Acryptolaria Norman 1875

Acryptolaria sp.

(Figs 2D, 5H, 6C, 7F)

Material examined. Eltanin : 5/254, one fragment 10 mm long; 6/339, one fragment 14 mm long; 9/740, stem fragment 30 mm long; 12/993, one fragment 6 mm long; 22/1595, two fragments up to 40 mm long. Hero: 715/885 , 12-mm-long stem fragment.

Description. Stem fragments up to 40 mm high, unbranched or with occasional branching. Fragments straight or barely geniculate. Hydrothecae in one plane or slightly in two planes as they bend to the same side. Hydrotheca tubular, free part cylindrical; diameter decreasing basally at basal third. Hydrotheca curved outwards, adnate to internode slightly over half its adcauline length. Adcauline wall slightly convex at free part; a little more at adnate part. Abcauline wall concave. A ring of desmocytes present at base of hydrotheca. Hydrothecal aperture circular, directed up- and outwards. Rim even, usually with a few short renovations. Some hydrothecae with a deciduous circular operculum.

Measurements (in µm). Hydrothecae: abcauline wall 1150–1450, free part of adcauline wall 580–900, adnate part of adcauline wall 800–1020, adcauline wall 1400–1710, diameter at aperture 260–290, diameter at base 100– 120. Cnidome (from 6/339): larger microbasic mastigophores, range 21–22.5 x 6.5–8.5, mean 21.7±0.5 x 7.3±0.6 (n=10); ratio, range 2.5–3.4, mean 3.0±0.2 (n=10); smaller microbasic mastigophores 7 x 3.

Remarks. In some hydrothecae from 9/740 and 22/1595 a closing apparatus consisting of a circular flap has been observed. This character is also found in A. frigida (present study) and A. operculata (Stepanjants 1979, present study). Similar as some hydrothecae of A. operculata and Acryptolaria sp. can be in their shape, their size is however much larger in A. operculata (e.g. 420–500 µm in diameter at aperture), which also has distinctly smaller nematocysts (14–15 x 4.5–5.5 µm).

Acryptolaria sp. is close to A. frigida in the general shape of the hydrotheca, in the presence of an operculum and in the size of the nematocysts, but clearly differs in having a shorter adnate portion. It also resembles A. longitheca, but in this species the hydrothecae are more directed upwards.

Acryptolaria sp. could represent a new species, but it cannot be characterized completely given the scarcity of material and absence of coppiniae.

Ecology and distribution. Acryptolaria sp. has been found at depths from 124 to 677 m in the southwest Atlantic, in the area encircled by Tierra del Fuego, the Falkland Islands, South Georgia and Elephant Island.