Order :  SACOGLOSSA (=sapsucker)
Superfamily : Elysioidea
Family : Elysiidae and Plakobranchidae
Superfamily : Limapontioidea
Family : Caliphyllidae
Family : Limapontiidae
Superfamily : Oxynoidea
Family : Oxynoidae and Volvatellidae

The most obvious characteristic distinguishing them ( externally) from other nudibranchs are the two rolled rhinophores on the head.

Some have flamboyant colours, others are all green (similar to their seaweed hosts) and many show extraordinary body filamentation for such small creatures.

Exept three species (abscent from Reunion island), all sacoglossans are herbivorous and possess a radula with a single tooth per row which is used for piercing algal cells and sucking out their liquid contents.

Most sacoglossan groups are associated with green algae of the genus Caulerpa

Dissociated chloroplasts from the prey may be retained and "farmed” in the cells of the digestive gland, persisting in Tridachia crispata for up to 6 weeks (Trench, 1969). It's a remarkabIe temporary endosymbiosis.

Sacoglossans are variable in form and may have a bulloid external shell (Volvatella, Oxynoe ) or may entirely lack a shell as an adult (Elysia). Some of the most unusual sacoglossans are the "bivalved gastropods". However, it has since been demonstrated that the larval stage has a typically coiled gastropod shell and that the bivalved condition has evolved secondarlly.


Family : The Elysiidae    Forbes & Hanley, 1851

The Elysiidae are shell-less, slender, elongate animals.

Laterally the body is expanded by a pair of flat, wing-like parapodia that are usually folded up on the dorsal side, meeting mediodorsally in a more or less wavy line.

On the dorsal surface is a system of variably branching vessels ("veins", "gill lamellae") which enter the pericardial prominence located mediodorsally behind the head.

Genus : Elysia   Risso, 1818

Body and mantle :

The genus Elysia has a distinct head with slender, dorsal rhinophores.

The colour is usually varying shades of green, but melanistic species do occur. Also, the parapodial margins may have strongly coloured bands or spots, and spots of varying size and colour may be distributed over the body,

The parapodia range in size from narrow folds, barely covering the dorsal body surface to extremely large, strongly "waving wings".

The anus is located anteriorly on the right side, as in Thuridilla

The pericardial prominence may be short, or have an elongate renal extension. The dorsal vessels usually ranch extensively, sometimes anastomosing distally.

sacoglossa : elysia

Photo : E. ornata

Branching vessels in Elysia sp1

in Elysia sp1

Genus : Thuridilla   Bergh, 1872

Body and mantle :

The rhinophores are large and always rolled. Their bases almost meet mediodorsally on the head.

Body coloration is usually striking. Most often the ground colour is dark, black, brown or purple. Bands or spots of bright red, orange, yellow, iridescent blue or green occur in various patterns.

The parapodia meet medio­dorsally in a smooth line.

The tail is usually rounded.

The anus is located anteriorly on the right side, as in Elysia.


sacoglossa : Thuridilla

Photo : T. moebii

Family : Limapontiidae    Gray, 1847

Genus : Ercolania   Trinchese, 1872

Ercolania is a distinct genus that is characterized by the following features :
              - presence of cerata (a), which are round in cross-section;
              - digitiform rhinophores (b);
              - elongate or inconspicuous reno-pericardial prominence,
              - presence of sabot-shaped teeth,
              - presence of a curved penial stylet,
              - probable absence of albumen gland in the cerata.

Family : Caliphyllidae Thiele, 1912

Members of the family have the back covered in leaf-like cerata

Presence of rolled oral tentacles and rhinophores, the latter bifid (bifurcated rhinophores) at the tips with eyes at the base

Genus : Cyerce   Bergh, 1871

Body and mantle :

In Cyerce the digestive gland reaches only into the basal ceratal stalk

The sole of the foot has a transverse groove behind the head

Photo : Cerata and sole foot from Cyerce elegans

Genus : Polybranchia    Pease, 1860

polybranchia orirentalis

Body and mantle :

In Polybranchia the leaf-like cerata contain fine branching digestive gland ducts

The sole of the foot hasn't a transverse groove behind the head

Photo : cerata and foot sole from Polybranchia orientalis