Elysia flava Verrill, 1901

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 : 47-48

Elysia flava Verrill, 1901

( Figs. 6 I, 21–23)

Elysia flava Verrill 1901: 30 , pl. 4, fig. 1 (Type Locality: Castle Harbor at Waterloo, Bermuda) — Pruvot-Fol 1946: 35; Er. Marcus 1957: 414; Thompson 1977: 124 –125, figs. 25a, 26e; Ev. Marcus 1980: 66; Clark 1984: 90 –91, figs. 22–24; Espinosa & Ortea 2001: 44; García et al. 2002: 50, fig. 2G; García et al. 2008: 71; Collin et al. 2005: 690; Espinosa et al. 2005: 56; Valdés et al. 2006: 68 –69; Krug et al. 2015: 990 –991, figs. 3B, 4.

Type material. Elysia flava —untraceable, not at YPMNH.

Material examined. Isla Chimana Grande, Venezuela, July 1989, 3 specimens ( LACM 178625 , LACM 178625 [2 in lot]); Cayo Solarte , Bocas del Toro , Panama, 21 February 2004, 1 specimen ( LACM 2004-9.1 ) ; Piscadera Bay, Curaçao, July 2010, 1 specimen ( LACM 173252 ) .

Live animal. Animals are typically found under rocks during the day and not associated with any specific alga.

External anatomy. Color yellowish-orange, with some conical opaque white papillae on sides and edges of parapodia ( Fig. 21 ). Edges of parapodia with line of opaque white pigment. Some scattered white spots also present on head and rhinophores. In most specimens digestive gland visible through skin as blotches of dark grey or black pigment. Body relatively short, wide and tall. Rhinophores relatively large, rolled, thick, with rounded blunt tips. Parapodia tall, thick, undulated edges when animal is resting and straight when animal is moving. Eyes conspicuously visible.

Renopericardium indistinct from pericardium on preserved specimens. One long pair of posterior dorsal vessels running length of body ( Fig. 22 ). Numerous lateral vessels emerging from each main vessel; side vessels running up side of parapodium, most unbranched but a few forking once or twice.

Internal anatomy. Radula with 18 teeth (LACM 178626), 6 teeth in the ascending limb and 11–12 in the descending limb ( Fig. 23 A). Leading tooth elongate, with a slightly curving cusp tip, bearing a short denticulate keel and at least one smooth lateral edge ( Fig. 23 B). Housing depression for interlocking teeth extending ½ total tooth length ( Fig. 23 A). Base of the tooth approximately ½ total tooth length. Ascus containing jumbled heap of discarded teeth (not figured).

Penis robust and cone-shaped, devoid of armature. Deferent duct long, thin, and convoluted ( Fig. 6 I).

Reproduction and development. No data available.

Host ecology. Little is known about this enigmatic species, with no published data on larval development mode or host alga. In the eastern Atlantic Marín & Ross (1988) found intact chloroplasts in the digestive system possibly of Cladophora sp., suggesting this alga could constitute the diet of E. flava . The sister species E. obtusa (see below) feeds on Bryopsis , which is another potential host alga for E. flava .

Phylogenetic relationships. The sister species of E. flava is the morphologically similar Elysia obtusa Baba, 1938 from the Pacific; these two species form a clade sister to a diverse clade including many Bryopsis -feeding taxa ( Fig. 4 ).

Range. Belize ( Clark & DeFreese 1987), Bermuda ( Verrill 1901; Clark 1984), Brazil ( García et al. 2002, 2008), Costa Rica ( Espinosa & Ortea 2001; Valdés et al. 2006), Cuba (Espinosa et al. 2005), Curaçao (present study), Jamaica ( Thompson 1977), Panama ( Collin et al. 2005), Puerto Rico ( Ev. Marcus 1980), Venezuela ( Valdés et al. 2006), and Mediterranean Sea ( Thompson & Jaklin 1988).

Remarks. Elysia flava is easily recognizable alive by its translucent yellowish color with the dark green branching of the parapodial digestive gland visible though the skin, and the presence of opaque white rounded papillae along the edge of the parapodia.

This species was first described by Verrill (1901) from Bermuda, in the western Atlantic, followed by several records from the Caribbean (see range section). The first eastern Atlantic record was by Thompson & Jaklin (1988) from the eastern Mediterranean. The Pacific species Elysia obtusa Baba, 1938 is very similar externally and has been considered a synonym ( Gosliner et al. 2008). However, Trowbridge et al. (2011) questioned this synonymy based on the geographic range separation between E. obtusa and E. flava . Our molecular phylogenetic analyses confirm that Indo-Pacific specimens of E. obtusa are genetically distinct from E. flava ( Fig. 4 ), and indeed represent a valid species.

Figures

FIGURE 4. Phylogenetic hypothesis for family Plakobranchidae rooted on genus Bosellia (not shown) to illustrate relationships within the genera Elysia, Plakobranchus and Thuridilla. Topology and branch lengths are from Maximum Likelihood analysis of concatenated DNA sequences (2,807 bp total) representing portions of two mitochondrial (COI, 16 S) and two nuclear (H 3, 28 S) genes. Significant support values are given as ML bootstrap percentages (below branch), or BI posterior probabilities (above branch); asterisk = 1.0 or 100 % support. Species discussed in this study are bolded. Triangle denotes presence of a penial stylet.

FIGURE 6. Penial morphology of some species examined. A, Elysia ornata (LACM 178583). B – E, Elysia crispata (LACM 178640) (B); (LACM 178641) (C); (LACM 2004.5.1) (D); (isolate Ecri _ 10 LKS 03) (E). F, Elysia chlorotica (LACM 178597). G – H, Elysia patina (LACM 178650) (G); (LACM 178651) (H). I, Elysia flava (LACM 178626). J, Elysia subornata (LACM 178629). K, Elysia canguzua (LACM 178644). L, Elysia serca (CPIC 00027). M, Elysia evelinae (MZUCR INB 0003312779). N, Elysia velutinus (LACM 178642), O, Elysia papillosa (LACM 178607). P, Elysia cornigera (LACM 173227). Q, Elysia marcusi (LACM 178647), R, Elysia pratensis (CPIC 00068). S, Elysia zuleicae (LACM 178656). Abbreviations: bw, body wall; dd, deferent duct; pe, penis; s, stylet.

FIGURE 21. Elysia flava, external morphology. A, Dark specimen in motion from Young Island, St. Vincent and the Grenadines. B, Dark specimen stationary from Bocas del Toro, Panama (LACM 2004 - 9.1). C, Light specimen stationary from Freeport Harbor, Grand Bahama, Bahamas.

FIGURE 22. Elysia flava, dorsal vessels drawn of a preserved specimen from Venezuala (LACM 178625; 5.5 mm long × 5 mm wide).

FIGURE 23. Elysia flava, SEM of the radula (LACM 178626). A, Radula. B, Leading tooth.