Gorgonolaureus bicornutus, Kolbasov, Gregory A., Chan, Benny K. K. & Petrunina, Alexandra S., 2015

Kolbasov, Gregory A., Chan, Benny K. K. & Petrunina, Alexandra S., 2015, Gorgonolaureus bicornutus sp. nov (Crustacea: Thecostraca: Ascothoracida) from off South-East Taiwan with notes on morphology and distribution, Zootaxa 3972 (3), pp. 328-342 : 330-338

publication ID	https://doi.org/ 10.11646/zootaxa.3972.3.2
publication LSID	lsid:zoobank.org:pub:8C688C67-9652-4DB7-8640-E1BA37EB76EC
DOI	https://doi.org/10.5281/zenodo.6111619
persistent identifier	https://treatment.plazi.org/id/03CB9D09-4E02-9715-4AE3-AE846CB0F980
treatment provided by	Plazi
scientific name	Gorgonolaureus bicornutus
status	sp. nov.

Treatment

Gorgonolaureus bicornutus sp. nov.

Type material. Six female specimens (holotype and 5 paratypes; no males found) in polyp-surrounded cysts on a single colony of an halaxonian alcyonacean (“gorgonian”) Echinogorgia sp. ( Plexauridae ; determined by Prof. T.N. Molodstova) in a jar from the collections of the Coastal Ecology Laboratory, Biodiversity Research Center, Academia Sinica, Taiwan, collected at 21º11’43.3’’ N, 120º51’47.3’’ E, depth 227 m, Bashi Channel, south-eastern Taiwan, and fixed in absolute ethanol. The holotype and 4 paratypes are deposited in the Zoological Museum of Moscow State University under registration numbers Mg. 1220 (holotype) and Mg. 1221 (paratypes). The other paratype (no. ASIZCR000327) is deposited in the Biodiversity Research Museum, Biodiversity Research Center, Academia Sinica, Taiwan.

Diagnosis. Carapace of adult female 2.7–3.0 mm height, length 70–80% height; covered with simple and multifid teeth, anterior part of aperture with edge straight, posterior with edge scalloped. Two long, naked, dorsal horns on second and third thoracomeres. Fifth antennular segment with 14–16 stout spinulose setae; sixth segment without spines of surfaces; claw guard with 4 thick aesthetasc-like terminal setae; proximal sensory process distinctly separated from claw guard, with 3 thick aesthetasc-like terminal and one short sub-terminal setae. Maxillae with bifid, harpoon-shaped tips. Thoracopods II–V each with 3 seminal receptacles. Telsonic spines rudimentary. Furcal rami without spines or teeth; ventral margin not recurved; with 3 terminal and 3 subterminal setae on distal end.

Description of female (based on holotype and paratypes Mg. 1221). Carapace milky-grey in alcohol; univalved with curved, slit-like ventral aperture along midline ( Figs 1 View FIGURE 1 , 2 View FIGURE 2 A–C), upper dorsal part with spherical brood chamber larger than lower ventral part ( Figs 1 View FIGURE 1 C, 2B, 5A). Carapace with three inflations on ventral side smaller than brood chamber, one postero-ventral (hillock with aperture, Figs 1 View FIGURE 1 B, 2 A, C) and two mid-ventral laterally to aperture ( Figs 1 View FIGURE 1 D, 2C). Dimensions of carapace (holotype): height 3.0 mm, length 2.3 mm, maximum width (at top) 2.16 mm, isthmus (just below globular dorsal part) 1.13 mm. Aperture long, single (no separate aperture for oral cone), with thickened margins, anterior half with straight margin ( Figs 1 View FIGURE 1 D, 2C), posterior half with scalloped interlocking margins ( Figs 1 View FIGURE 1 C, 2B). External surface of carapace covered with cuticular teeth, rare and simple on lateral sides, dense and multifid on postero ventral hillock with scalloped aperture ( Figs 1 View FIGURE 1 D, 5D). Lateral sides of carapace without noticeable gut and ovarian diverticula ( Figs 1 View FIGURE 1 B, 2A). Internal surface of carapace mantle in postero-ventral area covered with dense, ctenoid scales consisting of 10–20 long, thin denticles, 10–25 Μm in length, underlain by row of long, thin, simple setae near valve margin, tiny and rare pores found between ctenoid scales ( Fig. 5 View FIGURE 5 B, C).

Body attached antero-ventrally by adductor muscle, occupying ventral third of carapace chamber ( Figs 2 View FIGURE 2 D, 5A). Oral cone situated opposite anterior part of aperture, covered by host tissue; thorax with thoracopods and abdomen with furcal rami lie opposite to free, posterior, scalloped part of aperture. Length of body (anterior-most part to tips of furcal rami) 2.19 mm (holotype Fig. 2 View FIGURE 2 D), 1.86 mm (paratype Fig. 5 View FIGURE 5 A). Body consisting of head with prehensile antennules and prominent oral cone on ventral side, followed by 6 thoracic segments with 6 pairs of biramous thoracopods, and 5-segmented abdomen, including telson with a pair of furcal rami. Size of thoracomeres gradually decreasing from first to sixth ( Figs 2 View FIGURE 2 D, 5A). Transverse band of setae absent on anterio-dorsal side of first thoracic segment. Two long, naked, dorsal horns ~ 1.3–1.4 mm length, slightly curved posteriorly, on second and third thoracic segments ( Figs 2 View FIGURE 2 D, 5A). Feeble ctenoid scales cover all surfaces of trunk somites ( Fig. 5 View FIGURE 5 G). Sixth thoracic segment bearing pair of latero-ventral, drop-like epaulets ~150 Μm length, with dense, sharp, cuticular protrusions in distal bulbous part ( Fig. 5 View FIGURE 5 E, F).

Prehensile antennules 6-segmented, Z-shaped when folded, tips reaching to mid-length of oral cone ( Fig. 2 View FIGURE 2 D– F). First segment massive, irregularly-shaped, almost lacking setae; second segment short, trapezoidal, with tuft of thin setae on anterior (preaxial) edge; third segment subtriangular, with row of thin setae along anterior edge; fourth segment short, trapezoidal, with 5–6 stout, spinulose setae on anterior edge; fifth segment elongate, 210 µm long, sub-rectangular, with 14–16 stout, spinulose seate along curved anterior edge, several pairs of small, thin setae on distal half of straight posterior edge. Sixth segment slightly shorter than fifth, with slightly curved posterior and recurved anterior edges, several tufts of small, thin setae on posterior edge; both segments spineless, lateral surfaces bearing feeble ctenoid scales ( Figs 2 View FIGURE 2 E, F, 6A). Robust, curved claw with smooth surface inserted distally on sixth segment; 3 short, thick setae at base of claw, 1 each on outer and inner sides, 1 on anterior edge of segment ( Figs 2 View FIGURE 2 E, F, 6A, B). Claw guard cylindrical, ~50–60 µm long, inner surface with flange, bearing 4 thick, aesthetasc-like terminal setae ( Figs 2 View FIGURE 2 E, F, 6A, B). Proximal sensory process same size as but distinctly separated from claw guard, with 3 thick, aesthetasc-like terminal setae and 1 short, sub-terminal seta ( Figs 2 View FIGURE 2 E, F, 6C).

Oral cone triangular with elongated distal part ( Figs 2 View FIGURE 2 D, 3C), formed by large labrum surrounding mouthparts ( Figs 3 View FIGURE 3 A, 6D). Labrum with mid-line posterior suture corresponding to its lateral margins ( Fig. 6 View FIGURE 6 D), proximal part wide, inflated, distal tip narrow, sharp ( Fig. 6 View FIGURE 6 E), lateral surfaces with feeble ctenoid scales ( Fig. 6 View FIGURE 6 F). Mouthparts grouped together, maxillae longest ( Fig. 6 View FIGURE 6 G). Medial languette elongated, tongue-shaped, with pointed distal part covered by row of setae, 2 rows of setae along anterior (outer) edge at middle and proximal parts ( Fig. 3 View FIGURE 3 I). Mandibles ( Fig. 3 View FIGURE 3 B–D) with broad basal part, and narrow, sharply pointed distal tip; lateral (outer) edge with several bands of few, long setae at basal part, row of long setae along distal tip; cutting (inner) edge with row of long setae, several noticeable multifid teeth in basal half, small sharp denticles in distal part. Maxillules ( Fig. 3 View FIGURE 3 E, F) with broad base gradually narrowing to distal part, with blunt tip, row of dense, long setae along inner edge, row of thicker setae on outer edge in distal part. Long, piercing maxillae ( Figs 3 View FIGURE 3 G, H, 6G) fused at bases, ~80% of their length free, lateral flanges in distal part, bifid harpoon-shaped tips.

Thoracopods I and VI ( Fig. 4 View FIGURE 4 A, F) cylindrical, smaller than others; thoracopods II–V flattened, size decreasing from II to V ( Fig. 4 View FIGURE 4 B–E). Thoracopods covered by numerous fine setae, segments bearing large, plumose setae. Coxae longer than wide, extensively lined with fine setae along outer and inner margins of thoracopods II–IV ( Fig. 4 View FIGURE 4 B–C) but only along inner margin of thoracopod I ( Fig. 4 View FIGURE 4 A); tuft of fine setae at distal part of inner margin and row of fine setae along outer margin ofthoracopod V ( Fig. 4 View FIGURE 4 E). Protopod of thoracopod VI lacking fine setae ( Fig. 4 View FIGURE 4 F). Margins of bases of thoracopods I–V lined with fine setae. 3 elongated, ampoule-shaped seminal receptacles at outer margins of coxae of thoracopods II–V ( Fig. 4 View FIGURE 4 B–E). Exopods 2-segmented, slightly longer than 3-segmented endopods of thoracopods II–V. Exopods of thoracopods I, VI significantly larger than 2-segmented endopods ( Fig. 4 View FIGURE 4 A, F). Setation including large, plumose setae of holotype given in Table 1. Single lateral coxal seta (position 1) present in thoracopods II–IV ( Fig. 4 View FIGURE 4 B–D), but medial coxal seta (position 9) found only in thoracopod III ( Fig. 4 View FIGURE 4 C). Exopods having 5–7 setae on distal segments (position 4), endopods having 2–5 setae on distal segments.

Table 1. Thoracopodal setation of holotype of Gorgonolaureus bicornutus sp. nov., numbers of positions indicated in Fig. 4 View FIGURE 4 , parentheses used in case of 2-segmented endopods.

thoracopod/position 1 2 3 4 5 6 7 8 9

Abdominal segments of different sizes ( Fig. 5 View FIGURE 5 E), first largest, segments 3, 4 small and short, fifth segment (telson) with pair of terminal furcal rami. First segment with rudimentary, bifurcated penis, length ~240 µm, on ventral side ( Fig. 4 View FIGURE 4 I). Penis with two smaller distal processes (each 100 µm length) on elongated proximal shaft (140 µm). Telsonic spines rudimentary ( Fig. 7 View FIGURE 7 B). Furcal rami ( Figs 4 View FIGURE 4 G, 5E, 7C) 310–350 µm length, triangular, with convex outer and concave inner surfaces, ventral margin not recurved. External surface with ctenoid scales along dorsal and ventral margins ( Fig. 7 View FIGURE 7 B), field of dense, thin setae on lateral surface, denticles or teeth lacking ( Figs 4 View FIGURE 4 G, 7B). Inner surface covered by dense transverse rows of ctenoid scales ( Fig. 7 View FIGURE 7 C, D). Distal part of furcal ramus bearing group of 3 subterminal and 3 subterminal/medial thick setae covered by dense citicular villi, medial terminal seta longest ( Figs 4 View FIGURE 4 H, 7A).

Remarks. The main differences between all known species of Gorgonolaureus are indicated in Table 2 and, as will be noted, most of the species are characterized by the presence of a single dorsal horn on the second thoracomere. Only G. tricornutus from New Caledonia has two long and one short dorsal horn on thoracomeres 1– 3, respectively. The new species described in the present study differs from G. tricornutus in having only two long dorsal horns, and on thoracomeres 2 and 3, 14–16 stout setae on the fifth antennular segment, instead of the 5 in G. tricornutus , harpoon-shaped bifid tips of the maxillae (trifid and non harpoon-shaped in G. tricornutus ), and by fewer seminal receptacles and furcal setae (Table 2).

Two species G. vietnamianus and G. helenae are widely allopatric in the same region as G. bicornutus ( Grygier 1991, Kolbasov 2004), from which it differs not only in having two dorsal horns instead of one, but also by the greater number of stout setae on the fifth antennular segment. It also differs from G. helenae by the bifid harpoonshaped tips of the maxillae and the presence of 3 seminal receptacles in thoracopods II–V, and from G. vietnamianus in having 3 seminal receptacles in thoracopods II–V instead of 5–9, and by fewer furcal setae.

Etymology. From the Latin bi- meaning two, and cornu meaning horn, in reference to the two thoracic horns.