Caligus elongatus von Nordmann, 1832

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 : 556

Caligus guerini Guiart, 1913 and

Caligus elongatus von Nordmann, 1832 .

The original description of C. guerini was based on a single ovigerous female Caligus found settled on a Laminaria frond collected on the Glenan Islands off the Brittany coast in northern France ( Guiart, 1913). The description was very brief and was largely focused on overall body proportions. It was supported by a single illustration showing the type female in dorsal view. Guiart (1913) gave the body length as 6 mm, the width as 2.5 mm, and noted that the genital complex showed spots of reddish pigment. This species has never been reported since the original description although it was listed in Yamaguti’s (1963) compendium, in the catalogue of Caligus species by Margolis et al. (1975), and it is listed on the World of Copepods website ( Walter & Boxshall, 2023).

The Caligus species found in the waters off northwestern Europe are well known and were reviewed in detail by Kabata (1979) in his landmark monograph. Of these species, C. elongatus von Nordmann, 1832 is the closest fit to the inadequately described C. guerini . Both species have the same female body length: Kabata (1979) gives the length range for C. elongatus as 5 to 6 mm. Female C. elongatus also often show reddish-brown pigmentation spots all over the body including the genital complex and have been found free swimming away from any host sufficiently frequently to be included in a student manual for the identification of coastal marine zooplankton ( Todd et al., 1996). The size of the abdomen as illustrated for C. guerini is smaller relative to the genital complex than in C. elongatus but the triangular shape of the abdomen depicted in Guiart’s figure is extraordinary and almost certainly inaccurate. Other species in the European fauna that have a short abdomen, such as C. labracis T. Scott, 1902 , differ in body length (3.5 mm for C. labracis ) and their general habitus is more squat compared to the elongate habitus of C. elongatus and C. guerini .

The deposition of the type specimen is unknown ( Margolis et al., 1975) and in the absence of any other data, we propose to treat Caligus guerini Guiart, 1913 as a junior subjective synonym of Caligus elongatus von Nordmann, 1832 .