Amphinema biscayana

Amphinema biscayana (Browne, 1907)

Fig. 2A–E

Bimeria biscayana Browne, 1907: 21–23, pl. 1 figs 4–5.

Amphinema biscayana – Schuchert 2000: 415–417, fig. 3a–e; 2001a: 21–22, fig. 11a–d; 2007: 317–319, fig. 51.

SOUTH ATLANTIC OCEAN • 3 colonies, 23–30 mm high (1 with medusa buds); Valdivia Seamount, stn BT12; 24°49′01″– 24°47′38″ S, 6°24′40″– 6°25′26″ E; 887– 886 m depth; 7 Feb. 2015; SEAFO-2015 leg.; SEAFO-2015-40162, SEAFO-2015-40522.

Colonies up to 20 mm high, polysiphonic in their basal parts, grading to monosiphonic distally; ramified, with thick main stem and branches; axial tube surrounded by numerous, comparatively thinner, auxiliary tubes running parallel to one another (Fig. 2B, D). Branches originating from auxiliary tubes, and not from the main tube. Polyps scattered along the main stem and branches, placed at the distal end of short pedicels originating from both the main and auxiliary tubes (Fig. 2C–E); basal parts of the polyps covered by a pseudohydrotheca, ending below the tentacles; column cylindrical, with an apical, conical hypostome, surrounded by a whorl of 15–16 filiform tentacles. Nematocysts: desmonemes (5.5–6 × 3.5– 5 µm) and asymmetric microbasic euryteles (6–8× 3.5–4 µm).

Medusa buds given off from auxiliary tubes, far away from hydranths; almost rounded and enclosed in thin perisarcal envelope; four small bulbs are clearly differentiated distally (Fig. 2D).

In our material, we have not observed the distal ramification of the main axis with lateral branches, as described by Schuchert (2001a). Nevertheless, other features, such as the origin of lateral branches from auxiliary tubes, the morphology and type of nematocysts, as well as their measurements, concur with observations made by Schuchert (2000, 2001a) and, consequently, we identified our material as A. biscayana.

Amphinema biscayana has previously been reported from South Iceland (Schuchert 2000) and the Bay of Biscay (Browne 1907, as Bimeria biscayana). Its bathymetric distribution ranges from depths of 20 to 2076 m (Schuchert 2000, 2001b).

Our discovery is the first record of this species for South Atlantic waters.