Acryptolaria longitheca ( Allman, 1877 )

Peña Cantero, Álvaro L., 2020, Species of Acryptolaria Norman, 1875 (Cnidaria: Hydrozoa) collected by US Antarctic and sub-Antarctic expeditions, Zootaxa 4767 (2), pp. 277-294 : 287-288

Acryptolaria longitheca ( Allman, 1877)

( Figs 2C , 4 B–C, 5F, 7D)

Cryptolaria longitheca Allman, 1877: 18–20 , pl. 13, figs 4–5.

Acryptolaria longitheca— Peña Cantero et al., 2007: 252 –254, figs 9, 16A, 18B; Peña Cantero & Vervoort, 2010: 297–299, figs 15, 30, 32A; Calder, 2019: 26 –27, figs 6a, b, 7a.

Material examined. Eltanin: 27/1974, one stem, 31 mm high, and several fragments.

Description. Stem polysiphonic. Hydrothecae alternate, more or less in one plane, roughly with straight arrangement. Hydrotheca tubular, free part roughly cylindrical; diameter distinctly decreasing basally at adnate part. Hydrotheca smoothly curved outwards, sometimes with marked inflection point where it becomes free. Hydrotheca adnate to internode for half or less of its adcauline length. Adcauline wall faintly convex at free part, a little more at adnate part. Abcauline wall concave by the middle, practically straight at basal and distal thirds. A ring of desmocytes present at base of hydrotheca. Hydrothecal aperture circular, directed up- and outwards. Rim even, with up to four renovations.

Measurements (in µm). Hydrothecae: abcauline wall 1300–1350, free part of adcauline wall 600–750, adnate part of adcauline wall 810–900, adcauline wall 1500–1630, diameter at aperture 240–310, diameter at base 120. Cnidome: larger microbasic mastigophores, range 20–22 x 7.5–9, mean 21.3±0.7 x 8.1±0.4 (n=10); ratio, range 2.4–2.8, mean 2.6±0.1 (n=10); smaller microbasic mastigophores 8 x 3.5

Remarks. Acryptolaria longitheca resembles A. corniformis in the shape of the hydrothecae, although they are distinctly smaller in the former. Conversely, the nematocysts are larger in A. longitheca .

Acryptolaria longitheca is close to A. frigida in the size of hydrothecae and nematocysts and some hydrothecae can be similar in their shape. Nevertheless, they are easily recognisable, because in the latter the hydrothecae are strongly curved outwards and adnate in more than half of its adcauline length (one-quarter to one-half free). In addition, the hydrotheca is almost completely cylindrical in A. frigida , its diameter smoothly decreasing at adnate part; the diameter reduction is much stronger in A. longitheca .

Recently, Calder (2019) reported the species off Florida. His material agrees with the concept of A. longitheca , except for the more slender large nematocysts.

Ecology and distribution. Species known from depths between 80.5 (Calder 2019) and 567 m ( Allman 1877); present material at 112– 124 m. Peña Cantero & Vervoort (2010) reported it growing on corals and tubes of benthic organisms and with coppinia in February, and Calder (2019) found coppiniae in July.

Acryptolaria longitheca has an uncertain distribution because only three previous records are considered valid: the original description by Allman (1877), off Double-Headed Shot Key, Western Atlantic, and those by Peña Cantero & Vervoort (2010), from the Loyalty Islands and Norfolk Ridge areas, and by Calder (2019), from the southwest coast of Florida. Present material comes from off Macquarie Island, in the South Pacific.

Figures

FIGURE 2. Branch fragments showing hydrothecal arrangement and shape of hydrothecae: A, Acryptolaria corniformis Naumov & Stepanjants, 1962; B, Acryptolaria frigida Peña Cantero, 2014; C, Acryptolaria longitheca (Allman, 1877); D, Acryptolaria sp. (A from 27/1951; B from 2/2; C from 27/1974; D from 715/885). Scale bar: 500 µm.

FIGURE 4. Hydrothecae: A, Acryptolaria corniformis Naumov & Stepanjants, 1962; B–C Acryptolaria longitheca (Allman, 1877). (A from 27/1951; B–C from 27/1974). Scale bar: 250 µm.