Melicertum octocostatum

Oceania octocostata M. Sars, 1835: 24, pl. 4 fig. 9a-d.

Melicertum campanula. ‒ Agassiz, 1862: 349. – Mayer, 1910: 207, pl. 23 figs 4-5, pl. 24 fig. 5. – Naumov, 1969: 350, figs 215-216. [not Medusa campanula Fabricius, 1780 =? Catablema vesicarium]

Melicertum octocostatum. ‒ Kramp, 1919: 52, pl. 1 fig. 10, pl. 3 fig. 8. ‒ Kramp & Damas, 1925: 294. – Russell, 1953: 245, figs 138-142, pl. 13 figs 2-4. – Kramp, 1959a: 134, fig. 152. – Kramp, 1961: 136. – Kramp, 1968: 63, fig. 164. – Arai & Brinckmann-Voss, 1980: 79, figs 44-45. ‒ Bouillon, 1984: 87. – Cornelius, 1995: 124, fig. 17. – Okuizumi & Kubota, 2003: 39, fig. 1. ‒ Wang et al., 2014: 99, fig. 16.

Material examined: MHNG-INVE-48744, 3 specimens 4-5 mm wide and with up to 40 larger tentacles; Norway, Raunefjord, 60.2731°N 5.20728°E, 10 m depth; collection date 14.06.2006; one specimen used for DNA extraction, DNA isolate 433, 16S sequence FJ550510, 18S FJ550595, 28S FJ550451. ‒ MHNG- INVE-94100, one of> 4 specimens; Norway, Korsfjord, 60.1846°N 5.196°E; one other specimen used to obtain DNA isolate 1161, 16S KY363951, 18S KY363981, for archived photos see Table 1, remaining medusae used to extract RNA for transcriptome analysis.

Diagnosis: Umbrella 5-20 mm wide and high, conical to pyriform with thick, solid apex and thinner sides; per octant 3-7 fine, radial, subumbrellar tissue-thickenings with or without nematocysts (may be absent, or present in fully grown animals only); 40-80 large tentacles alternating with as many small ones, with distinct basal bulb formation; no ocelli, no cirri. Stomach short and broad, octagonal, mouth with 8 small lips when fully grown. 8 sinuous, linear gonads covering almost the full length of the 8 radial canals, getting thicker towards periphery. Colours: stomach and gonads yellow.

For polyp stage see Cornelius (1995).

Remarks: No subumbrellar nematocysts could be seen in the present animals which were relatively young (small). The tissue thickenings were present though.

Distribution: A strictly coastal species occurring in cooler waters of the North-western Atlantic from The English Channel to the Arctic Ocean; Iceland; North America from Woods Hole to Halifax and western coast of Greenland. Also present in the Pacific from Japan to the Arctic Ocean and British Columbia (Kramp, 1961; Arai & Brinckmann-Voss, 1980; Okuizumi & Kubota, 2003; Wang et al., 2014). An unexpected record is also known from Papua New Guinea (Bouillon, 1984). Type locality: Coastal region of Bergen, Norway.