Aethon garricki Hewitt, 1968

Boxshall, Geoff A., Bernot, James P., Barton, Diane P., Diggles, Ben K., Q-Y, Russell, Atkinson-Coyle, Toby & Hutson, Kate S., 2020, Parasitic copepods of the family Lernanthropidae Kabata, 1979 (Copepoda: Siphonostomatoida) from Australian fishes, with descriptions of seven new species, Zootaxa 4736 (1), pp. 1-103 : 12-13

Aethon garricki Hewitt, 1968

( Fig. 4 )

Material examined: 1♀ from gills of Nemadactylus macropterus (Forster, 1801) , Port MacDonnell , South Australia, 09 May 2007; collected by K.S. Hutson; NHMUK 2007.951 . 3♀♀ from gills of N. macropterus caught 210 km SW of Streaky Bay (33º 51’S, 132º 19’E), South Australia: collected by K.S. Hutson from host material in the Victoria Museum, Melbourne . 1♀ from gills of N. macropterus, Port MacDonnell , South Australia, 09 May 2007; collected by K.S. Hutson; SAMA Reg No. C6896 .

Differential diagnosis: Cephalothorax longer than wide, with distinct dorsal cephalothoracic shield; lateral margins weakly convex, without processes ( Fig. 4A ). Trunk distinctly wider than cephalothorax: anterior part with 2 well-defined dorsal tergites derived from second and third pedigerous somites, lateral margins extended into long pointed posterolateral processes ( Fig. 4 A–C); posterior part of trunk (fourth pedigerous somite) covered by dorsal trunk plate. Plate about 1.6 times longer than wide, with almost linear lateral margins; posterior margin of plate with deep median indentation. Loosely coiled egg strings entirely concealed beneath dorsal trunk plate in dorsal view. Urosome comprising fifth pedigerous somite, genital complex and 1-segmented abdomen, all fused. Anal somite bearing paired caudal rami, each about 2.5 times longer than wide and tapering to acutely pointed apex. Leg 2 with endopod fused to protopod forming curved process bearing reduced exopod as small protuberance on outer side of process. Leg 3 large, comprising 2 fleshy lamellate lobes ( Fig. 4 B–C); outer lobe (exopod) rigid and sclerotised, orientated vertically and running length of dorsal trunk plate, forming side wall of cavity containing coiled egg strings: inner lobe (endopodal) elongate, orientated horizontally and extending posteriorly about as far as end of dorsal trunk plate; lobes connected by ventrally-directed, curtain-like lamella. Leg 4 bilobate; both lobes lamellate with rounded tips, inner lobe shorter than outer. Mean body length of ♀ 3.86 mm, range 3.47 to 4.37 mm (based on 5 specimens).

Distribution: The original description of Aethon garricki was based on a single female collected from the cheilodactylid Nemadactylus macropterus (as Cheilodactylus macropterus ), caught off Somes Island in Wellington Harbour, New Zealand ( Hewitt, 1968). This new record from the same host, caught off South Australia, extends the known distribution of this distinctive species.

Remarks: This species is readily distinguished from its congeners by the smoothly convex lateral margins of its cephalothorax: in contrast the lateral margins of all other Aethon species have well developed lateral lobes. The holotype female from New Zealand was 3.82 mm long, while the Australian specimens are larger. Vooren & Tracey (1976) studied the metazoan parasites of N. macropterus in New Zealand waters and found A. garricki to have an overall prevalence ranging from 16.9% off East Cape to 26.9% in Tasman Bay, but it was absent from the Chatham Islands population.

Figures

FIGURE 4. Aethon garricki Hewitt, 1968, adult ♀. A, habitus, dorsal; B, habitus, lateral; C, habitus, ventral. Scale bar 2 mm.