Alcyonium roseum Ofwegen, 2007, n. sp.

Alcyonium roseum n. sp.

(Figs. 1 h, 2f–g, 3e, 9)

Holotype and three microscope slides: RMNH Coel. 34946, Chile, Bernardo, Fjord Isla van der Meulen SE, 48°17'13.0'' S, 74°20'10.'' W, depth 25 m, coll. VH & GF, 28 March 2005.

Paratypes: MZUC-UCCC 32683, Chile, Canal Messier, Puerto Eden/ Isla Pedro, 48°58'29'' S, 74°25'16.9'' W, boulders of different sizes, moderate slope, depth 26 m, coll. VH & GF, 1 April 2005; ZSM 20061195, Chile, Paso del Abismo, 49°34'38.7" S, 74°26'49.3" W, steep/overhanging wall, high diversity, depth 25 m, coll. VH & GF, 10 March 2006; ZSM 20061196, Chile, Seno Waldemar, 48°23'48.5" S, 74°43'48.8" W, slope/ wall, some terraces, patches of high diversity, depth 25 m, coll. VH, 15 March 2006; RMNH Coel. 34947, Chile, Grupo Dacres, 51°36'20.8" S, 73°55'33.8" W, large steps with slight overhangs, high biodiversity, strong current convection, depth 15 m, coll. VH & GF, 7 March 2006.

Description. The holotype is membranous, about 20 cm long and about 1 mm thick, completely encrusting the axis of a gorgonian (Figs. 1 h, 2f). At irregular intervals small lobes are present, these are up to about 1 cm high and wide.

Polyps are unevenly distributed over the colony; they are concentrated on the lobes, where they stand in close proximity. Calyces are dome shaped and most polyps are retracted, the few expanded polyps are up to 2 mm high and 1.5 mm wide; all polyps have the tentacles withdrawn.

Anthocodiae have a collaret composed of 5–6 irregularly arranged rows of spindles; the points with many spindles (Fig. 3 e). The anthocodial spindles are up to 0.55 mm long, with simple tubercles (Fig. 9 a–b). At the tentacle bases slender clubs are present, up to 0.30 mm long (Fig. 9 c). In the tentacles spiny rods are found, up to 0.20 mm long (Fig. 9 d).

The surface layer of the lobes has clubs, up to about 0.25 mm long, with spiny heads (Fig. 9 e). The interior of the lobes has tuberculated spindles, up to 0.30 mm long (Fig. 9 f).

The surface layer of the membrane has capstans and clubs (Fig. 9 g). The capstans are up to about 0.10 mm long, most of the clubs are slightly longer, some reaching 0.25 mm in length. The interior of the membrane contains tuberculated spindles (Fig. 9 h), up to 0.30 mm long; similarly shaped to those of the lobes.

Colour. Alive the colony was pink (Fig. 2 f), preserved it is white, and all sclerites are colourless.

Etymology. The species name is the Latin roseum, rose, referring to the colony colour.

Habitat, distribution and abundance. The species was regularly found on biogenic substrata (e.g. dead gorgonians, polychaete tubes) which were found on moderately steep or vertical rocky substratum below 15 m depth in the channels of the Central Patagonian Zone (see Pickard, 1973) between 48°17'30'' S, 74°20'10'' W and 51°36'20.8" S, 73°55'33.8" W in the Chilean fjord region. At these sites currents were moderate to strong and sedimentation relatively low. The colonies can cover entire dead gorgonians or just a part of them.

Variability. The paratypes are similar to the holotype, also encrusting gorgonians, but forming smaller colonies (Fig. 2 g).

Remarks. Alcyonium antarcticum Wright & Studer, 1889, from Antarctic and Sub Antarctic waters, and A. haddoni Wright & Studer, 1889, from the Messier Channel, Chile, have been described as having membranous colony forms. A. antarcticum indeed can be membranous (see Verseveldt & Ofwegen, 1992), but Wright & Studer described their A. haddoni as “In this species the colony forms very variously shaped and sized masses, which grow over the dead stems of a Muriceid”, suggesting it has a membranous colony form. However, none of the three specimens mentioned in their publication was depicted. Here we show two of these syntype specimens of A. haddoni, BMNH 89.5.27.125 (Fig. 1 d), which clearly demonstrate it is not an encrusting species.

A. antarcticum differs from the present species in having less tuberculate capstans in the surface and lacking the characteristic clubs at the tentacle bases reported for the present material.

Above we described encrusting specimens of A. grandis Casas et al. That species differs from Alcyonium roseum n. sp. in totally lacking clubs.