Elysia leucolegnote Jensen, 1990

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 : 29-30

Elysia leucolegnote Jensen, 1990

( Figs. 1–7 )

Material examined. – South China Sea, Hong Kong, inland, south side Starling Inlet , about 22°31'28"N, 114°31'28"E, tens, 11 Mar.2004 ; Near Ting Kok , about 22°28'14"N, 114°13'01"E, tens, 14 Mar.2004 ; Hong Kong, Mai Po Nature Reserve, in mangrove forest along Deep Bay (22°29'52"N, 114°01'48"E), tens, Nov.2007 ; Gulf of Thailand, south of Chumphon at about 1. Parapodia with white or yellowish border, triangular white-yellowish mark on head. No other colours on skin ............................. ................................................................................................................................................................ E. leucolegnote Jensen, 1990 .

–. Parapodia with tens of coloured dots ................................................................................................................................................ 2.

2. Old rose specks over dorsal and ventral sides including foot sole, forming line over dorsal sides of rhinophores .......................... ............................................................................................................................................................... E. singaporensis , new species.

–. No old rose, but white dots on parapodia ........................................................................................................................................ 3.

3. Tips of rhinophores pale or orange. Parapodial border with several orange or reddish glandular dots ............................................. ......................................................................................................................................................... E. bangtawaensis Swennen, 1998 .

–. Tips of rhinophores dark. Mainly white dots on parapodia and body .................................................. E. bengalensis , new species

10°22'20"N, 99°10'26"E, tens, 27 – 29 Mar.2007; Near Don Sak at about 9°18'59"N, 99°45'34"E, and 9°18'10"N, 99°48'08"E, about ten, 2 Oct.2007; Pak Phanang Bay , at about 8°35'37"N, 99°58'23"E and 8°29'19"N, 100°11'33"E, tens, 28-29 Sep.2007, 7, 13 Apr. and 30 Sep.2008; Near Bang Tawa , about 06°51'28"N, 101°09'31"E, tens, 30 Sept.2008; same site, 15, 16 Oct.2009; Andaman Sea Thailand, Ko Libong in mangrove at about 07°14'50"N, 99°26'30"E, tens, 9 Oct.2007; mangrove east of Krabi at about 08°03'17"N, 098°53'57"E, tens, 3 Oct.2010.

Live colouration. – Narrow white line along parapodial borders, often locally widened. Some have few white spots on renopericardial prominence, rarely few white spots on dorsal sides of parapodia. White triangle on head connected with white line over dorsal sides of rhinophores. Tips of rhinophores and often also posterior side of renocardial prominence lack tubules of digestive gland ( Fig. 1 ). Individuals with digestive gland yellowish starting in the central parts have not fed for some months as confirmed in captivity.

External morphology. – Length alive up to 41 mm. Length of renopericardial prominence about three times width. Two major dorsal vessels connected to posterior side ( Fig. 2A ). Renopore in vaginal aperture anterior right of renopericardinal prominence on dorsum ( Fig. 7A ).

Internal characteristics. – Pharynx small, round, ascus on stalk, length 330-350 µm, height without ascus stalk 280-320 µm ( Fig. 3A ). Radular teeth: ascending limb 4-6, descending limb 7-9, ascus 8 to 18 (N= 5). Teeth blade-shaped with upwards curved tips, cutting edges denticulate ( Fig. 4A ). Tooth length up to 63 µm. Oesophagus about 2.8 times length of pharynx. Stomach small compared to intestine ( Fig. 5A ). Green, glandular tissue of digestive gland starts in main branches far from stomach ( Fig. 5A ). Penis unarmed, conical with narrow extension, length 400-500 µm ( Fig. 6A ). Vas deferens convoluted just before entering penis. Gonadal follicles individually connected to ducts.

Biology. – Egg strings up to 55 cm long, irregularly curved, but when substrate allows in wide spirals, with yellow string of extra-capsular yolk in the jelly, single ovum per capsule, 11 March 2004 Starling Inlet, 13 April 2008 Pak Phanang Bay. Some specimens were kept in captivity in separate bottles for several years. One large specimen was collected and stayed alive in captivity for 53 months; three others reached four years then accidentally died. Food source is the tiny, siphonal green alga Boodleopsis c.f. pusilla .

Discussion. – It may be the result of a different treatment of the pharynx, but Jensen (1990) described the descending limb of the radula as attached over its whole length, while my specimens showed the ascus on a partly free stalk ( Fig. 3A ). Jensen (2003) reported that her specimens feed on Boodleopsis pusilla , Cladophora , Cladophoropsis and Enteromorpha in the laboratory. Only Boodleopsis was taken as food in my experiments. Cladophora and Enteromorpha were not touched even when the slugs finally lost size and colour. They started feeding when Boodleopsis was given and then became green again after a few days.

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.