Caligus robustus Bassett-Smith, 1898

Hayes, Polly, Justine, Jean-Lou & Boxshall, Geoffrey A., 2012, The genus Caligus Müller, 1785 (Copepoda: Siphonostomatoida): two new species from reef associated fishes in New Caledonia, and some nomenclatural problems resolved, Zootaxa 3534, pp. 21-39 : 34

Caligus robustus Bassett-Smith, 1898

The original description of C. robustus was based on material collected from four hosts, three carangids and a scombrid, in two localities in the northern part of the Indian Ocean ( Bassett-Smith, 1898). This species has been reported many times subsequently from a range of predominantly carangid hosts caught in the Atlantic and Indian Oceans ( Table 1). Pillai (1985) and Cressey (1991) both provided partial redescriptions of this species, but the female was fully redescribed by Ho & Lin (2007). The adult female is characterised by the possession of an elongate, 2-segmented abdomen that is about 2.8 to 3.0 times longer than wide, and a flask-shaped genital complex that is just wider than long or about as long as wide dependent upon the state of contraction of the anterior “neck” of the complex. Caligus robustus exhibits three really distinctive features: the myxal margin of the female maxilliped, the posterior process of the maxillule and the exopod of leg 4.

In C. robustus the female maxilliped has a large tapering process on the myxal margin, opposing the tip of the maxilliped claw. Arising in the axil of this process is a second, shorter and more slender spine-like process. The tapering posterior process of the maxillule of the female has a transverse structure separating off the apex. This has been figured as a membrane (Ho & Lin, 2007: figure 3c) or as a furrow ( Cressey, 1991: figure 170c). Leg 4 has a 3- segmented exopod with a I, I, III arrangement of outer spines. The pectens, which normally surround the base of the outer spine on each of the first two exopodal segments, extend along the entire outer margin of the second exopodal segment and along the distal section of the margin of the first exopodal segment.

A cluster of nominal species shares these distinctive features. Caligus oligoplitisi Carvalho, 1956 from Brazil shares the distinctive form of the myxal process on the female maxilliped, the arrangement of pectens on the proximal segments of the exopod of leg 4, and the subapical furrow on the maxillule ( Carvalho, 1956: figures 4, 9 and 11). Caligus validus Pearse, 1952 from the coast of Texas shares the distinctive myxal process on the female maxilliped, but although the form of the exopod of leg 4 is similar, Pearse’s figure does not show the pectens. The maxillule was not figured by Pearse (1952), however other features such as the proportions of the genital complex and abdomen, and the shape of the sternal furca agree with those of C. robustus . Although the illustration of the maxilliped of female Caligus mercatoris Capart, 1941 is drawn from an unusual angle ( Capart, 1941: figure 4D), this species also shares the distinctive myxal process. In addition the pectens on the first two exopodal segments of leg 4 extend along the segmental margins. Although the abdomen of the specimen of C. mercatoris figured by Capart (1941) appears relatively shorter than in C. robustus , as described by Cressey (1991) for example, the shape of the sternal furca is the same and the armature on the tip of the exopod of the first leg is also the same (with spine 1 reduced in size and located subdistally on the anterior margin rather than at the antero-distal corner).

We propose to treat C. oligoplitisi Carvalho, 1956 , C. validus Pearse, 1952 and C. mercatoris Capart, 1941 as junior subjective synonyms of C. robustus Bassett-Smith, 1898 . This species has a wide distribution across the Atlantic and Indian Oceans and utilises a broad range of hosts, although exhibiting a clear preference for carangids ( Table 1).