Subsequently, the jaws and an upper lip area are protruded. This ... Although the rostrum is densely covered with cilia, no apicalia (single, stiff cilia) could be ...
PROBLOGNATHIA MINIMA N. G., N. SP., REPRESENTATIVE OF A NEW FAMILY OF GNATHOSTOMULIDA, PROBLOGNATHIIDAE N. FAM. FROM BERMUDA^ WOLFGANG STERRER and RICHARD A. FARRIS2 Bermuda Biological Station for Research, Inc., St. George's West, 1-15, Bermuda and Department of Zoology, University of North Carolina, Chapel Hill, North Carolina 2751 4
STERRER, W. & FARRIS,R. A. 1975. Problognathia minima n, g., n. sp., representative of a new family of Gnathostomulida, Problognathiidae n. fam. from Bermuda. Trans. Amer. Micros. Soc., 94: 357-367. This paper, continuing a series dealing with Gnathostomulida from the Western Atlantic, describes a new genus and species found in Bermuda, Problognathia minima n. g., n. sp. Characterized by extremely small body size and a protrusile pharynx, it is placed within the order Bursovaginoidea, at the base of the 'higher" Scleroperalia. Diagnoses of the species, the genus, and the new family Problognathiidae n. fam, are given.
The present paper continues a series dealing with Gnathostomulida from the West Atlantic (Farris, 1973; Riedl, 1970a,b; 1971a,b; Sterrer, 1970, 1971b, 1973). The following description, based on studies of living individuals, is of the most recently discovered genus. Problognathia n. g.Vs of particular taxonomic interest as it was not known when the first classification of Gnathostomulida was proposed (Sterrer, 1972), and therefore can be used to check the validity of the present system of the phylum. It is one of the aims of this paper to demonstrate that "soft" meiofauna is as rigidly defined in terms of dimensions and proportions, and as amenable to biometric methods, as " h a r d meiofauna. Table I summarizes statistical data, including the sometimes astonishingly small standard deviations (e.g., in the jaw length). The type material, consisting of two syntypes, is deposited in the American Museum of Natural History, New York.
Our material consisted of 21 adult specimens which were studied alive with the aid of a Wild M-5 dissecting microscope before transferral to a glass slide with coverslip. Each was studied in squeeze preparation with a Wild M-20 phase contrast after first being relaxed with magnesium chloride (isotonic to sea water). Detailed drawings and measurements were made with the aid of a Wild drawing tube. Separation from the substrate was accomplished according to Sterrer ( 1 9 7 1 ~ ) . The organisms were narcotized with isotonic magnesium chloride; the supernatant was decanted twice through a 64 pm sieve, followed by a final washing with inillipore-filtered sea water. For purposes of comparing relative dimensions and 'Our work was supported by National Science Foundation Grants Nos. GA-29592 and GA-34211, and by the North Carolina Board of Science and Technology Grants Nos. RA-012 and RA-023. Contribution No. 610 from the Bermuda Biological Station. Present address: Department of Biology, Linfield College, McMinnville, Oregon 97128. The generic name is derived from the Greek words p~oblos (meaning to jut out or project) and gnathos (meaning jaw), referring to the manner in which the pharyngeal apparatus and jaws can be projected through the mouth opening. The species name refers to the fact that this is the smallest gnathostomulid known so far.
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TABLE I Biornetrics of Problognatlzia minima1 Measurement or index
Mean
S.D.
Maximum
Minimum
n
Body length Body width Body index (1 : w ) Length of rostrurn Width of rostrum Rostrum index (1 : w ) Length of pharynx Width of pharynx Length of jaws Length of basal plate Width of basal plate Basal plate index (1 : w ) Length of bursa Width of bursa Bursa index (1 : w ) Length of stylet Breadth of stylet All measurements are in pm, carried out on adult specimens, in comparable states of squeeze preparation.
proportions in the description, the total body length is taken as 100 units ( U ) beginning with the anterior tip of the rostrum and extending posteriorly. All measurements pertain to adult individuals; no juveniles were observed. Except where stated otherwise, measurements in the text are arithmetic means based on several specimens, and therefore given to 0.1 pm, although the actual measuring precision was probably no better than 0.5 pm.
Occurrence So far. Prohlognathia minima is known only from Bermuda. It occurs in benthic intertidal and subtidal sand rich in detritus, the typical environment for Gnathostomulida in general (Sterrer, 1971a). Type locality is Castle Harbour (Tucker's Town Cove) : intertidal fine-sand flat, with the following granulometry: < 4 mm: 0.07%, 2-4 mm: 0.75%,1-2 mm: 0.68%, 0.5-1 mm: 11.81%,250-500 pm: 54.69%, 125-250 pm: 30.37%, 63-125 pm: 0.90%, 37-63 pm: 0.22%, > 37 pm: 0.45%. Specimens were predominantlv found in the urmer 4 cm of sediment and were dktributed from h e a n tide level to sublittoral. SzaLmpling occurred during summer and fall, 1972 and 1973. Other localities for this species are: ( 1 ) Harrington Sound (near Trunk Island) : fine sand in 3 m depth; ( 2 ) Harrington Sound (Church Bay) : fine sand in 3-4 m depth; ( 3 ) Flatts Inlet (Gibbons Bay): fine sand in 2 m depth; ( 4 ) Shelly Bay: fine sand in 1 m depth; ( 5 ) Bailey's Bay (innermost part): fine sand in 0.5 m depth. Several other gnathostomulid species are usually found with P. minima, in particular a new species of Mesognathariidae (termed "Genus VII" in Sterrer, 1972).
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Organization and Behavior The animals are colorless and extremely fragile. TJnder a dissecting microscope the head has a transparent appearance offset by very dark jaws. The body appears opaque and granular. Movement is by slow gliding, often accompanied by n rhythmic oscillation of the head from side to side, with the body remaining fully extended. Periodically, the animal stops and twists into a U-shape or circular configuration, the head touching the posterior region. Specimens were never observed to move backwards. The total body length (from rostra1 tip to posterior end) has the rather narrow range of 230370 pm, with a mean of 329.3 pin. Body width varies between 45 and 70 pm at V50, with a mean of 53.2 pm. The average body index (length divided by width) is 6.03. Problognuthia is thus not only the smallest gnathostomulid yet described. but also one of the plumpest. A distinctive feature is the near-circular outline of the broad rostrum (head) with a mean width of 63.8 pm; 10.6 pm greater than the mean body width. The rostrum index (mean rostrum length as measured from the tip of the rostrum to the anterior tip of the jaws, through mean rostrum width) is 0.62. At times, the head is capable of changing the shape due to muscular contraction (Figs. 4, 5 ) ; however, in a relaxed swimming position it typically presents the broad appearance (Figs. 1, 8 ) . All measurements used for body proportions were taken from organisms in an extended posture under a coverslip prior to squeezing. The sulcus pre-pharyngealis is situated posterior to the head at U14-U19 and is laterally constricted, further delimiting the head. Behind the sulcus, the body increases gradually in width reaching a maximum at US0 and maintaining this width to approximately U90-U92, after which it decreases slightly terminating abruptly in a rounded posterior end. No tail is present. The pharynx is particularly interesting because of the manner in which the pharyngeal apparatus can be protruded out through the mouth. This is preceded by a retraction of the dorsal part of the rostrum, which is lifted upwards and backwards, making a longitudinal groove appear in front of the mouth opening (Figs. 3, 4 ) . Subsequently, the jaws and an upper lip area are protruded. This sequence of events is rapidly accomplished, often accon~paniedby a fast snapping action of the jaws. Epithelium and sensorium. A monociliated epithelium is well defined, being somewhat thicker at the posterior end than along the trunk where its thickness averages 2-3.5 pm. Individual cilia are 15 pm long, a few slightly longer sensory cilia are scattered around the posterior end. Whereas the normal body cilia tend to be straight with an anterior to posterior stroke, the cilia on the ventral posterior side are hooked, with the active beat directed towards the anterior end (Fig. 21). Rhabdoids or adhesive papillae are lacking, and small refractile granular inclusions so typical of other gnathostomulids, especially in the vicinity of the mouth, are very scarce in the present species, No regular epithelial pattern could be observed. The sensorium (Figs. 1, 2 ) consists of four pairs of compound bristles (frontalia, ventralia, dorsalia, and lateralia) each capable of independent movement, but never observed to join the beat of the body cilia. All are rather short; the longest are the lateralia, with a maximum length of 35 pm. Due to their evtremely fragile nature, exact measurements were difficult to obtain. Frontalia are situated close to the anterior tip of the head, followed by the ventralia, which originate and point ventrally; the dorsalia, originating and pointing dorsally, and finally the lateralia. In dorsal view, the ventralia and dorsalia do not coincide, but instead are separated by a distance of 9-11 pm.
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Abbreviations: b, bursa; bp, basal plate; bg, buccal gland; c, brain; dr, dorsal row of teeth; e, egg; f, frontalia; g, gut; hc, hooked cilia; j, jaws; 1, lateralia; mo, mouth opening; pb, prebursa; pg, pharyngeal gland; ph, pharynx; r, rostrum; s, sperm; st, stylet; sy, symphysis; te, testes; tt, terminal tooth; ul, upper lip; v, ventralia; vr, ventral row of teeth. FIGS. 1-7. Problognathia minima n. g., n. sp. Fig. 1. General features and organization, dorsal view. Fig. 2. Head, dorsal view. Fig. 3. Head with pharynx protruded as viewed from left side. Figs. 4, 5. Changes in rostrum shape due to muscular contraction. Figs. 6, 7. Cuticular structures found in gut lumen. Figures 2-7 to the same scales.
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Although the rostrum is densely covered with cilia, no apicalia (single, stiff cilia) could be identified, nor is there a distinct row of occipitalia on the dorsal surface of the head. Only in one specimen did we observe what might be considered a ciliary pit situated medially, between the pair of frontalia. Pharynx and digestive tract. The mouth (Figs. 1, 2, 8, 9 ) , situated between U4 and U10, has a mean length of 19 pm and terminates posteriorly at the basal plate. I t is dumbbell-shaped, surrounded by a nonciliated upper lip area which protrudes out through the mouth opening when the jaws are protruded (Fig. 3 ) . The basal plate (Figs. 11, 12, 17-20) is much wider than long, with a mean width of 35.5 pm and a mean length of 10.4 pm. Approximately 35-40 teeth line the rostro-ventral edge with only a slight differentiation in size and shape; those towards the lateral sides are slightly longer and sharper. In addition, one pair of tooth-like protrusions is located, about 10 pm apart, on the rostro-dorsal edge (Fig. 11). The central part of the basal plate lies ventrally, and the lateral wings point dorsally; the latter can only be seen in a highly squeezed condition. A jugum is lacking. A tripartite-type pharynx extends from the anterior tip of the mouth at U4 to the posterior region of the muscle sack at U22 and is surrounded by a thin muscular wall. A pair of strong lateral muscles can be clearly seen inserting on the jaws. Mean pharyngeal length is 65.4 pm; mean width 48.8 pm at U17. Two pairs of glands are present. One pair (pharyngeal glands), situated behind the jaws and lateral to the muscle sack, seems to lead into the jaws; the second pair (buccal glands) is situated lateral to the jaws at U12 (Fig. 2 ) . The jaws are distinct in an unsqueezed specimen under bright field illumination. Our specimens display extremely little variation with regard to jaw length; of the 40 jaws measured, the mean length was 23.51 pm, with a standard deviation of only 1.27 pm (Table I ) . Two rows of teeth and a strong terminal tooth form a slightly arched or basket-shaped configuration, but the actual arrangement and number of these teeth are hard to ascertain. In the ventral row (Figs. 11, 15, 16), teeth are finer but more numerous (usually 6-7), with the forenlost always being the largest; the size then decreases posteriorly. Teeth of the dorsal row are larger but fewer in number (usually 3 4 ) and also decrease in size posteriorly (Figs. 11, 13-16). The entire jaw apparatus is heavily lamellarized, and individual cuticular elements are extremely difficult to analyze. A cauda is lacking. The gut can be seen to extend from U22 to U80; it probably extends further towards the posterior end, but is obscured by reproductive organs. Relatively few vacuoles are present. but numerous conglomerations with highly refractile granules occur in large numbers throughout the gut. In approximately 50% of all specimens examined, the gut contained peculiar triangular rod-like structures (Figs. 6, 7 ) , which are heavily cuticularized at one end. As many as nine have been seen in one individual, usually two or three are clumped together, the remainder being dispersed throughout the gut. On one occasion, a thin, flat blade was observed attached to the base of a rod, being narrower at the more cuticularized end, the broadening towards the pointed end, thus giving a paddle- or scalelike appearance. The third ridge of the rod stood perpendicular to the blade. When squeezed out of the body, the entire structure maintained its shape. We have been unable so far to identify these inclusions or trace them to some prey organism we suspect they are part of. The total length was 47 pm; the width 12 pm at the widest point. Male genital organs. One pair of ventrolateral testes (Figs. 1, 8, 10, 21) extends from U77 to U96, each testis averaging 58 pm in length and 12 p n ~in width. Sperm (Fig. 27) are extremely small and angular to nearly spherical, with a diameter of approximately 1 pm. Flagella are lacking; however, some short filaments
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FIGS.11-18. Problogmthia minima n, g., n, sp. Fig. 11. Basal plate and jaws, moderately squeezed, ventral view. Fig. 12. Basal plate of another specimen. Figs. 13-15. Jaws of different specimens in varying degrees of squeezing. Fig. 16. Left jaw, strongly squeezed. Figs. 17, 18. Basal plates of two specimens. All to the same scale.
may be present. All sperm or stages of spermatogenesis (Fig. 26) shown are from the testes. The copulatory apparatus (Figs. 1, 10, 21-24) is situated between the testes at U80-U90. It consists of a straight, conical penis stylet composed of 10-12 cuticular rods which are arranged circularly, forming a tube around the genital canal. The length of the stylet varies from 24 to 32 pm, with a mean of 26.7 pm. The diameter at its proximal end averages 6 pm; distally 2 p n ~ .Two glands surround the stylet. One bladder-like vesicula seminalis is anterior and always filled with large, granular material. A second median stplet gland encloses the stylet; large granules similar to those in the vesicula seminalis form a sheath twothirds of the way down, decreasing in size distally. Fine granular material is usually found surrounding the genital pore at the distal end of the stylet where it opens ventrally to the outside.
FIGS.8-10. Problognathia minima n. g., n. sp. Phase-contrast photographs of live specimens. Fig. 8. Unsqueezed adult, dorsal view. Fig. 9. Pharynx, moderately squeezed, ventral view. Fig. 10. Posterior part of body. Figures 9, 10 to the same scale.
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FIGS. 19-20. Problognathia minima n. g., n. sp. Phase contrast photographs of live specimens. Basal plate and jaws of two specimens, strongly squeezed. Both to same scale.
Female genital organs. Although the anterior limit of the unpaired dorsal ovary is difficult to determine, it appears to be around U45; posteriorly, the ovary extends to U77. Usually only one large egg is found occupying the posterior-most portion of the ovary. On occasion, a second smaller egg can be seen in front of the larger one (Fig. 1 ) . No more than two eggs were seen in any individual. An interesting feature, not found in other species of gnathostomulids, is the manner in which the mature egg wraps around and extends quite far behind the bursaprebursa complex (Figs. 1, 10, 21). The bursa (Figs. 1, 8, 10, 21, 25, 28, 29) is only slightly cuticularized and of very unusual shape. Located between U61 and U67, it is almost perfectly round in a squeezed condition, with a mean length and width of 30.1 and 28.8 pm respectively. Although the dimensions may vary in relation to the size of the organism, the proportions stay constant as indicated by a bursa index (length through width) of 1.05 (Table I ) . A distinct mouthpiece is not present; however, the center of the bursa ventrally often shows a delicate star-shaped structure which is surrounded by a halo of sperm-free tissue (or vacuole). The fact that the bursa, when squeezed, always remains circular with the "mouthpiece" in the center suggests that it is not spherical but rather doughnut-shaped. It is usually densely packed with what presumably are sperm which appear quite different from those found in the testes. Each consists of a tiny dark dot, surrounded by a translucent area (Fig. 29). In unsqueezed specimens, the prebursa is very often partly wrapped around the bursa in such a way that the two bodies interlock (Fig. 25). When pressure is applied to the coverslip, the bursa and prebursa slide apart, with the prebursa usually dissolving into a shapeless mass. The latter sometimes contains highly refractile sperm with various inclusions. A vagina is not apparent.
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FIGS.21-29. Problognathia minima n. g., n. sp. Fig. 21. Posterior part of body showing reproductive organs. Figs. 22-24. Male copulatory organ of three specimens. Fig. 25. Schematic left lateral view demonstrating relative position of bursa-prebursa-complex. Fig. 26. Stages of spermatogenesis. Fig. 27. Sperm. Figs. 28, 29. Bursae of two specimens. Figures 22-29 (except 2 5 ) to the same scale.
The shape of the body and rostrum, the possession of paired sensory organs on the rostrum, as well as the droplet-shaped sperm clearly place Problognathia within the order Bursovaginoidea; the presence of a cuticular bursa and penis stylet require assignment to the suborder Scleroperalia (Sterrer, 1972). The inclusion of Problognathia in one of the existing families, however, presents difficulties. The majority of characters point to a close association of Problognathia with the "higher" Scleroperalia (i.e., the families Onychognathiidae and Gnathostomulidae) . This applies especially to the following: plump body and rostrum shape, lack of the ability to swim backwards, number and arrangement of sensory bristles (including the absence of postlateralia), ~ h a p eand low length-widthindex of the basal plate, shape and lamellarization of jawc, tripartition of pharyngeal bulb. and round dwarf sperm reminiscent of that of Gnathostornula ienneri ( Riedl, 1971b). A few features, however, do not conform with this pattern and are rather reminiscent of "lower" Scleroperalia: the lack of an epithelial pattern and of rhabdoids in the epidermis, the probable absence of paired apicalia and shortness of bristles in the sensorium, and the absence of a cauda in the jaws. The present species is rather unique among the Gnathostomulida because of
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the peculiar manner in which the jaws can be protruded, the interlocking nature of the bursa-prebursa complex, and the consistently circular bursa. P. minima is the smallest and also one of the plumpest gnathostomulids so far described. The small body size may also account for the unusual fact that the mature egg has to take up space laterally and caudally to the bursa. Inclusion of Problognathia in the Gnathostomulidne is opposed by the lack, in our new genus, of a jugum, as well as by the high homogeneity within this family in all but a few features (mainly of the rostrum and the sensorium). Similarly, the Onychognathiidae are well characterized by their basket-shaped jaws. Instead of diluting these taxa, therefore, we choose to establish the new family Problognathiidae, to be placed before the Onychognathiidae, at the basis of the "higher" Scleroperalia. Problognathiidae n. fam. Scleroperalia without distinct paired apicalia and with four pairs of short (30 p m ) compound sensory bristles which are fairly evenly spaced from each other. Ciliary pits absent. IVith paired buccal and pharyngeal glands. Epidermal cells not in stripes; epidermal inclusions scarce. Bursa and prebursa round, interlocking. Male stylet of the rod type. Sperm small and round, possibly with a bunch of short filaments. Basal plate broad; jaws rather lamellar and closed; without a cauda. Teeth arranged in rows. I\'ithout a jugum. IVithout ability to swim backwards.
Problognathia n. g. Problognathiidae with a very short rostrum (index ca. 0.6) and elongated mouth opening. Without a tail. Jaws with two short rows of teeth; a terminal tooth is developed. Basal plate broad (index ca. 0.3): the concave anterior edge beset with teeth. Pharynx protrusile. Type species: P. minima n. sp. Problognathia minima n. sp. Small, plump Problognathia (ca. 300 pm; body index about 6.0) with broad, short rostrum (index 0.6). Basal plate 10.4 pm long, 35.5 pm wide (index 0.3), with 35-40 teeth on its anterior margin. Jaws 23.5 pm long, with 3-5 larger teeth in dorsal, and $7 smaller teeth in ventral row. Bursa nearly perfectly circular, 30-35 pm in diameter. Sperm round to slightly angular, of 1 pm diameter; possibly provided with a few short filaments. Male stylet 26.7 pm long. The mature egg often extends laterally and caudally to the bursa1 organ.
FARRIS,R. A . 1973. On Austrognatharia str~rnki n. sp. from the Florida Keys (Gnathostomulida). Int. Rev. Ges. Hydrobiol., 58: 577-586. RIEDL, R. 1970a. Semaeognathia, a new genus of Gnathostomulida from the North American Coast. Int. Reo. Ges. Hydrobiol., 55: 359-370. 1970b. On Labidognathia longicollis nov. spec. from the West Atlantic Coast (Gnathostomulida). Int. Reo. Ges. Hydrobiol., 55: 227-244. 1971a. On Onychognathia, a new genus of Gnathostomulida from the tropical and subtropical West Atlantic. Int. Rev. Ges. Hydvobiol., 56: 201-214. 1971b. On the genus Gnathostornula (Gnathostomulida). Int. Reo. Ges. Hydrobiol., 56: 385496. STERRER,If'. 1970. On some species of Austrognatharia, Pterognathia and Haplognathia nov. gen. from the Korth Carolina Coast (Gnathostomulida). Int. Rev. Ges. Hydrobiol., 55: 371-385.
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1971a. On the biology of Gnathostomulida. Vie et Milieu, 22(Suppl.): 493-508. 1971b. Agnathiella beckeri nov. gen, nov. spec. from southern Florida: the first gnathostomulid without jaws. Int. Reu. Ges Hydrobiol., 56: 215-225. 1 9 7 1 ~ . Gnathostomulida: problems and procedures. Smithson. Contr. Zool., 76: 9-15. + 1972. Sy~tematicsand evolution within the Gnathostomulida. Syst. Zool., 21: 151-173. 1973. On Nanognathia, a new gnathostomulid genus from the east coast of the United States. Int. Reu. Ges. Hydrobiol., 58: 105-115.
CENTENNIAL CELEBRATION COMING UP! Members of the American ?r4icroscopical Society hardly need to be reminded that the year 1978 will mark the 100th birthday of our Society. To celebrate it in a fitting and meaningful way, the officers have already begun planning a major meeting for that year; and they are going to need all the aid and inspiration possible from the membership. So this notice is a plea for HELP! Ideas, offers to serve on subcommittees, etc., etc. should be sent directly to: Dr. Betty June Myers Chairman, Centennial Committee American ?r4icroscopicalSociety Box 28147 Southwest Foundation for Research and Education San Antonio, Texas 78284 Or you may prefer to give Dr. Myers a call, at the following number: 512/6741410. - John 0 . Corliss, Editor
