Caligus torpedinis Heller, 1865

Boxshall, Geoffrey A. & Bernot, James P., 2023, Resolving taxonomic and nomenclatural problems in the genus Caligus O. F. Müller, 1785 (Copepoda: Caligidae), Zootaxa 5360 (4), pp. 545-567 : 558

Caligus rotundigenitalis Yü, 1933 and

Caligus torpedinis Heller, 1865

Caligus torpedinis has not been reported since its original description by Heller (1865) which was based on a female found on the gills of a species of “ Torpedo ” caught in the Indian Ocean. The brief description can be summarised as follows: “ The cephalothorax, which corresponds to two-fifths of the whole length of the body, is almost as wide as long, narrowing somewhat anteriorly and rounded posterolaterally. The frontal margin appears almost straight, not bulging in the middle, and the lunules are small, crescent-shaped, surrounded in front by a somewhat protruding membrane. The antennules are short, comprising two segments about equal in length. The antennae do not reach the margin of the dorsal cephalothoracic shield. The postantennal processes are simple, directed backwards. The first legs are armed with only two spines, plus seta 4 and 3 plumose setae on the terminal segment. Leg 4 is 4-segmented, armed with 5 spines, the last three of which are fairly similar in length. The genital complex is shorter than the cephalothorax, broader than long, with rounded lateral margins and a straight posterior margin. The abdomen is almost the same length as the genital complex, but is very narrow and composed of two somites, the second somite appearing somewhat shorter than the first. The caudal rami are longer than wide and about half the length of the anal somite, and bear three long plumose setae on the distal margin plus a small single seta on the outer margin.” This description is supported by two figures, a dorsal view of the habitus of the female and leg 4 ( Heller, 1865: Tab. XV, figs, 6 and 6a).

The form of leg 4, with its 3-segmented exopod bearing I, I, III spines which are all of similar size and all directed obliquely away from the ramus, is shared with members of the C. diaphanus -group of species. Within this group of species, C. torpedinis closely resembles C. rotundigenitalis Yü, 1933 in overall body shape and body proportions, and has the same form of leg 4. Heller (1865) reported only 2 spines on the distal margin of the second exopodal segment of leg 1 but was presumably uncertain about this because he includes a question mark in the Latin diagnosis where he states: “ Pedes primi paris ad apicem duobus aculeis (?) “. In C. rotundigenitalis spine 1 is only half the length of spines 2 and 3 and all 3 spines lie on top of each other in ventral view (cf. Ho & Lin, 2004: fig. 10). It seems probable that Heller (1865) overlooked spine 1. The postantennal processes are typically reduced in members of the C. diaphanus -group but Heller’s (1865) description of these processes as simple and directed backwards is in accord with Ho & Lin’s (2004: fig. 8A) redescription of C. rotundigenitalis .

On the basis of the available evidence we propose to treat Caligus rotundigenitalis Yü, 1933 as a junior subjective synonym of C. torpedinis Heller, 1865 . This species has an extremely wide range of known hosts having been reported from at least 40 species of teleost fishes representing 26 different families of fishes (as listed by Ho & Lin (2004) and Walter & Boxshall (2023)), although this is the first record from an elasmobranch host.