Staurotheca abyssalis, Pena Cantero & Vervoort, 2003

Cantero, A. L. Peña & Vervoort, W., 2003, Species of Staurotheca Allman, 1888 (Cnidaria: Hydrozoa: Sertulariidae) from US Antarctic expeditions, with the description of three new species, Journal of Natural History 37 (22), pp. 2653-2722 : 2666-2668

Staurotheca abyssalis sp. nov.

(figure 1; table 1)

Material examined. 6 / 386, one colony ca 75 mm high, with female gonothecae (holotype, USNM 1003102 ) ; 6 / 451, one polysiphonic stem ca 70 mm high, with female gonothecae ( USNM 1003103 ; RMNH-Coel. 30237; MNCN 2.03 /247) .

Description. Colonies up to 75 mm high, fan-shaped and strongly polysiphonic even in finer ramifications. Hydrorhiza disc-shaped. Branching frequent, irregular or alternate, and approximately in one plane. Branches strongly constricted at their origin (figure 1B).

Hydrothecae alternately arranged in one plane forming two longitudinal series (figure 1A, B, E). Hydrotheca long, tubiform and adnate to internode for ca onequarter of its adcauline length (figure 1A–E). Adcauline hydrothecal wall with a sharp inflexion point where it becomes free. Abcauline hydrothecal wall concave basally and straight distally. Free adcauline hydrothecal wall straight or slightly concave. Hydrothecal diameter distinctly increasing at aperture; that aperture circular with even rim and usually with a few renovations. Hydrotheca without mushroom-shaped diaphragm.

Female gonothecae present in high numbers. Gonotheca ovoid (figure 1E), pedicel short, wall strongly ornamented by digitiform processes.

Cnidome composed of microbasic mastigophores in two size groups: a larger size group (16.1–17.5×4.2–4.9 Mm) and a smaller one (8.4–10.5×2.8 Mm).

Remarks. Staurotheca abyssalis sp. nov. is a remarkable species, both in morphology and in habitat, since it lives in very deep waters. It differs from the remaining species of the genus in both shape and arrangement of the hydrothecae. Although arrangement of hydrothecae in two longitudinal series was already known in the genus (cf. S. amphorophora and S. vervoorti ), in these species the hydrothecae are in opposite or subopposite pairs, but never in an alternate pattern as that found in S. abyssalis sp. nov. Assignment of the species to Staurotheca could therefore be questioned. However, the shape of the female gonothecae clearly indicates its relationship among a group of Antarctic species of Staurotheca ( S. antarctica , S. compressa , S. cornuta , S. frigida ) with female gonothecae having their surfaces ornamented by a series of digitiform processes. The female gonotheca in S. abyssalis sp. nov. differs in lacking the bifid, digitiform process on which the globular gonotheca rests; in S. abyssalis sp. nov. the gonotheca has only a simple pedicel.

Ecology and distribution. Staurotheca abyssalis sp. nov. originates from bathyal/ abyssal waters, having been collected from depths of 2599–4026 m in the deep basin of the Scotia Sea. Colonies with gonothecae were collected in January and December.

Etymology. The specific name abyssalis refers to the great depth at which this species lives.

Hydrothecae

Length of abcauline wall 1150–1500 Length of free adcauline wall 850–1200 Length of adnate adcauline wall 450–500 Length of adcauline wall 1350–1700 Diameter at rim 330–450 Gonothecae

Maximum diameter of female gonotheca ca 1000 Length of pedicel ca 300