Caligus longiramus, Venmathi Maran, Ohtsuka & Jitchum, 2012

Maran, B. A. Venmathi, Ohtsuka, Susumu & Jitchum, Pailin, 2012, Occurrence of Caligid Copepods (Crustacea) in Plankton Samples Collected from Japan and Ŋailand, with the Description of a New Species, Species Diversity 17 (1), pp. 87-95 : 89-93

Caligus longiramus sp. nov.

(Figs 2B–F, 3, 4)

Material examined. H olotype: One adult (KMNH IvR 500, 512), Amami Island , Kagoshima Prefecture, Japan, St . 4, 27°58 .3'N , 129°24.1'E, 399–403 m deep, 24 May 2010, beam trawl.

Description. F emale. Body (Fig. 2B) 5.12 mm long excluding caudal setae. Cephalothorax triangular, 2.65× 2.10 mm, longer than wide. Fourth pediger 0.43× 0.54 mm, wider than long. Genital complex 1.25× 0.81 mm, vase-shaped, longer than wide. Abdomen 0.65× 0.34 mm, longer than wide. Caudal ramus (Fig. 2C) 0.23× 0.07 mm, longer than wide, with 1 long, 1 short, and 1 thick setae terminally (Fig. 2C) (on right side, long seta broken o).

Antennule (Fig. 2D) 2-segmented; proximal segment armed with 27 setae; distal segment twice as long as proximal one, armed with subterminal seta on posterior margin and 11 setae plus 2 aesthetascs around apex. Antenna (Fig. 2E) 3-segmented; proximal segment small, unarmed; middle segment with lateral spinules; distal segment robust, drawn out into curved claw bearing seta laterally and another at midlength. Postantennal process (Fig. 2E) weakly curved, bearing 2 basal papillae, each with 4 setules; another similar papilla located on nearby sternite. Mandible (Fig. 2F) styliform with 12 teeth subapically. Maxillule (Fig. 2E) robust, curved midlaterally comprising main structure and separate anterior papilla with 3 short setae. Maxilla (Fig. 3A) 2-segmented, slender; proximal segment robust, unarmed; distal segment carrying small subterminal hyaline membrane on outer edge and 2 large spinulated elements. Maxilliped (Fig. 3B) indistinctly 3-segmented; proximal segment robust, unarmed; distal subchela robust with claw, armed with small seta at midlength. Sternal furca (Fig. 3C) long with sharp tines (le tine’s end slightly broken).

Armature on rami of legs 1–4 as in C. chiastos (see Table 1).

Leg 1 (Fig. 3D) with coxa armed with long, plumose outer (basal) and short, plumose inner (coxal) setae; vestigial endopod tipped with minute seta; middle 2 of 4 terminal elements on distal margin of second exopodal segment each with strong accessory process (Fig. 3E). Leg 2 (Fig. 4A) coxa with large, plumose inner seta; basis with small, naked outer seta and medial papilla bearing long setule; both outer and medial edges of basis fringed with marginal membrane; similar membrane present on outer margin of rst segment of exopod; proximal outer spine on distal segment of exo- pod longer than next more distal spine and crossing over it posteriorly. Leg 3 (Fig. 4B) having protopod with small, plumose outer seta in addition to posterior marginal membranes. Leg 4 (Fig. 4C) with 2-segmented exopod; all outer exopodal spines with pecten at base, outer terminal spine longer than adjacent spines. Leg 5 (Fig. 4D) represented by 2 papillae at posterolateral corners of genital complex tipped, respectively with 1 and 2 plumose setae.

Remarks.ffi e present new species is characterized by the following features: (1) a relatively long antennule with the distal segment twice as long as the proximal segment; (2) a blunt dentiform process of the proximal segment of the antenna; (3) a long sternal furca with a pair of sharp tines; (4) the 2-segmented exopod of leg 4 being armed with I-0; I, III spines; and (5) the proximal outer spine on the exopod of leg 2 being longer than the next more distal spine and crossing over it posteriorly.

Caligus longiramus is closely similar to two other species of Caligus in having long antennules: Caligus aesopus Wilson, 1921 from Chile, India, Japan, Korea, New Zealand, South Africa, and Taiwan (cf. Choe and Kim 2010) and Caligus spinosus Yamaguti, 1939 from Japan ( Yamaguti 1939) and Korea ( Choe and Kim 2010); however, it di ers from these, in characters of the maxillule and leg 4. ffie tip of the maxillule is bi d in C. aesopus and C. spinosus , but simply pointed in the new species. In leg 4 the outer spines on the exopod are robust and equal in length in C. aesopus and C. spinosus (cf. Choe and Kim 2010), while these are slender and the outer terminal spine is longer than the others in C. longiramus .

Caligus chiastos is also considered to be one of the closest congeners to C. longiramus on the basis of the armature of legs 2 and 4 ( Lin et al. 1994), but it di ers distinctly from the new species in the shorter antennules. Only these two species share a proximal outer spine on the exopod of leg 2 that is longer than the next more distal spine and crosses over it posteriorly. Additional di erences between these two species include: (1) the outer spines on the exopod of leg 4 are robust with the outer terminal spine slightly longer than the others in C. chiastos , while these are slender with the outer terminal spine distinctly longer than others in C. longiramus ; (2) the sternal furca has straight tines in C. chiastos , but is posteriorly broad in C. longiramus ; and (3) the dentiform process of the proximal segment of the antenna is small and blunt in C. longiramus , but large and sharply pointed in C. chiastos .

Etymology.ffi e speci c name, a noun in apposition, refers to the relatively long antennule of the new species (Latin “ longus ”, meaning long, and “ ramus ”, branch).