Pliciloricus diva, Gad, Gunnar, 2009

Gad, Gunnar, 2009, A clearly identifiable postlarva in the life cycle of a new species of Pliciloricus (Loricifera) from the deep sea of the Angola Basin *, Zootaxa 2096, pp. 50-81 : 55-72

Pliciloricus diva sp. n.

Type material: includes eight specimens, the holotype and paratypes from the DIVA 1 expedition have been deposited in the type collection ( UNIOL) now in the charge of the DZMB. The additional material from the DIVA 2 expedition are lodged at the central Senckenberg Institute and Museum Frankfurt ( SMF).

Holotype: adult male, with good fixation of external structures, DIVA-1, station 331/1 MUC 8 (mounted on slide UNIOL-2003.0029).

Paratype I: fully extended adult male, with good fixation of internal structures, DIVA-2, station 50 MUC 6 (slide SMF 16898).

Paratype II: fully extended Higgins-larva (of 4th or 5th instar), DIVA-1, station 346/3 MUC 11 (slide UNIOL-2003.030).

Paratype III: mature male with withdrawn introvert surrounded by simplified postlarva (type I) and enclosed into the exuvium of a seventh instar Higgins-larva, DIVA-1, station 331/1 MUC 8 (slide UNIOL- 2003.034).

Paratype IV: mature female with withdrawn introvert surrounded by simplified postlarva (type I) both enclosed into exuvium of seventh instar Higgins-larva, DIVA-1, station 346/7 MUC 1 (slide UNIOL- 2003.035).

Paratype V: young female with withdrawn introvert surrounded by reduced postlarva (type II) both enclosed into exuvium of seventh instar Higgins-larva, DIVA-2, station 50 MUC 6 (slide SMF 16899).

Paratype VI: simplified parthenogenetic female in immature stage surrounded by cuticles of reduced postlarva (type II) and of seventh instar Higgins-larva, DIVA-2, station 50 MUC 6 (slide SMF 16900).

Paratype VII: simplified parthenogenetic female in late stage of maturity enclosed together with egg, embryo and first instar larva inside exuvium of seventh instar Higgins-larva, DIVA-2, station 50 MUC 6 (slide SMF 16901).

Paratype VIII: exuvium of seventh instar Higgins-larva; DIVA-1, station 346/5 MUC 11 (mounted on slide UNIOL-2003.038 respectively).

Type locality: Holotypic male originate form the deep sea of the Angola Basin (Atlantic) near the coast of Namibia (Africa), DIVA 1, station 331 (two hauls).

Station data: 19° 07,0‘ S / 003° 52,0‘ E; 5423 m depth, July 17, 2000, DIVA 1, station 346 (eight hauls).

Type habitat: oligotrophic to eutrophic environment; sediment type white to light beige; with mud contents in the surface layer reaching 90 - 99% and decreasing towards 12 cm sediment depth; total carbon contents between 8 and 8,7%; with high amounts of globularian foraminiferans; sediments well oxygenated down to a depth of 20 cm; 94–171 mV measured in surface sediments; bottom temperature 2.48°C; salinity 34.8‰ ( Kröncke & Türkay 2003).

Additional material from DIVA 2 expedition also from the deep sea of the Angola Basin. Station data: 9° 56,0‘ S / 0° 54,1‘ E; 5648 m depth, March 11, 2005. other environmental data not yet available.

Etymology: From the Latin diva (goddess or famous lady), but in this case the species name refers to the acronym DIVA of the scientific expedition "Latitudinal Gradients of Deep-Sea Bio DIV ersity in the A tlantic Ocean" during which the new species was discovered.

Measurements: Morphometric data of holotypic and paratypic males listed in Table 1 and of paratypic Higgins-larva listed in Table 2 .

Description of adult male

External morphology ( Figs. 1 , 2A , B, 4A, D, E)

Body of holotypic male divided into stalked mouth cone, introvert, neck, thorax, and loricate abdomen. Thorax not fully extended in mounted specimen ( Fig. 4 A), all other body regions totally extended; total body length 302 µm, as measured from tip of mouth cone to caudal end; maximal width 115 µm, at level of anterior lorica. Lorica ventrally flattened with pronounced bilateral symmetry of trunk.

Mouth cone (mc, Fig. 1 ) large, reaching nearly 20 % of body length; divided into three sections. First or distal most section (mcs1) conical and pointed; mouth opening located terminally. Buccal tube (bu) being sclerotized part of buccal channel, short, narrow (3 µm), smooth, and weakly sclerotized; extended telescopically from the mouth (not in paratypic male which is drawn in Fig. 3 B); distally with four minute oral stylets (os, for internal structures see also description of paratypic male below and Fig. 3 B). Cuticle of first section strengthened by eight elevated, and strong longitudinal primary oral ridges (or), secondary oral ridges not observed ( Fig.1 ). Second section (mcs2) surrounding first section frill-like; bearing six anterior, strong longitudinal cuticular bars (bar); the posterior area divided into 12 plates folded transversally together. Mouth cone reaching broadest width at beginning of third section, marked by eight triangular formations. Third section (mcs3) narrowing posteriorly and forming a narrow stalk (sk); stalk basally surrounded by circular fibres of the ruff (ru). Fibres extending as part of cuticle from the base of the stalk down to first row of clavoscalids.

Introvert (in, Figs. 1 , 4 A, 2B) spherical, densely covered with nine transversal rows of closely standing scalids.

First row (cr1, Figs. 1 , 4 A) with eight strongly sclerotized and anteriorly oriented clavoscalids. All clavoscalids long (reaching over 50% of total body length), unsegmented and consisting of narrow, stalk-like bases and broad, flattened elements. Elements with reinforced dorsal margins and with pronounced median axis; subdivided into distal and proximal parts; ending in small ventral tips. Distal part longer and narrower than basal one; with more than 22 strong but narrow transverse cross walls (cw) with distally diminishing intervals between them. Intervals flat with fine longitudinal striae on lateral surfaces; alternation of protruded cross walls and flat intervals giving margins of distal parts an undulated appearance. Proximal parts visibly enlarged, lateral surfaces together with pronounced median axis with specific pattern of dots and fine striae. Second row (sr2, Figs. 1 , 2A . 1 , 4 B) with nine strong spinoscalids being more sclerotized than others, oriented posteriorly, distinctly shorter than clavoscalids, and arranged in alternation to them. Pair of midventral-most spinoscalids fused to (primary) double-organ ( Figs. 2A.2 , A.3, 4A); seven free spinoscalids ( Fig. 2A . 1 ) strong, leg-like and composed of four segments. First segment (sg1) large, angular, and broad; both lateral surfaces with three longitudinal arched weals (lw); segment also with four dorsal thorns (ds1–ds4) and two dorsolateral fringes of small spinules (fs1, fs2). Second segment (sg2) short with swollen joint which bears a ventral tooth; next segment filiform connected by swollen hinge-joint to second segment; last segment (sg4) as long as first one, ending in distinct sickle-like tip.

Double-organ (do, Figs. 2A.2 , A.3, 4A) strongly sclerotized, rigid and bifurcated. A comparison in Figs. 2A . 1 –A.3 with an untransformed spinoscalid of the second row best demonstrates its transformation. Doubleorgan divided into two branches being subdivided into an inner and an outer ramus. Both branches arising from a common stem-like base (ba), which is movably connected with the introvert. Bases of double-organ with two small dorsal thorns (ds1) having their equivalents in first dorsal thorn of free spinoscalids. Inner or ventral rami (ra1) long and divided into three segments with many similarities and with free spinoscalids. First segments of ventral rami with second (ds2) dorsal thorn having its equivalents in first dorsal thorn of free spinoscalids. Basal part of first segment (sg1) enlarged, dorsally with shield-like duplication, longitudinally fused, and reaching 30% of length of double-organ. Two comb-like dorsal fringes of spinules (fs1) located distally. Distal part of first segment free, not fused, tapers distally and ends in two inner thorns (ds3). Next two segments filiform, free, and equipped in a saw-like manner with inner row of stiff minute spinules (spr). Third segment (sg3) of inner ramus being a long movable spine. Both outer rami (ra2) shorter, basally swollen and fused longitudinally with inner rami, ending in a pronounced tooth-like tip.

Third row (sr3, Fig. 1 ) with 15 small leg-like, filiform spinoscalids consisting of four segments, 14 of them with following structure: First segment short and large, with double bases, flanked by two spines and divided by constriction in the middle, ending with fringe of minute spinules. Second segment short, narrow, with two swellings, and distinct hinge-joint flanked by two spines. Third segment short; fourth segment long, bristlelike, and distally sickle-shaped. Fifteenth spinoscalid of this row in midventral position beneath double-organ transformed (ssm), distinctly shorter (12 µm) and consisting of a base and a short, flattened element with rows of fine, hairy setules along both lateral margins (in this position two spinoscalids are sometimes modified to a secondary double organ e.g. in P. c o r v u s and P. shukeri ).

All following scalid rows consist of at most 30 spinoscalids and are inserted on small arched basal plates. Fourth row armed with two different types of 15 spinoscalids in alternating arrangement.

Type A spinoscalids (sr4a, Fig. 1 ) long, filiform and divided into four segments. First segment short with separate base and a dorsal tooth, being divided by constriction in the middle, and ending with fringe of minute spinules. Second and third segments short, whilst fourth segment long and bristle-like.

Type B spinoscalids (sr4b; Figs. 1 , 2A . 4, 4 D) short, strongly sclerotized, consisting of three segments. First segment more swollen than in type A scalids; base separated and also with small tooth. Second segment short and narrow with transversal constriction in its middle. Third segment enlarged, subdivided into three parts; first part round in cross section, and dorsally with small tooth; second part slightly narrower, laterally flattened, ventrally equipped with double row of five small teeth ( Figs. 2A . 4, 4 D); third part jaw-like, ventrally with double row of small denticles (den), ending in claw-tip (ct).

Fifth row (sr5, Fig. 1 ) with 30 uniform spinoscalids, seta-like, consisting of three filiform segments, first two segments short, ending in dorsal thorns, third segment long.

Sixth row (sr6, Fig. 1 ) with 30 uniform spinoscalids, similar to spinoscalids of fifth row.

Seventh row (sr7, Fig. 1 ) with 30 uniform spinoscalids, similar to spinoscalids of fifth row.

Eighth row (sr8, Fig. 1 ) with 30 uniform spinoscalids, of more hair-like structure, consisting of two segments; first one short and bulbous; second one long and thin.

Ninth row (sr9) equipped with 30 small and short teeth-like scalids.

Additional row of small protoscalids (psc, of an additional row?) between eighth and ninth row ( Fig. 1 ); covered by, and alternating with, spinoscalids of eighth row.

Neck (nk, Fig. 1 ) with eight single type A trichoscalids (tr a) and seven double type B trichoscalids (tr b) in alternating arrangement and covered with three transverse rows of accessory basal plates.

( Fig. 1 ) long, thin, rigid, flat, and with very fine serrated lateral margins; a third hardly visible serrated margin perpendicular to the median axis. Central channel usually extending inside, not visible. All trichoscalids end in simple pointed tips. Type A trichoscalids long and single, type B trichoscalids of two rami arising from a long, smooth common shaft; upper (secondary) ramus (tr2) of type B trichoscalids slightly shorter than lower (primary) one (tr1), but identical in structure and width. Midventrally there are two single type A trichoscalids standing close together; middorsally there is one type B double trichoscalid.

Accessory basal plates ( Fig. 1 ) standing close together in rows. Well-defined basal plates of the first row represent two types; eight large, leaf-like, and pointed protrusions representing type A basal plates of the first row (bp1a) alternating with seven smaller and triangular type B basal plates which have median keels. Type A basal plates of second row (bp2a) are angular, tricuspid, and with oval depression. They alternate with larger triangular type B basal plates, carrying a large tooth. Single type A trichoscalids arise with short shafts from large basal plates (bp3a), subdivided into a round upper and rectangular lower part. Double type B trichoscalids insert via a long shaft in round depressions of less defined angular type B basal plates.

In summary the number and arrangement of scalids (cs = clavoscalids, ss = spinoscalids, tr = trichoscalids) and basal plates (= bp) belonging to the head can be expressed in the following scalid formula: 8cs, 9ss(1do)+14ss/1ss, 15a+15b ss, 30ss, 30ss, 30ss, 30ss, 30ss (in) / 8a+7b bp / 8a+7b bp / 8a+7b bp, 8a (single)+7b(double) tr (nk)

See also diagram in Fig. 2 B as additional demonstration of the scalid arrangement.

Thorax (th, Fig. 1 ) movable, retracted, and with thin cuticle subdivided into three transverse rows of moderately developed thoracic plates.

Lorica (lo, Figs. 1 , 4 E) well-developed, consisting of thick cuticle covering abdomen and being divided longitudinally into 22 secondary plicae (pl). Each plica composed of two primary ones (giving the impression that the lorica consists of 44); each primary plica is framed by a strongly developed longitudinal primary ridge (lr1), adjacent plicae therefore separated by double ridges. Without additional single or secondary ridges. Midventral transformed plica (plm, Figs. 1 , 4 E) broad, being the result of total longitudinal fusion of four primary plicae, ending posteriorly in two small roundings. Anteriorly there are two short longitudinal bars. Lorica transversally subdivided by number of indistinct transversal ridges (tri); five of them are stronger and clearly visible in the midventral plica which posteriorly also has an incomplete longitudinal ridge along the midventral axis. Anterior edge (ed) of lorica paved with crescent-shaped ornamentation and 22 dicuspid protrusions (pro). Lorica divided halfway into two halves by a transverse constriction (tv). Posterior lorica flexible, consisting of transverse row of plates separated by zigzag border; last part of lorica separated as end cone. Midventral plicae posteriorly flanked by a pair of ventral warts (wa).

End cone (ec, Figs. 1 , 4 E) consisting of two transverse rows of plates; with round structure (ro) flanked by two short longitudinal protrusions (lop). Caudally anal field composed of many small anal plates surrounding terminal anus. Anal field with a pair of flosculi (fl1) composed of papillae. Holotypic male with two saccate testes compactly filled with flagelliform spermatozoa.

Anatomy ( Figs. 3 A, B, 4B, C, F)

Body of paratypic male ( Fig. 4 B) divided into same body regions as described in holotype and identical with that in all general external features, apart from being slightly smaller (see Table 1).

Mouth cone ( Fig. 3 B) fully extended and stalked; accompanied by close-fitting double organ.

Buccal structures ( Fig. 3 B, 4C) identical as in holotype. Internally, buccal channel extends straight through mouth cone. Pharyngeal bulb small and round, located in anterior part of mouth cone making up the second section. Buccal channel (bu) in front of pharyngeal bulb supported longitudinally by three small symmetrical bracelets (ia). Cells of buccal glands (bug) surround pharyngeal bulb and occupy space anterior of bracelets. Inner walls of pharyngeal bulb paved with three transversal rows of small placoids (p1–3) each row containing three placoids. Oesophagus narrow, and continues through the stalk. Apodemes) of mouth cone retractors connect anteriorly with inner wall of second section. Eight mouth cone retractors (mcr) run through the stalk and extend through the brain. Brain (br, Figs. 4 B, C) visible as large and dense mass of cells filling out the anterior part of introvert.

Main musculature ( Figs. 3 A, 4C) consists of large layers of transverse muscle (tm) being most distinct in anterior and posterior region of lorica. Pair of large main retractors of introvert (re) run dorsally down from brain to caudal end. Smaller neighbouring retractors of introvert connected posteriorly with ruff fibres. Longitudinal muscles located mainly inside anterior half of trunk where they run down from last row of thoracic plates to mid transversal constriction of lorica. Loose grid of characteristic transverse muscles bundles in thoracic region. Scalid rows on introvert with own band of ring muscle. Each scalid has its separate diagonal muscle for separate movement.

Digestive system ( Figs. 3 A, 4C, F) beyond oesophagus continuing as voluminous midgut (gu) with large absorptive cells, followed by narrow hindgut, and round cloaca cavity (clo) which opens dorsocaudally.

Thorax contains series of eight neck glands (ngl), which open into basal plates above double trichoscalids via pores. Two oval caudal glands (cgl) present. Large pair of saccate testes (te, Fig. 4 F) marking lateral sides of lorica and being densely filled with fibroid spermatozoa (spz) like in holotype. Protonephridia indistinct. Ducts of bothtestes end in cloaca (clo).

Description of female

Two mature females with retracted body ( Fig. 8 E) were found still enclosed in the cuticle of seventh instar larvae and both surrounded by cuticles of postlarvae. One female has moulted from a type I, and the other from a type II postlarva (see below). Adult females seem to be morphologically identical with males but differ internally by having paired ovaries of which only one is enlarged and filled with large oocytes and/or one large egg.

Description of simplified parthenogenetic female ( Fig. 5 A, B; 6A–F)

Simplified, not free-living adult stage represent unisexual phase of life cycle, with sack-like trunk, lacking buccal structures and introvert.

Body ( Figs. 5 A, B, 6A, C, D) retracted, with thin, weakly developed cuticle, consisting of indistinct thorax and abdomen, both united to simple sack-like trunk, containing ovaries. Introvert as anterior part of head lacking, only neck region present.

Neck with eight large hook-like scalids (sc) arranged tightly in one circle at anterior end. Additional two rows of indistinct tiny spiny scalids it was not clearly visible how many scalids were present per row.

Simplified adult female (sAd, Figs. 5 A, 6A, B) surrounded by thin cuticle of reduced postlarva (type II) and additionally enclosed in retracted exuvium of seventh instar Higgins-larva (LarVII). The latter showing characteristic features like structure of toes and trunk setae, but having introvert retracted and collar closed ( Figs. 5 A, B, 6A–C, E). One simplified female (paratype VI) found in immature phase ( Figs. 5 A, 6A, B, size 226 µm), which was starting to form twelve oocytes (oc) inside developing ovaries (ov). Other simplified female (paratype VII) being in phase of disintegration ( Figs. 5 B, 6C–F), body shrunk (“rest body”, size 90 µm) and tissue extensively disintegrated, even so the cuticle of type II postlarva. Exuvium of surrounding seventh instar Higgins-larva (LarVII, Figs. 5 B, 6E) acts as shelter for nine released eggs (eg, diameter 40 µm) of which some have already developed to embryos (em, length 60 µm) or first instar larvae.

Description of Postlarvae (Figs. 7B–C, 8A–E)

Two types of postlarvae were found enveloped by exuvia of seventh instar Higgins-larvae. These postlarvae are non free-living instars and contain adults, which have moulted from them.

Type I postlarva (Figs. 7B–C) has a simplified adult morphology, the anterior region being simpler than the posterior one:

Body length 175 µm; maximal body width 94 µm; exuvium with features of later adult morphology. Anterior half of trunk with thin cuticle (> 1 µm, see arrow in Figs. 7B and 8C) representing introvert and thoracic region.

Introvert densely covered with minute protoscalids (psc), which could be identical in number and arrangement with later scalids of the adult introvert (too small to allow distinction of rows in LM). There is no mouth cone nor any internal buccal structures.

Neck and thoracic region not clearly defined, with wrinkled cuticle and many longitudinal and transverse folds, posteriorly with a circle of eight hooks (ho) which have their equivalents in the eight type A basal plates (bp1a) on the neck of adults ( Fig. 1 ). Posterior half of trunk representing armoured abdominal region with fully developed lorica.

Lorica (lo) with thick cuticle (3 µm, see arrow in Figs. 7B and 8C), easily visible in LM, and almost identical in structure with lorica of adults but less prominent: distinct anterior margin with cuticle reinforcement consisting of protrusion and crescent-shaped ornamentation, lorica composed of 44 primary plicae surrounded by well-developed double ridges, modified midventral plicae with five transversal ridges. End cone (ec, Fig. 7B) distinct and ventrally with a round structure.

Type II postlarva ( Figs. 5 A, 8E) consisting only of uniform thin cuticle without any structures surrounding adults during metamorphosis as type I postlarva.

Description of Higgins-larva ( Figs. 8 F, 9A, B)

Body ( Figs. 8 F, 9A, B) bottle-like, divided into conical mouth cone, introvert, neck, collar, thorax, and slightly loricate abdomen.

All body regions fully extended; length 167 µm (from tip of mouth cone to caudal end); maximal body width 63 µm (in middle of lorica).

Mouth cone (mc; Figs. 9 A, B, 10A.1, A.2) divided into three sections. First section (mcs1) narrow, cylindrical, and telescopically retractable into slightly broader second section. Cuticle with six massive basal longitudinal cuticular bars (bar). Terminal end has mouth opening, which is surrounded by external armature ( Fig. 10 A.2). Second (mcs2) and third (mcs3) sections of mouth cone broad and separated by transverse constriction; or second section slightly conical and anteriorly with six oral loops (olp); cuticle of both sections sculptured by six fine longitudinal oral striae (ost). Single midventral oral seta (ms) situated at base of mouth cone ( Fig. 10 A.2).

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Internally there is a buccal channel (bc) with complex adjunctive structures ( Fig. 10 A.1). Pharyngeal bulb and prepharyngeal armature well recognizable in the paratypic Higgins-larva due to good fixation. Mouth opening (mo) located terminally on the first section, which can be seen extended from the second section. Mouth opening externally surrounded by six oral teeth (ot) in front of longitudinal cuticular bars. Ring of six long and broad oral stylets (os) inside the mouth and partly pushed out from it. Basal stylets followed by broad and cylindrical prepharyngeal armature. Cuticle of narrow buccal channel weakly sclerotized and smooth, not forming a buccal tube, but surrounded by hexaradially symmetrical prepharyngeal armature over its entire length.

Prepharyngeal armature (ia, Fig. 10 A.1) consisting of six longitudinal bracelets arranged in two stories, an anterior and a posterior one. Anteriorly, bracelets (bra1) stand in pairs, their bases bifurcate and are connected by six upper transversal bridges (bg1), and their other ends are connected with bases of oral stylets. Bracelet pairs covered anteriorly by six hyaline valve-like armature plates (apl) forming an outer cylinder. Posteriorly, bracelets continue as single straight elements (bra2) connected with each other also by transverse bridges (bg2). Behind bridges, single bracelets converge towards buccal channel, their posterior ends being fused with pharyngeal crown.

Pharyngeal bulb (pb, Fig. 10 A.1) large, rounded at both ends, and slightly cylindrical. Anterior part of bulb marked by a sclerotized ring-like structure called pharyngeal crown (pc). Crown with three small apodemes (apo). Muscles of bulb in longitudinal section arranged in five layers of three radial muscles. Lumen walls of pharynx bulb sclerotized by five rows of placoids each row containing three of them (p1–p5). Each placoid subdivided by constriction into two halves, from both of which extends a small apodeme (apo). Pharyngeal bulb followed by short oesophagus (oe). Buccal channel continues through oesophagus and round mass of brain (br) that fills the space in the larval head ( Fig. 8 F).

Introvert (in, Fig. 9 A, B) as anterior region of head, spherical, densely covered with four scalid rows ( Fig. 8 F).

First row (cr1, Figs. 9 A, B, 10B) with eight long and strong clavoscalids, being laterally flattened and divided into three segments; first segment with narrow base and as long as second segment; second segment broad and laterally flattened; third segment being small and spinose; ventral-most pair of clavoscalids slightly shorter and thinner.

Second row (sr2, Figs. 9 A, B, 10B) with ten strong spinoscalids of nearly same length as clavoscalids and divided into two segments; first segment arising with broad base from introvert, tapering distally, lateral surfaces with longitudinal weal; second segment spine-like, as long as first one, with fine ventral serration consisting of three minute denticles near the tip.

Third row (sr3, Figs. 9 A, B, 10B) with 15 strong spinoscalids of same structure as those of second row, but slightly shorter.

Fourth row (sr4, Figs. 9 A, B, 10B) with 14 strong spinoscalids of same structure as those of second row, but clearly shorter.

Neck (nk, 9A, B, 10B) as posterior region of head not distinct from introvert, and carrying fifth and sixth row of scale-like scalids.

Fifth row ( Figs. 9 A, B, 10B) with 15 scalids of two different types arranged in two alternating subcircles. Upper subcircle with seven large type B scalids (sr5b), consisting of two segments; first segment conical, with distal dorsal tooth; second segment rigid and spinous. Lower subcircle with eight type A scalids (sr5a); consisting of protruding double leaf-like elements, each with reinforced inner margins. Dorsally, type A double elements shorter, more triangular, protruded, and hook-like.

Sixth row ( Figs. 9 A, B, 10B)) also contains 15 scalids of two different types arranged in two subcircles. Seven minute double spines (sr6b) alternate with eight small single rectangular plates (sr6a), which posteriorly are tricuspid. In summary the number and arrangement of scalids (cs = clavoscalids, sc = scale-like scalids, ss = spinoscalids) belonging to the head can be expressed in the following scalid formula: 8cs, 10ss, 15ss, 14ss (in) / 7b+8a sc, 7b+8a sc (nk)

See also diagram in Fig. 10 B as additional demonstration of the scalid arrangement.

Collar (co, Figs. 9 A, B) intermediate between neck and thorax; well defined and distinct anteriorly and posteriorly. Cuticle of collar with many longitudinal folds and subdivided by transversal constriction; with seven papillate flosculi located along constriction in large distinct pentagonal pits (2–3 µm deep) called therefore pit flosculi (fl3).

Thorax (th, Figs. 9 A, B) consisting of thin and flexible cuticle divided into six ventral and five dorsal transversal rows of thoracic plates (thr1-6), highest number of 19 thoracic plates in fifth row, all plates can transversly be folded once. Transition zone between thorax and loricate abdomen with two pairs of short setae; anterolateral setae (Is1) and anteroventral setae (Is2) have the same structure: filiform, arising from small swollen bases and with fine serrated inner margins.

Loricate abdomen (lo, Figs. 9 A, B) urn-shaped, moderately armoured, with 22 primary longitudinal folds (lr) separating 22 plicae; ventrally secondary longitudinal folds present between plicae, not extending very far posteriorly. Lorica divided ventrally into two parts by a transverse constriction (tv) halfway. Toes (to, Fig. 9 A) long (55% of lorica length), rigid, and extending pair-wise ventrally from caudal end; articulating with balland-socket-joints on moderately developed basal plates. Toes with enlarged bases (tb), followed by hollow tubes (tu) (60% of length of toes) and ending in solid end spines (st); tubes opening with a pore (pt) at the beginning of the end spine. Two pairs of large caudal glands with long ducts to tubular parts of toes occupy posterior most region of abdomen. Other caudal appendages include three pairs of posterior setae. Posterodorsal setae (se1), modestly long, filiform, located dorsally at end of lorica; posterolateral setae (se2) short, sickle-shaped and visibly swollen pod-like; posteroterminal setae (se3) short, robust, spinous, standing close together between toes.

End cone (ec, Figs. 9 A, B) distinct, consisting of two rows of anal plates (ap), forming terminal anal field (af); anal cone with anus situated terminally on anal field.

Observations concerning life history stages and life cycle of P. d i v a sp. n.

The following observations on life history stages and instars of P. d i v a sp. n. add new information to the understanding of similar life cycles of Pliciloricus -species also found in the Angola Basin. The hypothetical life cycle of P. d i v a include a series of instars of Higgins-larvae, two types of postlarvae (type I simplified, type II reduced), and next to bisexually males and females a simplified stage reproducing parthenogenetically ( Fig. 11A). The life cycle, as figured out so far, probably has two phases ( Fig. 11 B PhI, PhII): (1) a bisexual phase with adults of both sexes finishing their metamorphosis enclosed in one (simplified) or other (reduced) type of postlarva and ( Fig. 11 B PhI); (2) a parthenogenetic phase with a simplified adult only ( Fig. 11 B PhII). The discovered bisexual adults shows no external sexual dimorphism ( Fig. 11 B PhI a, b). The males have a pair of testes, while the females have one matured ovary, which produces large single eggs, whereas the other ovary is not fully developed. From the egg, the first instar Higgins-larva hatches ( Fig. 11 B PhI c). The sixth or seventh larval instars are larger and have a greater volume than adults. The seventh or last instar Higginslarvae ( Fig. 11 B PhI e) are without any sign of reduction: for example toes, setae, and scalids are of normal length. When this seventh instar Higgins-larvae still contains adults in metamorphosis the introvert is, in all observed cases, withdrawn. Then the collar closes the thorax and shows a spoked-wheel-like structure. The seventh instar Higgins-larva has two possibilities of further development: it can develop into a mature male or female or into a parthenogenetic simplified female. The bisexual adults can probably moult from either of the two different types of postlarvae ( Fig. 11 B PhI g, h), which both shows clear signs of reduction and are not free-living stages. The type II postlarva ( Fig. 11 B PhI h) is strongly reduced to not more than a thin cuticle (as found in most other known Pliciloricus -species, see section "discussion" below). The type I postlarva ( Fig. 11 B PhI g) has a simplified anterior body region but shows a well developed lorica with the same ornamentation as seen later in the adults. The parthenogenetic adult is probably also a non free-living stage because it has a simplified body with numerous reductions ( Fig. 11 B PhII i). The trunk is a simple sack containing the mature ovaries that produces the many large eggs stored inside. There is no introvert but the neck region is preserved bearing eight large hooks and a few additional tiny spines. The parthenogenetic simplified adult, moulting from a type II reduced postlarva, disintegrates more or less completely after all eggs have been formed and released from the mature ovary.

Figures

FIGURE 1. Pliciloricus diva sp. n., holotype, adult male, ventral view.

FIGURE 3. Pliciloricus diva sp. n., paratype I, adult male; A, half schematic illustration of anatomy with details in different optic layers; B, internal structures of the mouth cone, both ventral view.

FIGURE 4. Pliciloricus diva sp. n., interference contrast light micrographs, holotypic male: A, anterior body region; paratypic male: B, habitus; C, mouth cone and introvert; D, type B scalid of fourth row; E, lorica and posterior end; F, internal view on testis.

FIGURE 5. Pliciloricus diva sp. n., A, exuvium of seventh larval instar with retracted introvert containing reduced postlarve (type II) and simplified parthenogenetic adult (female) being in immature phase, both developing ovaries containing many oocytes; B, simplified parthenogenetic adult (female) in phase of disintegration, which is still enclosed together with released eggs and embryos inside exuvium of seventh instar Higgins-larva (cuticle of type II postlarve disintegrated), drawings in ventrolateral view.

FIGURE 8. Pliciloricus diva sp. n., interference contrast light micrographs. A, exuvium of seventh larval instar with retracted introvert containing type I postlarva and adult (same specimens as drawn in Fig. 7 A – C); B, focus on enclosed adult; C, anterior region with focus on both stages enclosed into larval exuvium (arrows point to different thickness of cuticle of simplified type I postlarva); D, ornamentation of midventral plica of postlarval lorica shining through larval cuticle; E, young adult female enclosed in reduced type II postlarva and exuvium of retracted seventh larval instar; F, habitus of paratypic Higgins-larva.

FIGURE 9. Pliciloricus diva sp. n., Higgins-larva, paratype II, habitus. A, ventral view; B, dorsal view.

FIGURE 10. Pliciloricus diva sp. n., buccal channel of paratypic Higgins-larva with buccal structures like prepharyngeal armature and pharyngeal bulb, ventral view. A. 1, internal features; A. 2, external features; B, diagram of scalid arrangement on the head (introvert and neck) of paratypic Higgins-larva.

FIGURE 2. A Pliciloricus diva sp. n., details of scalids: double-organ compared with untransformed spinoscalids of second row of scalids; A. 1, free spinoscalid, lateral view; A. 2. double-organ, lateral view; A. 3, double-organ, dorsal view; A. 4. type B spinoscalid of fourth row; B, diagram of scalid arrangement on the head (= introvert and neck) of Pliciloricus diva sp. n., compared with the one of C, Pliciloricus corvus Gad, 2004.

Tables

TABLE 2. Morphometric data of Higgins-larva of P. diva sp. n.

Higgins-larva:	No.	Paratype II
Length of:
Body		162 µm
Mouth cone		28 µm
Midventral setae		4 µm
Introvert		19 µm
Lorica		70 µm
Toes		35 µm
Spine-tip of toes		10 µm
Anterolateral seta		14 µm
Anteroventral seta		14 µm
Posterodorsal seta		25 µm
Posterolateral seta		18 µm
Posteroterminal seta		10 µm
Clavoscalids of first row (cr1)	8	35 µm
Spinoscalids of second row (sr2)	10	35 µm
Spinoscalids of third row (sr3)	15	22 µm
Spinoscalids of fourth row (sr4)	14	18 µm
Spinoscalids of fifth upper subrow (sr5)	7	10 µm
Spinoscalids of fifth lower subrow (sr5)	8	3.5 µm
A-spinoscalids of fifth row (sr6)	7	2 µm
B-spinoscalids of fifth row (sr6)	8	2 µm
Diameter of:
Lorica		60 µm