Catablema vesicarium subsp. nodulosum Bigelow 1913

Catablema vesicarium nodulosum Bigelow, 1913

Fig. 11

Catablema vesicarium var. nodulosa Bigelow, 1913: 17, pl. 1 figs 8-9.

Catablema nodulosa. – Arai & Brinckmann-Voss, 1980: 45, fig. 21.

Type locality: Dutch Harbour, Unalaska Island, USA.

Material examined: 2 specimens, not in permanent collection; USA, San Juan Islands, Friday Harbor, 48.5451° -123.01206°; collection date 16.05.2011 and 20.05.2011; collected at water surface with a dipping jar; DNA isolates 932 and 957; GenBank numbers see Table 1.

Diagnosis: North Pacific Catablema medusa, up to 25 mm in size, including the apical projection of variable size and shape; gonads in long, irregular folds, oblique in lateral parts, almost perpendicular in middle part of each quadrant, gonadal folds usually without pits, rarely a few present; With 8 to 16 tentacles, rarely up to 25, with 2-6 small, rudimentary bulbs between adjoining tentacles, usually with small, inconspicuous abaxial ocelli on the rudimentary bulbs, fully formed tentacles lack ocelli; mesenteries about 1/3 of manubrium height. Manubrium gold-brown or peach colour in living specimens.

Hydroid unknown.

Remarks: In the examined material, only the smaller tentacles and the rudiments had small ocelli, the fully developed tentacles lacked them.

Bigelow (1913) found that some Catablema medusae from the North Pacific differed in tentacle numbers and gonad structure from C. vesicarium he had seen in the NorthAtlantic.Although he states that they were probably still within the extremes of the nominal species and no morphological discontinuity existed, he treated them as a variant of C. vesicularium and named it Catablema vesicarium var. nodulosa . Bigelow observed tentacle numbers of 14-25 tentacles, but the numbers were often difficult to establish as there was a continuum of sizes from mere knobs to fully grown tentacles. Hartlaub (1914: 321), Foerster (1924), and Kramp (1926, 1968) regarded Catablema vesicarium var. nodulosa Bigelow, 1913 as a synonym of C. vesicarium.

Arai & Brinckmann-Voss (1980) did not agree and raised the variant to full species level. They distinguished Catablema nodulosum from C. vesicarium solely on account of the lower tentacle number, being only 8-16 instead of 32. The shape of the gonads as argued by Bigelow (1913) was deemed unsuitable to distinguish the two species and I concur. Arai & Brinckmann-Voss (1980) based their decision on medusae from the southern limit of this genus, thus perhaps with a suboptimal growth. This could perhaps also explain the lower tentacle number compared to C. vesicarium, which is an Arctic species. Bigelow (1913), who had medusae from cooler waters (Aleutian Islands), founded his variety on animals having up to 25 tentacles. It is therefore reasonable to follow Bigelow, Hartlaub, and Kramp and regard C. nodulosum only gradually different from C. vesicarium, representing a local variant only. Moreover, tentacle numbers in Pandeidae medusae vary considerably and are deemed mostly unsuitable to delimit species. The COI sequence data did not show significant differences between the nodulosa form from the NE Pacific and typical C. vesicarium from the Greenland Sea (Fig. 9; the 16S data show very little divergences within this genus). Catablema nodulosum should therefore be regarded as conspecific with C. vesicarium, or at most be treated as a subspecies of the latter. According to the ICZN (§45.6.4), a name introduced as variety before 1961 gets the rank of subspecies.