A new species of Cephalodasys (Gastrotricha, Macrodasyida) from the Caribbean Sea with a determination key to species of the genus Author Kieneke, Alexander Author Schmidt-Rhaesa, Andreas Author Hochberg, Rick text Zootaxa 2015 3947 3 367 385 journal article 10.11646/zootaxa.3947.3.4 e21766fe-79b8-498e-954a-4c1844d7a81a 1175-5326 243618 41AF948D-57C2-4622-B4A5-55EF72BE1F01 Cephalodasys interinsularis sp. nov. Figs. 2–5A , 6 Habitat/ type locality. The new species was collected from rather fine calcareous biogenous sand from a sublittoral shoal between Lee Stocking Island and Norman’s Pond Cay at a water depth of approximately 2 m ( N 23°45.972´ ; W 76°06.897´ ). The area between both islands (Fig. 1) has the properties of a tidal channel and hence a strong tidal current was present at the time of sampling. Apart from Cephalodasys , the sample also contained specimens from the gastrotrich taxa Macrodasys , Paraturbanella , Tetranchyroderma (Macrodasyida) and Draculiciteria (Paucitubulatina) . Material examined. Two specimens were studied alive and a third specimen was studied after fixation. Among the two live specimens, one individual was fully mature and the second was a subadult. The third specimen was fixed and studied with light and electron microscopy. Since only a single mature specimen was studied alive, this specimen is designated as the holotype even though it is no longer extant (International Code of Zoological Nomenclature/ ICZN , Articles 73.1.1 and 73.1.4, International Commission on Zoological Nomenclature 1999, 2008, 2012). The specimen prepared for SEM (see Fig. 6 A-F) is designated as a paratype specimen ( ICZN , Recommendation 73D) and is stored in the collection of the National Museum of Natural History/Smithsonian Institution ( USNM 1274540). Digital light microscopic and SEM images of this paratype are also kept in the collection. Digital files (images and videos) of the holotype and the other live specimen (see Figs. 3 , 4 , 5A ) are also deposited at the National Museum of Natural History. The latter individual is designated as a further paratype specimen ( ICZN , Recommendation 73D), which is no longer extant. A fourth specimen of Cephalodasys that was studied alive (see Fig. 5 B) probably does not belong to the new species (see discussion for details). Diagnosis. Cephalodasys with a body length of 471 µm. Body divided into pyriform head, neck, and trunk regions, the latter two inconspicuously separated from each other at the level of the pharyngeal pores that are positioned close to the posterior end of the pharynx. Caudal trunk end rounded. The rather long buccal cavity is hourglass-shaped and has a strengthened cuticular lining. Intestine/midgut linear and without obvious differentiation. Arrangement of TbA/TbVL/TbP is 2x 3/ 2x 5/11–12, respectively. TbA arise directly from the body surface, a fleshy base is not present. TbVL present in the trunk region only, TbD and ventral adhesive tubes (TbV) are absent. Unpaired ovary in a dorsolateral position in the posterior half of the trunk, pair of short and stout testes posterior to the pharyngeal pores, with short and caudally directed sperm ducts that fuse ventral to the midgut. An unpaired male gonopore is present at the site of sperm duct fusion. A frontal organ as putative sperm storing device is situated just posterior to the mature oocyte, a caudal organ is absent. Arrangement of cilia does not deviate from other Cephalodasys (see diagnosis above). Etymology. The species name is compound from the Latin words inter (= between) and insularis (= belonging to an island) and denotes the type locality, a sublittoral sandbar between two islands. The name shall not indicate that the new species is limited to that special habitat. However, during our stay on Lee Stocking Island in 2010, we did not find the species at any other sampling station. Description . The following description is based on the adult specimen that was studied alive and digitally documented, viz. the holotype ( Figs. 2–4 ). A full overview of morphometric variability across all three studied specimens, including one subadult individual, is provided in Table 1 . It has to be stressed, however, that in particular length measurements of the fixed specimen may be erroneous due to contractions and/or shrinkage artefacts. Habitus. The new Cephalodasys is a medium-sized macrodasyid gastrotrich with a total body length of 431– 471 µm (n=2). Like most other species of Cephalodasys , it has a distinct, pear-shaped head that is delineated from the neck region at U11 by a constriction ( Figs. 2 , 3 , 4 A–C, 5A, 6A, C). The trunk region (approximately U35– U100) is slightly wider than the neck region (approximately U11–U35) and ends with a rounded caudum ( Figs. 2 , 3 , 5A ). Body widths are 47/37/42/48/51/25 µm at U 5/11/25 /50/75/94.5, respectively (see Table 1 ). The outline of the animal appears irregularly undulated, which is likely the result of the soft and folded integument ( Figs. 2 , 3 A– B). The body is ventrally flat but dorsally convex. In the testicular region, the trunk cross section appears to be trilobate. The cuticle is smooth and shows no ornamentations; epidermal glands per se are absent but the epidermis appears finely granular under the light microscope (e.g. Fig. 4 A, C, E). Adhesive tubes. The new species of Cephalodasys has adhesive tubes in an anterior (TbA), ventrolateral (TbVL), and posterior (TbP) series; ventral tubes and dorsal tubes are absent ( Fig. 2 ). There are three TbA per side (n=3) present at the transition from head to neck regions (U10.5–U12, n=3). The tubes are of equal size (length: 7– 11.5 µm, width: 1.5–2.5 µm, n=3) and are arranged in parallel ( Figs. 2 , 3 A, 4C, 6C–D). Their longitudinal axis is slightly tilted toward the midline of the animal (approximately 7°, see Fig. 6 C). If a living, anaesthetized specimen gets slight pressure from the cover slip, TbA may appear aligned parallel to the longitudinal axis of the animal (see Fig. 4 C). TbA arise directly from the ventral body surface but there is a shallow pit anterior to them ( Fig. 6 B). FIGURE 2. Cephalodasys interinsularis n. sp. Schematic drawings of the holotype specimen. Left: Ventral view. Right: Combined dorsal and internal view. an, anus; fo, frontal organ; fop, frontal organ pore; lc, locomotory cilia; me, mature egg; mgp, male genital pore; ov, ovary; ph, pharynx; pp, pharyngeal pores; sc, sensory cilia; TbA, anterior adhesive tubes; TbP, posterior adhesive tubes; TbVL, ventrolateral adhesive tubes; te, testis. FIGURE 3. Cephalodasys interinsularis n. sp. Light microscopic images (differential interference contrast, DIC) of the holotype specimen, assembled from two images, respectively. A) Ventral view showing the adhesive tubes and locomotory cilia. B) Horizontal focal plane showing internal organs. fo, frontal organ; in, intestine; lc, locomotory cilia; me, mature egg; ov, ovary; ph, pharynx; pp, pharyngeal pores; TbA, anterior adhesive tubes; TbP, posterior adhesive tubes; TbVL, ventrolateral adhesive tubes; te, testis. Posterior to the TbA and inside the body, one can observe two parallel filaments per TbA that seem to anchor each adhesive tube. Each adhesive tube has a slight furrow extending down its longitudinal axis, which probably indicates the presence of a duo-gland adhesive system ( Fig. 6 D). Terminally, each TbA has two tiny pores ( Fig. 6 D). Between U35 and U75, there are five pairs of bilateral-symmetrically arranged TbVL (n=3). The tubes appear long and slender and measure 10–16.5 µm in length and 1–1.8 µm in width (n=3). Their insertion points are somewhat ventral in position but mainly lateral to the bands of locomotory cilia ( Figs. 2 , 4 E, 5A). Hence, the TbVL are hardly visible from the dorsal side. In both adults and subadults, there is a consistent pattern concerning the arrangement of TbVL: the spaces between the 1st, 2nd and 3rd tubes is about half the distance (25.5–34.5 µm) of that between tubes 3, 4, and 5 (47–60.5 µm). Caudally, there are 11–12 TbP (n=3) arranged along the posterior margin ( Figs. 2 , 3 A, 5A). Lengths of individual TbP vary within and between specimens, generally from 6.5–13 µm (n=3), while the width is more consistent (2–2.25 µm, n=3). One or two short cilia may arise from the distal tip of each TbP ( Fig. 4 F). Cilia. Locomotory cilia on the ventral side are arranged in two longitudinal columns beginning at the anterior end and extending to the ventral anus at U94.5. Posterior to the anus, there is a short uniform field of ventral locomotory cilia, i.e. both longitudinal columns fuse ( Figs. 2 , 4 E, 6A–C). In the neck region, the space between the two columns is closer than on the rest of the body, giving the false impression that they fuse ( Figs. 4 C, 6C). The lateral flanks of the pear-shaped head bear additional cilia ( Fig. 6 B) that extend around the lateral and dorsal portion of the head to create a closed ciliary ring ( Fig. 4 A). The length of the locomotory cilia is ca. 10 µm. Dorsolaterally on the head region and along the whole trunk there are long (25–30 µm) and stiff sensory cilia (e.g. Fig. 6 B). These cilia are present along the length of the body: five pairs of cilia are present on the head and 11–12 pairs are bilaterally distributed along the neck and trunk. Shorter sensory cilia ( 5–7 mm ) are present on the flanks of the neck, trunk, and the dorsal side of the caudum. Approximately 25 short cilia surround the mouth opening ( Fig. 6 B–C). Sensory organs. Apart from the sensory cilia, there are no other obvious sensory organs (e.g., tentacles, pigmented eye spots) on the head region. However, dorsal to the pharynx there is a bilateral pattern of small vesicles ( Fig. 4 B). These may belong to a pair of photoreceptive head sensory organs that are, for instance, also known from Cephalodasys maximus (see, e.g., Wiedermann 1995 ). FIGURE 4. Cephalodasys interinsularis n. sp. Light microscopic images (DIC) of the holotype specimen. A) - C) Head region at different focal planes (dorsal to ventral). Note the paired array of vesicles dorsal to the pharynx (asterisks in B). D) Detail of the posterior trunk region showing the frontal organ. The roundish structure to the left of the frontal organ is the terminal section of the intestine. E) Ventral view of the mid trunk with adhesive tubes and the male gonopore. Note also the finely granular epidermis. F) Posterior adhesive tubes. Note the short associated sensory cilia (arrowheads). G) Mid trunk with paired testes. an, anus; fop, pore of frontal organ; in, intestine; lc, locomotory cilia; me, mature egg; mgp, male genital pore; sc, spermatocytes; sd, sperm ducts; sg, spermatogonia; sp, foreign spermatozoa (allosperm) within the frontal organ; TbA, anterior adhesive tubes; TbVL, ventrolateral adhesive tubes. FIGURE 5. A) Cephalodasys interinsularis n. sp. Light microscopic image (DIC, ventral view) of a subadult specimen, assembled from two images. The depicted animal is a paratype specimen that is no longer existent. B) An undetermined specimen of Cephalodasys . It represents a very large subadult or post-reproductive animal that had only four instead of five pairs of ventrolateral adhesive tubes. in, intestine; lc, locomotory cilia; ph, pharynx; TbA, anterior adhesive tubes; TbP, posterior adhesive tubes; TbVL, ventrolateral adhesive tubes. Digestive tract. The gut tube is divided into an anterior glandulo-muscular pharynx and a posterior intestine ( Figs. 2 , 3 B). The pharynx makes up 38–40% (adult specimens, n=2) of the total length of the whole gut tube ( Tables 1 and 2 ). The circular mouth opening is terminal (only inconspicuously tilted, see Fig. 6 B) and has a diameter of ca. 10 µm. Apart from the short cilia mentioned above, there are no other structures such as longitudinal ridges or hooks that line the mouth. However, the cuticular wall of the cylindrical to slightly hourglass-shaped buccal cavity (25–30 µm long) is thickened ( Fig. 3 B). The width of the pharynx (22 µm) is nearly equal along its whole length; it is only slightly narrower around the buccal cavity (U0–U05), and increases in width at the level of the pharyngeal pores. The position of the pores is at U31–U 35 in adult specimens (n=2). The actual pores are inconspicuous slits that lie dorso-laterally in the body wall ( Fig. 6 B); the pharyngeo-intestinal junction is at U36–U 38 in adult specimens (n=2). The shape of the intestine is quite irregular and the diameter varies considerably along its course. In the region where a large ovum is situated in adult specimens, the intestine forms a drawn-out curve to the right side of the trunk and its diameter is slightly reduced ( Figs. 2 , 3 B). The intestine ends in a ventral anus at U94.5 (n=2). In this area, the terminal part of the intestine may be widened (see, e.g., Fig. 4 D). Although no distinct regionalization of the intestine is visible, the abundance of small refractive spheres in its wall cells increases from anterior to posterior, possibly due to increased resorption processes in the midgut. Reproductive organs. The new species is hermaphroditic with paired testes and an unpaired ovary. The paired testes are present between U36.5–U38 and U49–U50 (n=2) and are broad and club-shaped (12–13 µm wide) with short, caudally projecting vasa deferentia ( Figs. 2 , 4 G). The sperm ducts immediately curve medio-ventrally and specimen ID (name of folder with digital notes Lt[µm] LPh PhJIn pos. PP pos. PP pos. anus material, i.e. images and videos) [µm] [U] [µm] [U] [µm] specimen ID (name of folder with digital notes Wtat pos. TbA per pos. TbA pos. TbA L TbA material, i.e. images and videos) anus testes side [µm] [U] [µm] FIGURE 6. Cephalodasys interinsularis n. sp. Scanning electron microscopic images of the second paratype specimen (USNM 1274540). A) Habitus, seen from ventral to ventrolateral (animal twisted and damaged). B) Pharyngeal region, lateral view. C) Head region, ventral view. D) Close-up of the anterior adhesive tubes. Note the longitudinal furrow and two apical pores on each tube. E) Close-up of the ventral male genital pore. F) External pore of the frontal organ on the left side. lc, locomotory cilia; mgp, male genital pore; mo, mouth; pp, pharyngeal pores; sc, sensory cilia; TbA, anterior adhesive tubes; TbP, posterior adhesive tubes; TbVL, ventrolateral adhesive tubes. TABLE 1. Meristic and morphometric characters of the four investigated specimens of the new and one undescribed species of Cephalodasys from the Bahamas. Abbreviations: L, length; LPh, length of pharynx; Lt, total body length; n.a., not applicable; pos., position; PP, pharyngeal pores; PhJIn, pharyngeo-intestinal junction; TbA, anterior adhesive tubes; TbP, posterior adhesive tubes; TbVL, ventrolateral adhesive tubes; W, width; Wt, trunk width.

C_ interinsularis _n_sp_adult	mature holotype	471	171	U36	164	U35	445
C_ interinsularis _n_sp_adult_F-100414-2A	mature (SEM and LM) paratype	431	165	U38	135	U31	408
C_ interinsularis _n_sp_subadult	developing testes visible, no ovary paratype	378	163	U43	153	U40.5	355
Cephalodasys _sp_subadult	no testes, no ovary different species	603	215	U35.5	199	U33	586

specimen ID (name of folder with digital material, i.e. images and videos)	notes	pos.anus Wt at U5 Wt at [U] [µm] TbA [µm]	Wt at U25 [µm]	Wt at U50 [µm]	Wt at U75 [µm]
C_ interinsularis _n_sp_adult C_ interinsularis _n_sp_adult_F-100414-2A C_ interinsularis _n_sp_subadult	mature holotype mature (SEM and LM) paratype developing testes visible, no ovary paratype	U94.5 47 37 U94.5 45 36 U94 43 35	42 39 40	48 47 48	51 44 41
Cephalodasys _sp_subadult	no testes, no ovary different species	U97 54 46	47	57	54

[µm] plus vasa deferenti a [µm] _ interinsularis _n_sp_adult mature holotype 25 172–237 3 53 U11 10 _ interinsularis _n_sp_adult_F- 100414 -2A mature (SEM and LM) paratype 27 165–212 3 49 U11 7 _ interinsularis _n_sp_subadult developing testes visible, no ovary paratype 27 164–209 3 44.5 U12 11.5 Cephalodasys _sp_subadult no testes, no ovary different species 32 n. a. 3 63 U10.5 10.5 … …continued on the next page specimen ID (name of folder with digital notes WTbA TbVL L TbVL W TbVL TbP L TbP material, i.e. images and videos) [µm] per side [µm] [µm] [µm) TABLE 1. (Continued) interinsularis _n_sp_adult mature holotype 2–2.5 5 13.5– 1.8 11 6.5–10.5 16.5 interinsularis _n_sp_adult_F- 100414 -2A mature (SEM and LM) paratype 1.5 5 10–11.5 1 11 n. a. interinsularis _n_sp_subadult developing testes visible, no ovary paratype 2 5 12 –14 1.7 12 7–13 Cephalodasys _sp_subadult no testes, no ovary different species 2.5 4 10–12 1.7 11 7–10 specimen ID (name of folder with digital notes W TbP [µm] ratio of LPh to total pos. testes plus vasa deferentia material, i.e. images and videos) digestive tract [U] interinsularis _n_sp_adult mature holotype 2.25 38% U36.5–U50 interinsularis _n_sp_adult_F- 100414 -2A mature (SEM and LM) paratype 1.5–2 40% U38–U49 interinsularis _n_sp_subadult developing testes visible, no ovary paratype 2 46% U43–U55 Cephalodasys _sp_subadult no testes, no ovary different species 2.25 37% n.a. TABLE 2. Meristic and morphometric characters with diagnostic value of all known species of Cephalodasys . Abbreviations: a, absent; IT, intertidal; n.a., not applicable; p, present;?, unknown character; the question mark in brackets (?) denotes an unsure character state. Further abbreviations: See Table 1. species Lt [µm] LPh [µm] position of ratio of LPh to shape of anterior end ("head") shape of caudum PhJIn total digestive tract a

Cephalodasys cambriensis	990	290	U30 32%	pyriform rounded disc
Cephalodasys caudatus	700–800	220	U33 39%	rhombic, Dactylopodola -like elongate lobe
Cephalodasys dolichosomus	615–772	205–215	U28–U33 29%	pyriform rounded, slightly flared
Cephalodasys hadrosomus	322	152	U47 53%	rounded rounded
Cephalodasys littoralis	600–650	200	U35.5 39%	pyriform tapering
Cephalodasys maximus Cephalodasys miniceraus	700 464g	235 138	U33.5 36% U32 36%	pyriform rounded disc with hornlike lobes, Turbanella -like tapering
Cephalodasys pacificus	294–368	105–125	U34–U37 37%	pyriform rounded, slightly flared
Cephalodasys palavensis	400–500	ca. 140	U38 44%	rhombic, Dactylopodola -like tapering with blunt apex
Cephalodasys saegailus	492–517	191–196	U38–U39 37%	pyriform rounded, slightly flared
Cephalodasys swedmarki	500	238	U47 51,5%	pyriform to ovoid rounded
Cephalodasys turbanelloides	1000	367	U36.5 38%	pyriform rounded to parable-shaped
Cephalodasys sp. nov.	431–471	171–215	U35.5–U36 38–40%	pyriform rounded

… …continued on the next page …….continued on the next page TABLE 2. (Continued)

species	position of testes plus TbA per L TbA vasa deferentia side [Μm]	W TbA b	TbVL per side	L TbVL [Μm]	TbVL in the pharyngeal region c	TbV
Cephalodasys cambriensis	U30.5–U68.5 5-6 8	common	15-20	8-12	p	a
Cephalodasys caudatus Cephalodasys dolichosomus Cephalodasys hadrosomus Cephalodasys littoralis	U37–U64.5 3 12 U28/33–U50+d 4 8–9?e 6 8 U36–U67.5f 4 -5?	common common common common	12–15 6 a 13–14	12 15–18 n.a.?	p a n.a. p	a a a a
Cephalodasys maximus Cephalodasys miniceraus Cephalodasys pacificus Cephalodasys palavensis Cephalodasys saegailus Cephalodasys swedmarki Cephalodasys turbanelloides	U33.5–U92 5??g 2 8–9 U32–U75+d 5–6 6.5–9 U38–U73+d 4 5 U38–U51+d 4 6–8?e 4 4–8 U35.5–U77+d 6–7 10	common common very thin very thin common common common	14 9–12 3 -7 (often 5) 10 10 5 15–20	? 5–6 9–13 5 10–16 16–21 9–12	a p a p p a p	a a a a p (2 pairs) a a
Cephalodasys sp. nov.	U36.5–U50 3 10–11.5	common	5 (4)	10–16.5	a	a

TABLE 2. (Continued)

species	TbDL	TbP	L TbP [Μm]	TbP arranged in two arcs	frontal organ	caudal organ	epidermal glands	finely granular epidermis
Cephalodasys cambriensis	a	17	8-12	a	p	p	a	p
Cephalodasys caudatus	a	10–12	12	a	p	p	a	p
Cephalodasys dolichosomus	a	16	7–10	a	?	?	a	p
Cephalodasys hadrosomus	a	20	9 -13	p	?	?	p	a
Cephalodasys littoralis	a	14–16	5 and 8–10	a	p	p	a	?
Cephalodasys maximus	p (11 pairs)	20	&	a	p	p	p	?
Cephalodasys miniceraus	a	6–8	10–13	a	?	?	a	p
Cephalodasys pacificus	a	13–17	7.5–8.5	a	p	a	a	p
Cephalodasys palavensis	a	10	5	a	p	a	a	?
Cephalodasys saegailus	a	18	5–7 and 8–10	p (?)	?	?	a	p
Cephalodasys swedmarki	a	10–12	9–10	a	?	?	a	p
Cephalodasys turbanelloides	a	10–15	ca. 10	a	?	?	a	p
Cephalodasys sp. nov.	a	11–12	6.5–13	a	p	a	a	p

…….continued on the next page Cephalodasys sp. nov. shoal close to Lee Stocking Island, Bahamas ( N 23°45.972´ ; fine calcareous sand 2 m this study TABLE 2. (Continued)

species	type locality and position (if provided in original description)	habitat / ecology	depth	reference
Cephalodasys cambriensis	Llandwyn and Rhosneigr, Anglesey, Wales (Irish Sea)	beach slope around low water line, fine to fairly fine sand (200–350 Μm)	IT	Boaden 1963
Cephalodasys caudatus	Puri Beach, Orissa, India (N 19°48'06''; E 85°51'14'') (Bay of Bengal)	beach slope between low and half tide levels, coarse and medium sand	IT	Rao 1981
Cephalodasys dolichosomus	different coastal sites of Egypt and Israel (Red Sea)	low water line to sublittoral, very fine to very coarse sand (silicious or coralline)	IT, 0.5–8 m	Hummon 2011
Cephalodasys hadrosomus	Santa Maria di Leuca, Apulia, Italy (N 39°47'; E 18°18') (Ionian Sea)	medium to coarse sand, mixed with shell and coral gravel	4 m	Hummon et al. 1993
Cephalodasys littoralis	Camp Américain, Bassin d'Arcachon, France (Atlantic)	moist sand at the low water line, varying salinity between 29–33 ppm	IT	RenaudDebyser 1964
Cephalodasys maximus	Stoller Grund, outer Kiel fjord, Germany (Baltic Sea)	mid-coarse sand	7–8 m	Remane 1926
Cephalodasys miniceraus	El Rodadero Beach, Santa Marta, Colombia (Caribbean Sea)	intertidal sand, mean grain size 189–203 Μm	IT	Hummon 1974b
Cephalodasys pacificus	Santa Cruz, Galapagos Archipelago, Ecuador (Pacific)	beach sand (coralline?), close to the high water line	IT	Schmidt 1974
Cephalodasys palavensis	Golfe d'Aigues-Mortes, France (Mediterranean)	coarse calcareous sand	IT	Fize 1963
Cephalodasys saegailus	Marsa Matruh, Sidi Abd al-Rahman, Egypt (Mediterranean)	very fine to fine, well to medium-well sorted sands, feeds on a diversity of diatoms	3 m	Hummon 2011
Cephalodasys swedmarki	Firemore Beach, Scotland (N 57°49'; W 05°41'); Glen Brittle, Isle of Skye; Ile de Jarre, France	fine to medium fine sand, medium-well or poorly sorted	IT / 8 m	Hummon 2008
Cephalodasys turbanelloides	Hallö / Väderöarna, Sweden (Skagerrak)	medium to fine grained sand	22 m	Boaden 1960

W 76°06.897´ ) (Caribbean Sea) this ratio has been re-measured from the drawings of the original descriptions 'common' means that TbA are comparably wide as other tubes of the animal considered are TbVL anterior to the pharyngeal pores termination of vasa deferentia was not observed description based on protogynous specimens posterior termination of testes in C. littoralis is unsure description based on subadult specimens join in an unpaired ventral male gonopore ( Figs. 4 E, 6E). Based on light microscopic observations, the male gonopore appears as a simple circular opening ( Fig. 4 E). However, scanning electron microscopy of that region indicates a slightly more complex, valve-like structure ( Fig. 6 E). Furthermore, light microscopy reveals a trefoilshaped structure directly underneath the male gonopore, possibly a glandular organ that aids sperm transfer in that species (indicated in the schematic drawing, see Fig. 2 ). At the anterior pole and along the median wall of each testis, cell-like compartments with granular content can be observed in some optical layers ( Fig. 4 G). We interpret this as early germ cell stages. According to this interpretation, spermatogenesis proceeds from posterior to anterior and spermiogenesis medio-laterally. A single mature egg is present dorso-lateral to the intestine and on the left side of the trunk between U65 and U85. The egg contains numerous small spheres, probably yolk material, and has a large globular nucleus, ca. 15 µm in diameter ( Fig. 3 B). Smaller oocytes with ovoid nuclei ( 6 x 12.5 µm) are present anterior the single large egg. Hence, oogenesis proceeds antero-posteriorly. Posterior to the mature egg on the left side of the posterior trunk (between about U82.5 and U88.5) there is an accessory reproductive organ, viz. the frontal organ. The shape of this structure is somewhat ovoid but irregular and lacks any obvious musculature. In its center, the putative organ lumen, there is a grain-like inclusion and few filiform structures coiled around it ( Figs. 3 B, 4D). We interpret these structures as foreign spermatozoa of a mating partner. The putative wall epithelium of the frontal organ is probably secretory since some small vesicles can be observed. Light and SEM observations indicate a lateral external pore to the frontal organ ( Figs. 4 D, 6F); an internal pore was not observed. Apart from the structure associated with the male gonopore, no further accessory reproductive organ (i.e. a caudal organ) is present.