---
title: Mercier's Elysia (Elysia mercieri)
scientific_name: Elysia mercieri
common_name: Mercier's Elysia
taxon: Sap-sucking slugs
published: 2026-08-07T16:29:44.234Z
updated: 2026-08-20T17:09:46.300Z
tags: Mercier's Elysia, Elysia mercieri, Sap-sucking slugs, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/invertebrate/molluscs/sap-sucking-slugs/merciers-elysia
---

# Mercier's Elysia (*Elysia mercieri*)

## Quick facts

- **Group:** Sap-sucking slugs (*Sacoglossa*)
- **Size:** up to 4 cm
- **Depth:** 1-20 m
- **Diet:** Herbivore
- **Activity:** Diurnal
- **Rarity:** Rare
- **Habitat:** Green algae on sheltered reef and rubble
- **Reproduction:** Egg layer, Simultaneous hermaphrodite

## How to recognise it

- flaps edged in a fine dark line over a pale border
- body green to gray-green with scattered white flecks
- flaps usually held loosely folded
- length up to 4 cm

A green to gray-green sacoglossan of about 4 cm (1.6 in), its side flaps bordered pale and finished with a fine dark line, the body scattered with white flecks. The flaps are usually carried loosely folded rather than spread, which alters the outline enough to confuse an identification made from a single photograph.

It grazes green algae on sheltered reef and rubble, draining cells one at a time and keeping the chloroplasts. Beyond that the species is barely studied - like many of the smaller sacoglossans it is known mostly from scattered photographic records and a handful of collected specimens, and its full range is a matter of guesswork. That is worth saying plainly rather than filling with what is true of the genus: a slug this small and this green gets recorded when somebody happens to look closely, and nowhere else.

## Also known as

- **Japanese:** キスマークミドリガイ
- **Russian:** Элизия Мерсье

## Scientific synonyms

- *Elysiobranchus mercieri* Pruvot-Fol, 1930

---

*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/invertebrate/molluscs/sap-sucking-slugs/merciers-elysia)*
*Updated: August 20, 2026*