Acanthoplacatus parvihamus Ernst & Jones & Whittington 2001, sp. nov.

Acanthoplacatus parvihamus sp. nov.

(Figures 3, 7A ±D)

Type host. Siganus vulpinus (Schlegel and MuÈller, 1845) (Siganidae).

Type locality. Heron Island, Great Barrier Reef, Queensland, Australia.

Site on host. This species was found most frequently on the dorsal ®n (see table 1).

Holotype. QM G215982.

Paratypes. QM G215983 ±4.

Etymology. Named from the Latin (parvi 5 little, hamus 5 hook) for the small size of the hamuli in this species.

Infection details. Prevalence 67%, six ®sh examined, LCF 176 mm (157± 194 mm); intensity 101±444, two ®sh examined, LCF 192±194 mm.

Description. Sclerite measurements taken from 22 specimens mounted in Malmberg’s ®xative. Numerous live worms examined for structure of soft body parts and excretory system. Total length 426 (354±504, n 5 5), maximum width 118 (98±133, n 5 8) (®gure 7A). Hamulus length 22.5 (20±25.5, n 5 22); hamulus point length 12 (10.5±13, n 5 22); hamulus root length 12 (10.5±13.5, n 5 22); hamulus shaft length 16.5 (15.5±18.5, n 5 22). Dorsal root tissue cap length 5.5 (5±6.5, n 5 20), width 2.5 (2±3, n 5 20) (®gure 7D). Ventral bar simple, variable in shape (®gures 3, 7D). Ventral bar 5 (4±6, n 5 13) long and 9 (8±10, n 5 16) wide. Ventral bar membrane 5 (4.5±5, n 5 4) long, rarely visible. Total length of ventral bar and membrane 8.5 (8±9, n 5 4). Transition between ventral bar and ventral bar membrane not distinct. Marginal hooks small with hook point extending to, or only slightly past toe; total length of marginal hook 21.5 (20.5±22.5, n 5 22); length of sickle 3 (3±3.5, n 5 20); length of handle 18.5 (17.5±19.5, n 5 19) (®gure 7B).

Gland cells posterolateral to pharynx range from minimum diameter of 16 (11±20, n 5 7) to maximum of 27.5 (22±32, n 5 6). Anterior lobe of pharynx 39 (36±45, n 5 9) wide, posterior lobe 48 (42±53, n 5 9) wide. Gut caeca extend posteriorly lateral to uterus, terminating posterior to testis. Male copulatory organ with one large, two moderate and three small spines (11 21 3) (®gure 7C). Male copulatory organ 16.5 (13±19, n 5 3) long, 14.5 (11±18, n 5 3) wide. Seminal vesicle elongate, posterior to male copulatory organ. Developing sclerites of F2 embryos may be visible within large F1 embryos; no sclerites of F3 embryos visible. Oocyte 18.5 (14±22, n 5 7) long, 32.5 (22±50, n 5 7) wide, contained within ECFR. Testis 17.5 (9±23, n 5 8) long, 27 (21±34, n 5 8) wide. Five cells surround posterior portion of each gut caecum and single cell lies medially near posterior terminations; cells range from minimum diameter of 16.5 (24±32, n 5 7) to maximum diameter of 26.5 (24±32, n 5 7) (®gure 7A).

Comments. Acanthoplacatus parvihamus sp. nov. has the smallest attachment sclerites in the genus and can be distinguished from all other species by the small size of its hamuli, marginal hooks, and ventral bar. The recorded ranges for hamulus length, hamulus point length, hamulus shaft length, hamulus root length, ventral bar width, ventral bar total length and ventral bar membrane length are smaller than those for all other species. Location of the posterior gland cells relative to the gut could not be determined for this species because only ¯attened specimens were available for study.