Oswaldella tottoni Pena Cantero and Vervoort 1996

Oswaldella tottoni Peña Cantero and Vervoort, 1996

Oswaldella tottoni Peña Cantero and Vervoort, 1996: 139–142, figure 2; Peña Cantero et al., 1997: 380–383, figure 12; Peña Cantero and García Carrascosa, 1998: 179; 1999: 214; Peña Cantero and Vervoort, 1998: 37; Peña Cantero and Marques, 1999: 85.

Oswaldella bifurca: Totton, 1930: 208–209, figure 50.

Remarks. Oswaldella tottoni is well characterized by the shape of the hydrotheca, which is low and situated on the distal half of the hydrocladial internodes, the presence of two axillary nematophores on the cauline apophyses, and the presence of only secondary hydrocladia (cf. table 1).

Ecology and distribution. Oswaldella tottoni is a shelf species (Peña Cantero et al., 1997), having been found at depths from 256 (Peña Cantero and Vervoort, 1996) to 400 m (Peña Cantero et al., 1997) on muddy bottoms.

Oswaldella tottoni seems to have a circum-Antarctic distribution. It is known from McMurdo Sound, Ross Sea (Peña Cantero and Vervoort, 1996), in East Antarctica, and from the east coast of the Weddell Sea (Peña Cantero et al., 1997), in West Antarctica.

Oswaldella vervoorti Peña Cantero and García Carrascosa, 1998 (figure 16)

Oswaldella vervoorti Peña Cantero and García Carrascosa, 1998: 175–179, figure 1; 1999: 214.? Oswaldella spec. 2 Peña Cantero and Vervoort, 1995: 336–339, figure 3; Peña Cantero and Marques, 1999: 85.

Material examined. 6/415, one stem ca 11 mm high (USNM 1003373); 6/445, four stem fragments up to 33 mm long (USNM 1003374); 691/002-B, numerous fragments and stems up to 20 mm high (USNM 1003375; RMNH-Coel. 30231; MNCN 2.03 / 246); 691/023, two stem fragments up to 25 mm high, with one immature gonotheca (USNM 1003376); 691/24, five stem fragments up to 45 mm long (USNM 1003377); 7/484, two stem fragments up to 35 mm long (USNM 1003378); 721/1062, one stem ca 46 mm high (USNM 1003379); 721/1063, three stems up to 28 mm high (USNM 1003380; RMNH-Coel. 30232); 721/704, four stems up to 30 mm high (USNM 1003381; RMNH-Coel. 30233); 721/816, one stem ca 40 mm high (USNM 1003382); SOSC-L42, one stem ca 33 mm high, with immature gonothecae (USNM 1003383).

Description. Colonies composed of monosiphonic and unbranched stems up to 45 mm high. Stems with alternately arranged apophyses forming two longitudinal rows, directed upwards and forming an angle of ca 45 ° with long axis of hydrocaulus. Stems divided into internodes with one, occasionally two apophyses per internode, each provided with three nematophores (figure 16B): two axillary nematophores, each emerging from a simple perisarc hole, and another emerging through a ‘mamelon’ and occasionally absent. Cauline apophyses supporting hydrocladia from which they are separated by distinct node (figure 16B); up to third-order hydrocladia observed (figure 16A).

Hydrocladia homomerously divided into hydrothecate internodes with one hydrotheca and two nematophores (figure 16 C–H): one mesial superior nematophore emerging from a perisarc hole situated behind free adcauline hydrothecal wall and one mesial inferior nematophore with a scale-shaped nematotheca and emerging through a perisarc hole situated on slight elevation of internode. Top of distal hydrocladial internodes truncated.

Hydrotheca shallow, situated on distal half of hydrocladial internode (figure 16 C–H). Hydrothecal aperture perpendicular to long axis of internode, sometimes slightly tilted adcaudally; rim circular and even. Adcauline wall of hydrotheca with distinct free portion; abcauline wall straight, angle with internodal long axis ca 30 °.

Immature gonothecae present, inserting on elevation of hydrocladial internode just under mesial inferior nematotheca. Gonotheca cone-shaped; maximum diameter at distal, truncated part (figure 16I).

Remarks. Oswaldella vervoorti is an easily recognizable species (cf. table 1), being characterized by the shape of the hydrotheca, the position of the hydrotheca on the distal half of the hydrocladial internodes, the much-branched hydrocladia and the presence of two axillary nematophores and one ‘mamelon’ on the cauline apophyses.

Ecology and distribution. Oswaldella vervoorti was previously known only from off Livingston Island, in the South Shetland Islands, where it was found at a depth of 46 m on muddy bottoms, epibiotic on ascidians (Peña Cantero and García Carrascosa, 1998). Our material comes from depths of 44 to 952 m. Immature gonothecae were found in February. We found it epibiotic on hydroids (Schizotricha sp.).

Oswaldella vervoorti appears to be endemic in West Antarctica. It had been reported from off Livingston Island, in the South Shetland Islands (Peña Cantero and García Carrascosa, 1998). Our material was collected north of the South Orkney Islands, north of d’Urville Island (Antarctic Peninsula), north-east of Livingston Island and off Nelson and King George Islands (South Shetland Islands) and off Brabant Island (Palmer Archipelago).