Staurotheca amphorophora Naumov

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 : 2668-2670

Staurotheca amphorophora Naumov and Stepan’yants, 1962

(figure 2) Staurotheca amphorophora Naumov and Stepan’yants, 1962: 90, figure 13; Blanco, 1971: 66;

1994a: 160; 1994b: 196; Stepan’yants, 1979: 99, pl. 19 figure 3a–g; Peña Cantero et al.,

1997: 336; 1999: 160.

Material examined. 22 / 1536, one stem ca 100 mm high; 601 / 008, two stems ca 250 and 130 mm high, with female gonothecae (USNM 1003104; RMNH-Coel. 30238; MNCN 2.03/248); 601 / 011, one stem ca 140 mm high, with female gonothecae (USNM 1003105); 601 / 016, two stems up to 90 mm high (USNM 1003106; RMNH- Coel. 30239); 601 / 036, one stem ca 380 mm high (USNM 1003107; RMNH-Coel. 30240; MNCN 2.03/249).

Description. Colonies with the appearance of a gorgonid, up to 380 mm high and for a large part strongly polysiphonic. Hydrorhiza disc-shaped or composed of a few thick stolonal tubes. Branching beginning at base of colony, in one plane and frequent, usually irregular, but sometimes alternate. Branches long, flattened, arising at an angle of ca 45°, later curving upwards and frequently continuing parallel to branches from which they originate. Many basal branches also polysiphonic.

Hydrothecae opposite or subopposite, forming two longitudinal series arranged in one plane (figure 2A). Hydrotheca cylindrical, but distally directed outward, with one-third or one-quarter of its adcauline wall free (figure 2A–E). Abcauline hydrothecal wall slightly concave. Free adcauline hydrothecal wall straight or slightly concave; adnate part convex. Hydrothecal aperture circular; rim even and frequently with renovations. Diaphragm circular, not mushroom-shaped.

Gonothecae urn-shaped (figure 2E); ovoid with bilobate aperture at end of a distal neck. External wall of gonotheca sometimes provided with a few upwardly directed digitiform projections.

Cnidome composed of microbasic mastigophores in two size groups: a larger (19.6–22.4×4.6–4.9 Mm) and a smaller group (8.8–9.5×2.1–2.8 Mm).

Remarks. Our material agrees with that described by Stepan’yants (1979) from South Georgia, and doubtfully referred by her to S. amphorophora . However, it differs from the original description of S. amphorophora . In our material the hydrothecae, opposite or subopposite, form two longitudinal rows, whereas in S. amphorophora as described by Naumov and Stepan’yants (1962) the hydrothecae are arranged in decussate pairs forming four longitudinal rows of hydrothecae. Moreover, in our material, the hydrotheca is free for one-third or one-quarter of its adcauline wall, whereas in their colonies of S. amphorophora the free part of the adcauline hydrothecal wall represents half or more of its length. Nevertheless, Stepan’yants (1979) indicated that, in characteristic material of S. amphorophora , the hydrothecae may be found in one plane in the proximal part of the colony. Moreover, the female gonothecae in our material are in complete agreement with those described by Stepan’yants (1979). Though we have reservations whether or not our material, and that described by Stepan’yants (1979) from South Georgia, actually belongs to S. amphorophora , because of the hydrothecal arrangement and the shorter free portion of the adcauline hydrothecal wall, we here consider our material as belonging to that species.

Ecology and distribution. Staurotheca amphorophora appears to be largely a shelf species, having been found from 180 (Stepan’yants, 1979) to 370 m depth (Naumov and Stepan’yants, 1962). We found it from 111 to 190 m depth. Stepan’yants (1979) found it on stones, gravel and sand. It has been collected with gonothecae in February and June (Stepan’yants, 1979) while the present colonies with gonothecae were taken in November. It is used as substratum by other hydroids ( Sertularella sp. , Lafoea sp. ).

Staurotheca amphorophora is endemic to West Antarctica (Stepan’yants, 1979). It was previously known from the South Shetland Islands (Naumov and Stepan’yants, 1962; Stepan’yants, 1979) and South Georgia (Stepan’yants, 1979). We found it in the same region, off Shag Rocks and near South Georgia, in the Scotia Sea.