Glaucus atlanticus

Glaucus atlanticus Forster, 1777


This is a bluish-purple nudibranch with a white underside. It resembles most nudibranchs. The elongated, flattened body is up to 3 cm long. The papillae (up to 84 in number) are placed in four or three pairs of clusters (Glaucus atlanticus). It lives in the pleuston of all oceans.

Taxonomic Description

The naked body is elongate and flat. The head is small and blunt. It has a pair of small oral tentacles near the mouth and a pair of extremely small rhinophores on the dorsal side. There are four or three pairs of clusters of papillae (cerata) placed on peduncles on the lateral side of the body. The papillae are placed in a single row (uniseriate), their may be 84 in total. The genital pore is on the ventral side at the right; the renal pore is on the right dorsal side between the first and second cluster of papillae; the anus is dorso-laterally at the right between the second and third pair of papillae. The penis is armed with a chitinous spine. The foot is flat and slender, at the ventral side; the metapodium is long. The body is deep bluish-purple ventrally (= upperside in living animals) the dorsal side is silvery white. The radula formula is 0-1-0 (Glaucus atlanticus radula).
Body length up to 43 mm.


A special description is not available.


This species is hermaphroditic. The eggs are 60-75 µm wide and 75-97 µm long. Eggs are laid in straight strings up to 17.5 mm long. At 19°C, division of the eggs starts after some hours. After 48-60 hours a trochophore is formed and after three days a veliger with larval shell (first ovoid, is coiled at the day 11 after hatching) leaves the egg string.


This species is carnivorous and lives in the pleuston where it feeds on Velella, Porpita and Physalia. The nematocysts of Physalia pass unharmed through the digestive system and are used as defence system in the papillae, this is an example of oplophagia (Donati and Porfirio (1986).

Practical Importance

As this species can use the stinging nematocysts of its prey animals it can be harmful to humans.


This species occurs in the tropical waters of all oceans, see the Glaucus atlanticus map.