Caligus curtus Müller, 1785

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 : 555

Caligus glacialis Gadd, 1910 and

Caligus curtus Müller, 1785

Despite its early twentieth century publication date, the original description of C. glacialis by Gadd (1910) provides detailed information on some important morphological features. Comparison of Gadd’s description of C. glacialis with the redescription of the type species C. curtus by Parker et al. (1968) reveals numerous detailed similarities. The general habitus of female C. glacialis is very similar to that of C. curtus and similarities between their appendages include: the presence of a blunt posterior process on the proximal segment of the antenna; a recurved postantennal process; a slender maxilliped lacking any myxal process; a sternal furca with short divergent tines; leg 2 with an unusually large outer spine of the first exopodal segment combined with an inconspicuous outer spine on segment 2, and neither lies obliquely across the surface of the ramus; leg 3 carries a slightly curved outer spine on the first exopodal segment that does not extend as far as the articulation between exopodal segments 2 and 3; and leg 4 is 3- segmented and bears 3 distal margin spines, the innermost of which is more than twice as long as the other 2 spines and longer than the segment. The male, as described by Gadd (1910), also shares numerous detailed features with C. curtus , including the presence of 2 well developed digitiform processes on the myxal surface of the maxilliped opposing the tip of the subchela, one proximal to and one distal to the tip of the subchela when adducted.

The female of C. curtus attains lengths up to 10.1 mm and the male, unusually for a Caligus species, is longer than the female, up to 12.3 mm according to Kabata (1979). The body lengths given by Gadd (1910) for female and male C. glacialis were 8.9 mm and 9.9 mm, respectively, and conform to this unusual pattern of gender-based size dimorphism. On the basis of all these similarities, and in the absence of significant differences, we propose to recognise Caligus glacialis Gadd, 1910 as a junior subjective synonym of Caligus curtus Müller, 1785 . This species is widespread at high latitudes in the Arctic-Boreal Atlantic.