Stephos projectus, Moon, Seong Yong, Youn, Seok-Hyun & Venmathi Maran, B. A., 2015

Moon, Seong Yong, Youn, Seok-Hyun & Venmathi Maran, B. A., 2015, Two new species of benthopelagic Stephos (Copepoda, Calanoida, Stephidae) from Korea, ZooKeys 495, pp. 21-40 : 23-27

Taxon classification Animalia Calanoida Stephidae

Stephos projectus sp. n. Figs 5, 6, 7, 8

Material examined.

Female holotype (NIBRIV0000304294) and male allotype (NIBRIV0000304297) undissected and preserved in 70% ethanol; 20 female paratypes (NIBRIV0000304295), and four male paratypes (NIBRIV0000304296) preserved in 70% ethanol. Dissected paratypes of both sexes are retained in the collection of the senior author. All specimens were collected at the type locality using a hand net on 28 February 2013 by the senior author (S. Y. Moon). The description below is based on the paratypes.

Additional material.

Female (NIBRIV0000304584) undissected, preserved in ethanol, female (NIBRIV0000304585) dissected on 1 glass slide, Daeyari, Wando Island, Wando-gun, Jeollanam-do, Korea, 19 July 2010.

Type locality.

Stagnant water in burrows of ocypodid crabs in intertidal mud flat, Bongyoungri, Naro Island, Goheung-gun, Jeollanam-do (approximately 34°29'13"N, 127°29'12"E), Korea.

Etymology.

The specific name, projectus, is derived from the dorsolateral spiniform projections present on the female genital double-somite.

Female.

Body (Fig. 5A, B) robust, length 1.51 mm (mean 1.54 ± 0.07, n = 5). Prosome 5-segmented; cephalosome and first pedigerous somite completely separated; fourth and fifth pedigerous somites incompletely fused, posterior corners of fifth pedigerous somite slightly asymmetrical. Rostrum represented by rounded knob. Prosome-urosome ratio 1.83:1. Urosome 4-segmented (Fig. 5C, D), comprising genital double-somite, two free abdominal somites and anal somite; length ratio of urosomites as 51.1: 18.9: 17.3: 12.7 = 100. Genital double-somite (Fig. 5E) elongated, asymmetrical, with pointed process at each side on dorsal surface; that on right side larger than left counterpart and with patch of spinules placed nearby; genital operculum bumpy with two outgrowths, one of them bifid on right side. First and second free abdominal somites (Fig. 5C, D) with transverse hyaline frill both dorsally and ventrally. Anal somite shortest (Fig. 5F). Caudal rami (Fig. 5C, F), with 6 setae, symmetrical, about 1.63 times longer than wide (72 × 44 μm), with 4 transverse rows of spinules on ventral surface; caudal seta I lacking; seta II reduced; seta VII displaced to medial margin.

Antennules (Fig. 6A) similar to preceding species except for not extending beyond distal margin of fifth pedigerous somite.

Antenna (Fig. 6B) similar to preceeding species except for presence of two transverse rows of spinules (instead of tiny serrated process plus spinule) on lateral margin of distal segment of endopod.

Mandible (Fig. 6C) similar to preceding species except for: (1) coxal gnathobase with straight row of moderately incised teeth; (2) outer margin of proximal segment of exopod with row of setules; and (3) distal segment of endopod with transverse row of spinules.

Maxillule (Fig. 6D) and maxilla (Fig. 6E) similar to preceding species except for presence of one additional seta on basal endite of maxilla.

Maxilliped (Fig. 6F) differing from Stephos geojinensis in presence of additional rows of tiny spinules on syncoxa.

P1 to P4 (Fig. 7 A–D) with armature formula as in preceding species but with outer spine on second exopodal segment of P1 transformed into seta.

Fifth legs (Fig. 7E) symmetrical, uniramous, 3-segmented with proximal segment fused to intercoxal sclerite; second segment similar to Stephos geojinensis but shorter (1.72 times longer than wide; 31 × 18 μm); distal segment with a seta instead of spine on lateral margin, and with spinulation on terminal spine not so coarse.

Male.

Body (Fig. 8A, B) robust, length 0.93 mm (mean 0.91 ± 0.05, n=4) and similar to female in all major features except for last pedigerous somite, urosomal segmentation, armature of antennules and morphology of fifth legs. Fourth and fifth pedigerous somites, incompletely fused, latter asymmetrical with lateral lobe on left margin. Rostrum as in female. Prosome-urosome ratio 1.87:1. Urosome 5-segmented, comprising genital somite, three abdominal somites and anal somite; length ratio of urosomites as 23.7: 25.6: 22.6: 18.6: 9.5 = 100. Genital somite asymmetrical, with protruding lobe on left side and patch of tiny spinules proximally at each side. Abdominal somites with transverse hyaline frill both dorsally and ventrally. Anal somite shortest. Caudal rami similar to those of female.

Antennules (Fig. 8C) similar to preceding species except for not extending beyond distal margin of fifth pedigerous somite and for failure to express an aesthetasc on ancestral segments VI, VIII, composite X-XI, XX and XIII. In addition, the composite segment I-II displays 4 setae (vs. 3 in Stephos geojinensis ).

Antenna, mandible, maxillule, maxilla, maxilliped and P1 to P4 similar to female.

Fifth legs (Fig. 8D, E) strongly asymmetrical, uniramous and filiform. Left leg 5-segmented; segments 3 and 4 each with rounded outgrowth on medial margin, outgrowth on segment 3 more slender and crowned with hyaline frill, that on segment 4 with ridged plate terminally; fourth segment with additional short conical outgrowth and longitudinal row of spinules; distal segment short, rounded, with 4 long hyaline lamellae on distal margin and patch of short spinules on posterior surface. Right leg 4-segmented; segment 3 elongate, straight and slender except for blunt triangular process proximally on lateral margin; fourth segment sickle-shaped with rounded tip; 4 rounded outgrowths along inner margin and single outgrowth subterminally on outer margin of segment.

Remarks.

Stephos projectus sp. n. falls within a group of species characterized by a 4-segmented right male P5 combined with a left leg in which the fourth segment is swollen (group III of Bradford-Grieve 1999). This group comprises 14 species from the Atlantic and the Indo-Pacific regions, namely: Stephos boettgerschnackae Kršinić, 2012, Stephos canariensis Boxshall, Stock & Sanchez, 1990, Stephos cryptospinosus Zagami, Campolimi & Costanzo, 2000, Stephos deichmannae Fleminger, 1957, Stephos fultoni T. Scott, 1898, Stephos hastatus Bradford-Grieve, 1999, Stephos kurilensis Kos, 1973, Stephos lamellatus G.O. Sars, 1902, Stephos lucayensis Fosshagen, 1970, Stephos maculosus Andronov, 1974, Stephos minor T. Scott, 1892, Stephos robustus Ohtsuka & Hiromi, 1987, Stephos scotti G.O. Sars, 1902, and Stephos tropicus Mori, 1942 (see Table 1 in Bradford-Grieve 1999; Zagami et al. 2000; Kršinić 2012). Only two of them, Stephos hastatus and Stephos robustus , share with the new species an asymmetrical female genital double-somite.

Stephos projectus sp. n. differs from Stephos hastatus in the following features: (1) presence of dorsolateral process at each side on the female genital double-somite (vs. processes absent, in Stephos hastatus ); (2) fourth segment of male left P5 without strong spine (vs. strong spine present in Stephos hastatus ); (3) fifth segment of male left P5 with 4 unequal long hyaline lamellae on distal margin (vs. two hyaline lamellae in Stephos hastatus ); and (4) distal segment of male right P5 sickle-shaped (vs. segment bifid in Stephos hastatus ). The new species can be easily differentiated from Stephos robustus based on the following features: (1) the presence of a dorsolateral pointed process at each side of the genital double-somite in female (vs. presence of a small mid-dorsal rounded process and not dorsolateral processes in Stephos robustus ); (2) fifth segment of male left P5 with 4 long hyaline lamellae on distal margin (vs. 5 large spines of unequal length in Stephos robustus ); and (3) fourth segment of male right leg sickle-shaped (vs. bifid in Stephos robustus ).

The two new stephids described herein, Stephos geojinensis sp. n. and Stephos projectus sp. n., are easily differentiated based on the ornamentation of both the female genital double-somite and genital operculum; the morphology of the distal segment of the male right fifth leg; the presence/absence of a tiny pointed process on the distomedial angle of second segment of female P5; and the condition (seta or spine) of the lateral armature element on distal segment of female P5, among other features.