Demoleus heptapus (Otto, 1821)

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 : 557

Caligus lessonius Risso, 1826 and

Demoleus heptapus (Otto, 1821)

This species was established by Risso (1826) to accommodate a parasitic copepod found on “squale griset” caught in the Mediterranean. In their catalogue of Caligus species, Margolis et al. (1975) listed the type host as Hexanchus griseus (Bonnaterre, 1788) , the bluntnose sixgill shark. Caligus lessonius has not been reported since 1826 although it has been listed in regional compendia such as Carus (1885) and Brian (1935), and in taxonomic compendia such as Wilson (1905) and Yamaguti (1963), all of which misspelled the name as Caligus lessonianus . Parker (1969) noted that C. lessonius did not belong in Caligus but he did not specify where it should be placed, and this treatment was followed by Margolis et al. (1975). In the absence of any formal transfer out of Caligus , this species has remained listed by the World of Copepods website ( Walter & Boxshall, 2023).

The very brief original description by Risso (1826) comprises the following (translated from French): an oblong body with a yellow coloration traversed by a brown stripe; cephalothorax heart-shaped, convex, traversed by two longitudinal sutures and ornamented with 2 golden spots which are touching; the eyes are close together; the antennae are small and 3-segmented; the oral cone is long and pointed; there are 7 pairs of legs, the first are short and armed with a curved hook, the third are thick, and the last are ornamented with 2 claws; the abdomen is composed of 4 segments, the first 2 of which are equipped with foliaceus lamellae, and the last is very long and divided into 2 parts each carrying a canaliculate appendage at the base of which are 2 pieces surrounded by spines.

This description includes sufficient characters, especially the presence of foliaceous lamellae on two postcephalothoracic body segments, to recognise that this species should be transferred to the family Pandaridae . The brief description given by Risso (1826) conforms reasonably closely to that of Demoleus heptapus (Otto, 1821) (cf. Kabata, 1979) and this species is known principally as an external parasite of Hexanchus Rafinesque, 1810 species ( Cressey, 1967). We consider it likely that Caligus lessonius Risso, 1826 is a junior synonym of Demoleus heptapus (Otto, 1821) .