Elysia bengalensis, 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 : 35

Elysia bengalensis , new species

( Figs. 1–7 )

Material examined. – HOLOTYPE: 1 ex. (length alive 43 mm) ( ZRC. MOL.2972), Bay of Bengal, Andhra Pradesh, delta of Godovari River about 20 km south of Kãkinãda , between 16°43'N, 16°52'N and 82°15'E, 82°22'E, May 2001, coll. Steven Bouillon.

PARATYPES: 2 ex. ( ZRC. MOL.2973), same site and date as holotype .

OTHERS: about 7 specimens internally rotten, same site and date as holotype.

Etymology. – The species name is derived from the Bay of Bengal into which the Godovari River discharges.

Live colouration. – Basic colour green from content of digestive gland. Irregular row of larger white spots along parapodial border. Conspicuous white specks irregularly spaced all over dorsal and ventral sides, not on foot sole. Tips of rhinophores and vaginal aperture dark coloured. Dark remains visible on both areas in specimens stored in 70% ethanol or 6% formaldehyde for five years.

External appearance. – Length alive up to 50 mm. Rhinophores with groove over whole length. Parapodia and body smooth. Anterior foot corners slightly extended, bluntly pointed. Renocardial prominence oval, length less than twice width; pair of major dorsal vessels on posterior side of prominence; one to four smaller vessels on each lateral side ( Fig. 2D ). Renopore could not be detected in available material. Male aperture below right rhinophore; anus and oviducal apertures close together in upper part of lateral groove. Vaginal aperture on ventral side of right parapodium near anterior border as in E. bangtawaensis , but black marked (Fig. D).

Internal characteristics. – Pharynx small, length about 380 µm, with strong dorsal septate muscle, ascus vestigial. Radula with 7 teeth in ascending row, 10–11 in descending row, and bundle of about 15 worn teeth in ascus. Length of radular teeth 68–80 µm (two individuals). Teeth bladeshaped, blade about 38% of total length, 20-35 denticles on cutting edge ( Fig. 4D ). Shape of blade slightly differs from E. bangtawaensis , but has fewer and larger denticles. Penis unarmed, conical ( Fig. 6D ).

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.