Halecium dyssymetrum Billard 1929
Creators: name: Galea, Horia R.
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Cnidaria
Hydrozoa
Leptothecata
Haleciidae
Halecium
Halecium dyssymetrum

description: Halecium dyssymetrum Billard, 1929
(fig. 3K, L)
Halecium dyssymetrum Billard, 1929: 307, fig. 1C.― Leloup, 1935: 8, fig. 1.―Millard, 1975: 150, fig. 48H, J.― Migotto, 1996: 32, fig. 7D–F.― Watson, 1996: 79, tab. 1.― Watson, 1997: 514, fig. 4A, B.― Watson, 2000: 9, fig. 6. Endothecium dyssymetrum ― Calder, 1991: 14, figs 6, 7.
Sagamihydra dyssymetra ― Calder & Kirkendale, 2005: 482.
Material examined. Stn.13: 0 3.12.2009, 10 m—three sterile stems, to 7 mm high, on Sertularella diaphana (Allman, 1885), morphotype 2.
Remarks. For descriptions of this species, see Calder (1991) and Migotto (1996).
Bouillon (1985) regarded Endothecium Fraser, 1935 as congeneric with Halecium Oken, 1815. Some authors (e.g. Calder 1991; Calder & Kirkendale 2005) recognized Sagamihydra Hirohito, 1995 (= Endothecium Fraser, 1935) as valid, on the account of the origin of gonophores, the presence of large nematocysts, and the likely existence of an intertentacular web.
However, gonothecae arising (sometimes not exclusively) from within the hydrothecal lumen are not uncommon within the genus, e.g. H. arcticum Ronowicz & Schuchert, 2007; H. cymiforme Allman, 1888 (see Galea et al. 2009); H. fragile Hodgson, 1950 (see Watson & Vervoort 2001); H. inhacae Millard, 1958; H. interpolatum Ritchie, 1907 (see Watson 2008); H. lankesteri (Bourne, 1890) (see Schuchert 2005); H. liouvillei Billard, 1934 (see Ramil et al. 1998).
The gonothecae of H. dyssymetrum, and the nominal species Endothecium reduplicatum Fraser, 1935, and E. paucinodum Fraser, 1947 share a quite unusual morphology among the haleciids. The ova of both E. reduplicatum and H. dyssymetrum are externally held in acrocysts (see Hirohito 1995 and Migotto 1996, respectively). On the other hand, the occurrence of an intertentacular web is rather uncommon in haleciids exclusive of Mitrocomium Haeckel, 1879, and it is certain for H. dyssymetrum (Calder 1991; Migotto 1996) and E. reduplicatum (see Hirohito 1995). Conversely, the presence of large nematocysts in these species does not seem particularly unusual.
Migotto (1996) showed that the capsules were holotrichous isorhizas in specimens of H. dyssymetrum from Brazil. In the present material none is discharged; they occur abundantly in the hydranth body, but also in the tentacular region, and their relationship with the intertentacular web could not be confidently ascertained, the latter being barely apparent in the rather contracted hydranths examined. According to A.E. Migotto (pers. comm.), the capsules are only scattered in the hydranth body and gonophore, and absent from the intertentacular web.
No information is presently available concerning the nematocyst type of E. reduplicatum, but Calder (1991) regarded them, with a query, as haplonemes.
Holotrichous isorhizas are now recognized to occur in other Halecium species, as for instance in H. fjordlandicum Galea, 2007 2. In this case, the capsules are organized in a belt around the hydranth body. No intertentacular web is reported in this species, and its gonothecae are unknown.
Taken together, these scanty data suggest that the distinction between Halecium and Endothecium is presently too vague to allow a confident separation. Accumulation of additional data on cnidome composition is necessary, as well as the study of living hydranths to detect the presence of a putative intertentacular web.
Caribbean records. Caribbean coast of Panama (Calder & Kirkendale 2005, as Sagamihydra dyssymetra).
World distribution. Indonesia (Billard 1929), Dry Tortugas (Leloup 1935), off Mozambique (Millard 1975), Bermuda (Calder 1991), Brazil (Migotto 1996), Australia (Watson 1996, 1997, 2000).
description: Published as part of Galea, Horia R., 2010, Additional shallow-water thecate hydroids (Cnidaria: Hydrozoa) from Guadeloupe and Les Saintes, French Lesser Antilles, pp. 1-40 in Zootaxa 2570 on pages 10-11, DOI: 10.5281/zenodo.197380