Elysia nisbeti Thompson, 1977

Krug, Patrick J., Vendetti, Jann E. & Valdés, Ángel, 2016, Molecular and morphological systematics of Elysia Risso, 1818 (Heterobranchia: Sacoglossa) from the Caribbean region, Zootaxa 4148 (1), pp. 1-137 : 72-74

Elysia nisbeti Thompson, 1977

( Fig. 41 )

Elysia nisbeti Thompson 1977: 126 , figs. 25b–c, 26d (Type locality: Port Royal mangroves of the Palisadoes, Jamaica) — Valdés et al. 2006: 70 –71.

Type material. Elysia nisbeti— Holotype (BMNH 20070189)

Material examined. Holotype (BMNH 20070189), corresponding to specimen #2364 of T. E. Thompson collection, and BMNH 19774.W in Thompson (1977); collected October 30, 1974. One specimen represented as a headless body, missing pericardial region.

Live animal. No specimens available.

External morphology. Summarized from Thompson (1977): Three specimens ranged from 5.5– 10 mm in length. Body slender, rich green in color; foot pale yellow-green. Rhinophores dark olive-green, sometimes arched backwards over dorsum and held in this position. Dorsal surface of head with conspicuous pale brown blotches forming “Y”-shape extending up rhinophores. Oral lobes shelf-like with dark brown edges and white pustules. Parapodial margin pale brown, thickened, swollen at intervals with white vessicles. Parapodial sides with black specks, retained through preservation ( Fig. 41 A). Rows of low white papillae running along body and up rhinophores.

From our inspection of the holotype: Body lacking head, 5.5 mm wide by 10 mm in length ( Fig. 41 A). Renopericardium extending half of remaining body length as a wide tube. Eight paired dorsal vessels emerging on either side of renopericardium, plus one vessel emerging from the terminus of the renopericardial extension and running straight towards tail ( Fig. 41 B). Vessels bifurcate repeatedly, with side branches sometimes anastomosing. Posterior vessel initially straight, then branching irregularly, with side branches anastomosing with those of posterior-most paired vessels. Parapodial margin densely lined with straight ends of terminal branches.

Internal morphology. Radula (specimen 10 mm long) with 20 smooth teeth and a large number of discarded teeth in ascus, according to Thompson (1977). Tooth drawn with notch at base ( Fig. 41 C), not mentioned in the text or depicted in any other radular figure by Thompson (1977). Penis morphology undescribed.

Reproduction and development. No specimens available.

Host ecology. Thompson (1977) reported collecting E. nisbeti from Caulerpa verticillata growing in drainage channels among mangroves, but no observations of feeding were recorded.

Phylogenetic relationships. No specimens available.

Range. Jamaica ( Thompson 1977), Bermuda ( Valdés et al. 2006; tentative assignment from photographic voucher of missing specimen)

Remarks. This enigmatic species has not been reported since it was described. Live animals did not swim. On the holotype, the renopericardial extension runs halfway along the body; the length of the renopericardium, and the pattern of the dorsal vessel network, are distinct from all known species that could loosely fit the description (e.g., E. velutinus or E. subornata ). A specimen photographed in Bermuda fit well the original description in its external coloration, arrangement and appearance of papillae, and brown “Y”-shaped marking on head flowing into dark rhinophores ( Fig. 41 D); however, this specimen was not available for morphological study.

Figures

FIGURE 41. Elysia nisbeti, external morphology, dorsal vessels and radula. A, Photograph of holotype (BMNH 19774. W), showing dorsal vessels on right inner parapodial surface; holotype lacking head. B, Renopericardium and dorsal vessel network drawn from right side of holotype. C, Drawings of live animal (fig. 25 b, c) and radula (fig. 26 d) reproduced from Thompson (1977). D, Live specimen tentatively identified as E. nisbeti by external morphology, including the distinctive “ Y ” - shaped marking on head; photographed by J. Hamann in Bermuda.