Oswaldella erratum Peña Cantero and Vervoort, 1997

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 : 827-830

Oswaldella erratum Peña Cantero and Vervoort, 1997

( figures 6, 7)

Oswaldella erratum Peña Cantero and Vervoort, 1997: 273–276 ; 1998: 36; Peña Cantero and García Carrascosa, 1999: 214; Peña Cantero and Marques, 1999: 85.

Oswaldella billardi: Broch, 1948: 13–16 , figure 4b; Peña Cantero et al., 1997: 349–353, figures 2, 13b.

Oswaldella billardi shetlandica p.p. Stepan’yants, 1979: 114, pl. 21 figure 3b, c (only a part belongs to Oswaldella shetlandica Stepan’yants, 1979).

Oswaldella billardi p.p. Blanco, 1984: 45–46, pl. 42 figures 96, 97 (partly Oswaldella shetlandica Stepan’yants, 1979).

Polyplumaria antarctica: Billard, 1914: 28–31 , figure 17.

Material examined.? 001/011, one stem ca 70 mm high ( USNM 1003311); 12/1001, one stem ca 10 mm high ( USNM 1003312); 12/1002, one fragmented stem (largest fragment ca 55 mm long) ( USNM 1003313); 12/1003, numerous stems up to 65 mm high, with gonothecae ( USNM 1003314; RMNH-Coel. 30209; MNCN 2.03 / 231); 575/061, three stem fragments up to 35 mm long ( USNM 1003315); 691/003, one stem fragment ca 55 mm long, with gonothecae ( USNM 1003316); 691/020, one stem ca 62 mm high ( USNM 1003317); 702/511, one distally broken stem ca 30 mm high ( USNM 1003318);? 721/1070, two stems up to 80 mm high, with gonothecae ( USNM 1003319; RMNH-Coel. 30210); 721/765, three stems up to 65 mm high, with gonothecae ( USNM 1003320; RMNH-Coel. 30211; MNCN 2.03 / 232); 731/1756, one fragment ca 23 mm long ( USNM 1003321); 824/041-1, one stem ca 23 mm high ( USNM 1003322); 833/018-1, one stem ca 130 mm high ( USNM 1003323); SOSC-L26, two stems up to 30 mm high ( USNM 1003324).

Description. Colonies consisting of monosiphonic and unbranched stems up to 130 mm high. Stems typically robust, with strongly developed perisarc ( figure 6 A–E). Hydrocaulus provided with apophyses alternately arranged in one plane, forming two longitudinal rows. Cauline apophyses directed upwards, forming an angle of ca 70 ° with long axis of stem, provided with two nematophores, each emerging through an axillary perisarc hole ( figures 6B, 7B). Stems with occasional nodes or completely without. Cauline apophyses supporting hydrocladia ( figures 6A, 7A); up to thirdorder hydrocladia present ( figure 6A). Node between cauline apophyses and hydrocladia absent ( figure 6B), indistinct or present in smallest stems with little developed perisarc ( figure 7B).

Hydrocladia homomerously divided into hydrothecate internodes each with one hydrotheca and two nematophores ( figures 6 C–E, 7C–J): one mesial superior, emerging through a simple perisarc hole behind free adcauline hydrothecal wall, and one mesial inferior nematophore emerging through a hole on an elevation of internode and provided with a scale-shaped nematotheca. Top of distal hydrocladial internodes truncated.

Hydrotheca elongate, usually situated in middle of internode ( figures 6, 7); sometimes, mainly in proximal part of hydrocladia, on distal half; part of adcauline wall of hydrotheca free. Aperture kidney-shaped and strongly tilted adcaudally. Abcauline wall of hydrotheca basally straight, strongly curving inwards distally.

Female gonothecae present, inserting just below mesial inferior nematophore, fusiform ( figure 6A, F); aperture circular and subterminal. Gonotheca sometimes provided with node or diaphragm at basal fourth.

Remarks. Oswaldella erratum is allied to O. billardi , sharing many features (cf. table 1). They can be distinguished by the larger size of the hydrothecae in O. billardi , in which the length of the abcauline hydrothecal wall may be 350 M m at the first hydrocladial internode and may reach 400 M m at the last. In O. erratum that length may be 240 M m at the first hydrocladial internode, reaching up to 360 M m in the last internodes. Moreover, in O. billardi the hydrocladia are always separated from the cauline apophyses by a distinct node, whereas in O. erratum that node is usually absent or little marked. In O. erratum , the stem is deprived of nodes or has only occasional internodes, whereas in O. billardi the stem usually presents internodes. In O. billardi only secondary hydrocladia are present, whereas in O. erratum there are typically up to third-order hydrocladia.

Ecology and distribution. Oswaldella erratum is a shelf species (Peña Cantero et al., 1997), having been found at depths from 70 ( Billard, 1914) to 696 m (Peña Cantero et al., 1997) on bottoms of mud and sand ( Broch, 1948), mud and pebbles ( Billard, 1914), and on rocky and stony bottoms (Peña Cantero et al., 1997). Our material comes from depths of 55 to 311 m and was found on gravel. It has been found with gonothecae in March (Peña Cantero et al., 1997) and in November ( Billard, 1914); we found fertile colonies in January, February and March.

Oswaldella erratum appears to be endemic to West Antarctica, where it has been recorded from Roosen Channel, Antarctic Peninsula ( Billard, 1914), off Bouvet and Peter I Islands ( Broch, 1948), the South Orkney Islands (Stepan’yants, 1979), Petermann Island (65 ° 10 ∞ S, 64 ° 10 ∞ W; Blanco, 1984) and off the east coast of the Weddell Sea (Peña Cantero et al., 1997). Our material was collected from off Visokoi Island, in the South Sandwich Islands, and from the Antarctic Peninsula region: at the north-east of Joinville Island, west of Renaud Island (Biscoe Islands), off Wiencke and Anvers Islands (Palmer Archipelago) and off Elephant Island.