Acryptolaria flabellum

Acryptolaria flabellum (Allman, 1888)

(Figs 1C, 3 B–C, 5D, 7B)

Cryptolaria flabellum Allman, 1888: lvii, lxii, lxviii, 40, pl. 19, fig. 1a; Peña Cantero et al., 2007: 247–249, figs 7, 15E, 17F, 19F.

Material examined. Eltanin : 5/221, eight fragments up to 15 mm long; 6/350, two fragments up to 15 mm long; 22/1520, two stems up to 30 mm high.

Description. Branching irregular, almost in one plane, up to third order. Branches and stems straight or slightly geniculate. Hydrothecae alternate, in one plane or in two planes making a very obtuse angle. Hydrotheca tubular, cylindrical, except for the most basal part, where diameter decreases. Hydrotheca curved outwards. Hydrotheca adnate to internode for two thirds to three fourths of its adcauline length. Adcauline wall convex. Abcauline wall concave, but practically straight at basal third. Hydrothecal aperture circular, directed up- and outwards. Rim even, with numerous renovations.

Measurements (in µm). Hydrothecae: abcauline wall 800–980, free part of adcauline wall 320–410, adnate part of adcauline wall 560–730, adcauline wall 920–1140, diameter at aperture 96–130, diameter at base 70–80. Cnidome (from Stn 5/221): larger microbasic mastigophores, range 12.5–15 x 5–5.5, mean 13.9±0.8 x 5.1±0.2 (n=10); ratio, range 2.5–3.0, mean 2.7±0.2 (n=10); smaller microbasic mastigophores 6 x 2.5

Remarks. Our material perfectly agrees with Acryptolaria flabellum in the size and shape of hydrotheca, the slightly geniculate stems, the high number of renovations of the hydrothecal aperture, and the size of the nematocysts. Concerning this last character, as the type material of A. flabellum was without coenosarc, only a single nematocyst (15 x 5 µm) could be found (Peña Cantero et al. 2007). As a result, there was uncertainty about this information. The present material, however, has allowed me to confirm this point. This new information about the size of the nematocysts also resolves the difference in this character with A. flabelloides Peña Cantero & Vervoort, 2010. While similar, the latter species is clearly distinguishable in having branches that are straight, hydrothecal apertures that are roughly parallel to the long axis of branch, rims of hydrothecal apertures that are deprived of renovations (though sometimes a few short ones are present) and nematocysts that are distinctly larger (17–19.5 × 6–7 µm).

Ecology and distribution. Acryptolaria flabellum had been previously found at a depth of 702 m (Allman 1888); present material collected between 1244 and 2754 m, considerably increasing its lower bathymetric limit.

Acryptolaria flabellum was only known with certainty off Culebra Island, Puerto Rico (Allman 1888). This study represents the second record of the species, reporting it from the Drake Passage and the southeast of the Falkland Islands.