Acanthoplacatus brauni, 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 : 325-327

Acanthoplacatus brauni sp. nov.

( Figures 3 , 6A ±D)

Type host. Siganus corallinus (Valenciennes, 1835) (Siganidae) .

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

Site on host. This species is found most frequently on the anal ®n (table 1).

Holotype. QM G215979 .

Paratypes. QM G215980 ±1.

Etymology. This species is named in recognition of Dr F. Braun’s investigations into gyrodactylid biology ( Braun, 1966).

Infection details. Prevalence 80%, 10 ®sh examined, LCF 168 mm (142± 223 mm); mean intensity 44 (12±76), four ®sh examined LCF 171 mm (146±223 mm).

Description. Sclerite measurements taken from 24 worms mounted in Malmberg’s ®xative. Measurements of other organs taken from 11 worms stained with Ehrlich’s haematoxylin. Numerous live worms examined for the structure of soft body organs and the excretory system. Total length 252 (235±277, n 5 11), maximum width 66.5 (48±81, n 5 11) (®gure 6A) at level of uterus or testis or pharynx for worms with small embryo. Hamulus length 30.5 (28±33, n 5 24); hamulus point length 15.5 (13.5±18, n 5 24); hamulus root length 16 (14±18, n 5 24); hamulus shaft length 23 (21.5±24.5, n 5 24). Hamulus shafts with a short longitudinal depression anteroventrally. Dorsal root tissue cap 6 (5.5±7, n 5 20) long, 3 (2.5±3.5, n 5 19) wide. Ventral bar simple, variable in shape (®gures 3, 6D). Ventral bar 5 (4±6, n 5 15) long, 12.5 (11±13, n 5 19) wide. Length of ventral bar membrane 13 (9±15, n 5 14). Total length of ventral bar and membrane 18 (17±20, n 5 13). 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 24 (22.5±25.5, n 5 18); length of sickle 3.5 (3±4, n 5 21); length of handle 20.5 (20±22, n 5 15) (®gure 6B).

Gland cells posterolateral to pharynx range from minimum diameter of 10 (8±12, n 5 8) to maximum diameter of 16.5 (14±20, n 5 8). Anterior lobe of pharynx 25.5 (23±31, n 5 11) wide, posterior lobe 31 (27±34, n 5 11) wide. Gut caeca extend posteriorly lateral to uterus, terminating posterior to testis. Male copulatory organ with one large, two moderate and four small spines (11 21 4) in a single arched row (®gure 6C). Male copulatory organ 13.5 (12±14, n 5 6) long, 14 (13±15, n 5 6) wide. Developing sclerites of F2 embryos may be visible within large F1 embryos; no sclerites of F3 embryos visible. Oocyte, 13 (10±15, n 5 9) long and 18.5 (7±23, n 5 9) wide, contained within ECFR. Testis 14.5 (6±24, n 5 7) long, 17.5 (11±25, n 5 7) wide. Testis overlaps ECFR ventrally. Five cells surround posterior portion of each gut caecum and single cell lies medially near posterior terminations; cells range from minimum diameter of 11.5 (9±13, n 5 7) to maximum diameter of 17.5 (15±21, n 5 7). Two anterior-most cell pairs and posterolateral cell pair ventral to gut; remaining two cell pairs and single medial cell lie dorsal to gut (®gure 6A) .

Sclerite size and seasonality. For this species at Heron Island 18 specimens were collected in summer (January 1997 and 1998) and six specimens in winter (July 1996). Signi ®cant diOEerences between summer and winter samples were found for marginal hook length, marginal hook handle length, ventral bar total length and dorsal root tissue cap length and width. Marginal hook length and marginal hook handle length were signi®cantly larger (p <0.001) in winter (25, n 5 6 and 21.5, n 5 4) than in summer (23.5, n 5 12 and 20.5, n 5 11). Ventral bar total length in winter (19, n 5 5) was signi®cantly larger (p <0.01) than in summer (17.5, n 5 8). Dorsal root tissue cap length was signi®cantly larger (p <0.01) in winter (6.5, n 5 6) than in summer (6, n 5 14) but dorsal root tissue cap width was signi®cantly smaller (p <0.01) in winter (3.0, n 5 6) than in summer (3.5, n 5 13).

Comments. Acanthoplacatus brauni sp. nov. is most similar to A. sigani sp. nov. It can be distinguished as described above for that species.

Figures

FIG. 3. Variation of ventral bar and ventral bar membrane within and between species of Acanthoplacatus gen. nov. Scale bar 5 20 mm.

FIG. 6. Acanthoplacatus brauni sp. nov. (A) Whole worm drawn from permanent whole mounts, ventral view. Scale bar 5 50 mm. (B) Marginal hook. (C) Male copulatory organ. (D) Hamuli and ventral bar. B±D to the same scale. Scale bar 5 20 mm.