Colobomatus absens sp. nov.

(Figure 6 A–E)

Material examined

Holotype female (NSMT-Cr 21863) and 2 paratype females (NSMT-Cr 21864), from head canals of two Pterocaesio digramma (Bleeker) ( Perciformes: Caesionidae), captured in the western North Pacific Ocean off Ishigaki-jima Island and subsequently purchased at Yaeyama Fisheries Cooperative (24 ◦ 19 ′ N, 124 ◦ 0 ′ E) in Ishigaki, Ishigaki-jima Island, 12 May 2010.

Description

Adult female. Body (Figure 6A) 1.89 (1.87–1.91) mm long (excluding cephalic processes and caudal rami) (n = 3). Pre-oral area of cephalosome (Figure 6A) bearing one anterior, spinulose pair of anteriorly directed and pointed processes. Cephalosome round and constricted at posterior margin. First pedigerous somite cylindrical, forming short neck; first pair of legs on ventral surface near anterior constriction. Second to fourth pedigerous somites fused, elongated, widest at posterior end and bearing one pair of anterolateral processes; latter with spinulose ornamentation and tapering into pointed tips (Figure 6E). Fifth pedigerous somite short, narrower than preceding tagma. Genital somite (Figure 6A) bearing one ventrolateral pair of slender, spinulose and posterolaterally directed processes; latter as long as anterior pair of thoracic processes. Abdomen (Figure 6A) indistinctly three-segmented, with single dorsomedian process at posterior end projecting between caudal rami; process spinulose, pointed at tip and as long as caudal rami. Caudal ramus (Figure 6A) posterolaterally directed, spinulose, tapering into pointed tips.

Antennule (Figure 6B) arising near base of cephalic processes, apparently foursegmented with armature of 1, 8, 4 and 5 + 2 aesthetascs. Antenna (Figure 6C) modified, forming large, longitudinally divided anterior margin of buccal capsule; latter (Figure 6A,C) tube-like, projecting ventrally. Labrum and mandibles not seen. Maxillule (Figure 6C) anteriorly located in buccal capsule and bearing one apical spine. Maxilla (Figure 6C) large, apparently one-segmented and armed with claw apically. Maxilliped (Figure 6C) blunt and unarmed. Labium (Figure 6C) undivided, anteriorly rounded. Posterior rim of buccal capsule undivided.

Leg 1 (Figure 6D) uniramous; protopod completely fused to somite, represented by long, lateral surface seta; exopod indistinctly two-segmented, with unarmed basal segment and four elements on distal segment. Legs 2 and 3 not observed.

Etymology

The species epithet, absens, is taken from the Latin for “missing”. It refers to the absence of a posterior pair of thoracic processes in the female.

Remarks

The presence of a posteriorly directed, median process at the posterior end of the abdomen of C. absens sp. nov. is a character shared with C. haeckeli, C. goodingi, C. exilis, C. collettei, C. creeveyae and C. ornatus . However, C. absens sp. nov. can be easily distinguished from these five species and all other congeners by having only one pair rather than two pairs of thoracic processes.

This study represents the first report of a species of Colobomatus parasitic in the family Caesionidae .