Staurotheca jaederholmi Stechow, 1920

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 : 2689-2691

Staurotheca jaederholmi Stechow, 1920

(figure 10)

Selaginopsis dichotoma Jäderholm, 1904b: 4 , pl. 1 figure 3, pl. 2 figure 1; Bale, 1915: 266; Hodgson, 1950: 20; Blanco, 1981: 276–277, figures 5–11; El Beshbeeshy, 1991: 143–145, figure 34; Wallin, 1994: 50; Peña (Cantero) et al., 1996: 8.

Staurotheca jaederholmi Stechow, 1920: 20 ; 1923b: 152; Leloup, 1974: 22, figure 18; Bouillon et al., 1995: 76; Peña Cantero et al., 1997: 336; 1999: 160; Peña Cantero and García Carrascosa, 1999: 215.

Thuiaria dichotoma: Naumov and Stepan’yants, 1962: 91; 1972: 34, 52; Blanco, 1994a: 160; 1994b: 195.

Material examined. 11 / 958, four fragments up to 9 mm long (USNM 1003234); 21 / 288, numerous fragments up to 110 mm long, with male and female gonothecae (USNM 1003235; RMNH-Coel. 30300; MNCN 2.03/282); 23 / 1621, six fragments up to 110 mm long (USNM 1003236); 5 / 222, one fragmented colony (fragments up to 47 mm long) (USNM 1003237; RMNH-Coel. 30301); 6 / 370, numerous fragments up to 55 mm long (USNM 1003238; RMNH-Coel. 30302); 715 / 870, several fragments and stems up to 75 mm high (USNM 1003239; RMNH-Coel. 30303; MNCN 2.03/283); 715 / 882, two stems up to 120 mm high (USNM 1003240).

Description. Stems up to 120 mm high, polysiphonic over part of their length. Branching alternate and in one plane; sometimes anastomoses amongst the branches.

Hydrothecae arranged in decussate verticils of two to four hydrothecae, forming four to eight longitudinal rows (figure 10A, E, F). Frequently, however, hydrothecal verticils with irregularities, and indistinct. Hydrothecae (figure 10A–F) low, sunken into branches for approximately one-third of their volume. Adcauline hydrothecal wall adnate to internode for almost its entire length. Hydrothecal abcauline wall straight or slightly concave; hydrothecal aperture slightly laterally depressed; rim uneven due to the presence of an elevation of the abcauline hydrothecal wall, aperture only slightly tilted downward. Hydrotheca without mushroom-shaped diaphragm.

Male and female gonothecae present. Female gonotheca arising from a stolonal process (modified branch) originating at the hydrothecal base (figure 10E). This process provided with alternately arranged, isolated hydrothecae with one gonotheca at the base of each hydrotheca. Female gonotheca pear-shaped (figure 10E), sometimes provided with a few spine-shaped projections. Gonothecal aperture not observed. Male gonothecae inserted directly at the hydrothecal base and arranged in close proximity on the branches; gonotheca fusiform with a small circular aperture at the distal end (figure 10F).

Cnidome composed of microbasic mastigophores in two size groups: a larger (21.7–24.5×5.6–7 Mm) and a smaller group (7.7–9.1×2.1 Mm).

Ecology and distribution. Staurotheca jaederholmi is a eurybathic species. It had been found from depths between 18 (Jäderholm, 1904b) and 500 m (El Beshbeeshy, 1991); our material comes from 76 to 4804 m. Jäderholm (1904b) found it on stony bottoms and Leloup (1974) found it on pebbles, whereas we observed it epilithic on gravel and epibiotic on bryozoans. It is used in turn as a substratum by other hydroids ( Campanularia sp. , Sertularella sp. , Symplectoscyphus sp. ). It was found with gonothecae in February (Blanco, 1981) and May (Jäderholm, 1904b); our fertile material was collected in December.

Staurotheca jaederholmi has been considered a Patagonian species (El Beshbeeshy, 1991). However, we have found it southwards to 61° 27∞S, so that it could be a Patagonian–West Antarctic species. So far it has only been recorded along both west and east coasts of the southern part of South America. On Pacific coasts it has been reported northwards to the northern part of Quellin Island ( Chile) (Leloup, 1974), being known also from the Guaitecas Islands (Jäderholm, 1904b). On the Atlantic coast it was known from the Patagonian shelf (Blanco, 1981; El Beshbeeshy, 1991). Our material comes from the South-East Pacific basin and South- West Atlantic basin, having been collected off the west and east mouths of the Strait of Magellan, off Tierra del Fuego and from the northern part of the Bellingshausen Sea (61°27∞S, 94°58∞–95°22∞W).