Staurotheca dichotoma Allman, 1888

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 : 2681-2683

Staurotheca dichotoma Allman, 1888

(figure 7)

Staurotheca dichotoma Allman, 1888: 76 , pl. 36 figure 1, 1a; von Campenhausen, 1896: 104; Hartlaub, 1901: 35; 1904: 4, 16; 1905: 617; Billard, 1904: 36; 1906: 3; 1910: 27, figures 11, 12; 1914: 15, figure 9; Stechow, 1919: 82; 1923b: 152; Blanco, 1971: 62; 1992: 155, figure 2; 1994a: 160; 1994b: 196; Millard, 1977: 22; Peña Cantero, 1991: 123, pls 20, 52, pl. 63 figure d; Branch and Williams, 1993: 10, figure; Peña Cantero and García Carrascosa, 1994: 123, figure 5g –i; 1995: 67–70, figures 29a–h, 30a–f, 63b; 1999: 212 et seq.; Peña Cantero et al., 1997: 347–350, figure 3; 1999: 160.

Staurotheca affinis?: Billard, 1914: 17 , figures 10–12.

Staurotheca dichotoma p.p. Totton, 1930: 178, figure 27a–c, pl. 2 figure 9.

? Thuiaria dichotoma: Naumov and Stepan’yants, 1962: 91; 1972: 52.

? Staurotheca dichotoma: Briggs, 1938: 27 ; Broch, 1948: 8; Stepan’yants, 1979: 97, pl. 18 figure 5, pl. 24 figure Zh, K, L; Blanco, 1992: 155–157, figure 2.

Not Staurotheca dichotoma Jäderholm, 1905: 33 , pl. 14 figures 1, 2 (= Staurotheca frigida Peña Cantero et al., 1997 ).

Not Dictyocladium fuscum Hickson and Gravely, 1907: 1 , 3, 21, pl. 3 figure 22; Vanhöffen, 1910: 331; Stechow, 1923a: 108.

Material examined. 22 / 1535, six fragments up to 40 mm long ( USNM 1003154); 32 / 2021, one fragment ca 13 mm long ( USNM 1003155); 32 / 2080, two fragments up to 17 mm long ( USNM 1003156); 575 / 031, a mass of branches ca 50 mm in diameter, with female gonothecae ( USNM 1003157; RMNH-Coel. 30261; MNCN 2.03/262); 575 / 052, one stem ca 60 mm high ( USNM 1003158); 575 / 070, a mass of branches ca 30 mm in diameter, with female gonothecae ( USNM 1003159; RMNH- Coel. 30262); 601 / 008, a mass of branches ca 60 mm in diameter ( USNM 1003160; RMNH-Coel. 30263; MNCN 2.03/263); 601 / 014, a mass of branches ca 50 mm in diameter, with male gonothecae ( USNM 1003161; RMNH-Coel. 30264; MNCN 2.03/264); 601 / 065, a mass of branches ca 50 mm in diameter, with female gonothecae ( USNM 1003162; RMNH-Coel. 30265; MNCN 2.03/265); 731 / 1812, a mass of branches ca 50 mm in diameter, with female gonothecae ( USNM 1003163; RMNH-Coel. 30266).

Description. Colonies monosiphonic, consisting of a mass of interwoven, anastomosing branches up to 60 mm in diameter; without distinct main stem.

Hydrothecae arranged in decussate pairs (figure 7A, B), forming four longitudinal rows of hydrothecae. Hydrothecae (figure 7A–E) immersed into the branches for ca one-third of their volume. Hydrotheca cylindrical in lateral view, curving slightly outwards; in frontal view slightly inflated basally. Adcauline hydrothecal wall largely adnate to internode, but with a distinct free portion; this part straight or slightly concave. Abcauline hydrothecal wall straight basally, but becoming concave distally. Hydrothecal aperture circular, large and slightly tilted downwards. Rim of hydrotheca even and frequently with renovations; diaphragm mushroom-shaped, provided with two abcauline perisarc projections pointing to the lumen of hydrotheca.

Male and female gonothecae present, both originating at hydrothecal base. Female gonotheca urn-shaped (figure 7F), provided with a wide neck with distal, circular aperture; gonothecal wall with a few transverse striae at base of neck. Male gonotheca fusiform (figure 7G), with a short neck, distally having a small, circular aperture.

Remarks. Peña Cantero et al. (1997) demonstrated that several allied species were included within S. dichotoma (e.g. material now assigned to S. glomulosa and S. nonscripta ).

Staurotheca dichotoma is closely allied to S. glomulosa ; we will discuss the differences when dealing with that species.

Ecology and distribution. Staurotheca dichotoma had been found from 82 (Totton, 1930) to 799 m depths (Peña Cantero et al., 1997). Our material was collected from 97 to 612 m depths. The species has been taken on bottoms of mud and mud with detritus (Totton, 1930), sand (Allman, 1888), pebbles (Totton, 1930; Peña Cantero and García Carrascosa, 1994) and stones (Peña Cantero and García Carrascosa, 1994). It is used as a substratum by other hydroids ( Halecium sp. , Lafoea sp. , Sertularella sp. ). Gonothecae were recorded from October (Allman, 1888), February (Peña Cantero et al., 1997), April (Millard, 1977) and from November to February (Peña Cantero and García Carrascosa, 1994). In our material, fertile colonies were collected in February, May, June and December. It therefore seems to be fertile throughout the year, maybe with the exception of the winter months.

Staurotheca dichotoma has an Antarctic–Kerguélen distribution, having been found both in Antarctic and in sub-Antarctic waters. In the latter, it has been recorded from off Marion Island (Allman, 1888) and Kerguélen, Crozet and Heard Islands (Millard, 1977). In Antarctic waters it has been reported from Cape Adare and McMurdo Sound, in the Ross Sea (Totton, 1930), off South Georgia (Blanco, 1992), off Shag and Clerke Rocks, South Georgia and the South Shetland Islands (Peña Cantero and García Carrascosa, 1994) and from the east coast of the Weddell Sea (Peña Cantero et al., 1997). Our material comes from the Ross Sea, the Scotia Ridge islands and the Antarctic Peninsula. In the first region, S. dichotoma was found in the central basin of the Ross Sea and at Pennell Bank (off Victoria Land). At the Scotia Ridge it was collected from off Saunders and Visokoi islands ( South Sandwich Islands), South Georgia, and Shag Rocks. Finally, at the Antarctic Peninsula it was obtained from off Anvers Islands (Palmer Archipelago).