Oswaldella bifurca ( Hartlaub, 1904 )

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 : 816-818

Oswaldella bifurca ( Hartlaub, 1904)

( figure 1)

Schizotricha bifurca Hartlaub, 1904: 16 , pl. 3 figures 4–8.

Oswaldella bifurca: Stechow, 1919: 852 ; 1920: 40 (32); Peña Cantero et al., 1997: 345–349, figures 1, 13A; Peña Cantero and García Carrascosa, 1998: 179; 1999: 214; Peña Cantero and Vervoort, 1998: 36; Peña Cantero and Marques, 1999: 85.

Not Oswaldella bifurca: Naumov and Stepan’yants, 1962: 98; Stepan’yants, 1979: 112, pl. 21 figure 4; Blanco, 1984: 43, pl. 39 figures 89, 90, pl. 40 figures 91–93, pl. 41 figure 94.

Not Oswaldella bifurca: Totton, 1930: 208 , figure 50 (= Oswaldella tottoni Peña Cantero and Vervoort, 1996 ).

Not Oswaldella bifurca: Peña Cantero, 1991: 175–179 , pl. 32; Peña Cantero and García Carrascosa, 1994: 125–126, figure 8 d–f; 1995: 101–104, figure 45A–E (= Oswaldella grandis Peña Cantero, Svoboda and Vervoort, 1997 ).

Not Oswaldella bifurca: Millard, 1977: 40 , figure 12 a–c (=? Ventromma sp.).

Material examined. 27/1924, one stem ca 40 mm high ( USNM 1003297); 27/1951, one fragmented stem (largest fragment ca 20 mm long) ( USNM 1003298); 32/1995, several stem fragments up to 20 mm long, with gonothecae ( USNM 1003299; RMNH-Coel. 30201); 32/1996, three stem fragments up to 17 mm long ( USNM 1003300); 32/2021, two stem fragments up to 5 mm long in bad condition ( USNM 1003301); 32/2095, numerous stems up to 60 mm high, with gonothecae ( USNM 1003302; RMNH-Coel. 30202; MNCN 2.03 / 230); 32/2128, three fragments and stems up to 42 mm high ( USNM 1003303).

Description. Colonies composed of monosiphonic, unbranched (occasionally branched) stems up to 60 mm high. Stem divided into internodes with one or two apophyses per internode, slightly geniculate. Apophyses alternately arranged in one plane, forming two longitudinal series, slightly directed upwards, forming an angle of ca 70–80 °. Cauline apophyses usually provided with one, sometimes two (27 / 1924, 32 / 2095, 32 / 1996 in part), axillary nematophores, but deprived of ‘mamelons’ ( figure 1 A–C). Cauline apophyses supporting hydrocladia ( figure 1A), usually without node in between (present in 27 / 1924). Hydrocladia up to fourth order present. Hydrocladial branching symmetrical ( figure 1A): first hydrocladial internode bifurcated, with two prongs of equal development ( figure 1B, C), and giving rise to two secondary hydrocladia, each one with some third-order hydrocladia. These, occasionally, forming fourth-order hydrocladia. Hydrocladia basally following angle of cauline apophyses, but distally curving strongly upwards.

Hydrocladia homomerously divided into hydrothecate internodes, provided with one hydrotheca and two nematophores ( figure 1 D–J): one mesial superior nematophore emerging through a perisarc hole situated at the end of adcauline hydrothecal wall and one mesial inferior nematophore emerging through a perisarc hole in a strongly marked elevation of internode (angle between long axis of hydrocladial internode and steep wall of infrathecal elevation usually ca 90 °, though sometimes less). Without mesial inferior nematotheca. Top of distal hydrocladial internodes pointed ( figure 1D, E, H).

Hydrotheca low, placed on basal half or third of hydrocladial internode, adcauline wall fully adnate ( figure 1 D–J). Rim either even, and then hydrothecal aperture circular, or uneven with frontally depressed hydrothecal aperture due to presence of two slightly raised lateral lobes.

Immature gonothecae present, inserting close to mesial inferior nematophore. Gonotheca cone-shaped, distally truncated ( figure 1K).

Remarks. Number of axillary nematophores on the cauline apophyses variable; even on the same stem we have observed apophyses bearing two and apophyses with a single axillary nematophore. There is a tendency, therefore, for the fusion of the two holes into one ( figure 1B, C).

Ecology and distribution. Oswaldella bifurca is a deep-water species, having been found from 450 to 640 m depth (Peña Cantero et al., 1997); our material comes from 342 to 1610 m depth. It has been found with gonothecae in November ( Hartlaub, 1904) and February (Peña Cantero et al., 1997); our colonies with immature gonothecae were found in January and February. It is used as a substratum by other hydroids ( Eudendrium sp., Filellum sp.).

Hitherto Oswaldella bifurca was only known from West Antarctica, being recorded at 70 ° 20 ∞ S–83 ° 23 ∞ W, in the Bellingshausen Sea ( Hartlaub, 1904), and off the south coast of the Weddell Sea ( Peña Cantero et al., 1997). Our material, however, comes from East Antarctica, where it was found at the central basin of the Ross Sea and off Victoria Land [Pennell Bank, east of Cape Hallett, off Cape Adare and off Buckle Island (Balleny Islands)] .