Symplectoscyphus

ÁLVARO L. PEÑA CANTERO, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa, Zootaxa 4293 (1), pp. 1-65 : 47

Symplectoscyphus sp. 2

( Figs 12 K, 13D)

Material examined. Stn 25, a few stems up to 12 mm high (MNCN 2.03/645); Stn 132, four stems up to 10 mm high on Staurotheca densa (NIWA 117590).

Description. Monosiphonic stems, up to 12 mm high. Highest stem with five primary branches, all to the left, except last one. Some primary branches with two secondary branches in alternate pattern, consequently up to second-order branches present. Without anastomoses. Hydrothecae alternately arranged in one or two planes, sometimes forming a quite acute, almost perpendicular, angle.

Hydrotheca ( Figs 12 K, 13D) distinctly directed upwards. Adcauline wall convex, except for adcauline cusp; without inflexion point where adcauline wall becomes free. Abcauline wall basally convex, more or less straight distally. Cusp sharp and separated by deep embayments. Adcauline cusp markedly curved adcaudally.

Measurements (in µm). Hydrothecae: length abcauline wall 360–370, length free part of adcauline wall 220–280, length adnate part adcauline wall 230–250, length adcauline wall 470–530, diameter at aperture 150–160, maximum diameter 170–200, diameter at diaphragm 120–160. Cnidome (from Stn 132): larger microbasic mastigophores, range 11.0–13.5 x 3.0–4.0, mean 12.2±0.6 x 3.8±0.3 (n=10); ratio, range 3.0–3.7, mean 3.2± 0.3 (n=10). Stn 25: range 11–13 x 3–4.

Remarks. The present material is morphologically close to S. glacialis in the shape of the hydrothecae, although these are larger and are more directed upwards. It also differs from Jäderholm’s species both in lacking anastomoses, although this could be related to the small size and little development of the stems, and in having slightly larger microbasic mastigophores [mean 11.3±0.4 x 3.5±0.0 (n=10), range 10.5– 12 x 3.5 in S. glacialis (cf. Peña Cantero 2013)]. The material studied could actually represent a different species, but the scarcity of material and its infertile condition prevent me from characterizing it completely.

Ecology and distribution. Material found at depths between 110 and 172 m, in Robertson Bay and off Possession Islands, epibiotic on Staurotheca densa .

Figures

FIGURE 12. Antarctoscyphus admirabilis Peña Cantero, Svoboda & Vervoort, 1999: A, branch internode with hydrotheca. Symplectoscyphus aggregatus (Jäderholm, 1917): B, fragment of branch with hydrothecal arrangement and shape. Symplectoscyphus anae Peña Cantero, Svoboda & Vervoort, 2002: C, internode with hydrotheca. Symplectoscyphus densus sp. nov.: D – E, fragment of branch with hydrothecal arrangement and shape; Symplectoscyphus exochus Blanco, 1982: F, internode with hydrotheca. Symplectoscyphus liouvillei (Billard, 1914): G, internode with hydrotheca. Symplectoscyphus vanhoeffeni Totton, 1930: H, internode with hydrotheca. Symplectoscyphus weddelli Peña Cantero, Svoboda & Vervoort, 2002: I, internode with hydrotheca. Symplectoscyphus sp. 1: J, internode with hydrotheca. Symplectoscyphus sp. 2: K, internode with hydrotheca. (A from Stn 17; B from Stn 112; C from Stn 126; D from Stn 7 (holotype); E from Stn 97 (paratype); F from Stn 67; G from Stn 150; H from Stn 130; I, from Stn 53; J from Stn 7; K from Stn 25). Scale bar: 250 µm.