Cateria gerlachi, Higgins, 1968

C. gerlachi Higgins, 1968 from Sri Lanka

( Figs 2–17 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 View FIGURE 10 View FIGURE 11 View FIGURE 12 View FIGURE 13 View FIGURE 14 View FIGURE 15 View FIGURE 16 View FIGURE 17 , Tables 2−6, 11)

Cateria gerlachi Higgins, 1968 : Neuhaus 2013: 323, fig. 5.1.9.

Material examined and locality. Table 1 lists the localities where specimens were obtained (see also Fig. 1 View FIGURE 1 ) and the museum collection where the material is deposited. All specimens from Sri Lanka are deposited at the Museum für Naturkunde Berlin and catalogued as 57 adult ( ZMB 11519 View Materials .n; n = original specimen number given prior to identification) and 47 juvenile specimens ( ZMB 11520 View Materials .n; n = original specimen number given prior to identification) ( Table 1) .

Diagnosis. Segments 1–6 with one midventral sternal plate and one tergal plate; segments 7–10 with single tergal plate whose lateral ends meet midventrally; segment 11 with single circular cuticular plate. With acicular spine middorsally on segments 2–4, 6, 8–10, and 11 (= midterminal spine); acicular spine lateroventrally on segments 6–10 and 11 (= lateral terminal spine); blunt tube in lateral accessory position on segment 5; acicular spine in lateral accessory position on segment 11 (= lateral terminal accessory spine). Type-1sensory spot middorsally on segment 1, paradorsally on both sides of segment 10 and either on the left or on the right side of segments 2, 3 and 7–9, subdorsally on segment 11 just anterior of a terminal type-3 sensory spot in the process neighbouring the midterminal spine, laterodorsally on segment 11 (central part of segment), midlaterally on segments 1 and 2 (the latter usually intermediate to sublateral position), ventrolaterally on segment 11 (central part of segment), and ventromedially on segments 2–4; type-3 sensory spot on segment 11 subdorsally terminally on the process neighbouring the midterminal spine; type-5 sensory spot middorsally on segments 2–9 (anterior part of segments), paradorsally on both sides of segments 4 and 6 and either on the left or on the right side of segment 5, laterodorsally on segments 2–9 (central part of segments) and 10 (posterior part), midlaterally on segment 10 (central part of segment), sublaterally on segments 3−5 (anterior part of segments), in the central part of segments 8 and 9 and on segment 6 (posterior part), in a lateral accessory position on segments 2 and 6–9 (anterior part), lateroventrally on segment 10 (anterior part of segment) and on segment 1 (posterior part), ventrolaterally on segment 1 (central part of segment), and ventromedially on segments 3–10 (anterior part) and on segments 1 and 10 (posterior part of segments). Papilla lateroventrally on segment 11. Gland cell outlet in posterior part of segment paradorsally on segment 1, subdorsally on segments (1)2–10, midlaterally on segments 1–9, sublaterally on segments 2–5 and 7–10, ventrolaterally on segment 2 (anterior part of segment), and ventromedially on segments 5–9; gland cell outlets occasionally paradorsally on segments 2, 5 and 7. Male differing from female (1) by modified acicular spine middorsally and lateroventrally on segment 10, (2) by almost rectangular cuticular flap about midlaterally and anteriorly on segment 11 vs lack of this structure in female, and (3) lack of paradorsal type- 1 sensory spot centrally on segment 10 vs its existence in female.

Redescription. The description refers to female adults. Specimens reveal a head, neck, and 11 trunk segments ( Figs 2A, B View FIGURE 2 , 5A, B View FIGURE 5 , 13A View FIGURE 13 ). For measurements and dimensions see Table 2; for summary of spine, gland cell outlet, and sensory spot locations see Table 4. The description of the mouth cone and introvert are based on observation of three adult specimens of undetermined sex but probably female mounted for SEM.

Mouth cone. In a single specimen (ZMB 11519.36) with an artificially protruded mouth cone, the inner oral styles become visible ( Fig. 13C View FIGURE 13 ). The anteriormost ring -03 of the mouth cone in its normal position consists of five spinose inner oral styles, the helioscalids. This style is broad at its base and tapers to a spinose tip. From this specimen, the oblique to tangential arrangement of the oral styles as seen in other Kinorhyncha cannot be corroborated here, because the artificial protrusion of the mouth cone leads to a distorted arrangement of the oral styles. The second ring -02 reveals five strongly sclerotized, hook-like styles in an alternating position to the styles of the previous ring. This ring is followed posteriorly by ring -01 exhibiting 10 spinose styles ( Figs 3 View FIGURE 3 , 13C View FIGURE 13 ).

TABLE 2. Measurements of adult Cateria gerlachi from Sri Lanka and India [µm].

The mouth cone bears at its anterior end nine outer oral styles (length ca. 50 µm) which consist of three jointed elements ( Figs 6A, C View FIGURE 6 , 13B View FIGURE 13 ). The apical element bends towards the mouth opening anteriorly and shows a very short, triangular, basal process with two basal knobby cuticular thickenings ( Figs 6C View FIGURE 6 , 13B View FIGURE 13 ). The length of the basal element of neighbouring outer oral styles alternates between shorter and longer resulting in alternating longer and shorter outer oral styles ( Fig. 13B View FIGURE 13 ). Basally, each style reveals two tufts of spinose hairs originating at different levels ( Fig. 6C View FIGURE 6 ). Otherwise the cuticle appears smooth. A triangular cuticular plate separates the oral styles basally. Three to four basal strands of circular muscles connect the oral styles with each other.

Scalids. Anterior of the primary spinoscalids, a ring of 10 pairs of thin cuticular spines (length about 49 µm) with a smooth surface occurs ( Figs 3 View FIGURE 3 , 6A View FIGURE 6 , 13G View FIGURE 13 ). In some specimens, the spines of each pair seem to be connected over most of their length by cuticle except apically ( Fig. 6A View FIGURE 6 ). In other specimens, this cuticular membrane is not recognizable or does not exist. Basally, the cuticle of the spines is strongly sclerotized over about 7 µm (for similar situation see C. styx : Fig. 26F View FIGURE 26 ). There are no other, shorter spinose processes near the paired long processes.

The introvert reveals six rings of scalids extending radially, namely 10 primary spinoscalids in ring 01, 10 spinoscalids each in rings 02–04, 5 spinoscalids in ring 05, and 13 trichoscalids. The positions of the primary spinoscalids mark the primary radii in the introvert and divide it into ten sectors, numbered clockwise from the midventral one ( Fig. 3 View FIGURE 3 ). The primary spinoscalids are the longest scalids of the introvert (87–125 µm) and may reach until the end of segment 2 ( Figs 5B View FIGURE 5 , 6E View FIGURE 6 , 7J View FIGURE 7 , 13G View FIGURE 13 ). Six of these spinoscalids are longer (about 125 µm) than the 4 others of ring 01 (about 87 µm); the shorter spinoscalids seem to occupy a subdorsal position (at the border of introvert sectors 4 and 5 as well as of sectors 7 and 8) and a ventrolateral position (at the border of introvert sectors 1 and 2 as well as of sectors 1 and 10). The primary spinoscalids possess a slightly broader long basis, a long central part with internal septa and an outer annulation, and a distal, very flexible element which ends in a more or less spinose tip. These scalids are covered with few hairs basally and more intensely anteriorly in the central part. The internal septa and the outer annulation of the central part of the spinoscalid are weak and barely visible both in light microscopy and SEM ( Fig. 7J View FIGURE 7 ).

All remaining spinoscalids consist of a basal and a distal element with cuticular hairs as a fringe at the terminal end of the basal part ( Figs 6B View FIGURE 6 , 13G View FIGURE 13 ). Ring 02 spinoscalids alternate in position with ring 01 primary spinoscalids. They are slim, cuticular hairs concentrate in the second quarter of the scalids’s length ( Figs 3 View FIGURE 3 , 6B View FIGURE 6 , 13G View FIGURE 13 ). Ring 03– 05 spinoscalids are more robust and reveal a lateral fringe of cuticular hairs on each side of the scalid ( Figs 6B View FIGURE 6 , 13G View FIGURE 13 ). Two spinoscalids flank the position of the ring 02 spinoscalids in the next ring in odd sectors adding to a total of 10 scalids in this ring ( Fig. 3 View FIGURE 3 ). In ring 04, 10 spinoscalids occur in even sectors. Only 5 ring 05 spinoscalids are located in odd sectors ( Fig. 3 View FIGURE 3 ). Summarized sector-wise, all odd sectors show one central anterior (ring 02) and one central posterior spinoscalid (ring 05), with two lateral spinoscalids in ring 03; all even sectors contain only one central anterior spinoscalid (ring 02) and two lateral spinoscalids in ring 04.

The posteriormost ring of spinoscalids is followed by 14 areas of cuticle covered with short cuticular hairs appearing as fine ‘denticles’ in light microscopy and separated from each other by longitudinal folds of smooth cuticle ( Figs 3 View FIGURE 3 , 6B View FIGURE 6 ). Each of the areas with the short cuticular hairs is succeeded posteriorly by a trichoscalid except midventrally ( Fig. 3 View FIGURE 3 ). Therefore, 13 trichoscalids occur. Each trichoscalid is densely covered with long cuticular hairs, especially posteriorly ( Fig. 6A, B View FIGURE 6 ). The length of the trichoscalids varies, namely between a very short middorsal trichoscalid (7 µm), a long paradorsal scalid (31 µm), a short subdorsal scalid (7 µm), a long midlateral scalid (25–31 µm), a short lateral accessory and a short lateroventral scalid (6 µm), and a very long ventromedial scalid (30–33 µm) ( Fig. 3 View FIGURE 3 ). The trichoscalids are located on weak cuticular plates except for the middorsal one.

Neck. The neck consists of 12 trapezoidal placids with a thin and flexible cuticle which appear in light microscopy clearly separated both from the trunk and from each other in some specimens but not in all ( Figs 6B, E View FIGURE 6 , 13D, G View FIGURE 13 , 17C View FIGURE 17 ). However, occasionally a shorter or longer longitudinal fold seems to separate an additional placid at different positions. This is interpreted as an artifact resulting from the thin cuticle of the placids. Two specimens with almost entirely withdrawn introvert reveal only 7 or 8 placids, namely the middorsal (?) and midventral placid as well as all placids with a sensory spot. Probably, the 4 intermediate placids are folded inwards. The surface of the placids appears as a leather-like, weak sculpturing ( Fig. 6B, E View FIGURE 6 ). A type-5 sensory spot occurs paradorsally to subdorsally, about midlaterally or sublaterally, and lateroventrally on the placids ( Figs 3 View FIGURE 3 , 6A, B, E View FIGURE 6 , 13D–G View FIGURE 13 , 17C View FIGURE 17 ). Below the cuticle, a highly curled cuticular tube extends from the sensory spot deeper into the body ( Figs 13E, F View FIGURE 13 ).

Trunk. The trunk cuticle is thin, flexible, quite transparent, and bulges irregularly ( Figs 5A–F View FIGURE 5 , 8A–D View FIGURE 8 , 13A, H View FIGURE 13 , 14A–D View FIGURE 14 , 15H, J View FIGURE 15 ). At the anterior margin, each segmental cuticular plate does not seem to thicken towards the interior of the body, so a pachycyclus is lacking ( Figs 13H View FIGURE 13 , 14A–D View FIGURE 14 , 15H, J View FIGURE 15 ). When alive, the specimens exhibit an almost circular cross-section. The trunk contains 11 segments which consist of a tergal plate and a midventral sternal plate on segments 1–6 ( Figs 2A, B View FIGURE 2 , 6E, F View FIGURE 6 , 13H View FIGURE 13 ), a single tergal plate whose lateral ends meet midventrally on segments 7–10, and a single circular cuticular plate on segment 11 ( Figs 2B View FIGURE 2 , 7B View FIGURE 7 ). On segments 7–11, the midventral area is covered by a patch of short, straight cuticular hairs; this area is broader on segment 11 ( Figs 7A, B, D View FIGURE 7 , 14D View FIGURE 14 ). Segments 1 and 2 may be withdrawn together with the introvert until the insertion area of the middorsal spine ( Figs 5C View FIGURE 5 , 7H View FIGURE 7 , 17D View FIGURE 17 ). The midventral sternal plate of segments 1–5 is more or less rectangular whereas this plate appears triangular with a rounded tip on segment 6 ( Figs 6E, F View FIGURE 6 , 7A View FIGURE 7 , 13H View FIGURE 13 , 14D View FIGURE 14 ). A deep notch occurs in the free flap where the middorsal and lateroventral spines originate, lateroventrally on segments 2–5, ventrolaterally on segment 10, and ventromedially on segments 7–10 ( Figs 2A, B View FIGURE 2 , 5B, E, F View FIGURE 5 , 6D, F View FIGURE 6 , 7A, B, D, E View FIGURE 7 , 8 View FIGURE 8 A−D, 13H, 14C, D, 15H). These notches result ventrally on each side of segments 7–9 in two lobes and on segment 10 in three lobes of the free flap ( Figs 7A, B, D View FIGURE 7 , 14D View FIGURE 14 ). The paraventral lobes of segments 7–10 are narrower, more or less triangular, and reveal rounded margins on more anterior segments. The tergal plate of segment 11 shows on both sides a caudal, triangular extension that exceeds the posterior margins of the ventral cuticle and accompanies the midterminal spine ( Fig. 7B, D View FIGURE 7 ). Terminally each extension bears a type-3 sensory spot ( Fig. 7B, D View FIGURE 7 ).

The surface of the cuticle reveals from anterior to posterior the intersegmental cuticle, the secondary fringe consisting of leaf-like and spinose hairs, a central area with cuticular scales, and a posterior free flap ending in a primary fringe and extending partly over the subsequent segment ( Figs 5B, D–F View FIGURE 5 , 6E, F View FIGURE 6 , 7A, B, D, E View FIGURE 7 , 8A–D View FIGURE 8 , 13H View FIGURE 13 , 14A–D View FIGURE 14 , 15H, J View FIGURE 15 ). The anterior margin of segment 1 and the intersegmental cuticle exhibit a weak, leather-like sculpturing ( Fig. 6E View FIGURE 6 ). The secondary fringe may take up more than one third of the length of segments 2−11 and consists of cuticular, leaf-like hairs which are usually deeply split into two hairs and a posterior row of spinose hairs about 6 µm long ( Figs 5 View FIGURE 5 C−F, 6E, F, 7J, 8A–D, 14A, C). The leaf-like hairs are much stronger on segment 1 than on the remaining segments. The bases of especially the midventral hairs on segment 1 appear as knobby ‘denticles’ in surface view in light microscopy, but the bifid tip of the hairs can be observed with careful focussing as well ( Figs 6E View FIGURE 6 , 13D, H View FIGURE 13 ). In longitudinal optical section, the hairs show as ‘hooks’. The leaf-like hairs of the secondary fringe are arranged more or less regularly in 4 (anterior segments) to 6 (more posterior segments) lines. Anterior of these lines, up to four areas of smooth cuticle per side and additional 2–4 lines of leaf-like hairs alternate ( Figs 8B–D View FIGURE 8 , 14A–C View FIGURE 14 , 15H View FIGURE 15 ). Posterior of the lines, one line of straight spinose cuticular hairs occurs. These hairs are considerably more prominent on the ventral side of the tergal plate on segments 3–6 and especially on segments 4 and 5 ( Figs 6F View FIGURE 6 , 8B–D View FIGURE 8 , 14A, B View FIGURE 14 ). The secondary fringe is often covered by the free flap of the previous segment making observations more difficult. The central area of each segment shows a hexagonal sculpturing of the cuticle elevating slightly above the surface like cobbled pavement which represent scales; especially on more posterior segments, each element of the sculpturing ends in a short posterior process raising above the surface. This becomes especially visible on the dorsal site of segment 11 ( Fig. 7E View FIGURE 7 ). The sculpturing is interpreted as to represent scales which become more three-dimensional on posterior segments ( Figs 5E, F View FIGURE 5 , 7E View FIGURE 7 , 8A–D View FIGURE 8 , 15H, J View FIGURE 15 ). The attachment sites of the dorsoventral muscles appear midlaterally and paraventrally as single, elongate-oval cuticular areas without any scales but with a slightly wrinkled surface ( Figs 7J View FIGURE 7 , 9A View FIGURE 9 ). The quite extensive free flap exhibits a narrower and more elongate sculpturing (= scales) than the central area and ends in the primary fringe which consists of numerous thin cuticular hairs ( Figs 6E, F View FIGURE 6 , 7A, B, J View FIGURE 7 , 8D View FIGURE 8 ).

On segment 1, regularly arranged cuticular leaf-like hairs occupy an area more than half of the segment’s length from dorsally to the lateral accessory position on the tergal plate and the anterior half of the midsternal plate. Laterally, the tergal plate yields a flat hexagonal sculpturing ( Figs 5C View FIGURE 5 , 6E View FIGURE 6 , 8A View FIGURE 8 , 13D View FIGURE 13 , 14A View FIGURE 14 ). Tufts of prominent cuticular hairs are located anterior of the origin of the lateroventral tube of segment 5 but not of the remaining acicular spines ( Figs 6D View FIGURE 6 , 8B–D View FIGURE 8 ). All these acicular spines originate from a horseshoe-shaped, smooth cuticular area.

Sensory spots appear on all segments in a characteristic pattern and are usually arranged bilateral symmetrically ( Tab. 4; Figs 2A, B View FIGURE 2 , 5B, D–F View FIGURE 5 , 8 View FIGURE 8 A−D, 14A−D, 15H, J). Three types of spots can be identified. Type- 1 sensory spots as defined by Nebelsick (1992) contain usually 1–3 cuticular tubes extending through the body cuticle ( Figs 5E, F View FIGURE 5 , 6F View FIGURE 6 , 7J View FIGURE 7 , 8A View FIGURE 8 , 13H View FIGURE 13 ). Each tube widens up below the body cuticle to form a cuticular funnel or cavity. Each tube opens to the cuticular surface simply as a pore. A single cilium with or without an apical balloonlike enlargement may jut out of the pore ( Fig. 5F View FIGURE 5 ). On the surface, a pore of the tubes is surrounded by one ring of circularly arranged micropapillae and a wide circular to oval area covered by numerous small cuticular micropapillae ( Fig. 7J View FIGURE 7 ), which are also usually recognizable in specimens mounted in glycerin for light microscopy. Type-1 sensory spots appear middorsally on segment 1, paradorsally on segment 10 (central part of segment), on both sides of segment 10 (posterior part) and either on the left or on the right side of segments 2, 3 and 7–9, subdorsally on segment 11 just anterior of a terminal type-3 sensory spot in the process neighbouring the midterminal spine ( Fig. 2A View FIGURE 2 ; identical situation in C. styx from Chile, see Fig. 28A, C View FIGURE 28 ), laterodorsally on segment 11 (central part of segment), midlaterally on segments 1 and 2 (usually intermediate to sublateral position), ventrolaterally on segment 11 next to the lateral terminal spine, and ventromedially on segments 2–4; a type-3 sensory spot is located on segment 11 subdorsally and terminally on the process neighbouring the midterminal spine ( Tab. 4; Fig. 7B, D View FIGURE 7 ).

The largest type-1 sensory spot exists midlaterally to sublaterally on segment 2 ( Figs 7J View FIGURE 7 , 8A View FIGURE 8 ). It shows two pores at the anterodorsal margin of the spot and one or two pores centrally in the oval area with micropapillae ( Fig. 7J View FIGURE 7 ) giving the impression of a small and a large sensory spot fused in a single organ (comp. also Fig. 26G View FIGURE 26 for C. styx from Chile).

A different type of spot appears in many positions on the trunk ( Tab. 4) in a narrow depression as a small circular patch of micropapillae around at least one pore ( Figs 5D–F View FIGURE 5 , 6D, E View FIGURE 6 , 7B, J View FIGURE 7 , 8A–D View FIGURE 8 ). Light microscopy reveals usually two pores and tubes through the body cuticle ( Figs 14A–D View FIGURE 14 , 15H, J View FIGURE 15 ). This sensory spot is often difficult to discriminate from a gland cell outlet in light microscopy, also because the processes of the hexagonal sculpturing may partly cover the spots and gland cell outlets. The sensory spot resembles a type-5 sensory spot according to the definition by Neuhaus (2013), but differs from it by its occurrence in a small depression. These type-5 sensory spots occur middorsally on segments 2–9 (anterior part of segment), paradorsally on both sides of segments 4 and 6 and either on the left or on the right side of segment 5 ( Fig. 5D View FIGURE 5 ), laterodorsally on segments 2–9 (central part) and 10 (posterior part), midlaterally on the neck and on segment 10 (central part), sublaterally on segments 3−5 (anterior part), 8 and 9 (central part) and 6 (posterior part), in a lateral accessory position on segments 2 and 6–9 (anterior part), lateroventrally on segment 10 (anterior part), on the neck (central part) and on segment 1 (posterior part), ventrolaterally on segment 1 (central part), and ventromedially on segments 1 and 3–10 (anterior part) and on segments 1 and 10 (posterior part)( Tab. 4; Figs 5D–F View FIGURE 5 , 6D, E View FIGURE 6 , 7B, J View FIGURE 7 , 8A–D View FIGURE 8 , 14A–D View FIGURE 14 , 15H, J View FIGURE 15 ). In light microscopy, anterior middorsal, lateral accessory, and lateroventral sensory spots exhibit a well developed cuticular ring around each of the two pores ( Fig. 14B View FIGURE 14 ); this ring cannot be observed with SEM, but the pores are surrounded by several hair-like micropapillae ( Fig. 5E View FIGURE 5 ).

On segment 11 of all specimens, one type-3 sensory spot according to the definition by Nebelsick (1992) is located subdorsally in the lateral, triangular extension next to the midterminal spine ( Fig. 7B, D View FIGURE 7 ). This sensory spot exhibits thicker tubes than all remaining sensory organs.

A papilla occurs lateroventrally on segment 11 just next to the lateral terminal accessory spine ( Table 4; Fig. 2B View FIGURE 2 ). The papilla is conical and covered by numerous short cuticular hairs ( Fig. 7B View FIGURE 7 ).

Gland cells appear on all segments in a characteristic pattern and are usually arranged bilateral symmetrically ( Table 4; Figs 2A, B View FIGURE 2 , 5B View FIGURE 5 , 8A View FIGURE 8 ̄D). They open to the outside via a short cuticular tube with an elongate-oval to almost rectangular cross-section ( Figs 5D–F View FIGURE 5 , 6D, E View FIGURE 6 , 7J View FIGURE 7 , 8A–D View FIGURE 8 , 9A View FIGURE 9 , 13H View FIGURE 13 , 14A–D View FIGURE 14 , 15H, J View FIGURE 15 ). The tube is surrounded by a narrow circular groove and does not elevate above the surface of the cuticle. Apically, each tube bears few thin cuticular hairs which are only recognizable by SEM ( Figs 6D View FIGURE 6 , 7J View FIGURE 7 ). A gland cell outlet ( Table 4) appears in the posterior part of a segment at the intersegmental joint line paradorsally on segments 1 and often but not always (cf. Table 4 with Table 5) either on the left or on the right side of segments 2, 5 and 7, subdorsally on segments (1)2–10, midlaterally on segments 1–9, sublaterally on segments 2–5 and 7–10, lateroventrally on segments 3 and 4, and ventromedially on segments 5–9; the ventrolateral gland cell outlet on segment 2 is located in the anterior part of the segment within the secondary fringe ( Fig. 13H View FIGURE 13 ).

An acicular spine occurs lateroventrally on segments 6–10 and 11 (= lateral terminal spine), in a lateral accessory position on segment 11 (= lateral terminal accessory spine), middorsally on segments 2–4, 6 and 8–10, and as an extremely elongated midterminal spine on segment 11 ( Table 4; Figs 2A, B View FIGURE 2 , 5A, B, D–F View FIGURE 5 , 7B View FIGURE 7 , 8B–D View FIGURE 8 , 9A View FIGURE 9 , 13A View FIGURE 13 , 14A–D View FIGURE 14 , 15A, B View FIGURE 15 ). All acicular spines show a smooth cuticle basally and numerous shorter or longer cuticular hairs more apically. The midterminal spine tapers abruptly after quite some length and possesses 27–40 internal septa in its broader basal part ( Fig. 15A View FIGURE 15 ). Each lateral terminal accessory spine possesses a lateral apodeme from which at least one muscle connects the two spines with each other.

A blunt tube in the lateral accessory position on segment 5 originates slightly anterior of the free flap and appears much broader and flatter than the acicular spines; it tapers gradually towards its tip ( Table 4; Figs 6D View FIGURE 6 , 14B View FIGURE 14 ). Probably, the broad shape represents a preparation artefact in both light and electron microscopy, because the thin-walled tube seems to be simply collapsed. Interiorly, the tube shows in its basal part a cuticular tube and some longitudinal substructures ( Fig. 14B View FIGURE 14 ). There is a lateroventral notch in the free flap of segment 5 but no notch in the lateral accessory position where the tube originates ( Figs 6D View FIGURE 6 , 8C View FIGURE 8 ). The basal half of the tube length possesses a smooth cuticle but is covered with short cuticular hairs in the apical half. Few of these hairs may extend well beyond the end of the tube and may appear fuzzy ( Fig. 6D View FIGURE 6 ) or as two bundles of hairs.

Longitudinal muscles attach to the anterior trunk cuticle of subsequent segments on the left and right side dorsally and ventrally in all segments. One pair of dorsoventral muscles, each consisting of two strands stretches between the tergal and sternal plate of each segment. A strong muscle connects the lateral terminal accessory spines with each other. Oblique muscles do not seem to exist.

The pharynx consists of an outer muscular bulb with alternating radial and circular muscle cells and an inner epithelium. In several specimens, the midgut contains remnants of food or erroneously swallowed material appearing as light-refractive or smaller, irregularly shaped, chaotic particles.

Position md pd sd ld ml sl la lv vl vm

Segment

C. gerlachi from Sri Lanka neck ssp5 ssp5 ssp5

1 ssp1 gc gc ssp1; gc ssp5 ssp5 ssp5; ssp5

2 ssp5; ac le: ssp1, ri: gc gc ssp5 ssp1; gc gc ssp5 gc ssp1

3 ssp5; ac le: −, ri: ssp1 gc ssp5 gc ssp5; gc gc ssp5; ssp1

4 ssp5; ac ssp5 gc ssp5 gc ssp5; gc gc ssp5; ssp1

5 ssp5 le: gc, ri: ssp5 gc ssp5 gc ssp5; gc tu ssp5; gc

6 ssp5; ac ssp5 gc ssp5 gc ssp5 ssp5 ac ssp5; gc

7 ssp5 le: ssp1, ri: gc gc ssp5 gc gc ssp5 ac ssp5; gc

8 ssp5; ac le: −, ri: ssp1 gc ssp5 gc ssp5; gc ssp5 ac ssp5; gc

9 ssp5; ac le: ssp1, ri: − gc ssp5 gc ssp5; gc ssp5; pr? ac ssp5; gc

10 ♀: ac; ♂: be ssp1; ♀: ssp1 gc ssp5 ssp5 gc ssp5; ♀: ac; ♂: be ssp5; ssp5

11 mts ssp1; ssp3 ssp 1 ♂: cf ltas lts; pa ssp1

C. gerlachi from India neck ssp5 ssp5 ssp5

1 n. a. gc gc ssp1; gc ssp5 ssp5; ssp5 ssp5

2 ssp5?; ac le: ssp1, ri: − gc ssp5 ssp1; gc; gc gc ssp5 gc gc ssp1

3 ssp5; ac le: −, ri: ssp1 gc ssp5 gc ssp5; ssp5; gc gc ssp5; ssp1

4 ssp5; ac ssp5 gc ssp5 gc ssp5; ssp5; gc ssp5; ssp1

5 ssp5 le: gc, ri: ssp5 gc ssp5 gc ssp5; gc tu ssp5; gc

6 ssp5; ac ssp5 gc ssp5 gc ssp5; gc ssp5 ac ssp5; gc

7 ssp5 le: ssp1, ri: gc gc ssp5 gc gc ssp5 ac ssp5; gc

8 ssp5; ac le: −, ri: ssp1 gc ssp5 gc ssp5; gc ssp5 ac ssp5; gc

9 ssp5; ac le: ssp1, ri: − gc ssp5 gc ssp5; gc ssp5; pr? ac ssp5; gc

10 ♀: ac; ♂: be ssp1 gc ssp5 ssp5 ssp5; gc ssp5; ♀: ac; ♂: be ssp5; ssp5

11 mts ssp1; ssp3 ssp 1 ♂: cf ltas lts; pa ssp5; ssp1

.......... continued on the next page Position md pd sd ld ml sl la lv vl vm Segment

C. styx from Brazil neck ssp5 ssp5

1 ssp1 gc ssp1 gc

2 ssp5; ac le: ssp1, ri: − gc ssp1 gc gc ssp1 3 ssp5; ac le: −, ri: ssp1 gc gc gc ssp5 gc ssp1 4 ssp5; ac ssp5 gc ssp5? gc ssp5 ssp1 5 ssp5 le: −, ri: gc gc gc ssp5 tu

6 ssp5; ac ssp5 gc ssp5 ssp5 ssp5 ac ssp5 gc 7 ssp5 le: ssp1, ri: gc gc ssp5 gc ssp5 ac ssp5 ssp5 8 ssp5; ac le: −, ri: ssp1 gc ssp5 gc ssp5; ac ssp5 gc 9 ssp5; ac le: ssp1, ri: − ssp5 ssp5 gc pr? ssp5; ac ssp5 gc 10 ssp5; ♀: ac; ♂: sh ssp1 gc ssp 5 ♀: ac; ♂: be ssp5; ssp5 ssp5 11 mts ssp1; ssp3 ssp1 ac ♂: cf ltas lts; pa ssp1; ♀: gc

C. styx from Chile neck ssp5 ssp5

1 ssp1 gc ssp1; gc gc gc ♂?: gc

2 ssp5; ac le: ssp1, ri: − gc ssp1 gc gc gc ssp1 3 ssp5; ac le: −, ri: ssp1 gc gc gc gc ssp5 gc ssp1 4 ssp5; ac ssp5 gc ssp5 gc ssp5; gc ssp1 5 ssp5 le: −, ri: gc gc ssp5 gc ssp5 tu gc 6 ssp5; ac ssp5 gc ssp5 gc ssp5 ac ssp5 gc 7 ssp5 le: ssp1, ri: gc gc ssp5 gc ssp5 ac ssp5 ssp5 8 ssp5; ac le: −, ri: ssp1 gc ssp5 gc ssp5; ac ssp5 gc 9 ssp5; ac le: ssp1, ri: − ssp5 ssp5 gc pr? ssp5; ac ssp5 gc 10 ssp5; ♀: ac; ♂: sh ssp1 gc ssp 5 ♀: ac; ♂: be ssp5; ssp5 ssp5 11 mts ssp1; ssp3 ssp1 ac ♂: cf ltas lts ssp1; ♀: gc

Position md pd sd ld ml sl la lv

Segment

8 le: −, ri: ssp1 ssp5; gc ssp5

--------------------- --------------------- --------------------

16> le: ssp1, ri: − 1> +gc 4> ssp5: la → lv

19> le: −, ri: ssp1 1> −gc

1> gc → ssp5 (ri)

3> −ssp5 (le/ri)

1> + ssp5 (ri)

3> ssp5 → ssp5

9 le: ssp1, ri: − gc ssp5; gc ssp5; pr?

--------------------- ----------------- ------------------- ---------------------

21> le: ssp1, ri: − 1> gc → ssp5 1> −ssp5 13> ssp5: la → lv

17> le: −, ri: ssp1 3> ssp5 → ssp5

1> +ssp5 (ri)

10 ssp1; ♀: ssp1 ssp5 ssp5 gc ssp5

--------------------------- --------------- -------- ------------------ ---------------------

1> le: −ssp1, ri: −ssp1 1> le: −ssp5 1> −gc 2> +ssp5 (le/ri) 16> ssp5: lv → la 3> +ssp5

11 pa

-----------

3> +ssp5

It remains a bit doubtful where on segment 9 each protonephridium opens to the outside. There is an opening sublaterally in the central part of the segment which seems to consist of several even narrower openings ( Fig. 14C View FIGURE 14 ). However, this opening cannot be observed in the late juvenile stage (see below). In light microscopy, the sublateral opening agrees more with a type-5 sensory spot. Alternatively, a more pore-like opening exists in a lateral accessory position next to the lateroventral spine. This opening can also be traced in the late juvenile stage. It probably represents the outlet of the protonephridium on each side of segment 9 ( Table 4; Fig. 14C View FIGURE 14 ).

One pair of oval lateroventral, weakly sclerotized, oval gonopores is recognizable at the anterior margin of segment 11 of at least some specimens ( Fig. 15B View FIGURE 15 ). Gonads with eggs ( Fig. 15A View FIGURE 15 ) are found in 22 specimens.

Sexual dimorphism. Among the 57 adult specimens, 22 specimens reveal gonads with eggs and are therefore regarded as females. Another 13 specimens show female characters but no obvious eggs; of these, 10 yield a paradorsal sensory spot centrally on segment 10 whereas this character cannot be found with certainty in the remaining three specimens. All 13 specimens are tentatively regarded here as adults of undetermined sex but probably female. No specimen has been found revealing obvious elongate sperm. However, 22 specimens do differ in three characters from females with obvious eggs in their gonads. These assumed male specimens exhibit large vesicular structures in their gonads ( Fig. 15E–G View FIGURE 15 ) suggesting that these vesicles once may have contained spherical (?) or at least short and coiled up sperm and have been emptied. The potential male agrees in almost all cuticular characters with the female but can be distinguished from the female (1) by a modified acicular spine middorsally and lateroventrally on segment 10 ( Table 4; Figs 2C View FIGURE 2 , 7D–F View FIGURE 7 , 15D, E View FIGURE 15 ), (2) by the existence of an almost rectangular cuticular flap about midlaterally and anteriorly on segment 11 ( Figs 2C View FIGURE 2 , 7E–G View FIGURE 7 , 15C View FIGURE 15 ) vs the lack of this structure in the female, and (3) the lack of a paradorsal type-1 sensory spot centrally on segment 10 ( Table 4; Figs 2C View FIGURE 2 , 15C View FIGURE 15 ) vs its existence in the female ( Figs 2A View FIGURE 2 , 14C View FIGURE 14 , 15J View FIGURE 15 ). On segment 10, the more lateral ventral lobe of the free flap seems sometimes to be less indented giving the appearance of only two lobes on this segment.

The lateral spine on segment 10 of males seems sometimes to originate more in a lateral accessory position than lateroventrally. The lateroventral and middorsal acicular spine on segment 10 of males is not straight as in females but modified revealing usually a broader base and tapering towards its tip. Also, the tip of these spines is bent upwards terminally and possesses an indentation in this part ( Figs 7D–F View FIGURE 7 , 15D, E View FIGURE 15 ). The length of the middorsal spine on segment 10 of males reaches less than one third of the length of this spine in females (Table 2; comp. Figs 5B View FIGURE 5 and 15A View FIGURE 15 with Fig. 15E View FIGURE 15 ). The cuticular flap about midlaterally and anteriorly on segment 11 may flip over on to segment 10 ( Fig. 7F, G View FIGURE 7 ). However, the cuticular flap is often hidden under the free flap of the previous segment and consequently difficult to trace in both light microscopy and SEM.

Variation of characters. The spine pattern of C. gerlachi is remarkably stable in all specimens studied. Only in a single specimen, the lateroventral spine on segment 7 is not fully developed ( Fig. 7C View FIGURE 7 ).

Most positions of sensory spots and gland cell outlets are also quite constant, only occasionally some minor variability can be traced in favourably oriented specimens (Table 5). However, on certain segments and positions the occurrence of sensory spots and gland cell outlets varies significantly, e.g. paradorsally on segments 2, 3, 5 and 7–9, subdorsally on segment 1, midlaterally on segment 3, sublaterally on segments 3, 6, 8–10, in the lateral accessory position on segment 9, and lateroventrally on segment 10 ( Tables 4, 5). A paradorsal type-1 sensory spot is found either on the left or on the right side of segments 2, 3 and 7–9 and a paradorsal type-5 sensory spot is found either on the left or on the right side of segment 5; a paradorsal gland cell outlet occurs often but not always on the opposite side on segments 2, 5 and 7 (Table 5; Fig. 5E, F View FIGURE 5 ). On segments 8 and 9 without a paradorsal gland cell outlet and if the paradorsal gland cell outlet is missing on segments 2, 3, 5 or 7, the subdorsal gland cell outlet of the same side of the respective segment may appear closer to the middorsal acicular spine in an almost paradorsal position ( Fig. 5F View FIGURE 5 : right side of segment 8). In addition, the central laterodorsal type-5 sensory spot and the posterior midlateral gland cell outlet may appear in the same intermediate position between laterodorsal and midlateral ( Fig. 9B View FIGURE 9 ). It remains a bit unclear whether the lateroventral gland cell outlet on segment 2 is expressed only in some specimens or whether it can only be recognized in favourably oriented specimens.

Postembryonic stages. The sample reveals 57 specimens identified as juvenile stages of which 10 have been mounted for SEM. The individuals are preliminarily assigned to four different stages based on different character sets (see below) which in no way is meant to indicate that C. gerlachi develops via just four juvenile stages. For measurements see Table 3, for summary of characters see Table 6.

Two early juvenile stages. In 9 specimens, the trunk reveals 9 anterior segments and a still fused segment consisting of the two prospective segments 10 and 11 ( Table 6). Segments appear more or less circular in cross-section, and it remains unclear whether midventral sternal plates exist or whether the contracted dorsoventral muscles just give the impression of ventral cuticular plates. The thin body cuticle results in an irregularly bulging cuticle (see Figs 9E, F View FIGURE 9 , 11A, B View FIGURE 11 for later stages). A free flap overlapping partly the subsequent segment is missing ( Table 6). Consequently, notches in the cuticle at the origin of spines are also lacking (see Figs 9E, F View FIGURE 9 , 10 View FIGURE 10 A−E, 11A, B for later stages). The trunk cuticle yields numerous rows of regularly arranged cuticular leaf-like hairs. The leaf-like hairs are missing ventrolaterally to almost sublaterally on segment 1 (see Figs 9D View FIGURE 9 , 10A, E View FIGURE 10 for later stages). Most trunk segments carry at their posterior margins cuticular postmarginal spicula (see below; see Figs 9E, F View FIGURE 9 , 10A–E View FIGURE 10 , 11A, B, E, F View FIGURE 11 , 16C, E, F View FIGURE 16 for later stages). At least earlier juvenile stages reveal considerably fewer sensory organs and gland cell outlets. Sensory spots appear as type-1 spots with a more or less oval patch of micropapillae around a pore (see Figs 9E View FIGURE 9 , 10A View FIGURE 10 for later stages) as well as type-3 spots with a small circular patch of micropapillae around a pore on a cone-like base (see Fig. 9F View FIGURE 9 for later stage). Type-1 sensory spots reveal considerably fewer micropapillae in early juveniles than in adult specimens. Gland cell outlets elevate above the trunk surface as a thick-walled spherical structure (see Fig. 10A View FIGURE 10 for later stage). Individual placids exist. The middorsal spine of the prospective segment 10 and the midterminal spine taper abruptly after some length and show internal septa ( Fig. 16A View FIGURE 16 ).

Among the 9 early juvenile specimens, three specimens representing the earliest stage found (named early juvenile stage 1 in Table 6) possess an acicular spine middorsally on segments 2–4, 6, 8, 9 and 10+11, midterminally, lateroventrally on segments 6–9 and centrally on segment 10+ 11 in a lateroventral position ( Table 6; Fig. 16A View FIGURE 16 ). The middorsal spine on segment 10+11 and the midterminal spine show internal septa in their basal parts. The lateral terminal spine appears as an elongate spinose anlage without a basal articulation but with a broad basis ( Table 6; Fig. 16A, B View FIGURE 16 ). A lateral terminal accessory spine is not developed. A blunt tube in the lateral accessory position on segment 5 appears much broader and flatter than the acicular spines; it tapers gradually towards its tip and exhibits in its basal part an inner tube. Postmarginal spicula are found on segments 1–9 and on the posterior segment ( Table 6). A type-1 sensory spot occurs sublaterally on segments 1 and 2. A type-3 sensory spot may be seen with a short conical stalk paradorsally on segments 6 and on one side of segment 8 and with a longer basal stalk twice subdorsally to laterodorsally on the posterior segment. A gland cell outlet may exist laterodorsally to midlaterally on segment 2. The paired spines anterior of the primary spinoscalids exist in this stage already. Areas with short cuticular hairs occur between the last ring of spinoscalids and the trichoscalids which show a variable length like in the adult.

Six specimens with a still fused segment 10+11 are regarded as a following juvenile stage, named early juvenile stage 2 in Table 6. These specimens agree with the three specimens of the earlier stage, but reveal additional characters: the lateral terminal spine possesses an articulation ( Table 6; Fig. 16C, D View FIGURE 16 ); the lateral terminal accessory spine appears as an elongate spinose anlage without a basal articulation but with a broad basis ( Table 6; Fig. 16C, D View FIGURE 16 ); an additional type-1 sensory spot is found paradorsally on segment 7 on one side and a gland cell outlet on the other side as well as ventromedially at least on segments 2 and 4; a type-5 sensory spot may be traced paradorsally on one side of segment 9; a gland cell outlet may occur ventromedially on segment 9 ( Table 6). The primary spinoscalids each with a pair of anterior spines and at least one ring of spinoscalids are developed.

Intermediate juvenile stage. This stage represented by 18 specimens yields 11 clearly separated trunk segments ( Table 6; Figs 9C, D View FIGURE 9 , 16E, F View FIGURE 16 ). Otherwise it agrees in its outer morphology and in its arrangement of spines with the previous stage except that the lateral terminal accessory spine is articulated ( Table 6). The middorsal spine of segment 10 and the midterminal spine taper abruptly after some length and show internal septa ( Table 6). Spines show the same outer appearance as in adult specimens. The trunk cuticle yields numerous rows of regularly arranged cuticular leaf-like hairs which are usually split almost from their bases ( Figs 9C–F View FIGURE 9 , 10A–E View FIGURE 10 , 11A, B, E View FIGURE 11 , 16E, F View FIGURE 16 ). The intersegmental cuticle, the lateral cuticle of segment 1 devoid of hairs, and the cuticle of the placids and of the introvert reveal a weak, leather-like sculpturing ( Fig. 10A, E View FIGURE 10 ). The cuticular hairs are missing at those sites where the dorsoventral muscles attach to the trunk cuticle ( Figs 9D, F View FIGURE 9 , 10A–D View FIGURE 10 ). Each segment carries at its posterior margin cuticular postmarginal spicula ( Table 6; Figs 9E, F View FIGURE 9 , 10A–D View FIGURE 10 , 11A, B, E View FIGURE 11 , 16E, F View FIGURE 16 ). Sensory spots and gland cell outlets are more numerous. A type-1 sensory spot occurs middorsally on segment 1 ( Fig. 9E View FIGURE 9 ), paradorsally left or right on segments 2 ( Fig. 9E View FIGURE 9 ), 3, 5 and 7, subdorsally on segment 11 just anterior of a terminal type-3 sensory spot in the process neighbouring the midterminal spine, laterodorsally on segment 11 (central part of segment), midlaterally on segments 1 and 2, ventrolaterally on segment 11 next to the lateral terminal spine, and ventromedially on segments 2–4 ( Table 6). A type-5 sensory spot is found paradorsally on segments 4, 6, 10 and left or right on segments 8 and 9, in a lateral accessory or lateroventral position on segments 7–10, as well as subdorsally, midlaterally and lateroventrally on the placids. A gland cell outlet appears paradorsally left or right on segments 2, 5 and 7, subdorsally on segments 3, 5 and 7–9, midlaterally on segments 2, 3 and 10, sublaterally on segments 3–5 and 7–9, and ventromedially on segments 6, 8 and 9 ( Table 6). A conical papilla is found lateroventrally on segment 11 just next to the lateral terminal accessory spine ( Table 6).

Scalids. The following notes on the introvert are based on two juvenile specimens mounted for SEM. Anterior of the primary spinoscalids, a ring of 10 pairs of cuticular spines with a smooth surface occurs ( Figs 4 View FIGURE 4 , 10E View FIGURE 10 , 11C, D View FIGURE 11 ). Numerous short cuticular hairs occur on these spines in their apical part where the spines of each pair are not connected by cuticle ( Fig. 11C View FIGURE 11 ).

The spinoscalids exist either as spinose anlagen of a scalid, a protoscalid, with few or even no cuticular hairs or alternatively as developed spinoscalids consisting of a basal and a distal part ( Figs 4 View FIGURE 4 , 10E View FIGURE 10 , 11C, D View FIGURE 11 ). The primary spinoscalids resemble those of the adult specimens and are the longest scalids. The internal septa are much weaker and barely recognizable. Developed spinoscalids of ring 02 are slim, cuticular hairs concentrate in the second quarter of the scalid’s length. The distal element of each ring 03–05 developed spinoscalid is covered with a fringe of cuticular hairs laterally on both sides ( Fig. 11D View FIGURE 11 ). In the odd introvert sectors, two spinose protoscalids appear laterally in ring 02, a single developed spinoscalid centrally in ring 03, and two lateral developed spinoscalids in ring 04 ( Figs 4 View FIGURE 4 , 11D View FIGURE 11 ). In even sectors, a developed spinoscalid appears centrally in rings 02 and 05, and two spinose protoscalids occupy the lateral position in ring 03 ( Figs 4 View FIGURE 4 , 11D View FIGURE 11 ). Trichoscalids are located in the same position and number as in adult stages. However, at least the longer trichoscalids are thinner and exhibit fewer and shorter cuticular hairs than the adult ( Fig. 11C View FIGURE 11 ). Between each spinoscalid of the posteriormost ring and each trichoscalid an area of short cuticular hairs occurs appearing as “denticles” in light microscopy ( Fig. 10E View FIGURE 10 , 11C, D View FIGURE 11 ). An additional area with hairs exists midventrally where no trichoscalid is found ( Figs 10E View FIGURE 10 , 11C View FIGURE 11 ).

Neck. The neck consists of placids which are weakly separated both from the trunk and from each other and cannot be counted with certainty. The surface of the placids appears as a leather-like, weak sculpturing ( Figs 10E View FIGURE 10 , 11C, D View FIGURE 11 ). A type-5 sensory spot occurs subdorsally, about midlaterally, and lateroventrally on the placids ( Figs 10E View FIGURE 10 , 11C, D View FIGURE 11 ). Below the cuticle, a highly curled cuticular tube extends from the sensory spot deeper into the body.

Late juvenile stage. Three specimens mounted for SEM and 20 specimens mounted on slides agree in their morphology but differ from both the adult and the juvenile stages described before; therefore, they are interpreted here as late juvenile stage. The latter differ from the younger juvenile stages in that they show postmarginal spicula only on each midsternal plate of segments 1–5 and to a lesser degree on segment 6 ( Figs 11F View FIGURE 11 , 12D View FIGURE 12 , 17A View FIGURE 17 ) but not on the tergal plates ( Figs 12C View FIGURE 12 , 17A, B View FIGURE 17 ) as in the remaining juvenile stages ( Table 6). Also, cuticular leaf-like hairs are limited to the secondary fringe and to the midsternal plates ( Figs 11F View FIGURE 11 , 12D View FIGURE 12 , 17A, C View FIGURE 17 ) instead of the entire trunk as in the earlier juveniles ( Table 6). In addition, the middorsal spine on segment 10 tapers only slightly and does not possess internal septa ( Table 6). The trunk cuticular characters of late juveniles resemble that of adult specimens widely including the posterior line of stronger spinose hairs of the secondary fringe on segments 3–6 ( Figs 11F View FIGURE 11 , 17A View FIGURE 17 ). However, the late juvenile stage differs from the adult by the existence of cuticular leaf-like hairs on the midsternal plates of segments 1–6 ( Table 6; Figs 11F View FIGURE 11 , 17A View FIGURE 17 ), only a single lobe of the free flap ventrally on each side of segments 7–9, and the lack of the following type-5 sensory spots: middorsally on segments 2–9 (anterior part of segment), laterodorsally on segments 1–9 (central part) and 10 (posterior part), midlaterally on segment 10 (central part), sublaterally on segments 8 and 9 (central part), and ventromedially on segments 1 and 3–10 (anterior part) ( Tab. 6). The paradorsal type-5 sensory spot in the central part of segment 10 is missing like in the male.

Scalids. The following notes on the introvert are based on one late juvenile stage mounted for SEM. Anterior of the primary spinoscalids, a ring of 10 pairs of cuticular spines with a smooth surface occurs ( Fig. 12A, B View FIGURE 12 ). The single late juvenile stage studied possesses exclusively fully developed scalids like the adult stage and arranged as in adults ( Fig. 12A, B, D View FIGURE 12 ).