Halicyclops itohi, Ueda & Nagai, 2012

Ueda, Hiroshi & Nagai, Hidefumi, 2012, Two New Species of Halicyclops (Crustacea: Copepoda: Cyclopidae) from Honshu with a Key to the Species of the Genus in Japan, Species Diversity 17 (1), pp. 97-107 : 102-104

Halicyclops itohi sp. nov.

(Figs 6–8)

Halicyclops sp.1: Tadasugi and Itoh 1999: 30. Halicyclops cf. rotundipes: Ishida 2002: 42–43 , g. 2a–d.

Material examined.H olotype: female, NSMT Cr- 21566, dissected and mounted on three glass slides. Paratypes: 13 females, of which 7 are undissected ( NSMT Cr- 21567), and 6 dissected .

Description. F emale. Body (Fig. 6A) length 0.57– 0.67 mm (n=5, holotype 0.67 mm). Prosome L/ W 1.4 –1.7, widest at end of cephalothorax, and 1.6–1.9 times as long as urosome. Forehead gently arched as compared with previous species. Genital double-somite (Fig. 6B, C) L/ W 1.0 –1.1, without lateral protuberances; in some specimens, lateral margin depressed at midlength as in Fig. 6D. Genital double-somite and next urosomite with smooth dorsal margins and fourth urosomite with nely serrate dorsal frill. Anal somite (Fig. 6E, F) as in previous species.

Caudal rami (Fig. 6E, F) L/ W 1.2 –1.3, armed distally with rows of large spinules on ventral side; dorsal and posterolateral setae 3.1–3.8 and 1.0–1.3 times as long as ramus, respectively; terminal accessory seta absent (or indistinguishable from distomedial spinules); outer and inner terminal setae (Fig. 6G) 0.8–0.9 and 1.4–1.6 times as long as urosome, respectively; outer terminal seta spinulose on lateral side and plumose on distal half of medial side; inner terminal seta naked on proximal half, spinulose on next one- tenth and plumose on distal two- hs.

Antennule (Fig. 6H) rst segment lacking spinules; fourth segment 2 or more times as long as wide, and longer than sixth segment; no setae inserted on dorsal surface; setal formula as in previous species.

Post-antennuar appendages as in Halicyclops setiformis described above except for the following points.

Antenna (Fig. 7A) coxobasis proximally bearing 2 rows of spinules on anterior surface; setal formula as in previous species; setae on coxobasis and rst endopodal segment nearly as long as rst endopodal segment; second endopodal segment 1.4 times longer than rst endopodal segment, with rows of short spinules.

Mandible (Fig. 7B) with proximal ring of spinules.

Maxillule (Fig. 7C) with 7 armature elements medially on praecoxal arthrite.

Maxilla (Fig. 7D) with basis expanded into unilaterally toothed claw.

Maxilliped (Fig. 7E) protopod with row of ne spinules on distolateral corner; endopod with thick apical seta bearing long setules.

Leg 1 (Fig. 7F) intercoxal sclerite with row of hairs near distal margin and row of tiny spinules on posterior surface; coxa with normally plumose medial seta; basis with medial spine reaching slightly beyond second endopodal segment; spinules on distal margin of coxa and basis shorter than those of H. setiformis ; second and third exopodal segments with bilaterally toothed spines; second lateral spine of third exopodal segment slightly shorter than this segment and as long as third spine.

Legs 2 and 3 (Figs 6G and 7A) intercoxal sclerites armed distally with spinules on each side; leg 4 (Fig. 8B) intercoxal sclerite naked. Legs 2–4 bases with shorter spinules on anterior surface near base of endopod than those of H. setiformis . ffiird exopodal segment of legs 1–4 with 3, 4, 4 and 3 spines, respectively. Leg 4 third exopodal segment L/ W 1.4 – 1.5; 2 medial elements completely spiniform, all resembling lateral spines; apical spine 1.0–1.2 times as long as this segment and 1.4–1.5 times as long as distolateral spine.

Leg 5 exopod (Fig. 8C) ovoid, L/ W 1.4; medial spine 1.0– 1.1 times as long as segment, 1.1 times as long as proximolateral spine, and 1.3–1.5 times as long as distolateral spine; terminal seta 1.1–1.3 times as long as segment.

Etymology.ffi e epithet itohi is dedicated to Dr Hiroshi Itoh, who collected the specimens.

Remarks. H alicyclops itohi sp. nov. appears allied to H. caneki Fiers, 1995 , H. cryptus secundus Monchenko and Polischuk, 1982 , H. gauldi Plesa, 1961 , H. korodiensis Onabamiro, 1952 , and H. ryukyuensis in sharing the following characteristics: (1) the third exopodal segment of legs 1–4 with spine formula 3.4.4.3; (2) genital double-somite with no conspicuous lateral protuberances; and (3) terminal accessory seta of caudal ramus absent or as small as distomedial spinules. ffiese allied species are distinguishable from H. itohi with respect to the following (corresponding morphologies of H. itohi in brackets): H. caneki has 8 setae on the anterior side of the antenna ( Fiers 1995) [5 setae as in most congeners]; in H. cryptus secundus the caudal ramus is 1.53–1.65 times as long as wide and the terminal spine of the third endopodal segment of leg 4 is 1.55–1.65 times as long as the segment ( Monchenko and Polishchuk 1982) [these ratios are 1.2–1.3 and 1.0–1.2, respectively]; the terminal segment of leg 5 of H. gauldi has much shorter spines (e.g., the lateral spine is 0.3 times as long as the segment according to the original description by Plesa (1961)) [the lateral spine is as long as the segment]; the second and third urosomites of H. korodiensis have denticulate dorsal margins ( Onabamiro 1952) [smooth margins]; and H. ryukyuensis has two normal medial setae on the third endopodal segment of leg 4 ( Ito 1962) [two medial spines]. In the other Halicyclops species, at least one of the three common morphological characteristics noted above is di erent from H. itohi .

Halicyclops cf. rotundipes reported by Ishida (2002) from northernmost Honshu is identi able to H. itohi by its lack of lateral protuberances of the genital double-somite, the extremely rudimentary terminal accessory seta of the caudal ramus, and the two medial spines on the third endopo- dal segment of leg 4. According to the redescription of H. rotundipes by Kiefer (1936), the species has obvious lateral protuberances on the genital double-somite and a longer terminal accessory seta on the caudal ramus, thereby differing from H. itohi . Halicyclops sp. 1 reported by Tadasugi and Itoh (1999) is H. itohi , which was con rmed by one of the authors, Itoh (pers. comm.), who provided us with the specimens of H. sp. 1.