Oswaldella monomammillata, Peña Cantero & Vervoort, 2004

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 : 842-844

Oswaldella monomammillata sp. nov.

( figure 13; table 4)

Material examined. 12/1002, one stem fragment ca 15 mm long (holotype, USNM 1003342 ) .

Description. Colonies composed apparently of monosiphonic and unbranched stems ( figure 13A). Hydrocaulus provided with apophyses alternately arranged in one plane, forming two longitudinal rows. Cauline apophyses directed upwards, forming an angle of ca 45 ° with long axis of stem and provided with two nematophores ( figure 13 B–D): one axillary emerging through a simple perisarc hole and another emerging through a ‘mamelon’, placed laterally on upper surface of apophysis. Stem divided into internodes; one apophysis per internode. Cauline apophyses supporting hydrocladia ( figure 13 A–C); up to secondary hydrocladia present. A distinct node separates cauline apophysis and hydrocladium.

Hydrocladia homomerously divided into internodes each provided with one hydrotheca and two nematophores ( figure 13E, F): one mesial superior emerging through a simple perisarc hole situated just behind free adcauline hydrothecal wall, and one mesial inferior emerging through a hole situated on a sharp elevation of the internode and provided with a much-reduced nematotheca. Top of distal hydrocladial internodes truncated.

Hydrotheca elongate, placed nearly in the middle of internode ( figure 13E, F). Hydrothecal aperture circular, rim even and more or less perpendicular to long axis of internode. Adcauline hydrothecal wall with a distinct free part. Abcauline wall approximately straight, but sometimes convex basally and with a slight distal concavity.

Gonothecae absent.

Remarks. In spite of the scarcity of material, O. monomammillata sp. nov. is a well-characterized species, clearly distinguishable from the remaining species of the genus (cf. table 1).

Hydrothecae

Length of abcauline wall 200–300

Length of free part of adcauline wall ca 30

Diameter at rim 170–200

Nematothecae

Length ca 20

Internode

Length 740–930

Diameter under hydrotheca 150–175

Oswaldella monomammillata sp. nov. is allied to O. garciacarrascosai in general aspect of the colony and in shape of the hydrothecae (cf. table 1). Differences concern the number of nematophores on the cauline apophyses, since in O. garciacarrascosai there are two axillary nematophores and one ‘mamelon’, whereas in O. monomammillata sp. nov. there is a single axillary nematophore besides the ‘mamelon’. They also differ because in O. garciacarrascosai there is no nematotheca at the mesial inferior nematophore of the hydrocladial internodes, whereas in O. monomammillata sp. nov. there is a much-reduced nematotheca. The hydrothecae in O. garciacarrascosai are also slightly larger; Peña Cantero et al. (1997) reported a length of the abcauline hydrothecal wall of 228–312 M m, whereas in O. monomammillata sp. nov. that length is 240–280 M m.

In the shape of the hydrotheca O. monomammillata sp. nov. also resembles O. delicata , but these species differ in the number of nematophores present on the cauline apophyses (cf. table 1); in O. delicata there is a single axillary nematophore emerging through a perisarc hole, whereas in O. monomammillata sp. nov. there is also a ‘mamelon’. They also differ in the development of the mesial inferior nematotheca, since in O. delicata there is a conspicuous scale-shaped nematotheca, whereas in O. monomammillata sp. nov. that nematotheca is much less developed, being rather inconspicuous. Moreover, in O. monomammillata sp. nov. the hydrocladia are bifurcated but in O. delicata usually unbranched.

Ecology and distribution. Oswaldella monomammillata sp. nov. was collected at 265 m depth off Elephant Island.

Etymology. The specific name monomammillata refers to the presence of a single ‘mamelon’ at the cauline apophysis.

Oswaldella obscura Peña Cantero, Svoboda and Vervoort, 1997 Oswaldella obscura Peña Cantero et al., 1997: 370–373 , figures 9, 15A, B; Peña Cantero and Vervoort, 1998: 36; Peña Cantero and García Carrascosa, 1998: 178; 1999: 214; Peña Cantero and Marques, 1999: 85.

Remarks. Oswaldella obscura is characterized by the polysiphonic and branched stems, the presence of mesial inferior nematothecae in the hydrocladial internodes, the presence of two axillary nematophores and one ‘mamelon’ in the cauline apophyses and the presence of only secondary hydrocladia (cf. table 1).

Ecology and distribution. Oswaldella obscura has been found on muddy bottoms at depths between 260 and 830 m, along the south and east coasts of the Weddell Sea. Fertile colonies were found in January and February. It is used as a substratum by other hydroids (Peña Cantero et al., 1997).