Oswaldella incognita Pena Cantero, Svoboda and Vervoort 1997

Oswaldella incognita Peña Cantero, Svoboda and Vervoort, 1997

(figure 11)

Oswaldella incognita Peña Cantero et al., 1997: 367–369, figure 8; Peña Cantero and Vervoort, 1998: 36; Peña Cantero and García Carrascosa, 1999: 212 et seq.; Peña Cantero and Marques, 1999: 85.

Oswaldella antarctica: Peña Cantero, 1991: 168, pls 31, 56, pl. 68 figure a; Peña Cantero and García Carrascosa, 1994: 125, figure 8 a–c; 1995: 96–101, figures 43A–E, 44A–F, 64E.

Material examined. 691/023, one stem ca 35 mm high, with a single hydrocladium (USNM 1003334); 691/27, two stems and one stem fragment up to 80 mm high, with male gonothecae (USNM 1003335; RMNH-Coel. 30216; MNCN 2.03 / 236); 7/484, two stems up to 60 mm high (USNM 1003336); 721/776, one basally broken stem ca 60 mm high, with male gonothecae (USNM 1003337); 721/801, one stem ca 48 mm high (USNM 1003338).

Description. Colonies composed of monosiphonic and unbranched stems (forked in the material from Stn 7 / 484), provided with apophyses alternately arranged in one plane and forming two longitudinal series. Apophyses directed upwards at an angle of ca 45 °. Stem divided into internodes with one apophysis each. Cauline apophyses supporting hydrocladia; up to second-order hydrocladia present (figure 11A). Node separating cauline apophyses and hydrocladia inconspicuous (figure 11B). Cauline apophyses provided with two axillary nematophores, each emerging through an axillary perisarc hole (figure 11B); ‘mamelons’ absent. Top of distal hydrocladial internodes truncated.

Hydrocladia homomerously segmented; internodes each with one hydrotheca and two nematophores (figure 11 C–G): one mesial inferior emerging through a perisarc hole on a slight elevation of the internode and provided with a scale-shaped nematotheca, and one mesial superior emerging through a perisarc hole situated behind the free adcauline hydrothecal wall.

Hydrothecae placed either in middle of hydrocladial internode or on its distal half (figure 11A, C–G). Hydrotheca elongate, with circular aperture slightly tilted adcaudally. Rim even; sometimes with a tiny adcauline elevation. Abcauline wall of hydrotheca slightly convex, or straight; angle with long axis of internode 30 ° or less. Free adcauline hydrothecal wall distinct.

Male gonothecae present, inserted at hydrothecal base on elevation of internode (figure 11A), fusiform, with a subterminal, oval aperture (figure 11A, H).

Remarks. Oswaldella incognita is a well-characterized species, easily recognizable by the unbranched stems divided into internodes, the presence of secondary hydrocladia only, the existence of two axillary nematophores on the cauline apophyses and the shape of the hydrotheca (cf. table 1).

Ecology and distribution. Oswaldella incognita has been found at depths from 234 (Peña Cantero and García Carrascosa, 1995) to 414 m (Peña Cantero et al., 1997); our material comes from 73 to 952 m. Peña Cantero and García Carrascosa (1995) found fertile colonies in January; colonies with gonothecae in our material were collected in January and February.

The species was previously known only from off Elephant Island (Peña Cantero and García Carrascosa, 1995; Peña Cantero et al., 1997). Our material comes from north of the South Orkney Islands, off Brabant Island (Palmer Archipelago), off Deception and Livingston Islands (South Shetland Islands) and off Low Island.