Oswaldella shetlandica

Peña Cantero, A. L. & Vervoort, W., 2004, Species of Oswaldella Stechow, 1919 (Cnidaria: Hydrozoa: Kirchenpaueriidae) from US Antarctic expeditions, with the description of three new species, Journal of Natural History 38, pp. 805-861 : 845-847

Oswaldella shetlandica Stepan’yants, 1979

( figure 14)

Oswaldella billardi: Blanco and De Redolatti, 1977: 1–8 , pls 1–4.

Oswaldella billardi shetlandica p.p. Stepan’yants, 1979: 114, pl. 21 figure 3V, G, pl. 25 figure 7.

Oswaldella billardi p.p.: Blanco, 1984: 45–46, pl. 41 figure 95.

Oswaldella sp. 2 Peña Cantero, 1991: 182–186, pl. 34 figures a–j, pl. 58 figures a–f, pl. 68 figure c; Peña Cantero and García Carrascosa, 1994: 126, figures 8 i–l; 1995: 107–111, figures 48A–J, 49A–F, 64G.

Oswaldella shetlandica Peña Cantero et al., 1995: 342–347 , figure 1; 1997: 344; Peña Cantero and Vervoort, 1998: 36; Peña Cantero and García Carrascosa, 1999: 212 et seq.; Peña Cantero and Marques, 1999: 85.

Material examined. 6/445, one stem ca 11 mm high ( USNM 1003343); 691/023, one stem ca 45 mm high in bad condition ( USNM 1003344); 691/23, numerous broken stems without hydrocladia; only one stem ca 45 mm high with hydrocladia and with a single gonotheca ( USNM 1003345); 691/24, two stems up to 40 mm high ( USNM 1003346); 691/27, several stems up to 90 mm high, with gonothecae ( USNM 1003347; RMNH-Coel. 30218; MNCN 2.03 / 238); 7/484, one stem ca 42 mm high ( USNM 1003348); 721/1063, two stem fragments up to 28 mm long, with gonothecae ( USNM 1003349; RMNH-Coel. 30219); 721/704, one colony with several stems up to 170 mm high ( USNM 1003350; RMNH-Coel. 30220; MNCN 2.03 / 239); 721/801, one distal stem fragment ca 30 mm long ( USNM 1003351); 721/816, numerous stems up to 170 mm high, with gonothecae ( USNM 1003352; RMNH-Coel. 30221; MNCN 2.03 / 240); 731/1944, three stems up to 25 mm high ( USNM 1003353); 824/013-1, three fragments or stems up to 50 mm high ( USNM 1003354); 824/030- 1, eight stems up to 85 mm high, with gonothecae ( USNM 1003355; RMNH-Coel. 30222); 824/040-1, one stem fragment ca 4 mm long, with a single gonotheca ( USNM 1003356); 833/022-4, numerous stems up to 110 mm high, with male gonothecae ( USNM 1003357; RMNH-Coel. 30223; MNCN 2.03 / 241); SOSC-L46, one distally truncated stem ca 18 mm high, with gonothecae ( USNM 1003358).

Description. Stems polysiphonic and unbranched, divided into internodes. Sometimes colonies apparently with branched stems, but actually such ‘secondary’ stems originate from stolons ascending on ‘main’ stems. Hydrocaulus provided with alternately arranged cauline apophyses, forming two longitudinal series; usually one or two, sometimes three, apophyses per internode. Cauline apophyses forming an angle of ca 45 ° with long axis of cauline internodes, provided with four nematophores ( figure 14B): two emerging through axillary perisarc holes and two additional nematophores each emerging through a ‘mamelon’; occasionally a single ‘mamelon’ present. Cauline apophyses supporting much-branched hydrocladia ( figure 14A); up to fourth-order hydrocladia observed, hydrocladial arrangement symmetrical. No node between cauline apophysis and hydrocladium ( figure 14A, B). Top of distal hydrocladial internodes pointed; occasionally truncated.

Hydrocladia homomerously segmented, all internodes hydrothecate and provided with one hydrotheca and two nematophores ( figure 14 C–F): one mesial inferior emerging through a simple perisarc hole situated at dorsal surface of strong elevation of internode (without remnants of nematothecae) and one mesial superior nematophore, emerging through a perisarc hole situated behind free adcauline hydrothecal wall.

Hydrotheca placed in middle of hydrocladial internode ( figure 14 C–F), elongate, part of adcauline wall free. Abcauline wall slightly convex; aperture kidney-shaped, slightly tilted adcaudally and strongly depressed at adcauline side.

Male and female gonothecae present, inserting on hydrocladial internodes directly under inferior nematophore. Both male and female gonothecae pear-shaped; gonothecal aperture circular, large and situated at distal oblique end. Female gonothecae ( figure 14G) much larger than male ones ( figure 14H).

Remarks. This is a common and well-characterized Antarctic species (cf. table 1). It is easily recognizable by the strong division of the stems into internodes, the abundant branching of the hydrocladia, the presence of two axillary nematophores and two ‘mamelons’ on the cauline apophyses, the absence of a mesial inferior nematotheca at the hydrocladial internodes and the shape of hydrothecae and gonothecae.

Ecology and distribution. Oswaldella shetlandica is a shelf species (Peña Cantero et al., 1995), having been recorded at depths from 30 (Stepan’yants, 1979) to 216 m (Peña Cantero et al., 1995); our material comes from 44 to 952 m. It has been found on rocky (Stepan’yants, 1979) and stony bottoms (Peña Cantero et al., 1995). We have found it epibiotic on hydroids ( Billardia subrufa and Staurotheca sp.). Oswaldella shetlandica has been collected with gonothecae in January and February (Peña Cantero et al., 1995). In our material, fertile colonies were collected in January, February, March, April and December.

Oswaldella shetlandica appears to be endemic to West Antarctica, where it has been reported from off King George Island, in the South Shetland Islands (Stepan’yants, 1979; Peña Cantero et al., 1995) and off Low Island ( Blanco and De Redolatti, 1977). Our material comes from off King George, Livingston and Nelson Islands (South Shetland Islands), Anvers and Brabant Islands (Palmer Archipelago), Low Island, Argentine Island (Antarctic Peninsula) and from north of the South Orkney Islands.