Tuberocaulus Galea, 2019

Galea, Horia R. & Schuchert, Peter, 2019, Some thecate hydroids (Cnidaria: Hydrozoa) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program, European Journal of Taxonomy 562, pp. 1-70 : 53-54

Genus Tuberocaulus Galea , gen. nov.

urn:lsid:zoobank.org:act:317807A0-E2BB-4EBF-9305-9917A818E1E9

Diagnosis

Stems unbranched, strongly fascicled basally, arched downwards distally, and there giving rise to a row of cladia arranged unilaterally; division into internodes indistinct; each equivalent of internode with short, lateral apophysis supporting a cladium, an axillar nematotheca and second nematotheca on opposite side and slightly above; cladia divided into moderately-long internodes, each bearing a hydrotheca distally; the two rows of hydrothecae forming a sharp angle; hydrothecae long, tubular, tapering in lower halves, adnate for a minute portion of their adaxial wall to the internode, aperture with three pointed cusps (one abaxial, two latero-adaxial) separated by deep, rounded embayments, rim thickened. Gonothecae given off laterally from below the hydrothecae; short, club-shaped, aperture subterminal, semi-circular. Perisarc filmy and easily collapsible on both hydro- and gonothecae.

Type species

Thyroscyphus scorpioides Vervoort, 1993 , as Tuberocaulus scorpioides ( Vervoort, 1993) gen. et comb. nov. The genus is currently monotypic.

Etymology

From the Latin ‘ tūbĕr ’, meaning ‘protuberance’, and ‘ caulis ’, meaning ‘stem’, to illustrate the presence of putative nematothecae on stems.

Remarks

The genus Tuberocaulus gen. nov. is monotypic so far and comprises Tuberocaulus scorpioides ( Vervoort, 1993) gen. et comb. nov. This species was originally placed in Thyroscyphus Allman, 1877 on account of the attachment of the hydranth to the inner hydrothecal wall (whose surface is lined by “a sheath of tissue” = mantle) “by means of a circular fold”. However, unlike Thyroscyphus , the hydrotheca of this species is given off from the internode, and it is not borne on a distinct apophysis; additionally, it has a well-defined (though short) adnate adaxial wall, as well as a base (see description above).

The fascicled condition of the stem and its peculiar appearance, the presence of what appears to be stem nematothecae, as well as the unilateral arrangement of cladia and their hydrothecae, are not features shared by the genus of Allman (1877).

The systematic position of T. scorpioides could not be ascertained on morphological grounds alone. Indeed, its long, tubular, tricuspidate hydrothecae superficially recall those of Parascyphus simplex (Lamouroux, 1816) , but in that species, the thecae are borne on distinct stem apophyses, their ‘bases’ are represented by an internal annular thickening of the perisarc, and the marginal cusps adopt a different position (one adaxial and two latero-abaxial cusps, see Galea et al. 2014).

Being fused to the corresponding internodes, the hydrothecae of T. scorpioides are reminiscent of those met with in members of the Sertulariida Maronna et al., 2016 (with only Gonaxia Vervoort, 1993 showing the same position of the marginal cusps), although nematothecae have never been reported in any genus belonging to it.

The relationship of Tuberoscyphus gen. nov. to the other Leptothecata families remains to be investigated by molecular phylogenies. In the absence of such studies for the time being, the genus is left provisionally in the Thyroscyphidae .