Stephos fortipes, Moon & Soh & Cho, 2020

Moon, Seong Yong, Soh, Ho Young & Cho, Dae Hyun, 2020, Three new species of the genus Stephos Scott, 1892 (Crustacea, Copepoda, Calanoida, Stephidae) from Jeju Island, Korea, ZooKeys 944, pp. 1-30 : 1

Stephos fortipes sp. nov. Figures 9 , 10 , 11

Material examined.

Holotype ♀ (NIBRIV0000293110) dissected on a glass slide collected by D. H. Cho, 9 May 2012.

Type locality.

Near the bottom (ca. 4 m depth), Wimi port, Jeju Island (approximately 33°16'13"N, 126°39'43"E), Korea.

Etymology.

The specific name fortipes is the combination of Latin words fortis (strong) and pes (leg), alluding to the strong feature of the female fifth leg.

Description of female.

Body (Fig. 9A, B ) robust, length 1.12 mm. Prosome five-segmented; cephalosome and first pedigerous somites completely separated; fourth and fifth pedigerous somites incompletely fused (Fig. 9A ), posterior corners of prosome slightly asymmetric. Rostrum represented by a rounded knob. Prosome-urosome ratio 2.45:1. Urosome 4-segmented, comprising a genital double-somite, two free abdominal somites, and anal somite; length ratio of genital double-somite, first free abdominal somite, second free abdominal somite, and anal somite as 39.1: 18.7: 17.1:15.1:10.0 = 100. Genital double-somite (Fig. 9C, E ) slightly asymmetric with a differing groups of minute spinules on each side, anterior to mid-length; on the left side is a group of minute spinules that tend to be obscured by detritus and difficult to observe, patches and rows of fine spinules on the right side; genital double-somite not produced ventrally, operculum slightly round, with rows of spinules on the ventral surface. First and second abdominal somites (Fig. 9C ), with transverse hyaline frill dorsally and ventrally. Anal somite shortest. Caudal rami (Fig. 9F ), with six setae, symmetric, 1.19 times longer than wide (56 × 47 μm), with minute spinules on the dorsal surface; caudal setae II to VII present (seta I lacking); seta II spiniform, seta III ca. half the length of seta V, seta V longer (right longer than left) than seta IV, both plumose; dorsal seta VII short, plumose.

Antennule (Fig. 10A ) symmetric, extending near to distal area of genital double-somite; 24-segmented, apparently ancestral, segments I-II, III-IV, X-XI, and XXVII-XXVIII are fused. Segmentation and setation pattern as follows (ancestral segment number-setae+aesthetasc): I-II-3+ae, III-IV-4+3ae, V-2+ae, VI-2, VII-2+ae, VIII2+ae, IX-2, X-XI-4+ae, XII-1, XIII-1, XIV-2+ae, XV-1, XVI-2+ae, XVII-1, XVIII-1, XIX-1, XX-1, XXI-1+ae, XXII-1, XXIII-1, XXIV-1+1, XXV-1+1, XXVI-1+1, XXVII-XXVIII-5+ae. Ancestral segments I-XIV and XVI-XXV with a row of spinules on the posterior surface.

Antenna (Fig. 10B ) biramous; coxa and basis separate, coxa with one and basis with two setae; endopod 2-segmented, proximal segment with two setae, compound distal segment bilobed with eight and seven plumose setae subterminally and terminally, respectively, outer margin ornamented with a small serrated process subdistally on the medial margin; tiny spinule adjacent to the serrated process; exopod 7-segmented, with intersegmental articulation between segments 2 and 3 not completely expressed, with setal formula of 1, 3, 1, 1, 1, 1, 3.

Mandible (Fig. 10C ): well-developed coxal gnathobase, with a straight row of moderately incised teeth, ornamented with spinule rows on the medioventral part. Mandibular palp biramous; basis with four setae on inner margin. Exopod 5-segmented, with setal formula of 1, 1, 1, 1, 2; endopod 2-segmented, proximal with four setae and distal segments with ten setae.

Maxillule (Fig. 10D ): praecoxa and coxa incompletely fused; praecoxal arthrite with ten marginal spines plus four stiff setae on posterior surface, rows of tiny spinules on posterior surface. Coxal epipodite with nine setae; coxal endite with three stiff setae. Basis with cluster of denticles on the anterior surface; proximal basal endite with four setae; distal basal endite indistinct, with five setae; no trace of basal exite. Exopod with eleven marginal setae. A row of setules along the distal portion of the medial margin. Endopod not articulated to basis, indistinctly 3-segmented, setal formula 4, 4, 7.

Maxilla (Fig. 10E ): apparently 6-segmented, comprising coalesced praecoxa and coxa, allobasis, and 3-segmented endopod. Armature of praecoxal and coxal endites 5,3,3,3, respectively. Basal endite with four setae, one stouter than the rest; endopodal endite with one seta on tip. Free endopod setal formula 1, 1, 3, respectively. Integument of praecoxa ornamented with patch of spinules on the posterior margin. Praecoxal and coxal endites with a cluster of long spinules subdistally on the lateral surface; distal coxal endite with an additional row of spinules proximally on the medial surface.

Maxilliped (Fig. 10F ): syncoxa robust, with setal formula 1, 2, 2, 3 and an oblique row of tiny spinules on the posterior distal part; basis with three setae and a row of setules on the mediolateral margin; endopod six-segmented, with setal formula 2, 4, 4, 3, 3+1, 4.

Legs 1-4 (Fig. 11A-D ), progressively larger towards posterior, each comprising coxa, basis, and 3-segmented exopod; endopod of leg 1 (Fig. 11A ) 1-segmented, that of leg 2 (Fig. 11B ) 2-segmented; endopods of leg 3 (Fig. 11C ) and P4 (Fig. 11D ) 3-segmented. Armature formula of legs 1-4 as in S. jejuensis sp. nov.

Leg 1 (Fig. 11A ) biramous, coxa with hairs and spinules on the inner and posterior surfaces; basis with a row of spinules on the inner distal corner and long, curved inner setae, and endopod with a lobe on the outer margin, bearing a minute spinous process; second and distal exopodal segments with patched minute spinules; second and terminal exopodal segment with a row of spinules on the posterior margin.

Leg 2 (Fig. 11B ) biramous, endopod 2-segmented; coxa with hairs on the inner margin, row of spinules on the posterior surface; basis unarmed; each first and second endopodal with row of spinules on the medial and distal edge, with pointed process on distolateral corner; exopod 3-segmented, with a row of spinules on the medio to distal margins of distal exopodal segment.

Legs 3 (Fig. 11C ) and 4 (Fig. 11D ) biramous, with 3-segmented rami: coxa with hairs on the inner margin and a row of spinules on the anterior surface; first to distal endopodal segments with a row of spinules on distal edges, with pointed process on each distolateral corner; exopod with a row of spinules on the medio to distal margins of distal exopodal segment.

Leg 5 (Fig. 11E ) symmetric, uniramous, 3-segmented with proximal segment fused to intercoxal sclerite; basis separated from the single, tapering terminal segment. Second segment (basis) 1.38 times longer than wide (44 × 32 μm), with an anteromedial patch of minute spinules on the anterior surface. Distal segment constricted slightly at ca. mid-length with seven large spinules and inner stout spine and with two rows of denticles along the tapering portion

Male. Not collected.

Variations.

Within this new species, there was a minor variation in the number of spinules on the genital double-somite and on the surfaces of legs 1-4 in the female.

Remarks.

The new species closely resembles its congeners S. angulatus Bradford-Grieve, 1999, S. hastatus , and S. pacificus Ohtsuka & Hiromi, 1987; however, it differs in the following characteristics in the female: the antennule extends to the end of the genital double-somite (vs. first abdominal segment end in S. angulatus , and fifth pedigerous end in S. hastatus and S. pacificus ); the operculum is slightly round (vs. triangular in three species); and the stout and present large row of spinules on the terminal tapering part of leg 5 (vs. not stout and absent in three species).

Figures

Figure 9. Stephos fortipes sp. nov. Female paratype A habitus, dorsal view B habitus, lateral view C urosome, dorsal view D urosome, lateral view E genital double-somite, ventral view F c audal rami, dorsal view. Scale bars in µm.

Figure 10. Stephos fortipes sp. nov. Female paratype A antennule B antenna C mandible D maxillule E maxilla F maxilliped. Scale bars in µm.

Figure 11. Stephos fortipes sp. nov. Female paratype A leg 1 B leg 2 C leg 3 D leg 4 E leg 5, dorsal view. Scale bars in µm.