Stephos geojinensis, 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 : 22-23

Taxon classification Animalia Calanoida Stephidae

Stephos geojinensis sp. n. Figs 1, 2, 3, 4

Material examined.

Female holotype (NIBRIV0000304586) and male allotype (NIBRIV0000304587) undissected and preserved in 70% ethanol; female paratype (NIBRIV0000304738) and male paratype (NIBRIV0000304739) dissected on two glass slides; one female paratype and seven male paratypes (NIBRIV0000304293, 1 vial) preserved in 70% ethanol. All specimens were collected from the near-bottom using a light trap at high tide at dusk, on 28 August 2010 by the senior author (S. Y. Moon). The description below is based on the paratypes.

Type locality.

Geojin fishery port, Gosung-gun, Gangwon-do (approximately 38°26'58"N 128°27'46"E), Korea.

Female.

Body (Fig. 1A, B) robust, length 883 μm. Prosome 5-segmented; cephalosome and first pedigerous somites completely separated; fourth and fifth pedigerous somites completely fused, posterior corners of prosome symmetrical. Rostrum represented by rounded knob. Prosome-urosome ratio 2.42:1. Urosome (Fig. 1C, D) 4-segmented, comprising genital double-somite, two free abdominal somites and anal somite; length ratio of urosome somites as 48.7: 17.0: 19.8: 14.5 = 100. Genital double-somite (Fig. 1C, D) symmetrical with proximolateral margins produced in dorsal aspect (Fig. 1C), asymmetrical in ventral aspect with smooth evenly rounded operculum displaced to the right; double-somite with row of spinules anteriorly on ventral surface and patch of spinules at each side as figured. First and second free abdominal somites with transverse hyaline frill both dorsally and ventrally. Anal somite (Fig. 1C, D) shortest. Caudal rami (Fig. 1C, D), with 6 setae, symmetrical, about 1.35 times longer than wide (43 × 31 μm), with several rows of spinules on dorsal and ventral surface; caudal seta I absent; seta II reduced; seta VII displaced to medial margin.

Antennules (Fig. 1E) symmetrical, extending beyond distal margin of second urosomite; 24-segmented, with ancestral segments I-II, III-IV, X-XI, and XXVII-XXVIII fused. Segmentation and setation pattern as follows (ancestral segment number-setae+aesthetasc): I-II-3s; III-IV-4s + 1ae, V-2s, VI-2s, VII-2s + 1ae, VIII-2s, IX-2s, X-XI-4s + 1ae, XII-1s, XIII-1s, XIV-2s + 1ae, XV-1s, XVI-2s + 1ae, XVII-1s, XVIII-1s, XIX-1s, XX-1s, XXI-1s + 1ae, XXII-1s, XXIII-1s, XXIV-1s +1s, XXV– 1s +1s, XXVI– 1s +1s, XXVII-XXVIII– 5s + 1ae. Ancestral segments II, III, V-XII, and XV-XXVI each with row of spinules on posterior surface.

Antenna (Fig. 2A) biramous; coxa and basis separate, bearing 1 and 2 setae on distomedial angle, respectively; endopod 2-segmented, proximal segment with 2 setae, compound distal segment bilobed with 8 and 7 setae, respectively, outer margin with small serrated process subdistally and tiny spinule adjacent to serrated process; exopod 7-segmented, setal formula 1, 3, 1, 2, 1, 1, 3.

Mandible (Fig. 2B) with well developed coxal gnathobase, cutting edge with isolated unicuspid tooth and 7 heterogeneous teeth plus dorsal spinulose seta. Mandibular palp biramous; basis with 4 setae on inner margin. Exopod 5-segmented, setal formula 1, 1, 1, 1, 2; endopod 2-segmented, proximal segment with 4 setae, distal segmentwith 10 setae.

Maxillule (Fig. 2C) praecoxa and coxa incompletely fused; praecoxal arthrite with 9 marginal spines plus 4 stiff setae on posterior surface; several rows of tiny spinules on posterior surface as figured. Coxal epipodite with 9 setae; coxal endite with 3 stiff setae. Proximal basal endite with 4 setae; distal basal endite indistinct, with 5 setae; no trace of basal exite. Exopod with 11 marginal setae; row of setules along distal portion of medial margin. Endopod apparently unsegmented with 4, 4, 7 setae.

Maxilla (Fig. 2D), indistinctly 6-segmented. Armature of praecoxal and coxal endites as 5, 3, 3, 3, respectively. Basal endite with 4 setae, 1 stouter than rest. Endopod 4-segmented, setal formula 1, 1, 1, 3. Praecoxal, coxal and basal endites with cluster of long spinules subdistally on lateral surface.

Maxilliped (Fig. 2E) syncoxa robust, with setal formula 1, 2, 3, 3 and several oblique rows of tiny spinules as figured; basis with 3 setae and row of setules on medial margin; endopod 6-segmented with proximal segment partially incorporated into basis, setal formula 2, 4, 4, 3, 3+1, 4.

P1 to P4 (Fig. 3 A–D) progressively larger towards posterior, each comprising coxa, basis and 3-segmented exopod; endopod of P1 (Fig. 3A) 1-segmented, that of P2 (Fig. 4B) 2-segmented; endopods of P3 (Fig. 3C) and P4 (Fig. 3D) 3-segmented. Endopod of P2-P4 with transverse row of spinules distally on terminal segment. Exopod of P2-P4 with row of spinules on anterior surface of terminal segment. Armature formula of P1-P4 as follows (Roman numerals indicate spines, Arabic numeral indicate setae):

Fifth legs (Fig. 3E) symmetrical, uniramous, 3-segmented with proximal segment fused to intercoxal sclerite; second segment elongated, 2.62 times longer than wide (42 × 16 μm), with distomedial angle produced into tiny pointed process. Distal segment elongated, tapering with short spine implanted mid-laterally and coarsely serrated spine incorporated (i.e. non-articulating) to segment distally.

Male.

Body (Fig. 4A, B) robust, length 819 μm (mean 821 ± 0.06, n=4). Prosome 5-segmented; cephalosome and first pedigerous somite almost completely separated; fourth and fifth pedigerous somites completely fused; fifth pedigerous somite symmetrical, with lateral lobe at each side. Rostrum as in female. Prosome-urosome ratio 2.12:1. Urosome 5-segmented, comprising genital somite, three free abdominal somites and anal somite; length ratio of urosomites as 28.3: 20.5: 18.6: 17.0: 15.7 = 100. Genital somite asymmetrical, with lobe protruding anterolaterally on left side. First to third abdominal somites with transverse hyaline frill both dorsally and ventrally. Anal somite shortest. Caudal rami similar to those of the female.

Antennules (Fig. 4C) extending beyond distal margin of second urosomite, non-geniculate, 24-segmented with failure to express articulations between ancestral segments I-IV (although vestige of articulation between segments II and III expressed dorsally), X-XI and XXVII-XXVIII. Segmentation and setation pattern as follows (ancestral segment number-setae+aesthetasc): I-II - 3s + 2ae, III-IV– 4s +3ae, V– 2s + 1ae, VI– 2s+1ae, VII– 2s + 1ae, VIII– 2s+1ae, IX– 2s + 1ae, X-XI– 4s + 1ae, XII– 1s, XIII– 1s, XIV– 2s + 1ae, XV– 1s, XVI– 2s + 1ae, XVII– 1s, XVIII– 1s, XIX– 1s, XX– 1s + 1ae, XXI– 1s + 1ae, XXII– 1s, XXIII– 1s + 1ae, XXIV– 1s +1s + 1ae, XXV– 1s +1s, XXVI– 1s +1s, XXVII-XXVIII– 5s+ 1ae. Ancestral segments V-IX, XI and XV-XXVI each with row of spinules on posterior surface.

Antenna, mandible, maxillule, maxilla, maxilliped and P1-P4 similar to those of female. Fifth legs (Fig. 4D) strongly asymmetrical, uniramous and filiform. Left leg 5-segmented, shorter than right counterpart; second segment with blunt prominence medially; third and fourth segments elongated, about equal in length; distal segment reduced, with row of seven unequal long and 13 short hyaline lamellae disposed as figured. Right leg 4-segmented; third segment very elongated with short, curved proximolateral spur-like process; distal segment elongated and curved, bifid with short inner branch.

Etymology.

The specific name geojinensis is taken after the type locality Geojin Port, Gosung-gun, Gangwon-do, Korea.

Remarks.

Stephos geojinensis sp. n. is easily recognizable by the display of the following five diagnostic features: (1) female genital double-somite with protruding proximolateral margins in dorsal aspect; (2) genital double-somite with row of spinules anteriorly on ventral surface and patch of spinules at each side; (3) basis and distal segment of P5 elongated in female; (4) distal segment tapering with short spine implanted mid-laterally and coarsely serrated spine incorporated to segment distally in female P5; and (5) male right P5 distal segment elongated and curved, bifid with short inner branch.

Bradford-Grieve (1999) divided the species of Stephos in four groups based on the morphology of the male fifth legs. Stephos geojinensis falls within a "group IV" characterized by a 4-segmented male right P5 combined with a left leg with a narrow fourth segment. This group includes eight species from the western Pacific and the Atlantic: Stephos angulatus Bradford-Grieve, 1999, Stephos marsalensis Costanzo, Campolmi & Zagami, 2000, Stephos morii Greenwood, 1978, Stephos pacificus Ohtsuka & Hiromi, 1987, Stephos pentacanthos Chen & Zhang, 1965, Stephos rustadi Strömgren, 1969, Stephos tsuyazakiensis Tanaka, 1967, and Stephos vivesi Jaume, Boxshall & Gràcia, 2008 (see Table 1 in Bradford-Grieve 1999; Costanzo et al. 2000; Jaume et al. 2008).

The male fifth legs are diagnostic to distinguish Stephos goejinensis from other congeners in this group. Thus, Stephos angulatus is easily differentiated from the new species by the more developed inner branch of thebifid distal segment of the right P5, and by the distal segment of the left male P5 with only three elongate hyaline lamellae and a rounded cluster of short spinules (see Bradford-Grieve 1999). In Stephos marsalensis , the distal segment of right male P5 is not bifid whereas there are only 5 lamellate hyaline processes on the distal segment of left male P5 (see Costanzo et al. 2000).

Stephos morii differs from the new species in having the right P5 pseudochelate with a large inner branch on the distal segment,and the left leg carrying about 5 lamellate processes on the distal segment, which is produced into a long spinous process about 1.6 times longer than the segment (see Greenwood 1978 as Stephos tropicus ). In Stephos pacificus , the distal segment of the right leg is not bifid and is bordered by a narrow lamella, whereas the left leg carries three terminal and two subterminal lamellate processes on the distal segment (see Ohtsuka and Hiromi 1987).

Stephos rustadi is easily separated from the new species by having the segment 3 of the right leg slightly shorter than segment 4, which terminates in a finely serrated claw-like structure, whereas the left leg carries two strong hook-like processes on the terminal segment, the larger one bifid (see Strömgren 1969).

Stephos pentacanthos and Stephos tsuyazakiensis share with the new species the same ornamentation on the male P5, but the new species has 7 unequal long and 13 short hyaline lamellae on the distal segment of left leg and a bifid distal segment with a short inner branch on right leg ( Chen and Zhang 1965; Tanaka 1966).

Finally, Stephos vivesi can be differentiated from Stephos goejinensis based on the male right fifth leg distal segment, which is spatulate and displays two rounded outgrowths proximally on the anterior surface (vs. segment not spatulate, slender and bifid in Stephos goejinensis ) (see Jaume et al. 2008).