Halisiphonia Allman, 1888

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 : 1048-1049

Genus Halisiphonia Allman, 1888

Halisiphonia Allman 1888, p 30 –31; Stepanjants 1979, p 55.

Type species: Halisiphonia megalotheca Allman, 1888 , by monotypy.

Diagnosis

Colonies stolonal with creeping hydrorhiza. Hydrothecae tubular or slightly conical, deep, borne on pedicels of varied length; pedicels arising singly from hydrorhiza and almost imperceptibly merging into hydrothecae; diaphragm present, though inconspicuous in some hydrothecae, thin and membranous. Operculum and nematophores absent.

Gonangia developing medusae. Gonothecae solitary, laterally compressed, pedicellate, arising from hydrorhiza.

Remarks

Allman (1888, p 30) established the genus Halisiphonia based on H. megalotheca (see Allman 1888, p 31, Plate 16, Figure 1, 1a ), a species he thought lacking a diaphragm, and of which he stated the hydrothecal cavity was ‘‘directly continuous with that of the peduncle or stolon’’. Therefore, since its erection, the presence of a diaphragm is generally not mentioned in the diagnosis of Halisiphonia species. Halisiphonia nana Stechow, 1921 was also described as lacking a diaphragm ( Stechow 1921, p 228; 1925, p 452, Figure 22). In both cases, however, the diaphragm was originally overlooked: for H. megalotheca the presence of a diaphragm was confirmed by Billard (1910, p 5), who examined the holotype; for H. nana , we found a very thin, membranous diaphragm, although it was indistinct or even absent in some hydrothecae. Kramp (1932, p 40) comments: ‘‘a diaphragm may be more or less distinctly developed or altogether lacking in this genus’’. Indeed, Kramp (1937, 1956) described two other species of Halisiphonia , H. arctica and H. galatheae , respectively, in which he recognized a diaphragm. For the former, the diaphragm is stated as being ‘‘a very delicate membrane with a central opening’’ ( Kramp 1937, p 38), whereas for the latter, it was said that ‘‘a very slight internal thickening may sometimes indicate the base of the hydrotheca, and in a few cases an extremely delicate diaphragm may be discerned’’ ( Kramp 1956, p 17). Similarly, Vervoort (1966, p 121, for H. galatheae ) states, ‘‘in some thecae there is an extremely delicate membrane basally of the place of attachment, in some theca present as a hollowed meniscus, in others as a tight membrane. It may represent a very thin diaphragm’’. Bouillon (1985) regarded the feature as present in only some species and Calder (1991, p 31) implied the existence of a diaphragm or annular thickening for Hebellinae (his rank), including Halisiphonia .

The inconspicuousness of the diaphragm makes some of the Halisiphonia species superficially resemble stolonal colonies of Lafoea , a genus usually characterized by erect colonies (occasionally stolonal, see Calder 1991, p 36) and gonothecae aggregated into coppinia. Lafoeids with coppinia are included within the subfamilies Lafoeinae A. Agassiz, 1865 and Zygophylacinae Quelch, 1885, although the genus Cryptolarella , with single gonothecae, is exceptionally included among the Eulafoeinae [sic] sensu Bouillon (1985) (cf. Marques et al. 2005). In the past, lafoeids with solitary gonophores were assigned to the subfamily Hebellinae Fraser, 1912 . The subfamily Hebellinae has been raised to family level (e.g. Schuchert 2001, 2003), and kept separate from the Lafoeidae , a hypothesis corroborated by the presence of medusa buds in the gonothecae of H. arctica ( Schuchert 2001) ; an opinion with which we concur.

In H. arctica , H. galatheae , and H. megalotheca the gonotheca is spatulate, being round or pear-shaped in frontal view, strongly compressed in lateral view, truncated distally, and attached to the hydrorhiza by a short pedicel (see below). However, according to the original description and single record, H. spongicola ( Haeckel 1889, p 77, Plate 4, Figure 9) has gonotheca ‘‘not compressed or spatuliform, with a slit-shaped opening; their transverse section and the distal opening are circular’’. Nonetheless, the frontal outline of its gonotheca seems similar to those of the other Halisiphonia .

The gonothecal profile of Halisiphonia recalls that of Hebella and Scandia , two genera assigned to the family Hebellidae (plus Bedotella , see Marques et al. 2004, 2006); in Halisiphonia and Bedotella , however, the gonotheca is strongly laterally compressed.

Figures

Figure 1. Halisiphonia arctica Kramp, 1932. (A) Hydrotheca, lateral view; (B) portion of a colony; (C) hydrothecal diaphragm; (D) base of hydrotheca showing desmocytes; (E) gonothecae, lateral view. Scale bars: 200 Mm (A); 1.0 mm (B); 25 Mm (C); 100 Mm (D); 500 Mm (E).