Elysia singaporensis, Cornelis & Kees & Swennen, 2011

Cornelis, Kees & Swennen, 2011, Large Mangrove-Dwelling Elysia Species In Asia, With Descriptions Of Two New Species (Gastropoda: Opistobranchia: Sacoglossa), Raffles Bulletin of Zoology 59 (1), pp. 29-37 : 30-32

Elysia singaporensis , new species

( Figs. 1–7 )

Material examined. – HOLOTYPE: 1 ex. (length alive 23 mm)( ZRC, MOL.2974), coll. Singapore, Western Johor Straits , old mangrove forest bordering east side of Sungei Buloh Wetland Park, about 1°26'47"N, 103º43'57"E, 21 May 2002.

PARATYPES: 3 ex. ( ZRC, MOL. 2974) ; 3 ex. ( ZMA, Cat. nr. Moll. 179181), same site and date as holotype .

OTHERS: 22 ex., length alive 20-31 mm, with egg strings, 21 May 2002; same site, 18 Oct.2009, 12 ex. Length alive 15-22 mm, with egg strings.

Etymology. – The species name is derived from the island state of Singapore where the specimens were found.

Live colouration. – Basic colour green from content of digestive gland. Ruddy specks over dorsal and ventral sides including foot sole, forming line over dorsal sides of rhinophores. Tubules of digestive gland lacking in tips of rhinophores and over posterior part of renopericardial prominence ( Fig. 1B ).

External morphology of live specimens. – Length alive up to 31 mm. Eyes not conspicuous, wide apart behind rhinophores; rhinophores with groove over whole length. Lateral groove on right side from anterior border of right parapodium to foot; transversal groove dividing foot into two parts; anterior foot corners slightly extended, bluntly pointed; frontal border can be kept notched, but also smoothly curved; foot behind transverse groove weakly developed. Thin tributaries of digestive gland visible over whole body, missing in tips of rhinophores, over eyes, and sometimes partly above renopericardium. Renopericardial prominence long and narrow, tapering posteriorly, length three to four times width. Renal part posterior of cardial part, about 2/3 of total length, posterior with pair of major dorsal vessels and on each lateral side zero to two vessels, varying in number and position ( Fig. 2B ). Renopore in vaginal aperture on dorsum at anterior right side of pericardium ( Fig. 7B ). Parapodia and body do not bear protuberances. Male aperture below right rhinophore; anus and oviducal apertures close together in upper part of lateral groove.

Internal features. – Pharynx small, ascus on stalk, length 570-760 µm, height without ascus stalk 550 to 630 µm (three 25 mm long specimens) ( Fig. 3B ). Radula with 4 to 7 teeth including ghost teeth in ascending row, 6 to 9 in descending row, few in ascus. Teeth narrow blade-shaped ( Fig. 4B ), used teeth often with slightly incurved tips, finely denticulate cutting edges. Tooth length 140-180 µm. Oesophagus short about as long as pharynx. Relatively massive intestine plicate near anus. Glandular tissue of digestive gland starts in main branches far from stomach ( Fig. 5B ). Penis, unarmed, tapered, ( Fig. 6B ).

Biology. – Egg strings have been found in May and October. Strings had 3–4 ova per capsule, but older string had one veliger per capsule. Yellow extra-capsular yolk, in interrupted line over whole length of string ( Fig.7F, G ). The strings were irregular on algae, but more or less in counter-clockwise, loose spirals on glass in captivity. The longest measured string was 320 mm.

Figures

Fig. 1. The four mangrove Elysia species: A, E. leucolegnote Jensen, 1990; B, E. singaporensis, new species; C, E. bangtawaensis Swennen, 1998; D, E. bengalensis, new species. A and B photographed in-situ, respectively Pak Phanang Bay and Singapore, C and D photographed in captivity. Ab, Bb, Cb, Db group photographed in-situ, respectively Pak Phanang Bay, Singapore, Bangtawa, and Andhra Pradesh (India). D and Db photographed by Dr. S. Bouillon.

Fig. 2. Renopericardial bulbs and attachments of dorsal vessels of: A,: Elysia leucolegnote; B, E. singaporensis, new species; C, E. bangtawaensis; D, E. bengalensis, new species. The highest variation in number of vessels is shown by E. singaporensis. Figures in the bulbs of this species indicate the number of specimens with that pattern found in a sample of 28 individuals.

Fig. 3. Lateral view of the shape of the pharynx: A, Elysia leucolegnote; B, E. singaporensis, new species; C: E. bangtawaensis; D, E. bengalensis, new species.

Fig. 4. Lateral view of the radular teeth: A, Elysia leucolegnote; B, E. singaporensis, new species; C, E. bangtawaensis; D, E. bengalensis, new species.

Fig. 5. Dorsal view of the main parts of the digestive systems: A, E. leucolegnote; B, E. singaporensis; C, E. bangtawaensis. Legend: dg – digestive gland; in – intestine; oe – oesophagus; op – oesophageal pouch; ph – pharynx; st – stomach. Note that two specimens per species were studied for making the drawings. They were collected from the same site and day. When the distribution of the coloured glandular parts is influenced by the feeding condition then the differences do not indicate differences between species.

Fig. 6. Shape of the penis of: A, Elysia leucolegnote; B, E. singaporensis, new species; C, E. bangtawaensis; D, E. bengalensis, new species.

Fig. 7. Position of vaginal apertures in: A, Elysia leucolegnote; B, E. singaporensis, new species; C: E. bangtawaensis; D, E. bengalensis, new species. E, part of an egg string of Elysia leucolegnote showing uninterrupted band of extra-capsular yolk; F, part of an egg string of E. singaporensis showing interrupted band of extra-capsular yolk and more than one ovum per capsule; G, E. singaporensis, new species, producing an egg string in algae in aquarium. Position of vaginal apertures indicated by arrow.