typical in the Californian records of X.
turgida. In his illustrations, spines are completely absent (Hirohito 1988: Fig. 26a) or
entirely covering the gonothecal surface (Hirohito 1988: Figs 26b–f; 1995: Figs 77a, c). The
samples of Hirohito (1983, 1995) were collected from water depths ranging from 4 m to 150
m. It seems possible that the material he attributed to S. turgidus included several species
and, therefore, should be re-examined.
Xingyurella pedrensis (Torrey, 1904) comb. nov.
(Figs 5, 8)
Sertularella conica – Torrey, 1902:60.
Setularella pedrensis Torrey, 1904: 27, figs 19–21.
Not Setularella pedrensis – Park & Rho, 1986: 17–18, figs 4e–g, pl.1, fig. f [ =Xingyurella xingyuarum sp. nov.].
Type locality. San Pedro, Los Angeles, California, USA.
Type material. USNM43716, 110 m, 1901.VIII.01, Torrey H.B., not examined in the present
Specimens examined. CASIZ material, see collecting information in Supplementary material
1 and measurements in Table 4.
Description. Trophosome. Colony erect, hydrocaulus unbranched or rarely branched, if
branched, with an axillary hydrotheca, without axillary apophysis, the basal internode of
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each branchlet is longer than other internodes, without pedicle at the base (Fig. 5E).
Hydrocaulus and hydrocladium with regular and oblique internodes, slightly contracted at
both ends of each internode; each internode bearing a hydrotheca. Hydrothecae arranging
alternately in two longitudinal rows in one plane; hydrotheca tubular, the upper part with
three to four transverse grooves which are stronger on the adcauline side (Figs 5D, F), half
of the adcauline part adnate, becoming narrow towards the distal end, margin with three
cusps, one adcauline and two lateral abcauline, no intrathecal teeth observed; operculum
composed of three valves forming a pyramid, retracted hydranth with poorly developed
abcauline caecum (Fig. 5F).
Gonosome. Gonotheca absent in examined material. A gonotheca (Fig. 3H) was
redrawn with reference to Torrey (1904).
Distribution. Coasts of California (Torrey 1902, 1904) and Oregon, USA (Fig. 8), water
depth 77–110 m.
Remarks. Torrey (1902) overlooked the gonotheca material, mentioned “the gonosome still
remains unknown”, and then he discovered two gonothecae in the same San Pedro colonies
(Torrey 1904). According to the online registration platform hosted by NMNH (National
Museum of Natural History, USA), the registered information of the type material of
Sertularella pedrensis was consistent with Torrey (1902, 1904). Although we have not
re-exanimated the type material, the original descriptions and illustrations of hydrotheca and
gonotheca by Torrey (1902, 1904) are sufficient to assign this species to the genus
For the CASIZ specimens examined in this study, the morphological characters of
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branching patterns and hydrotheca, as well as the collecting locality and water depth are
consistent with the original description of Sertularella pedrensis. Even without available
gonotheca material, it differs from Antarctoscyphus and Symplectoscyphus species by the
presence of a basal internode of the branchlet that is much longer than other internodes, as
well as the absence of an axillary apophysis (Fig. 5E). Similar structures are also present in
Xingyurella xingyuarum (Fig. 7B).
Xingyurella gotoi (Stechow, 1913) comb. nov.
(Figs 6, 8)
Sertularella gotoi Stechow, 1913a: 142; 1913b: 132, fig. 104.
Symplectoscyphus gotoi – Stechow, 1923c, 12; Yamada, 1959: 59.
? Sertularella turgida – Nutting, 1904: 95, pl. 22, figs 2–5.
Type locality. Sagami Bay, Japan.
Lectotype. ZSM20040227, the largest fertile colony in type material (Fig. 6A). Paralectotype,
ZSM20050746–20050752 (Figs 6B–G). See collecting information in Supplementary
material 1 and measurements in Table 4.
Description. Trophosome. Colonies arising from irregular stolons creeping on the
hydrocaulus of another hydroid species (Fig. 6A), hydrocaulus rarely branched at the angle
of 60–100°, with an axillary hydrotheca, without axillary apophysis, the basal internode of
each branchlet is longer than other internodes, without a pedicle at the base (Figs 6B–C),
secondary hydrocladium not observed. Hydrocaulus and hydrocladium with regular and
oblique internodes, contracted at both ends of each internode; each internode bearing a
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hydrotheca. Hydrothecae sparsely arranged (Figs 6B–E), alternately in two longitudinal
rows forming one plane; hydrotheca tubular, surface almost smooth, one to two fine
transverse grooves observed in the adcauline side of several hydrothecae (Fig. 6E); a third of
the adcauline part adnate, becoming narrow towards the distal end (Figs 6E–F), margin with
three cusps, one adcauline and two lateral abcauline, two intrathecal teeth observed in
several hydrothecae (Figs 6E–F); operculum composed of three valves, retracted hydranth
with poorly developed abcauline caecum (Fig. 6F).
Gonosome. Gonotheca oval, pedicellate, growing directly from lower part of
hydrocaulus, gonothecal surface with upward strong spines throughout (Figs 6A, C–D, G),
Distribution. Sagami Bay, Japan (Fig. 8), water depth 600 m.
Remarks. Xingyurella gotoi is the only known species of the genus Xingyurella recorded in
the deep-sea (600 m). It resembles X. pedrensis and X. xingyuarum, which are distributed in
relatively shallow (no more than a hundred meters) and cold coast waters. In its original
description, Stechow (1913a, 1913b) mentioned that it is very similar to X. pedrensis (as
Sertularella pedrensis), but distinguishes these two species by three characters, including the
difference of grooves (girdling racks, strong or weak) on the hydrothecal surface, the
branching pattern and the length of the gonothecal spines. Xingyurella xingyuarum bears the
characteristic feature of strong transverse grooves distributed almost throughout the
hydrothecal surface. These grooves are stronger than in any other known species of the
genus. Moreover, no hydrothecal internal teeth were observed in X. xingyuarum, while there
are two internal teeth in some hydrothecae of X. gotoi (Figs 6E–F, Table 5).
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Xingyurella xingyuarum sp. nov.
Setularella pedrensis – Park & Rho, 1986: 17–18, figs 4e–g, pl.1, fig. f.
Sertularella gotoi – Rho & Chang, 1974: 142: pl.5, figs 3–5; Rho, 1977: 269, pl. 85, fig. 83;
Park & Rho, 1986:17; Park, 1990: 80; 1992: 291; 1995:14; 2010: 92–94, fig. 50. Etymology. The same as the genus name.
Type locality. Yellow Sea.
Specimens examined. See details in Supplementary material 1.
Type material. Holotype, MBM000479. Paratype, MBM280254 (with 16S, 18S and 28S
rRNA data, Supplementary material 2), MBM280259 (with COI, 18S and 28S rRNA data,
Supplementary material 2), MBM000482, MBM000483, MBM000453, MBM000484. See
collecting information in Supplementary material 1 and measurements in Table 4.
Description. Trophosome. Colonies yellowish-brown, slender, with one or several
hydrocauli, hydrocaulus zigzag-shaped, hydrocladium spirally, repeatedly ramified
dichotomously at the angle of 20–30° (Fig. 7A), with an axillary hydrotheca, without
axillary apophysis, the basal internode of each branchlet is much longer than other
internodes, without pedicle at the base (Fig. 7B); hydrocaulus and hydrocladium with
oblique internodes, contracted at both ends of each internode (Figs 7B–C); hydrocaulus
internodes irregular in length, hydrocladium internodes regular; generally each internode
bearing a hydrotheca, except some hydrocaulus internodes without hydrotheca (Fig. 7B).
Hydrothecae sparsely arranged (Figs 7B–C), alternately in two longitudinal rows forming
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one plane; hydrotheca tubular, surface with five to nine strong transverse grooves throughout,
always stronger in the adcauline side (Figs 7B–C, E–G); hydrotheca almost totally free, only
an eighth to a fifth of the adcauline part adnate; hydrotheca becoming slightly narrower
towards the distal end, but extended at the hydrotheca mouth, margin with three cusps, one
adcauline and two lateral abcauline, no intrathecal teeth observed (Figs 7B–C, E–G);
operculum composed of three valves forming a pyramid (Figs 7E–G); retracted hydranth
with well-developed abcauline caecum (Fig. 7G). See also Supplementary material 4 for
light micrographs (raw data for drawings).
Gonosome. Gonotheca oval, pedicellate, growing directly from hydrocaulus or
hydrocladium, gonothecal surface with upward strong spines throughout (Figs 7D–F). Two
distinct morphological types of gonothecae observed, possibly sexually dimorphic, vary in
the length and the density of spines. The first morphological type with long and sparse
spines (Fig. 7D), while the other type with dense and short spines (Figs 7E–F). Sex
Nematocysts. Only one morphological type observed (Supplementary material 5),
possibly microbasic mastigophores, undischarged capsules spindle-shaped, a discharged
nematocyst with a well-developed long shaft, no thread observed.
Distribution. Korea (Park 1986), Bohai Sea, Yellow Sea, East China Sea (Fig. 8), water
depth 10–70 m.
Remarks. This new species is characterized by its slender colony, with spirally, repeatedly
and dichotomously branched hydrocaulus, an almost totally free hydrotheca, as well as
strong transverse grooves throughout the hydrotheca. See morphological comparisons with
Page 29 of 77
related species in Table 5 and the Remarks of other Xingyurella species. The Korean specimens of Sertularella pedrensis by Park and Rho (1986) resemble
Xingyurella xingyuarum by the morphologies of colony, hydrotheca and gonotheca. They are
also characterized by strong grooves on the hydrothecal surface. Some other coastal records
from Korea (20–30m) were identified as Sertularella gotoi by Rho and Chang (1974), Park
and Rho (1986) and Park (2010). The hydrothecal grooves of these specimens (Park and Rho
1986; Park 2010: 93) are stronger than X. gotoi, but a bit shallower than X. xingyuarum.
Indeed, these specimens much resemble X. xingyuarum, except for some minor differences,
e.g. the gonothecal spines being slightly shorter. As a result, we treated all the above Korean
samples as X. xingyuarum.
Fine generic diagnoses and fine systematics
Although only limited molecular data (Figs 1–2) are available, they are important for the
establishment and integrative review of the new genus Xingyurella. The morphological
diversity of gonothecae within the family Sertularellidae (Figs 1–3, Supplementary material
3) suggests a conspicuous complexity in systematics of this family. Currently we are still far
from conducting a comprehensive taxonomic revision of the whole family, which would
require many more re-descriptions of species and sequences from fresh material. It remains
unclear whether some morphologically related genera provisionally attributed to the family
Sertulariidae Lamouroux, e.g. Calamphora Allman, 1888, Papilionella Antsulevich &
Vervoort, 1993, Polysertularella Antsulevich, 2011, should be assigned to this recently
Page 30 of 77
proposed family Sertularellidae.
Some morphological characters listed in Supplementary material 3 may be used as fine
generic diagnoses of Sertularellidae in the future, especially the diversified gonosome
characters (Fig. 3). In fact, some gonosome characters have been commonly used in other
families of the order Leptothecata (Hydrozoa), e.g., the gonothecal protecting structures that
are important generic characters for the families Aglaopheniidae L. Agassiz, 1862 and
Plumulariidae Agassiz, 1862 (Bouillon et al. 2006).
Other trophosome characters beyond hydrotheca should also be paid attention to. For
example, Sertularella mirabilis is characteristic with net-like colonies (Hirohito 1995; Song
2016). Stechow (1920) treated this character as generic diagnosis, establishing the genus
Serta. However, Billard (1925) and Hirohito (1995) preferred to move Serta mirabilis to
Sertularella. Interestingly, net-like colonies are not unique for Sertularella mirabilis: Song
(2016) noticed that Sertularella valdiviae Stechow, 1923 also have similar colonies after
re-examination of the type material deposited in the ZSM. Similar colonies were also
confirmed in Sertularella cervicula Choong, 2015 and S. sacciformis Choong, 2015 (H.
Choong, pers. comm.). Accordingly, it should be further clarified whether they should be
moved back to the genus Serta or not.
Possible intermediate morphological forms
It is intriguing that Xingyurella clusters together with Sertularella simplex (Fig. 1). In other
unpublished 16S and COI trees by Song (2016), the same Sertularella simplex clade also
contains Sertularella mirabilis and Sertularella miurensis Stechow, 1921. Nevertheless, it is
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still difficult to imagine or conceive any intermediate forms between such morphologically
deviant clades (Fig. 1). Could Sertularella inabai and Sertularella spirifera be candidate(s)
for potential intermediate forms between Sertularella and Xingyurella? At least both species
have gonothecal spines (Figs 3Q–R, U) similar to those of X. turgida (Fig. 4L).
The assignment of both Xingyurella gotoi and X. pedrensis to the genus Xingyurella may
appear justified by significant morphological similarities. Sertularella nodulosa may
possibly belong to Xingyurella (see Systematics). According to biogeographic data available,
the genus Xingyurella (Fig. 8) and S. nodulosa (Calkins 1899) seem to be endemic to the
eastern and western coasts of the North Pacific Ocean. Another species of the family
Symplectoscyphidae, Fraseroscyphus hozawai, is also reported to have a similar
transoceanic distribution pattern (Song et al. 2016b).
Several Sertularella species with net-like colonies discussed above are reported to be
distributed in wider regions. They are not only distributed in the shallow water of the eastern
(Choong 2015) and the western coasts (Jäderholm 1896; Hirohito 1995; Song 2016) of the
North Pacific Ocean, but also in the deep-sea of the Indian Ocean (Stechow 1923a, 1925,
water depth, 672 m). It is most likely that the distribution range of Xingyurella will expand
when more species and specimens are recorded; nevertheless, future research will be
valuable for understanding the evolution and speciation accompanied with the transoceanic
Page 32 of 77
Although Xingyurella turgida and X. xingyuarum seem to be distinct morphological species,
their genetic distance of the 16S rRNA (0.014–0.016) is not very divergent compared with
the 18S (0.052–0.053) and 28S rRNA (0.090). This still suggests high genetic relevance of
both species existed in the eastern and western side of the Pacific Ocean. Even higher
sequence similarity of some species of the genus Sertularia (Sertulariidae Lamouroux) was
also detected elsewhere, e.g. Sertularia plumosa (Clark, 1877) and Sertularia robusta (Clark,
1877) have very distinct morphological characters in hydrotheca marginal cusps and
opercular valves, yet their 16S rRNA similarity is 99.0% (Song et al. 2016a). This may be
partially attributable to the conservative nature of the 16S rRNA gene (Song et al. 2016a).
Xingyurella pedrensis, X. gotoi and X. xingyuarum, with similar gonothecal characters (also
see differences in Table 5), might also have high sequence similarity and genetic relevance
across the Pacific Ocean.
Potential evolutionary trend
The variation of branching patterns within Xingyurella seems to be heuristic. Song et al.
(2016b) newly introduced this character complex for generic diagnoses of three closely
related Symplectoscyphidae genera. They inferred that the lack of a hydrocauline apophysis
and an axillary hydrotheca represents the plesiomorphic condition, while the developed
branching pattern, emerging of the apophysis and axillary hydrotheca represents the derived
condition (Song et al. 2016b). Similarly, Xingyurella could be also split into two types by
similar morphological differences of the branching pattern. (1) Xingyurella turgida has a
Page 33 of 77
simple branching pattern; it is unbranched or rarely abnormally branched; if branched, an
axillary hydrotheca is absent (Fig. 4E); it only occurs in temperate shallow waters no more
than 30 m deep (Trask 1857; this study). (2) Xingyurella pedrensis, Xingyurella gotoi and X.
xingyuarum represent the other type with a relatively complex branching pattern with an
axillary hydrotheca (Figs 5E, 6B–C, 7B). They are reported in deeper cold waters ranging
from 77 m to 110 m (Torrey 1902; this study), in the Cold Water Mass of the Yellow Sea
(10–70 m, this study) or in the deep-sea (600 m, Stechow 1913a, 1913b), respectively. This
might hint towards an evolutionary trend: Xingyurella might have evolved a complex colony
organization by migration from temperate shallow water to cold water and deep-sea. More
evaluations at the species and population levels for the genera Xingyurella and Sertularella
should be undertaken to test this hypothesis.
As a result, the present study may serve as a research case of how inconsistent or
incongruent molecular and morphological inferences can be integrated to refine systematics,
and as a prelude to improved generic diagnoses integrating tropho- and gonosome traits for
Sertularellidae and other hydrozoans.
XS examined the MBM material, prepared the manuscript drafts, ML and XS conducted
molecular analyses; XS and CG prepared the systematics; BR examined the ZSM material,
revised the language; JW provided partial financial support; all authors wrote the paper.
Conflicts of interest
Page 34 of 77
The authors declare no conflicts of interest.
We thank Dr Peter Schuchert (MHNG), Zyanya Mora Vallín and Christina Piotrowski
(CASIZ) for images, and two anonymous reviewers for constructive revisions. XS wishes to
express sincere thanks to Zefeng Xiao (Liaocheng University), Jinjing Chen, Lu Fang
(Ocean University of China), Wei Lin (XMU) and other members of his previous team. XS
was mainly supported by the Outstanding Postdoctoral Scholarship from the State Key
Laboratory of Marine Environmental Science at XMU and partially by his previous PhD
scholarship from UCAS and IOCAS. This is the QT scientific research report QT04.
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Billard, A. (1925). Les hydroïdes de l'Expédition du Siboga. II. Synthecidae et Sertularidae.
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895 896 897
Table 1. New primers for the 18S and 28S rRNA genes designed in the present study The primers succeeded in several tested Leptothecata (Sertulariidae and Campanulariidae) and Anthoathecata (Tubulariidae) species collected 3–7 years ago, fixed in 70%-100% ethanol. Marker
Sequence of primer (5´-3´)
~ 530 bp
~ 760 bp
~ 870 bp
~ 760 bp
~ 970 bp
~ 640 bp
~ 550 bp
~ 570 bp
~ 850 bp
R: GGAATTACCGCGGCTGCTGGCACC 18S2
R: CACCTACGGAAACCTTGTTACGAC 28S1
F: ACAAGGATTCCCTGAGTAACG R: AGACTCCTTGGTCCGTGTTTCAAGAC
R: GGAATGTTAACCCGATGCCCTTTCG F: AGTGCAGATCTTGGTGGTAGTAG
R: AGAGCCAATCCTTTTCCCGAAGTT F: CGTACTCATAACCGCAGCAGGTCT
899 900 901
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Table 2. Genetic pairwise Kimura 2-Parameter distances for partial sequences of the 16S rRNA gene (589 bp) of Xingyurella Three haplotype replicates of MF135580 were obtained in the single hydroid fragment of MBM280254 Species
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Table 3. Genetic pairwise Kimura 2-Parameter distances for partial sequences of the 18S (1707 bp) and 28S (3273 bp) rRNA genes of Xingyurella Marker
Page 46 of 77
Table 4. Measurements of the species of the genus Xingyurella *Gonothecal spines were not included for measurements Internode
length, aperture width (mm)
length, width (µm)
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909 910 911 912 913 914 915 916 917 918
Table 5. Comparative characters for the genus Xingyurella and doubtful species References: 1, Stechow (1913a, 1913b); this study; 2, Torrey (1902, 1904); this study; 3, Trask (1857); this study; 4, as Diphasia sp., Inabai (1890); 5, as Symplectoscyphus turgidus, Hirohito (1983, 1995) and Park (1998); 6, this study; 7, Calkins (1899). * The pedicle of the basal internode of hydrocladium, present in X. turgida, is part of the hydrocladium. It is similar as but different from the axillary apophysis in some Symplectoscyphus species which belongs to one of the two extended processes of the hydrocaulus. ** The samples examined by Hirohito (1983, 1995) may consist of several species (see the Systematics).
Branching pattern - hydrocaulus
- hydrocladium with
- axillary apophysis
- axillary hydrotheca
a basal pedicle*
- tapering towards
- surface grooves
Water depth (m)
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