Acryptolaria crassicaulis

Acryptolaria crassicaulis (Allman, 1888)

(Fig. 3A–B)

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 (synonymy); Peña Cantero & Vervoort, 2010: 282 –283, figs 6, 30.

Material examined. 50303, one stem 40 mm high, no coppiniae; JC037/019, a stem 50 mm high, no coppiniae.

Description. Stems up to 50 mm high, almost completely polysiphonic, and divided into internodes with a distinct zigzag arrangement. Some anastomoses between branches present.

Hydrothecae alternately arranged in approximately one plane. Hydrotheca (Fig. 3A) tubular, but curved outwards, particularly at distal part. Diameter roughly constant in free part, but gradually decreasing towards basal part. Free part of adcauline wall distinctly convex; adnate one only slightly convex. Abcauline wall concave at distal third, straight basally. Hydrothecal aperture circular, rim even, sometimes with renovations.

Measurements (in µm). Hydrotheca: diameter at aperture 250–260; length of free adcauline wall 300–470. Cnidome: macrobasic mastigophores (Fig. 3B), 15.5–17.5 x 5.5–6.

Remarks. The material from JC037/019 has slightly larger hydrothecae than previously recorded.

This constitutes the third confirmed record of the species. See Peña Cantero et al. (2007) for a re-description of the type material and a discussion of its relationship with other species in the genus. The material examined agrees with A. crassicaulis in the shape and size of the hydrotheca, the size of the nematocysts and the marked zigzag arrangement of the internodes. Acryptolaria conferta (Allman 1877) also has a marked zigzag arrangement of the internodes and a similar hydrotheca, but the nematocysts are distinctly larger and the hydrothecae are smaller.

Ecology and distribution. This is a deep-water species, found at depths from 236 (Peña Cantero & Vervoort 2010) to 756 m (Allman 1888). Present material ranges from 2000 to 2754 m, considerably increasing its lower bathymetric limit.

The species has an uncertain distribution. It is recorded with certainty off Ascension Island (07°54’20’’N, 14°28’20’’W), and in waters of the Loyalty Islands and New Caledonia (Peña Cantero & Vervoort 2010). The present material, which constitutes the third confirmed record of the species, comes from Rockall Trough and the Mid-Atlantic Ridge.