Colobomatus acanthuri Madinabeitia & Tang & Nagasawa 2013, sp. nov.

Colobomatus acanthuri sp. nov.

(Figure 4 A–H)

Holotype female (NSMT-Cr 21861), from head canal of Acanthurus olivaceus Bloch and Schneider (Perciformes: Acanthuridae), captured in the western North Pacific Ocean off Okinawa-jima Island and subsequently purchased at Yonashiro Fish Cooperative (26◦22′ N, 127◦58′ E) in Uruma, Okinawa-jima Island, 12 September 2009.

Adult female. Body (Figure 4A) 1.64 mm long (excluding cephalic processes and caudal rami). Pre-oral area of cephalosome (Figure 4A) with one anterior pair of parallel processes; latter slightly constricted on anterolateral margin and bearing rows of tiny spinules and three small claw-like processes distally. Cephalosome swollen posterior to buccal capsule and then slightly constricted at posterior margin of tagma; sensillum present on anterolateral margins of swelling. First to fourth pedigerous somites fused to form short neck at first pedigerous somite and large, slightly swollen trunk at second to fourth pedigerous somites and bearing anterolateral pair of anteroventrally directed processes and smaller mid-lateral pair of posterodorsally directed processes; ornamentation of trunk processes similar to those of cephalosome except with several tubercles and one or more papillae bearing one sensillum along inner margin. Second and third pairs of legs occurring ventrally along same plane as anterolateral and midlateral processes, respectively. Fifth pedigerous somite elongate, about 1.5 times longer than wide. Genital somite (Figure 4A) bearing posteroventral pair of posterolaterally directed processes; latter ornamented as in those of thorax. Abdomen (Figure 4A) four-segmented, gradually tapering towards caudal rami. Caudal ramus (Figure 4A) fused to anal somite and bearing proximolateral seta and spinules at tip.

Antennule (Figure 4B) laterally directed, arising near base of cephalic process and two-segmented with armature of 7 and 8. Antenna (Figure 4C) modified, forming longitudinally divided anterior margin of buccal capsule; latter (Figure 4C) tube-like, projecting ventrally from conical base. Labrum, mandibles and maxillules not seen. Maxilla (Figure 4C) robust, two-segmented; basal segment large, bearing one semicircular row of spinules and distolateral spinulated element; distal segment short, ornamented with spinules along distal margin. Maxillipeds absent. Labium (Figure 4C) divided, tapering into sharp tips. Posterior rim of buccal capsule undivided.

Leg 1 (Figure 4D) biramous; protopod carrying long, lateral seta; exopod small, partially fused to protopod, indistinctly two-segmented and bearing outer spine on basal segment and four short apical spines on distal segment; endopod larger than exopod, indistinctly two-segmented and bearing three short spines on distal segment. Leg 2 (Figure 4E) biramous; protopod completely fused to somite and represented by long, lateral surface seta; exopod indistinctly two-segmented, with naked basal segment and two tiny distomedial spines on distal segment; endopod rudimentary, indistinctly two-segmented and unarmed. Leg 3 (Figure 4F) vestigial, reduced to long surface seta.

The species epithet, acanthuri, refers to the generic name of the host.

Colobomatus acanthuri sp. nov. resembles C. lamnae Hesse, 1873, C. bergyltae Hesse, 1876, C. edwardsi (Richiardi, 1876), C. agassizi (Richiardi, 1877), C. haeckeli, C. pagelli (Richiardi, 1877), C. minimus (Richiardi, 1877), C. canthari Delamare Deboutteville and Nunes-Ruivo, 1952, C. embiotocae, C. exilis, C. fusiformis Izawa, 1974, C. collettei, C. gymnoscopeli Grabda and Linkowski, 1978, C. mugilis Raibaut, Caillet and Ben Hassine, 1978, C. caribbei Cressey and Schotte, 1983, C. quadrifarius, C. creeveyae West, 1992, C. cresseyi, C. cribbi West, 1992, C. gietzelae West, 1992, C. hispidus West, 1992, C. lesteri West, 1992, C. mackayi West, 1992, C. nanus West, 1992, C. asiaticus Hayward, 1996 and C. arabicus Hayward, 1996 in the presence of one pair of unbranched processes along the anterior margin of the cephalosome. However, C. acanthuri sp. nov. can be separated from those species by having a short neck between the head and the first pair of thoracic processes and rows of tiny apical spinules and three apical claw-like processes on the cephalic, thoracic and genital processes.

Our finding represents the first report of a species of Colobomatus parasitic in the family Acanthuridae.