Colobomatus collettei Cressey, 1977

Madinabeitia, Ione, Tang, Danny & Nagasawa, Kazuya, 2013, Four new species of Colobomatus (Copepoda: Philichthyidae) parasitic in the lateral line system of marine finfishes captured off the Ryukyu Islands, Japan, with redescriptions of Colobomatus collettei Cressey, 1977 and Colobomatus pupa Izawa, 1974, Journal of Natural History (J. Nat. Hist.) 47 (5 - 12), pp. 563-580 : 565-567

Colobomatus collettei Cressey, 1977

( Figure 1A – F )

Material examined

Four adult females (NSMT-Cr 21858), from head canals of two Hemiramphus far Forsskål ( Beloniformes : Hemiramphidae ), captured in the western North Pacific Ocean off Okinawa-jima Island and subsequently purchased at Hama Fisheries Cooperative (26 ◦ 34 ′ N, 127 ◦ 14 ′ E) in Nakagusuku, Okinawa-jima Island, 22 April 2010.

Description

Adult female. Body ( Figure 1A ) 3.58 (3.43–3.72) mm long (excluding cephalic processes and caudal rami) (n = 4). Pre-oral area of cephalosome ( Figure 1A ) slightly extended anteriorly and bearing one anterior pair of short, unadorned processes. First pedigerous somite greatly elongated, neck-like, approximately one-third of total body length and separated from cephalosome by slight lateral constriction. Second to fourth pedigerous somites fused, swollen and bearing two pairs of lateral processes; posterior pair of processes slightly longer than anterior pair; both pairs of processes naked and with rounded tips. Fifth pedigerous somite short and separated from preceding somites by slight lateral constriction. Genital somite bearing ventrolateral pair of processes. Abdomen ( Figure 1A ) composed of four indistinct somites; pre-anal somite with apically rounded, ventral process ( Figure 1G ) projecting over anal somite and between caudal rami; process slightly shorter than caudal rami. Caudal ramus ( Figure 1G ) fused to anal somite, naked and with rounded distal margin.

Antennule ( Figure 1B ) laterally directed, arising anterior to buccal capsule and apparently three-segmented with armature of 7, 3 and 5 + 2 aesthetascs. Antenna ( Figure 1C ) modified, forming longitudinally divided anterior margin of buccal capsule; latter ( Figure 1C ) tube-like, projecting ventrally from conical base. Labrum and mandibles not seen. Maxillule ( Figure 1C ) one-segmented, lobate and bearing two short spines on distal margin. Maxilla ( Figure 1C ) robust, two-segmented; basal segment with proximomedial and distomedial clusters of spinules and distolateral spinulated element; distal segment short, bearing three short apical spines. Maxillipeds absent. Labium ( Figure 1C ) undivided. Posterior rim of buccal capsule longitudinally undivided.

Leg 1 ( Figure 1D ) biramous; protopod fused to somite and represented by long, lateral seta; exopod indistinctly two-segmented, with basal segment bearing lateral spine and distal segment bearing one spine and two setae; endopod vestigial, unsegmented and unarmed. Leg 2 ( Figure 1E ) similar to leg 1, except distal exopodal segment armed with two spines and two setae. Leg 3 ( Figure 1F ) rudimentary, reduced to single surface seta.

Remarks

This species was originally described by Cressey (1977) based on females collected from the interorbital canals of Hemiramphus robustus Günther collected in McCluer Gulf off New Guinea. Cressey’s description of C. collettei was incomplete because the author did not include information on the legs ( Cressey 1977) so this study supplements the description of C. collettei by providing detailed illustrations of legs 1–3. The only difference between Cressey’s and our specimens is the body length: the Japanese specimens (mean length = 3.58 mm) are slightly larger than the New Guinean ones (2.63 mm). No males have been found so far. The present finding represents the first report of C. collettei from Japanese waters.

Colobomatus collettei resembles C. haeckeli (Richiardi, 1877) , C. goodingi Cressey and Collette, 1970 , C. exilis Izawa, 1974 , C. creeveyae West, 1992 and C. ornatus West, 1992 in the presence of a process at the posterior end of the abdomen that projects posteriorly between the caudal rami. However, in C. goodingi the pre-oral area of the cephalosome bears a single unadorned cephalic process separating it from C. collettei . Colobomatus haeckeli , C. exilis and C. creeveyae can be distinguished from C. collettei by having a short neck between the head and the first pair of thoracic processes. Colobomatus ornatus can be differentiated from C. collettei by the presence of two pairs of cephalic processes.

Figures

Figure 1. Colobomatus collettei Cressey, 1977, adult female. (A) Habitus, ventral; (B) antennule, ventral; (C) buccal capsule and mouthparts, ventral; (D) leg 1, ventrolateral; (E) leg 2, ventrolateral; (F) leg 3, ventrolateral; (G) posterior end of abdomen and caudal rami, ventral. Abbreviations: A, antenna; la, labium; mx, maxillule; Mx, maxilla.