Halisiphonia nana Stechow, 1921

Marques, Antonio Carlos, Cantero, Alvaro Luis Peña & Migotto, Alvaro Esteves, 2006, Revision of Halisiphonia Allman, 1888 (Cnidaria, Hydrozoa, Hebellidae), with comments on its taxonomic position, Journal of Natural History 40 (17 - 18), pp. 1047-1062 : 1057-1059

Halisiphonia nana Stechow, 1921

( Figure 3 ; Table III)

Halisiphonia nana Stechow 1921, p 227 –228; Stechow 1925, p 452–453, Figure 22; Kramp 1932, p 41; Stepanjants 1979, 56, Plate 9, Figure 10; Blanco 1984, p 273, Figure 7; Blanco, Zamponi and Genzano 1994, p 20–21, Figure 20; Rees and Vervoort 1987, p 34–35; Peña Cantero and Gili 2006.

? Halisiphonia ? nana ; Millard 1977, p 14, Figure 3C .

Material examined

Holotype: Halisiphonia nana Stechow, 1921 ; colony with many hydrothecae and without gonothecae in four slides and alcohol ( ZSM no number).

Additional material

XXI/2 German Antarctic expedition, Bouvet Island, four hydrothecae on Sertularella sp., PS65/029, 25 November 2003, 54 ° 31.599– 54 ° 31.519S, 03 ° 13.059– 03 ° 12.849’E, 377– 365 m, leg. R. V. Polarstern .

Type locality

East of Bouvet Island, South Atlantic, 54 ° 28.79S, 03 ° 309E, 457 m, 28 November 1898, ‘‘Valdivia’’ Expedition Sta. 131 .

Description of holotype

Colony stolonal, with hydrorhiza creeping on spicules of sponges and other material aggregated on a polychaete tube, and on hydrorhiza and hydrocaulus of Eudendrium antarcticum Stechow, 1921 . Hydrorhiza smooth, 0.037 –0.075 mm in diameter. Pedicel smooth, with thin perisarc, without annulations (usually with a constriction at base), 0.040 –0.062 mm wide at base, slightly and progressively widening to base of hydrothecae, merging into it almost imperceptibly. Base of hydrothecae either with or without a thin, almost undetectable membranous diaphragm; few desmocytes present above diaphragm in some hydrothecae. Distance between hydrorhiza and diaphragm 0.195 –0.462 mm. Hydrotheca almost cylindrical, slightly widening towards aperture, 0.352 –0.750 mm long, with thin perisarc and smooth walls; margin entire, slightly flaring, with up to six renovations (though usually without renovations); aperture round, 0.107 –0.162 mm in diameter. Hydrotheca usually slightly curved to one side; aperture perpendicular or slightly inclined to concave side. Without operculum and nematothecae. Hydranth with about 10 filiform tentacles in one whorl; tentacles with rings of nematocysts; hypostome domeshaped. Gonotheca not present.

Nematocysts apparently of one category, rice grain-shaped, on tentacles (6–7X2.0 Mm). Remarks

Halisiphonia nana was redescribed by Stechow (1925) on the same original material, asserting the absence of a diaphragm. Nevertheless, in the holotype of H. nana , which includes plenty of material with well-preserved hydrothecae and hydranths, we found hydrothecae with diaphragm clearly recognizable as a very thin, transversal membrane at the base of the hydrotheca, although it was indistinct or even absent in some. The diaphragm is better seen at its insertion with the hydrothecal wall. Millard (1977, p 14) doubtfully assigned material from off Crozet Island (Indian Ocean) to the species. We agree with Rees and Vervoort (1987, p 31–34) in considering Millard’s record dubious. Besides the absence of ‘‘diaphragm or annular thecal thickening’’, the specimens described by Millard (1977) are larger, with the diameter of the hydrothecae at the margin twice as wide (0.14–0.23 diameter at margin) as H. nana (see above and Table IV). The general dimensions, the everted hydrothecal margin, and the absence of a diaphragm indicate that Millard’s specimens are possibly part of a stolonal, young colony of Lafoea . The absence of gonophores, however, hinders any better conclusion. Blanco (1984) recorded the species from off South Georgia (54 ° 089S, 36 ° 029W, 180 m deep) and also remarked on the absence of a diaphragm or thecal thickening, though her drawing suggests, at least, the presence of desmocytes marking the base of the hydrotheca.

Distribution

The species is known from off Bouvet Island ( Stechow 1921; Peña Cantero and Gili 2006), off South Georgia ( Blanco 1984), and a doubtful record from off Kerguelen ( Millard 1977) at depths varying from 180 ( Blanco 1984) to 457 m ( Stechow 1921).

Figures

Figure 3. Halisiphonia nana Stechow, 1921. (A) Hydrothecae, lateral view; (B) portion of a colony; (C) terminal part of hydrotheca with renovations; (D) base of hydrotheca, showing diaphragm. Scale bars: 250 Mm (A); 125 Mm (B); 100 Mm (C); 25 Mm (D).