Acryptolaria crassicaulis

Acryptolaria crassicaulis (Allman, 1888)

(Figs 1B, 5C)

Cryptolaria crassicaulis Allman, 1888, lvii, lxvii, lxviii, 41, pl. 19, figs 3, 3a.

Acryptolaria crassicaulis— Peña Cantero et al., 2007: 245–247, figs 6, 15D, 17E; Peña Cantero & Vervoort, 2010: 282–283, figs 6, 30; Peña Cantero & Horton, 2017: 7–8, fig. 3A–B.

Material examined. Eltanin: 2/11 , four fragments up to 7 mm long (mounted on a microslide).

Description. Hydrothecae alternate in two planes, making an obtuse angle. Internodes in a distinct zigzag pattern. Hydrotheca tubular, free part roughly cylindrical; diameter smoothly decreasing basally at adnate part. Hydrotheca curved outwards. Hydrotheca adnate to internode for about two thirds of its adcauline length. Adcauline wall convex. Abcauline wall concave at distal half, practically straight at basal half. Hydrothecal aperture circular, directed upwards and outwards. Rim even, with none or a few, quite long, renovations.

Measurements (in µm). Hydrothecae: abcauline wall 1200–1300, free part of adcauline wall 520–640, adnate part of adcauline wall 900–1000, adcauline wall 1420–1600, diameter at aperture 220–250, diameter at base 100. Cnidome: larger microbasic mastigophores, range 14–15 x 4.5–5, mean 14.7±0.4 x 4.8±0.2 (n=5); ratio, range 2.9–3.3, mean 3.1±0.1 (n=5); smaller microbasic mastigophores 7 x 3.

Remarks. Despite of the scarcity of material, it clearly belongs to this species, agreeing in the marked zigzag arrangement of internodes, the shape and size of hydrotheca, and the size of nematocysts (larger group 14–16.5 x 4.5–5.5 µm in the holotype). Acryptolaria conferta, whose hydrotheca is similar, and whose internodes are also arranged in a marked zigzag, has smaller hydrothecae and distinctly larger nematocysts.

Ecology and distribution. Acryptolaria crassicaulis had been reported at depths between 236 (Peña Cantero & Vervoort 2010) and 2754 m (Peña Cantero & Horton 2017); present material at 2357 m.

The species has been recorded with certainty off Ascension Island (07°54’20’’N, 14°28’20’’W) (Allman 1888) and from Rockall Trough and the Mid-Atlantic Ridge (Peña Cantero & Horton 2017), in the Atlantic Ocean, and from waters of the Loyalty Islands and New Caledonia (Peña Cantero & Vervoort 2010), in the Pacific Ocean. The present material, which constitutes the fourth confirmed record for the species, was collected at 49°33’S, 48°19’W, between the Falklands Islands and South Georgia, in the south-west Atlantic Ocean.