Oswaldella Stechow 1919

Oswaldella sp. 2

(figure 18)

Material examined. 000AZ, one stem ca 47 mm high, almost without hydrocladia (USNM 1003390); 000DW, six stem fragments up to 100 mm long (USNM 1003391; RMNH-Coel. 30236).

Description. Stems unbranched and apparently monosiphonic. Stem provided with apophyses alternately arranged in one plane, forming two longitudinal series. Cauline apophyses directed upwards, forming an angle of ca 45 ° with longitudinal axis of stem and provided with two axillary nematophores (figure 18B), each one emerging from a simple perisarc hole. Stem divided into internodes, each with one apophysis supporting hydrocladia that are usually bifurcated and have two secondary hydrocladia (figure 18A); third-order hydrocladia are also present. Hydrocladial arrangement symmetrical (figure 18A). A distinct node separating cauline apophyses and hydrocladia (figure 18A, B).

Hydrocladia homomerously divided into hydrothecate internodes with one hydrotheca and two nematophores (figure 18 C–G): one mesial superior emerging from a perisarc hole behind free adcauline hydrothecal wall, and one mesial inferior nematophore provided with a scale-shaped nematotheca, emerging from a perisarc hole in a slight elevation of internode. Top of distal hydrocladial internodes truncated.

Hydrotheca elongate, placed on distal half of internode (figure 18 C–G). Hydrothecal aperture slightly tilted adcaudally, rim circular and even. Adcauline wall with a distinct free portion; abcauline wall almost straight, angle with long axis of internode very acute.

Gonothecae absent.

Remarks. Oswaldella sp. 2 is allied to O. incognita (cf. table 1), sharing the division of the stem into internodes, the presence of two axillary nematophores on the cauline apophyses and the general shape of the hydrothecae. There are, nevertheless, distinct differences, such as the longer hydrocladial internodes and shorter hydrothecae in Oswaldella sp. 2. Also, in Oswaldella sp. 2 the hydrothecae are placed on the distal half of the internodes, whereas in O. incognita they occur approximately in the middle. Finally, in O. incognita only secondary hydrocladia have been reported whereas in Oswaldella sp. 2 third-order hydrocladia have also been observed. These differences, along with the absence of gonothecae in the present material, prevent us from properly evaluating the systematic position of Oswaldella sp. 2.

Ecology and distribution. Oswaldella sp. 2 was found at depths from 18 to 146 m, north of Wilkes Station, at the Budd Coast (Wilkes Land).