Melithaea cervicornis

(Figs. 5 – 7)

Description. Only a few fragments, totaling 12 cm, of this species were collected (Fig. 5 a, d). The diameter of the largest axis fragment is 3.6 mm, that with the polyps is 1.3 mm. Most fragments have no polyps. About 30 polyps are present. The polyps are mostly retracted into a calyx of 1 – 1.5 mm diameter and 0.5 mm height (Fig. 5 e, f). The axis is typical for the family, with elongate (~ 5 – 12 mm) internodes interrupted by short (~ 1 mm long), golden nodes (Fig. 6 a). The internodes are solid with an exterior layer of elongate stick-like sclerites 0.16 – 0.35 mm in length (Fig. 6 b – d). The nodes are of the same diameter as the internodes and contain numerous short (0.75 – 0.13 mm), smooth rods embedded in a thin organic matrix (Fig 6 e, f). The sclerites of the coenenchyme and calyx (Fig. 7 d, e) are simple, densely tuberculate, somewhat flattened plates or more elongate, tuberculate rods up to 0.4 mm length. No clubs or other complex sclerites typical of the genus Melithaea were found. Sclerites on the upper part of the polyp are long, curved rods or flat rods, up to 0.41 mm in length, arranged in a collaret and points. Those of the points are more tuberculate and shorter (up to 0. 32 mm length) than those of the collaret (Fig. 7 b, c). Tentacle sclerites are flattened tuberculate rods (Fig. 7 a) up to 0.17 mm length. No sclerites were retrieved from the pharynx.

Diagnosis. Colony with irregular branching, axis white, nodes gold-colored. Polyps fully retractable into calyx. Sclerites spindles or flattened spindles with large tubercles.

Remarks. The construction of the axis and nodes is typical of the genus Melithaea. In particular, the small, smooth rods in the node are similar to those seen in other members of the genus. On the other hand, the relative simplicity of the sclerites is uncommon, occurring only in one or a few other Melithaea species. Melithaea cervicornis is most similar to M. modesta from Japan (Matsumoto and Ofwegen, 2015) in the lack of clubs in the calyx and well as the look of the axis and nodes. However, the two species differ in the degree and form of the tuberculation on the sclerites. In M. cervicornis the tubercles are large, rounded, and crowded whereas in M. modesta they are taller, more spine-like, and more widely spaced (the distance between the tubercles being larger than the tubercle diameter). The two species are found in different biogeographic provinces (Watling et al., 2013; Summers and Watling, in press), but could be closely related taxa.

Type specimen. Zoölogisches Museum Amsterdam. Type locality. Siboga Expedition, Station 139, 0 ° 11 ’ S, 127 ° 25 ’ E., in channel between Pulau Bacan and Pulau Laluin in the South Halamahara Regency, Indonesia. Depth, 397 m.