Acryptolaria minuta Watson, 2003

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 : 288

Acryptolaria minuta Watson, 2003

( Figs 1D , 3 E–F, 5G)

Acryptolaria minuta Watson, 2003: 163–164 , fig. 13A–C; Peña Cantero et al., 2007: 256–258 , figs 11, 16C; Peña Cantero & Vervoort, 2010: 302–304 , figs 18, 30.

Material examined. Eltanin: 27/1852, several fragments and stems up to 15 mm high, on bryozoans (mounted on two microslides).

Description. Branches and stems roughly straight. Hydrothecae alternate in two planes making a very obtuse angle. Hydrotheca tubular, free part cylindrical; diameter slightly decreasing basally at adnate part. Hydrotheca curved outwards; sometimes quite strongly. Hydrotheca adnate to internode for around two thirds of its adcauline length. Adcauline wall convex; much more at free part. Abcauline wall concave at distal half; practically straight at basal half. Hydrothecal aperture circular, directed up- and outwards, sometimes almost parallel to long axis of branch. Rim even, without renovations.

Measurements (in µm). Hydrothecae: abcauline wall 690–810, free part of adcauline wall 310–400, adnate part of adcauline wall 440–580, adcauline wall 776–930, diameter at aperture 95–100, diameter at base 50. Cnidome (taken with x40): larger microbasic mastigophores, range 16–19 x 6.3–7.5; smaller microbasic mastigophores 7 x 2.5

Remarks. Although Acryptolaria minuta resembles A. flabellum in having small, relatively long and thin hydrothecae, the latter species is easily distinguishable in the larger size and numerous renovations of its hydrothecae. Meanwhile, A. minuta differs in having hydrothecae with relatively longer free adcauline walls and larger nematocysts.

Acryptolaria minima Totton, 1930 also has a small hydrotheca, but its shape is clearly different and is adnate in most of its adcauline length. In addition, the nematocysts are much larger (25–27 x 9–10 µm).

Ecology and distribution. Species collected at depths from 300 m ( Peña Cantero & Vervoort 2010) to 1422 m ( Watson 2003); present material from 952 to 1336 m. Epibiotic on dead primnoid gorgonian ( Watson 2003), sponges, axis of gorgonians and hydroid stem ( Peña Cantero & Vervoort 2010) and bryozoans (present study).

The species was previously known off Macquarie Island ( Watson 2003) and from the Loyalty Islands and Norfolk Ridge areas ( Peña Cantero & Vervoort 2010). This study represents the third record for the species; the material comes from off Antipodes Island, southeast of New Zealand.

Figures

FIGURE 1. Branch fragments showing hydrothecal arrangement and shape of hydrothecae:A, Acryptolaria conferta (Allman, 1877); B, Acryptolaria crassicaulis (Allman, 1888); C, Acryptolaria flabellum (Allman, 1888); D, Acryptolaria minuta Watson, 2003; E, Acryptolaria operculata Stepanjants, 1979. (A from 715/885; B from 2/11; C from 22/1520; D from 27/1852; E from 715/885). Scale bar: 500 µm.

FIGURE 3. Hydrothecae: A, Acryptolaria conferta (Allman, 1877); B–C, Acryptolaria flabellum (Allman, 1888); D, Acryptolaria frigida Peña Cantero, 2014; E–F, Acryptolaria minuta Watson, 2003 (A from 715/885; B from 22/1520; C from 5/221; D from 2/2; E–F from 27/1852). Scale bar: 250 µm.