Elysia buonoi, Krug, Patrick J., Vendetti, Jann E. & Valdés, Ángel, 2016

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 : 120-122

Elysia buonoi new species

( Figs. 56 A, 73–74)

Elysia cf. zuleicae— Krug et al. 2015: 990, fig. 3B

Type material. San Salvador, Bahamas, July 2007, (Holotype LACM 3315 , Paratype LACM 3316 ), collected by PJK.

Type locality. San Salvador, Bahamas

Material examined. Bahamas: San Salvador, July 2004, 2 specimens (isolate Ebuo_04Ssal02, isolate Ebuo_04Ssal03), July 2007, 2 specimens (Holotype LACM 3315 , Paratype LACM 3316 ) .

Live animal. No data available; live specimens were among a bulk collection of E. zuleicae from Udotea , and were not initially recognized as distinct by external morphology.

External anatomy. Four preserved specimens examined, similar in general shape to E. zuleicae . Preserved holotype specimen ~ 3.5 mm long, and 3.8 mm across at widest point of parapodia when flattened; paratype ~ 3.7 mm in length ( Fig. 73 ). Scattered brown spots along inner parapodial surface. Smooth parapodial margin. Large rounded pericardium; no dorsal vessels evident ( Fig. 73 A, C). No extended tail visible on any specimens.

Internal anatomy. Radula with 21 teeth (LACM 3316), 8 teeth in ascending limb and 13 in descending limb ( Fig. 74 A). Leading tooth narrow and elongate with approximately 50 small denticles on cusp ( Fig. 74 B). Teeth without the typical “V”-shaped depression of many other elysiids. Instead, teeth overlapping slightly with their tips resting on lateral side of adjacent teeth. Base of the tooth thickened, tall, and elongate, about ½ total tooth length.

Penis elongate with kink in distal end and tapering into a conical apex, devoid of armature ( Fig. 56 A, Fig. 74 C). Deferent duct long, narrow, and highly convoluted.

Reproduction and development. No data available.

Host ecology. Found on Udotea flabellum together with specimens of the more common species, E. zuleicae .

Phylogenetic relationships. Elysia buonoi n. sp. was detected in a population-genetic study of E. zuleicae , its sister species; the two taxa were minimally 10.2% divergent at COI, above our initial threshold for species delimitation, and were recovered as a distinct species by ABGD analysis of COI data ( Figs. 3 A, 4). The four Bahamas specimens also shared distinctive alleles at the nuclear H3 locus that were not sampled in any population of E. zuleicae , and were distinguished from all E. zuleicae alleles by a fixed difference at position 34 of the 328-bp fragment amplified (G for E. buonoi n. sp., A for E. zuleicae ) (Trathen 2010; authors’ unpublished data).

Range. Known only from San Salvador Island, Bahamas.

Etymology. Named in honor of Thomas Buono, for profoundly deepening PJK’s appreciation of marine life at many unforgettable family dinners.

Remarks. Further work integrating molecular data with morphological and developmental characters is needed to more fully describe E. buonoi n. sp., known only from a single Bahamas island. Elysia buonoi n. sp. closely resembles its sister species E. zuleicae , but may be distinguished by the absence of an extended tail and penial stylet in E. buonoi ; moreover, the two species differ genetically at both mitochondrial and nuclear loci. The COI distance between E. buonoi n. sp. and E. zuleicae exceeds the threshold gap proposed for delimiting species of Elysia (Krug et al. 2013) . Distinctive alleles and a fixed difference at the nuclear H3 locus distinguished sympatric specimens from San Salvador, indicating E. buonoi n. sp. does not interbreed with E. zuleicae when they co-occur. The combined divergence at COI and H3 support recognition of E. buonoi n. sp. as a distinct species. The radular morphology of E. zuleicae and E. buonoi n. sp. is virtually undistinguishable, both having radular teeth with small denticles, curved cusps and a thickened base. Both dissected specimens of E. buonoi n. sp. lacked a penial stylet, whereas most specimens of E. zuleicae possess a scoop-shaped stylet. Although additional specimens must be examined to confirm that a penial stylet is always absent in E. buonoi n. sp., differences in penial armature could result in reproductive isolation, and thus explain how sympatric sister species avoid interbreeding when they cooccur.

Ortea, Caballer, Moro & Espinosa in Ortea et al. (2005) described E. deborahae as similar to E. zuleicae but lacking a tail, while having a lighter coloration, a penial stylet, and subtly different radular tooth morphology. In contrast to E. deborahae , our specimens of E. buonoi n. sp. lacked a penial stylet. Furthermore, radular teeth were described as smooth in E. deborahae , whereas the teeth of E. buonoi n. sp. are finely denticulate. The radula of E. buonoi n. sp. also does not match the description of the radula in E. deborahae , in which the maximum height was attained after the edge of the base, and fewer teeth were present in the descending limb. We could not determine the living color of E. buonoi n. sp., as our specimens were preserved, but no specimens collected from San Salvador, Bahamas matched the description of external coloration given for E. deborahae . Thus, we conclude that E. buonoi n. sp. is not conspecific with E. deborahae Ortea, Espinosa & Moro, 2005 .

Figures

FIGURE 3. Mismatch distributions based on TrN-corrected pairwise distances at the COI locus for three subclades of Elysia. Based on ABGD analysis, genetic distances were classified as intra-specific (white bars) or inter-specific (black bars). Dashed horizontal line indicates the a priori threshold distance used provisionally to delimit candidate species.

FIGURE 56. Penial morphology of some species examined. A, Elysia buonoi n. sp. (LACM 178675) B, Elysia orientalis (CPIC 00842). C, Elysia ellenae (LACM 178663). D, Elysia pawliki n. sp. (LACM 3303). E, Elysia christinae n. sp. (LACM 3309). F, Elysia zemi n. sp. (LACM 3307). G, Elysia taino n. sp. (LACM 178607). H, Elysia hamanni n. sp. (LACM 178667). Abbreviations: dd, deferent duct; pe, penis; s, stylet.

FIGURE 73. Elysia buonoi n. sp., external morphology of preserved type specimens. A, Dorsal view of preserved holotype (LACM 3315); body 3.5 mm long × 3.8 mm wide at widest part of parapodia. B, Ventral view of preserved holotype. C, Dorsal view of preserved paratype (LACM 3316); body length = 3.7 mm.

FIGURE 74. Elysia buonoi n. sp., SEM of the radula and penis. A, Radula (LACM 3316). B, Leading tooth (LACM 3316). C, Penis (LACM 3315).