Cladocarpus asymmetricus Galea 2020, sp. nov.

Cladocarpus asymmetricus sp. nov.

urn:lsid:zoobank.org:act: 765A957F-FEF6-47A6-B09A-314F31F0440E

Figs 1 D–E, 4; Table 1

Cladocarpus with lightly fascicled, unbranched stems divided into fairly long internodes, each with 2–3 frontal nematothecae, a mamelon and an axillar nematotheca. Cladia close to one another. Cormidia with up to 7 intranodal, adaxial septa. Hydrothecae elongated, asymmetrical in frontal view, with two lateral transverse ridges projecting into the lumen, rim with 9 rounded cusps. Phylactocarps given off from first cormidium, gonothecae concrescent with the rachis basally, crescent-shaped, with three types of nematothecae on both body and apex.

From the Latin ‘ ăsymmĕtĕr, -tra, -trum ’, meaning ‘asymmetrical’, with reference to the shape of the hydrotheca in frontal view.

Material examined

Holotype

PACIFIC OCEAN • 1 single plume, ca 8.5 cm high, hydrorhiza missing; off New Caledonia, stn DW4979; 19°42ʹ S, 158°37ʹ E; 315– 295 m; 9 Sep. 2017; KANADEEP leg.; MNHN-IK-2015-530.

Colony erect, at least 8.5 cm high, hydrorhiza missing. Stem unbranched, fairly fascicled, accessory tubes forming a beam around the main tube; no deeply-cut, proximal, oblique nodes; elsewhere division into internodes indistinct, except for distalmost, monosiphonic part, with thinner perisarc, where transverse nodes (165–180 µm wide) delimit rather long (820–1030 µm) internodes composed of 2–3 (occasionally 4) proximal nematothecae in a row, a lateral cladial apophysis with its associated conical nematotheca (with rounded, apical aperture), and an axillar nematotheca rather lateral to the apophysis; dorsal axillar nematotheca absent; all stem nematothecae sac-shaped, adnate for ⅔ of their length, with apical, guttershaped aperture facing adaxially; each accessory tube of the stem with a row of saccate, deeply immersed nematothecae, with only their ovoid apertures slightly protruding from the perisarc. Cladial apophyses alternate along the stem, ending distally in a deeply oblique node; cladia close to one another, up to 1.9 cm long, divided into rather long internodes (1025–1090 µm) by means of slight, transverse (115– 120 µm wide) constrictions of the perisarc, each accommodating a hydrotheca and its 3 nematothecae: one mesial and a pair of laterals flanking the aperture. Hydrotheca elongated, 895–950 µm deep, slightly compressed laterally below the rim, with straight adaxial and slightly curved abaxial walls, with an intrathecal septum given off from the lower ¼ of the adaxial wall, and projecting for a short distance into the lumen; in frontal view, lower part of hydrotheca asymmetrical, due to the presence of two conspicuous, semicircular, intrathecal plates given off at two different levels from the lateral walls; free edges slightly overlapping in the middle of the lumen; in a lateral view of the hydrotheca, the attachment sites of these septa are distinctly sigmoid. Mesial nematotheca long, tubular, adnate for about ¾ its length, leaving distally a short (90–95 µm), gutter-shaped aperture; lateral nematothecae short (195–200 µm), tubular, tapering towards the distal aperture, the latter with deeply scooped margin on adaxial side. Hydrothecal aperture 300–305 µm wide, rim with 9 cusps: one median, abaxial with squared outline, and 4 pairs of laterals, the latter triangular in shape, with rounded tips, becoming gradually lower and wider towards the adaxial side of the theca; up to 7 intranodal septa, all given off from the adaxial wall of the hydrothecae and projecting for a relatively short distance into the lumen of the internode; of these, 2 cusps are given off from the adaxial thecal wall below the intrahydrothecal septum, while up to 5 others from above it. Phylactocarp given off laterally from first cormidium, borne on distinct, athecate apophysis with distal, oblique node; phylactocarp up to 6 mm long, composed of a slightly geniculate rachis divided into up to 20 short (250–305 µm) internodes by means of slightly-marked, transverse nodes; each internode with a proximal nematotheca, a basally concrescent gonotheca, and a second nematotheca lateral to its insertion (both nematothecae elongated, with scooped rims adaxially); the proximalmost internode has an extra proximal nematotheca. Gonothecae crescent-shaped in lateral view, ca 850 × 250 µm, those with curvature on one side alternating with those curved oppositely from the other side; circular in transverse section, tapering gently below and gradually above to form a pointed apex bearing a nematotheca with scooped rim; two dissimilar nematothecae, placed at nearly the same level on the adaxial side of the thecal wall, at about ⅓ of the length above from the insertion of the gonotheca on the rachis: one nematotheca is conical, with thick walls and has a small, slightly scooped aperture, while the other is barrel-shaped, with thin walls and has a broad, circular aperture with entire margin; upper third of the adaxial gonothecal wall with 1 (occasionally 2) sac-shaped nematotheca(e) with scooped rim on adaxial side.

The relationships between several related aglaopheniid genera, viz. Cladocarpus Allman, 1874, Aglaophenopsis Fewkes, 1881, Streptocaulus Allman, 1883 and Nematophorus Broch, 1918, have been discussed and interpreted by a number of authors (e.g., Ramil & Vervoort 1992a; Ansín Agís et al. 2001; Altuna et al. 2013) on the account of morphological characters alone. To these should be added other genera, such as Carpocladus Vervoort & Watson, 2003, Cladocarpoides Bogle, 1984 and Wanglaophenia Vervoort & Watson, 2003, that make the case even more complex and, taken globally, it becomes evident that only a genetic study can be expected to clarify their relationships objectively.

The present hydroid, as well as Cladocarpus partitus sp. nov. and C. pennatus sp. nov. (see below), have gonosomes that do not conform accurately to any diagnosis of the abovementioned genera, displaying only some of their characters, as well as additional, distinctive ones. For this reason, these three new species are provisionally accommodated in the genus Cladocarpus, the oldest available name, pending a future phylogenetic study based on molecular markers.

A few congeners have hydrothecae resembling those of C. asymmetricus sp. nov., notably with respect to their elongated appearance and the presence of two lateral, oblique, intrathecal ridges. Their distinctive features are summarized in Table 1.

The new species is also highly distinctive in that its gonothecae are provided with nematothecae, a situation unknown in any of the Cladocarpus -like species described so far. Moreover, these nematothecae have three different morphologies and are present at different positions on the gonotheca.

Known only from its type locality, off New Caledonia (present study).