Elysia  pusilla   (Bergh, 1871)

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This species has been observed on Reunion, Mayotte and Madagascar Islands

Order : Sacoglossa
Superfamily : Plakobranchoidea
Family : Plakobranchidae
Distribution : Indo-West Pacific
Maximal size : 30 mm
Abundance :

Species characteristics :

The body is very compact, bright green to dark green with various among of white speckling, especially on the head and parapodial margins.

The short rolled rhinophores are mottled with beige

Elysiella pusilla
Showing species characteristics...

Photo Eva Fontaine
Mayotte, Mtsanga Mtiti Sada, less 1 m, on Halimeda, 30 Jully 2010, size : 4-5 mm

See more about : Sightening and mating periods

Remarks :

Identification confirmed by Kathe Jensen
    According Kathe Jensen : "The Elysia pusilla are on Halimeda. Halimeda has calcareous encrustations below the top layer of utricles, and is composed of small segments attached by only a narrow bundle of filaments. As for the name, E. pusilla was originally described as Elysiella pusilla by Bergh in 1871/1872, and in my publications I have retained this name. However, phylogenetic analyses have placed the species in the middle of other Elysia species, and so these authors have changed the name. However, I think that probably the genus Elysia will have to be split into several genera when more species have been thoroughly examined, and therefore I would like to keep the name Elysiella".
    Synonymous : (according Worms)
               - Elysia halimedae Macnae, 1954                         - Elysiella pusilla Bergh, 1871

Bibliographic data :

The body shape of living animals of this species is extremely variable depending on the size of the animal and on whether it is actively crawling or sitting still
    When living on Halimeda with broad flattened segments, the slugs are very flattened, especially the larger individuals, but on Halimeda with cylindrical segments, the animals match the cylindrical shape of the plant
    This species is always well camouflaged, matching the colour of the part of the Halimeda plant on which it is living. Smaller specimens are usually a uniform bright green and are found on the smaller uniformly green growing segments of the plant. Larger animals can have the same mottled appearance as the larger more heavily calcified older segments of Halimeda
    The characteristic, white, zig-zag feedind scars left on the thallus of Halimeda by E. pusilla are immediately noticeable.

References :

Bill Rudman Seaslug site : Sea Slug Forum : Elysiella pusilla
   Philippines seaslug Elysia pusilla

Publications :

Bergh, L.S.R. (1872). Malacologische Untersuchungen. In: C.G. Semper, Reisen im Archipel der Philippinen, Wissenschaftliche Resultate. Band 2, Heft 3 : 137-176, Pls. 17-20.
    Händeler K. & Wägele H. (2007) Preliminary study on molecular phylogeny of Sacoglossa and a compilation of their food organisms. Bonner Zoologische Beiträge 55: 231-254.
    Jensen, K.R. (1992). Anatomy of some Indo-Pacific Elysiidae (Opisthobranchia: Sacoglossa [=Ascoglossa]), with a discussion of the generic division and phylogeny. Mal. Soc. London, 58 : 257-96
    Paul, V.J. & van Alstyne, K.L. (1988) Use of ingested algal diterpenoids by Elysiella halimedae Macnae (Opisthobranchia: Ascoglossa) as antipredator defenses. Journal of Experimental Marine Biology and Ecology, 119 : 15-29.
    Silva, P.C., Basson, P.W. & Moe, R.L. (1996). Catalogue of the benthic marine algae of the Indian Ocean. University of California Publications in Botany 79: 1-1259.

Other photos of Elysia pusilla :

Alain-Benoît Rassat

Madagascar, Nosy bé, 26 July 2017



Like some specimen in Philippines seaslug Elysia pusilla

Philibert Bidgrain

Mayotte, N'gouja, on the reef flat zone, less 1 m, 1 October 2011, size : 12 mm


Two specimens with tree spawns... on Halimeda sp


A spawning behavior

In this specimen the white speckling coloration in more important...

Photo Eva Fontaine
Mayotte, Mtsanga Mboueanatsa, less 1 m, 29 Jully 2010, size : 3-4 mm

This species is always well camouflaged... on its algae

Philibert Bidgrain


Mayotte, Mtsanga Guini, on the reef flat zone, less 1 m, 3 August 2010, size : 7 mm

Photo Eva Fontaine

Mayotte, Mtsanga Mboueanatsa, less 1 m, 27 Jully 2010, size : 1-2 mm


Only the head for this decapitated specimen... Who is the predator ????



Philibert Bidgrain


Mayotte, Mtsanga Guini, on the reef flat zone, less 1 m, 7 August 2010, size : 10-12 mm

A large specimen with a very rare white speckling...

Alain-Benoît Rassat


Madagascar, la licorne, Nosy bé, 14 m, 1 November 2013, size : 10 mm


A strange coloration...

 More photos from Indian Ocean

Reunion, Elysiella pusilla on Halimeda, at Etang salé, by Christophe Cadet

Madagascar, Elysiella pusilla, at Nosy bé, by Philibert Bidgrain