Bimeria corynopsis Vanhöffen, 1910

Peña Cantero, Álvaro L., 2015, Review of some little-known benthic hydroids (Cnidaria, Hydrozoa) from the Southern Ocean, Zootaxa 3972 (3), pp. 369-392 : 370-373

Bimeria corynopsis Vanhöffen, 1910

( Figs 1 A, 2A–B, 3A–B)

Bimeria corynopsis Vanhöffen, 1910: 287 –288, fig. 12; Stepanjants, 1979: 12, pl. 1 fig. 5; Peña Cantero, 2014b: 1713 –1714, fig. 2a.

Material examined. Gauss Deutschen Südpolar-Expedition 1901–1903: Syntype ( ZMB Cni 7280), Gauss Station, 7.II.1903, 65°21'S – 86°06'E (Davis Sea), 385 m, a few stems, without gonophores, on Staurotheca noscripta .

Description. Colonies with little-developed stems ( Fig. 1 A), usually with single distal polyp ( Fig. 2 B), but branched stems, with up to three polyps observed ( Figs 1 A, 2A). Stem perisarc strong ( Fig. 2 A, B), mostly annulated, continuing on hydranth body as a thin film. Polyps 550–600 µm high and c. 240 µm in maximum diameter. Polyps with conical hypostome and a crown of about 12 tentacles in apparently two closely set rows ( Figs 2 A, B, 3A). Tentacle distal tips apparently with concentration of nematocysts giving them appearance of slightly capitate tentacles ( Fig. 3 A).

Gonosome unknown.

Measurements (in µm). Cnidome: heteronemes [range 8.0–9.0 x 5.0–5.5, mean 8.7±0.4 x 5.1±0.2 (n=10); ratio, range 1.6–1.8, mean 1.7±0.1 (n=10)], desmonemes [range 4.5–5.0 x 3.0–3.5].

Remarks. Although I could not clearly identify the heteronemes (discharged capsules could not be observed) in the material examined, Peña Cantero (2014b) found them in material from the same area, confirming they are microbasic euryteles [range 8.5– 9 x 5–5.5, mean 8.9±0.2 x 5.1±0.2 (n=13); ratio, range 1.6–1.8, mean 1.8±0.1 (n=13)].

This is a very uncommon species, only found twice.

Hirohito (1988) considered B. corynopsis a synonym of Bimeria vestita Wright, 1859 , and Marques et al (2002) pointed to the possibility that both were conspecific, though acknowledging that the knobs in the tip of the tentacles of B. corynopsis are a distinctive character. Schuchert (2007: 250) also included the species in the synonym of B. vestita , although indicated that “the biogeographic differences argue also in favour of the two being separate species”. I consider that both species are clearly distinguishable. Apart from the capitate appearance of the tentacles in B. corynopsis , confirmed after the examination of the type material and also observed in recently studied new material (cf. Peña Cantero 2014b), this species lacks a distinct pseudohydrotheca as that present in B. vestita , which also covers the hypostome and forms tubular sheaths around the basal part of the tentacles. As Schuchert (2007: 250) indicated, “with its ensheathed tentacles this is a very characteristic species”.

Ecology and distribution. Bimeria corynopsis has been collected at depths between 385 ( Vanhöffen 1910) and 527 m ( Peña Cantero 2014b), epibiotic on hydroids ( Vanhöffen 1910; Peña Cantero 2014b).

Endemic to East Antarctica ( Peña Cantero 2014b), hitherto only known from the Davis Sea ( Vanhöffen 1910; Peña Cantero 2014b).

Figures

FIGURE 1. Bimeria corynopsis Vanhöffen, 1910: A, a few stems growing on Staurotheca.? Koellikerina belgicae (Vanhöffen, 1910): B, colony with several stems. Rhizorhagium antarcticum (Hickson & Gravely, 1907): C – D, several stems and gonophores. Scale bar: 2 mm (A – B), 1 mm (C – D).

FIGURE 2. Bimeria corynopsis Vanhöffen, 1910: A, branched stem showing polyp; B, unbranched stem with polyp.? Koellikerina belgicae (Vanhöffen, 1910): C, polyp; D, gonophore. Rhizorhagium antarcticum (Hickson & Gravely, 1907): E – F, polyps. Scale bar: 250 µm (A – C, E – F), 125 µm (D).

FIGURE 3. Bimeria corynopsis Vanhöffen, 1910: A, polyp showing tentacle swollen ends; B, detail of junction between polyp and pedicel.? Koellikerina belgicae (Vanhöffen, 1910): C – D, polyps showing pseudohydrotheca and distal ends of tentacles; E, gonophore with medusa bud. Rhizorhagium antarcticum (Hickson & Gravely, 1907): F, gonophore showing medusa bud. Scale bar: 200 µm (F), 100 µm (A – D), 50 µm (E).