Oswaldella blanconae El Beshbeeshy 1991

Oswaldella blanconae El Beshbeeshy, 1991

(figure 3)

Oswaldella blanconae El Beshbeeshy, 1991: 263, 265; Peña Cantero et al., 1997: 344; Peña Cantero and García Carrascosa, 1998: 179; 1999: 214; Peña Cantero and Vervoort, 1998: 36; Peña Cantero and Marques, 1999: 85.

Oswaldella antarctica: Blanco, 1984: 41, pl. 38 figures 86–88.

Material examined. 32/1996, one stem ca 8 mm high (USNM 1003307).

Description. Stem monosiphonic, unbranched (figure 3A), provided with apophyses alternately arranged in two longitudinal rows. Stem divided into internodes each with one apophysis, internodes arranged in zigzag fashion; stem internodes with bifurcation at origin of cauline apophysis. Angle between long axis of cauline internode and apophyses wider than 45 °; angle between cauline apophyses and succeeding cauline internode ca 90 ° (figure 3A). Cauline apophyses provided with two nematophores: one emerging through a hole in perisarc of axil (figure 3B) and another nematophore emerging through a ‘mamelon’ situated laterally on dorsal side of apophysis (figure 3C). Distinct node present between cauline apophyses and hydrocladia (figure 3C). Hydrocladia undivided or bifurcated (figure 3A); up to secondary hydrocladia present; arrangement always symmetrical. Hydrocladia homomerous; all internodes hydrothecate; distal internodes apically truncated.

Hydrocladial internodes provided with one hydrotheca and two nematophores (figure 3B, D–G): one mesial superior emerging through a perisarc hole situated behind free portion of adcauline hydrothecal wall and one mesial inferior, deprived of nematotheca, emerging through a perisarc hole situated on a strongly marked elevation of internode (angle between long axis of hydrocladial internode and steep slope of infrathecal elevation almost 90 °).

Hydrothecae placed on basal half or basal third of hydrocladial internodes (figure 3), shallow; aperture circular and either perpendicular to longitudinal axis of internode or slightly tilted downwards; rim even. Adcauline wall of hydrotheca with conspicuous free portion, abcauline wall straight, running smoothly into wall of internode; angle with long axis of internode ca 45 °.

Gonothecae absent.

Remarks. Oswaldella blanconae is a rare species, hitherto only recorded by Blanco (1984). It is a distinctive species, characterized by hydrotheca placed on basal half or third of the internode, the absence of mesial inferior nematothecae (although a nematophore is present), the shape of the hydrotheca, the presence of one ‘mamelon’ besides the axillary nematophore on the cauline apophyses, and the arrangement of cauline internodes.

Ecology and distribution. Oswaldella blanconae appears to have a circum-Antarctic distribution. The only previous record was from off Low Island, in West Antarctica, at a depth of 90–100 m (Blanco, 1984). Our material comes from east of Cape Hallett (Victoria Land), in the Ross Sea region, where was collected between 344 and 351 m depth.