Acanthoplacatus sigani, Ernst & Jones & Whittington, 2001

Ernst, Ingo, Jones, Malcolm K. & Whittington, Ian D., 2001, A new genus of viviparous gyrodactylid (Monogenea) from the Great Barrier Reef, Australia with descriptions of seven new species, Journal of Natural History 35 (3), pp. 313-340 : 317-319

Acanthoplacatus sigani sp. nov.

( Figures 2A ±D, 3)

Type host. Siganus fuscescens (Houttuyn, 1782) (Siganidae) .

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

Site on host. This species was found most frequently on the caudal, dorsal and anal ®ns (table 1).

Holotype. QM G215991 .

Paratypes. QM G215992 ±3.

Etymology. This species is named after the host genus.

Infection details. Prevalence 100%; mean intensity 28 (6±95); six ®sh examined, LCF 253 mm (210±275 mm).

Description. Sclerite measurements taken from 31 worms mounted in Malmberg’s ®xative. Measurements of other organs taken from 15 whole mounts stained with Mayer’s haematoxylin. Numerous live worms examined for structure of soft body organs and excretory system. Total length 257 (226±299, n 5 12), maximum width 63 (47±81, n 5 14) at level of uterus (®gure 2A). Hamulus length 35 (32.5±37.5, n 5 29); hamulus point length 18 (15.5±20, n 5 29); hamulus root length 20 (17±22.5, n 5 29); hamulus shaft length 25 (22.5±27, n 5 29). Dorsal root tissue cap length 8 (7±9, n 5 31), width 3 (3±4, n 5 23) (®gure 2D). Ventral bar simple, variabl e in shape (®gures 2D, 3). Ventral bar 5 (4±6, n 5 18) long, 14 (12±16, n 5 27) wide. Length of ventral bar membrane 17 (13±20, n 5 23). Total length of ventral bar and membrane 23 (19±25, n 5 25). Transition between ventral bar and ventral bar membrane not distinct. Marginal hooks small with hook point extending to toe; total length of marginal hook 25.5 (24±27, n 5 24); length of sickle 3.5 (3±4, n 5 22); length of handle 22.5 (21.5±24, n 5 17) (®gure 2B).

Gland cells posterolateral to pharynx range from minimum diameter of 8.5 (7±12.5, n 5 14 worms) to maximum of 13 (10±17, n 5 14 worms). Anterior lobe of pharynx 18.5 (16±21, n 5 15) wide, posterior lobe 25.5 (23±27, n 5 13) wide. Gut caeca extend posteriorly lateral to uterus, terminating adjacent to testis. Male copulatory organ with one large, two moderate and four small spines (11 21 4) (®gure 2C). Male copulatory organ 10.5 (9.5±11, n 5 4) long, 10 (9±11, n 5 4) wide. Seminal vesicle elongate, posterior to male copulatory organ. Developing sclerites of F2 embryo may be visible within large F1 embryo; no sclerites of F3 embryo visible. Oocyte 18.5 (10±27, n 5 15) long, 17.5 (11±25, n 5 15) wide, contained within ECFR. Testis 12.5 (6±25, n 5 14) long, 14 (7±24, n 5 14) wide, overlaps ECFR ventrally. Five cells surround posterior portion of each gut caecum and single medial cell lies near posterior terminations; cells range from minimum diameter of 12.5 (11±15, n 5 15) to maximum diameter of 18.5 (16.5±21, n 5 15). Two anterior-mos t cell pairs and posterolateral cell pair lie ventral to gut; remaining two cell pairs and single medial cell lie dorsal to gut (®gure 2A) .

Sclerite size and seasonality. For this species, 14 specimens were collected in summer (January 1997) and 17 specimens were collected in winter (July 1996). Hamulus point length, hamulus shaft length, marginal hook length, ventral bar membrane length and ventral bar total length showed signi®cant diOEerences between summer and winter samples and in each case, means of the winter samples were larger. Two hamulus characters, hamulus point length (summer 5 18.0, n 5 14; winter5 18.5, n 5 15; p <0.01) and hamulus shaft length (summer 5 24, n 5 14; winter5 25.5, n 5 15; p <0.001), showed signi®cant seasonal diOEerences. The only marginal hook character to show a signi®cant diOEerence between samples was marginal hook length (summer 5 25, n 5 11; winter5 26, n 5 13; p <0.01). Of the four ventral bar characters, ventral bar membrane length (summer 5 15.5, n 5 10; winter 5 18, n 5 13; p <0.01) and ventral bar total length (summer5 20.5, n 5 10; winter5 23, n 5 15; p <0.001) showed signi®cant seasonal variation.

Comments. The haptoral sclerites of Acanthoplacatu s sigani sp. nov. most closely resemble A. adlardi sp. nov., A. brauni sp. nov. and A. shieldsi sp. nov. Acanthoplacatus sigani sp. nov. can be distinguished from A. adlardi and A. shieldsi because it has shorter marginal hook length and marginal hook handle length (table 2). The species most di cult to distinguish from A. sigani sp. nov. is A. brauni sp. nov. Acanthoplacatus sigani sp. nov. has longer hamulus length and marginal hook handle length although a small amount of overlap (0.5 m m) occurs between these species for both characters (see table 2). Acanthoplacatus sigani can be further distinguished from A. brauni sp. nov. by its larger dorsal root tissue cap length and absence of anterior, longitudinal depressions on the ventral surface of the hamuli.

Figures

FIG. 2. Acanthoplacatus sigani sp. nov. (A) Whole worm drawn from permanent whole mounts, ventral view. Scale bar 5 50 mm. (B) Marginal hook. (C) Male copulatory organ. B±C to the same scale. Scale bar 5 10mm. (D) Hamuli and ventral bar. Scale bar 5 20 mm. ap, anterior lobe of pharynx; dl, dorsal lobe of haptor; do, gland duct openings; F1, F1 embryo; F2, F2 embryo; g, gut; gc, gland cells; gd, gland ducts; m, mouth; mco, male copulatory organ; o, oocyte; pp, posterior lobe of pharynx; sv, seminal vesicle; t, testis; vl, ventral lobe of haptor.