Dugesia aethiopica sp. n. (Platyhelminthes

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African planarians: Dugesia aethiopica sp. n. (Platyhelminthes, Tricladida) from lake Tana (NW Ethiopia) a

a

a

Giacinta Angela Stocchino , Gavina Corso , Renata Manconi & Maria Pala

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Dipartimento di Zoologia Antropologia Biologica , dell'Università , via Muroni 25, Sassari, 1–07100, Italy b

Dipartimento di Zoologia , Antropologia Biologica dell'Università , via Muroni 25, Sassari, 1–07100, Italy E-mail: Published online: 28 Jan 2009.

To cite this article: Giacinta Angela Stocchino , Gavina Corso , Renata Manconi & Maria Pala (2002) African planarians: Dugesia aethiopica sp. n. (Platyhelminthes, Tricladida) from lake Tana (NW Ethiopia), Italian Journal of Zoology, 69:1, 45-51, DOI: 10.1080/11250000209356437 To link to this article: http://dx.doi.org/10.1080/11250000209356437

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Ital. J. Zool., 69. 45-51 (2002)

African planarians: Dugesia aethiopica sp. n. (Platyhelminthes, Tricladida) from Lake Tana (NW Ethiopia) GIACINTA ANGELA STOCCHINO GAVINA CORSO RENATA MANCONI MARIA PALA

Downloaded by [223.86.112.144] at 07:23 22 March 2014

Dipartimento di Zoologia e Antropologia Biologica dell'Università, via Muroni 25, 1-07100 Sassari (Italy) e-mail: [email protected]

INTRODUCTION The genus Dugesia Girard, 1850, family Dugesiidae (Ball, 1974; De Vries & Sluys, 199D, widely distributed throughout Europe, Asia, Australia, and Africa, includes a complex of allied species known as the 'D. gonocephala group'. The species belonging to this group share very similar external morphology and are recognisable solely by internal anatomy and karyology (Benazzi & Benazzi-Lentati, 1976). The recent synopsis of African and Madagascan planarians belonging to the 'D. gonocephala group' (De Vries, 1988) reported 20 species (Bohmig, 1897; Neppi, 1904; Laidlow, 1906; De Beauchamp, 1913, 1932, 1939, 1951a, b, 1952; Marcus, 1953; Dahm, 1967, 1971; Banchetti & Del Papa, 1971; Kawakatsu, 1972; Kenk, 1974; Young & Young, 1974; Kawakatsu et at., 1976) including three species inquirendae (Kenk, 1974). The present paper reports on the first finding of freshwater flatworms from Lake Tana in NW Ethiopia and on a new species belonging to the genus Dugesia and its phylogenetic relationships. MATERIALS AND METHODS

ABSTRACT A new species of Dugesia from East Africa is described as a first report of Platyhelminthes from Lake Tana. Dugesia aethiopica sp. n. is characterized by the shape of its bursa copulatrix; length, diameter, course, and opening of the bursal canal; opening of the oviducts; shape of the penis papilla; penial parenchymatic cavity. The taxonomic position of the new species within the D. gonocephala group is discussed in comparison with the other African and Madagascan species.

A survey on the freshwater benthic fauna of northern Ethiopia and Eritrea was performed during the spring of 1988 and 1989; planarians were only found along the southern coast of Lake Tana in May 1988 (Fig. 1). Collected specimens (28) were reared in a small tank and fed with liver up to June 1988 at the Invertebrate Laboratory of the University of Asmara, and then transferred to our laboratory. A sexualization process during rearing was displayed by 30% of planarians in spite of the fact that all specimens were fissiparous at collection. The sexualized specimens attained large size showing the habitus of the so-called ex-fissiparous individuals. Morphological analyses were performed on 5-mm-thick histological serial sections following Pala et al. (2000). The sections were stained with hematoxylin-eosin (Harris) and acetaldehyde fuchsin (Jennings) for histological details.

KEY WORDS: Freshwater flatworms - Dugesiidae - New species - River Nile - Morphology. AKNOWLEDGEMENTS This research was supported by grants from the Italian Ministero dell'Universita e. della Ricerca Scientifica e Tecnologica (MURST ex-40-60%), the Istituto Italo-Africano, the Italian Ministero degli Affari Esteri (MAE Italo-Ethiopian-Eritrean cooperation project) and the Universita di Sassari. We are grateful to Prof. A. Casale for his criticism of the text and to Dr. R. A. Vacca for her valuable help and experience in the field of planarian research. We thank Dr. G. M. Delitala for technical assistance. (Received 31 May 2001 - Accepted 22 November 2001)

Fig. 1 - Type locality of Dugesia aethiopica sp. n. along the southern shore of Lake Tana in NW Ethiopia.

46

G. A. STOCCHINO, G. CORSO, R. MANCONI, M. PALA

Abbreviations used in the figures: ae, atrial enlargement; at, atrium; be, bursa copulatrix; bg, bulb glands; bs, bursal canal; eg, cement glands; dp, diaphragm; ed, ejaculatory duct; en, epithelial nuclei; go, gonopore; ov, oviduct; pb, penis bulb; pc, penial parenchymatic cavity; pg, penis papilla glands; pgr, penial groove; pp, penis papilla; sg, shell glands; sv, seminal vesicle; vd, vas deferens.

TAXONOMIC ACCOUNT Suborder TRICLADIDA Lang, 1884 Family

DUGESIIDAE

Ball, 1974

Genus Dugesia Girard, 1850

Dugesia aethiopica sp. n.


(Figs 2-6)

B

Material examined Type materials and all specimens, both living and preserved, are at present deposited in the collection of Prof. Maria Pala at the Dipartimento di Zoologia e Antropologia Biologica dell'Universita di Sassari (DIZAB). Types Holotype: DIZAB Pla 2.1, one set of sagittal sections on 11.slides, Lake Tana, Bahir Dar Ql°36' N, 37°23' E), Ethiopia, May 1988, R. Manconi & R. Pronzato. Paratypes: DIZAB Pla 2.2-3, two sets of sagittal sections on 17 and 18 slides, respectively; DIZAB Pla 2.4-6, three sets of transverse sections on 42 slides, 6 slides, 66 slides; DIZAB Pla 2.7, one set of frontal section on 18 slides. Same location as for holotype.

Fig. 2 - Dugesia aethiopica sp. n.: external features (from photographs of living specimens). A, ex-fissiparous specimen. B, fissiparous specimen; pale colour and size of tail is due to a recent regenerative process. Scale bar, 1.5 mm.

Diagnosis Dugesia aethiopica is characterized by the peculiar shape of bursa copulatrix (Figs 4, 5A); length, diameter, course, and opening of bursal canal (Figs 4, 5D); opening of the oviducts (Figs 4, 5C); shape of penis papilla (Figs 3, 5F); penial parenchymatic cavity (Figs 3, 5F).

Etymology

Ecology and distribution

The specific epithet, aethiopica, refers to the Ethiopian biogeographic region. '

Only known from the type locality in southern Lake Tana (Fig. 1) in shallow standing waters up to a depth

Fig. 3 - Dugesia aethiopica sp. n.: holotype Pla 2.1. Sagittal reconstruction of the copulatory apparatus (anterior is to the right). Scale bar, 100 pm.

47

A NEW DUGES1A FROM EAST AFRICA


of 20 cm on the lower or lateral surfaces of littoral volcanic pebbles, cobbles, and boulders. Planarians were found associated with gastropods, bivalves, and sponges. Lake Tana, located in the northern highlands of Ethiopia at an altitude of ca. 1800 m a.s.l. and isolated downstream by the Tis Issat Falls, is a tributary of the Nile hydrographic catchment basin with its single outlet in the Blue Nile (River Abay). It is the largest lake in Ethiopia (ca. 3150 km2) with a maximum depth of 14 m (mean 8 m). Water level fluctuations (ca. 0.4-2.30 m) are markedly seasonal according to rainfalls. The rainy and wet seasons occur, respectively, in summer and winter, with a recurrent long-lasting drought period (Bini, 1940a; Nagelkerke & Sibbing, 1996). Waters with a temperature ranging from 15.6-20 °C were characterized as oligotrophic (Bini, 1940a; Brunelli & Cannicci, 1940; Rzoska, 1976). Description External features Body size of the living ex-fissiparous specimens is about 20-22 mm in length and 2.5-3 mm in width (Fig. 2A). Fissiparous specimens are notably smaller, measur-

Fig. 4 - Dugesia aetbiopica sp. n.: paratype Pla 2.7. Frontal reconstruction of the copuiatory apparatus (anterior is to the top). Scale bar, 100 um.

" '""'" •••

ing about half the ex-fissiparous ones (Fig. 2B). The head is high triangular-shaped, and along its anterior margin shows 10 sensory fossae. Two eyes are present in the middle of the head. Auricular grooves, lacking pigment, are marginally placed just behind eye level. The colour is brown dorsally, and pales ventrally. Oral and genital pores open on the ventral side. Internal features The inner and outer pharyngeal musculature is bilayered. The ovaries are hypertrophic and hyperplastic with several masses scattered in the retro-cephalic area, visible through the dorsal body wall (Fig. 2A). Each oviduct arises dorsally from the ovaric masses with a seminal receptaculum in a variable position related to the hyperplastic condition. The oviducts curve toward the ventral area running in a caudal direction up to the vaginal area of the bursal canal. The testes are well developed. Vitellaria are located, as usual, between testes. The copuiatory apparatus with bursa copulatrix and its canal, the penis and atrium are schematically represented in Figures 3 and 4. The bursa copulatrix, sac-like shaped and compressed in the antero-posterior direction, occupies the dorso-ventral space of the body. The bursa outline, highlighted in frontal section (Fig. 5A), is characterized by deep evaginations of the wall along its entire height. High glandular cells with basal nuclei form its epithelium. The bursal canal, unusually long, starts from a dorsal evagination of the bursa copulatrix. It runs on the left side of the copuiatory apparatus, gradually increasing in diameter and occupying a lateral position. In its terminal course, it exceeds, by about 350 um, the gonopore, and then turns toward the right side of the body with a wide U-shaped curve (Fig. 5B). At the end of the curve, the elongated vaginal tract of the bursal canal receives the symmetrical ventral openings of the oviducts (Fig. 5C), and then the shell glands ducts before opening into the posterior wall of the atrium (Fig. 5D). The wide lumen of the bursal canal is lined by an infranucleate longitudinally pleated epithelium. The underlying longitudinal muscular layer is arranged to support the epithelial folds, and is surrounded by both a thick layer of circular muscles and the layer of epithelial nuclei (Fig. 5E). The pleats of the bursal canal involve the entire wall thickness starting from the level where the canal curves to the right side, up to the atrial opening (Fig. 5C, D). The penis, about 500 pm long, is formed by the penis bulb and the penis papilla. The oval-shaped penis bulb is scarcely developed and hosts a narrow, elongated seminal vesicle devoid of a proper epithelium. In its latero-caudal portion, the seminal vesicle receives the symmetrical openings of the vasa deferentia. The seminal vesicle is separated from the ejaculatory duct by a small diaphragm. The penis papilla is blunt and gland-shaped. It appears slightly narrow at the basis with a frontal groove for almost its entire length.

48

tures, protrudes into the atrial cavity (Fig. 5B). The atrium opens ventrally into the gonopore, forming a small enlargement where numerous cement glands open (Figs 3, 5D). Nucleate epithelium cells of variable height (Fig. 5E) line the atrial cavity.

CONCLUSIVE REMARKS Comparative discussion The occurrence of Dugesia aethiopica sp. n. in Lake Tana is the first record for the Nile catchment basin; the


Dorsally with respect to the groove, the penis papilla bears an apical parenchymatic cavity devoid of proper wall, but with homogeneous material (Fig. 5B, E, F). The penis papilla is lined by an infranucleate epithelium. The ejaculatory duct is ventral with sub-terminal opening (Fig. 5F). This condition makes the penis papilla asymmetrical, with the dorsal part greater than the ventral one. For the entire course of the ejaculatory duct, the bulb and the penis papilla show a notable amount of glands revealed by acetaldehyde fuchsin stain (Fig. 6A, B). The atrium is divided and slightly shifted toward the right side. The penis papilla, devoid of accessory struc-

G. A. STOCCHINO, G. CORSO, R. MANCONI, M. PALA

Fig. 5 - Dugesia aethiopica sp. n.: light micrograph sections (hematoxylin-eosin) throughout the copulatory apparatus. A, frontal section of the bursa copulatrix. B, frontal section of the penis and the bursal canal. C, transverse section at the level of the bursal canal terminal tract with the opening of the right oviduct. D, sagittal section showing the opening of the bursal canal into the atrium; note the ventral enlargement of the atrium. E, transverse section of the penis papilla and the bursal canal. F, sagittal section of the penis. Scale bar, 100 pm.

49

A NEW DUGESIA FROM EAST AFRICA


new species could be considered an endemism of Lake Tana, in agreement with the endemic status of fishes, molluscs, insects, crustaceans, nematodes, and sponges (Bini, 1940b; Brunelli & Cannicci, 1940; Nagelkerke et al., 1995; Manconi et al, 1999). The peculiar fauna of the lake could be related both to the notable isolation downstream and the age of the volcanic lake, estimated as Late Pliocene to Early Pleistocene (Mohr, 1966) from 5 to about 2 My BP, according to data obtained for Ciprinidae (Dixon et al., 1996; Berrebi & Valiushok, 1998). It seems, however, that the quite poor but endemic fauna hosted in the lake could be related to a drastic catastrophic extinction, probably during one of the Quaternary glaciations, followed by a process of rapid speciation, as demonstrated for the Barbus intermedius species flock (Berrebi & Valiushok, 1998). The comparative analysis highlighted the fact that D. aethiopica shares both plesiomorphic and apomorphic traits with other African and Madagascan species of the genus (Table I). The enlargement of the atrium is shared with D. machadoi, and the longitudinally pleated bursal canal with D. sicula and D. astrocheta (Lepori, 1948; De Vries, 1988). Moreover the bilayered

pharynx, the bursal canal infranucleate epithelium, and the ventral ejaculatory duct are shared with D. aethiopica in about 50% of the species. Dugesia aethiopica sp. n. displays some exclusive diagnostic features diverging from those of all known African and Madagascan planarians of the genus Dugesia, particularly in the morphology of the bursa copulatrix, bursal canal, oviducts and penis papilla (Figs 3, 4). The bursa copulatrix is compressed in antero-posterior direction and its peculiarity is the deep pleating of the wall in its entire height. The bursal canal, of very unusual length and diameter, runs to the left side of the penis in lateral position. Ectal reinforcement of the bursal canal is absent in spite of its being shared with all African and Madagascan species. The terminal course of the bursal canal describes a wide curve towards the right side where it opens into the posterior wall of the atrium. The oviducts, remaining in their ventral position, open symmetrically into the vaginal area of the bursal canal. The dorsal part of the asymmetrical penis papilla constantly houses a groove running in a frontal plane, and a parenchymatic cavity of homogeneous material.

TABLE I - Diagnostic traits of 'Dugesia aethiopica sp. n. compared to African and Madagascan species of the genusDugesia (abbreviations as in the figures).

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I I 8 astrocheta colapha congolensis debeauchampi didiaphragma ectophysa aethiopica lamottei lanzai machadoi milloti mirabilis monomyoda myopa neumanni sicula subtentaculata sudanica

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50

G. A. STOCCHINO, G. CORSO, R. MANCONI, M.PALA

D. biblica, D. lamottei, D. lanzai^ and D. neumanni. The clustering of all these species is consonant with their geographic range, restricted to Africa, Madagascar, and the Mediterranean area. In addition, they all share a weakly muscular penis bulb, elongated and narrow seminal vesicle, and small diaphragm. With its symmetrical and ventral opening of oviducts, D. aethiopica differs in one of the main diagnostic traits from the whole of the subgroup. The last phylogenetic analysis of Dugesia, performed by Sluys et al. (1998), subdivided the genus into two large groups of species, each characterized by the different size and shape of diaphragm. Group 1 includes most species, sharing a large or pointed diaphragm as opposed to Group 2, characterized by a small diaphragm. Dugesia aethiopica fits Group 2, according to this analysis, and more precisely it shows most affinities to the D. sicula subgroup of De Vries (1987). The species clustering highlighted by Sluys et al. (1998) approximately coincides with that of De Vries (1987), considering the correspondence between Group 2 of the former authors and Group 1 of the latter.

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REFERENCES

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