Staurotheca compressa Briggs, 1938

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 : 2673-2678

Staurotheca compressa Briggs, 1938

(figure 4)

Staurotheca compressa Briggs, 1938: 27 , figure 1a–c, pl. 15 figure 2; Blanco, 1971: 66; 1994a: 160; 1994b: 196; Naumov and Stepan’yants, 1972: 51, figure 13b; Stepan’yants, 1979: 98, pl. 19 figure 2; Peña Cantero, 1991: 118–123, pls 18, 19, 51, pl. 64 figure a; Peña Cantero and García Carrascosa, 1994: 123, figure 5a–d; 1995: 62–67, figures 26a–e, 27a–e, 28a–f, 63a; 1999: 212 et seq.; Peña Cantero et al., 1997: 336; 1999: 160.

Staurotheca tubifera Blanco, 1971: 67 , figures 1–23; 1984a: 40–41, pl. 37, figure 82.

Thuiaria sp. no. 2 Naumov and Stepan’yants, 1962: 93.

Thuiaria shetlandica Naumov and Stepan’yants, 1972: 52, figure 13a.

Material examined. 12 / 1002, several fragments up to 17 mm long, with male and female gonothecae (USNM 1003124); 12 / 1003, three fragments up to 10 mm long (USNM 1003125); 22 / 1582, four fragments up to 7 mm long (USNM 1003126); 27 / 1953, three fragments up to 13 mm long (USNM 1003127); 575 / 066, a mass of branches ca 100 mm in diameter, with male and female gonothecae (USNM 1003128; RMNH-Coel. 30247; MNCN 2.03/254); 575 / 069, seven fragments up to 40 mm long (USNM 1003129); 575 / 073, a mass of branches ca 10 mm in diameter (USNM 1003130); 575 / 076, a mass of branches ca 50 mm in diameter, with male gonothecae (USNM 1003131; RMNH-Coel. 30248; MNCN 2.03/255); 6 / 418, numerous fragments up to 15 mm long, with male and female gonothecae (USNM 1003132; RMNH-Coel. 30249); 6 / 441, a few fragments, with male and female gonothecae (USNM 1003133); 691 / 023, a mass of branches ca 10 mm in diameter, with male gonothecae (USNM 1003134); 691 / 23, a mass of branches ca 40 mm in diameter, with male and female gonothecae (USNM 1003135; RMNH-Coel. 30250; MNCN 2.03/256); 691 / 26, two masses of branches and stems up to 110 mm in diameter, with male and female gonothecae (USNM 1003136; RMNH-Coel. 30251; MNCN 2.03/257); 691 / 27, a mass of branches ca 130 mm in diameter, with male and female gonothecae (USNM 1003137; RMNH-Coel. 30252; MNCN 2.03/258); 691 / 28, a mass of branches ca 15 mm in diameter (USNM 1003138); 691 / 30, a mass of branches ca 20 mm in diameter, with male gonothecae (USNM 1003139; RMNH- Coel. 30253); 691 / 33, two fragments up to 30 mm long (USNM 1003140); 721 / 1018, a mass of branches ca 30 mm in diameter (USNM 1003141; RMNH-Coel. 30254); 766, a mass of branches ca 50 mm in diameter, with male and female gonothecae (USNM 1003142; RMNH-Coel. 30255); 767, a mass of branches ca 30 mm in diameter, with male and female gonothecae (USNM 1003143; RMNH-Coel. 30256); GLD-13, two fragments up to 10 mm long (USNM 1003144).

Description. Colonies formed by a mass of stems and branches up to 130 mm in diameter. Branching frequent and irregular, with frequent anastomoses, giving the colony a compact appearance.

Hydrothecae arranged in decussate pairs, forming four longitudinal rows (figure 4A, B). Hydrotheca small, with a small part immersed into the branch (figure 4A–E), cylindrical, more or less abcaudally directed. Adcauline hydrothecal wall adnate to internode for ca seven-eighths to one-half of its length. Free adcauline wall straight, or slightly concave or convex. Abcauline hydrothecal wall concave or straight. Hydrothecal aperture laterally depressed, resulting in the presence of both an adcauline and an abcauline cusp; the latter sometimes much better developed than the former. Hydrothecal diaphragm mushroom-shaped.

Female and male gonothecae present. Female gonothecae (figure 4E) as in S. antarctica , resting on a bifid, digitiform process, globular and with a set of digitiform projections ornamenting the external wall. Gonothecal aperture circular and facing the bifid process. Male gonothecae originating directly at hydrothecal base, ovoid (figure 4F), provided with a small, circular, distal aperture, sometimes ornamented with a few digitiform projections.

Ecology and distribution. Staurotheca compressa is a eurybathic species, distributed over the Antarctic shelf and upper slope. It had been recorded from 45 (Briggs, 1938) to 475 m depths (Peña Cantero and García Carrascosa, 1995); our material was collected from 55 to 1042 m depths. It has been found on bottoms of small rocks with red algae (Briggs, 1938), bottoms formed by bryozoans, hydrozoans, sponges, alcyonarians and ascidians (Naumov and Stepan’yants, 1972), bottoms of pebbles and gravel (Stepan’yants, 1979), and bottoms of mud, mud with stones, pebbles, stones with mud, and stones (Peña Cantero and García Carrascosa, 1995). It has been found epibiotic on other hydrozoans (Naumov and Stepan’yants, 1972; Stepan’yants, 1979; Peña Cantero and García Carrascosa, 1995) and bryozoans (Naumov and Stepan’yants, 1972; Stepan’yants, 1979). It may be used in turn as substratum by other hydroids ( Campanularia sp. , Symplectoscyphus sp. ). It has been found with gonothecae in January (Briggs, 1938; Stepan’yants, 1979; Peña Cantero and García Carrascosa, 1995), February (Peña Cantero and García Carrascosa, 1995), April (Stepan’yants, 1979) and December (Briggs, 1938; Stepan’yants, 1979). In our material fertile colonies were found in January, February, March, May and June. It therefore seems to be fertile most of the year, with the possible exception of the winter months.

Staurotheca compressa has a circum-Antarctic distribution (Stepan’yants, 1979), being known from both East and West Antarctica. In the former, it has been reported from Commonwealth Bay and at 65°42∞S, 92°10∞E (Briggs, 1938) and off Adélie Coast (Naumov and Stepan’yants, 1972; Stepan’yants, 1979). In West Antarctica, S. compressa was recorded at 60°S, 57°W, in the Weddell Sea (Blanco, 1971), and from off the South Shetland Islands (Naumov and Stepan’yants, 1972; Stepan’yants, 1979; Peña Cantero and García Carrascosa, 1995), Low Island (Blanco, 1984a) and Elephant Island (Peña Cantero and García Carrascosa, 1995). Our material comes from the Antarctic Peninsula region, the Scotia Ridge islands and off Victoria Land. At the Antarctic Peninsula, S. compressa has been collected north-east of Joinville Island and to the north of d’Urville Island, off Low Island and Deception Island (South Shetland Islands), and off Brabant, Ronge and Hoseason islands (Palmer Archipelago). It has also been found off Visokoi and Zavodovski islands ( South Sandwich Islands) and off Elephant Island at the Scotia Ridge. Finally, S. compressa has been obtained from Victoria Land off Buckle Island (Balleny Islands) and Scott Coast.

Staurotheca cornuta Peña Cantero, García Carrascosa and Vervoort, 1999 (figure 5)

Staurotheca cornuta Peña Cantero et al., 1999: 156–159 , figures 1, 3A.

Selaginopsis sp. 6 Peña Cantero, 1991: 103–105, pls 15, 49, pl. 66 figure d; Peña Cantero and

García Carrascosa, 1994: 122, figure 4r; 1995: 51–55, figures 21A–D, 22A–F, 63D.

Material examined. 12 / 992, a mass of stems ca 90 mm in diameter (USNM 1003145; RMNH-Coel. 30257; MNCN 2.03/259); 12 / 993, several fragments up to 25 mm long (USNM 1003146).

Description. Colonies compact, consisting of a mass of anastomosed branches, up to 90 mm wide. Branching frequent, irregular and in several planes; branches mainly monosiphonic, but polysiphonic in some parts. Hydrothecae arranged in decussate verticils of three hydrothecae forming six longitudinal rows (figure 5A, B); occasionally, however, at the origin of branches decussate pairs may be present. Hydrothecal verticils closely packed (figure 5A). This, together with the strong perisarc development, gives the colony the aspect of a closely knit net.

Hydrothecae immersed into branches for ca one-third or less of their volume (figure 5A–E). Adcauline hydrothecal wall with a short, but distinct free portion; abcauline wall almost straight or slightly concave. Hydrothecal aperture slightly tilted downwards; rim uneven with an abcauline elevation due to the greater length of the abcauline hydrothecal wall (figure 5D, E). Hydrothecal aperture frequently with renovations. Hydrothecal diaphragm mushroom-shaped, provided with two abcauline projections pointing into the hydrothecal lumen.

Gonothecae absent.

Remarks. Peña Cantero et al. (1999) discussed the similarities and differences of S. cornuta with the other known species of the genus, particularly with S. antarctica , S. compressa and S. frigida , with which S. cornuta forms a clearly distinctive group (cf. table 6). Staurotheca cornuta is well characterized by the arrangement of the hydrothecae in decussate verticils of three hydrothecae, by the shape of the hydrothecae (with a sharp abcauline elevation of the rim) and by the shape of the female gonothecae.

Ecology and distribution. Staurotheca cornuta had been found from 111 to 407 m on bottoms of stones with pebbles or mud (Peña Cantero et al., 1999). It was found with gonothecae in January (Peña Cantero et al., 1999). Our material was collected from 300 to 396 m and is infertile. It sometimes provides a substratum for other hydroids [ Stegopoma plicatile (M. Sars, 1863) ].

Staurotheca cornuta is endemic to West Antarctica, being known from off King George Island (South Shetland Islands), Elephant Island and Powell Island (South Orkney Islands) (Peña Cantero et al., 1999). Our material comes from the same region, between the South Shetland Islands and Elephant Island.