Glaucus Atlanticus


What are Glaucus Atlanticus?

Glaucus atlanticus (common names include the sea swallow, blue angel, blue glaucus, blue dragon, blue sea slug and blue ocean slug) is a species of small, blue sea slug.These sea slugs are pelagic: they float upside down using the surface tension of the water to stay up, where they are carried along by the winds and ocean currents. Glaucus atlanticus is camouflaged: the blue side of their body faces upwards, blending in with the blue of the water. The silver/grey side of the sea slugs faces downwards, blending in with the silvery surface of the sea.

What do they eat?

Glaucus atlanticus feeds on other pelagic creatures, including the venomouscnidarian, the Portuguese man o' war. This sea slug stores stinging nematocystsfrom the cnidarian within its own tissues as defense against predation. Humans handling the slug may receive a very painful and potentially dangerous sting.This species looks similar to, and is closely related to, Glaucus marginatus, which is now understood to be not one species, but a cryptic species complex of four separate species which live in the Indian Ocean and Pacific Ocean.

Some pictures

More facts

At maturity Glaucus atlanticus can be up to 3 centimetres (1.2 in) in length.It is silvery grey on its dorsal side and dark and pale blue ventrally. It has dark blue stripes on its head. It has a tapering body which is flattened, and has six appendages which branch out into rayed, finger-like cerata.With the aid of a gas-filled sac in its stomach, G. atlanticus floats at the surface. Due to the location of the gas sac, this species floats upside down. The upper surface is actually the foot (the underside in other slugs and snail), and this has either a blue or blue-white coloration. The true dorsal surface (carried downwards in G. atlanticus) is completely silver-grey. This coloration is an example of counter shading, which helps protect it from predators that might attack from below and from above.The blue coloration is also thought to reflect harmful UV sunlight.

G. atlanticus preys on other larger pelagic organisms. The sea slugs can move toward prey or mates by using their cerata to make slow swimming movements.They are known to prey on the dangerously venomous Portuguese Man o' WarPhysalia physalis; the by-the-wind-sailor Velella velella; the blue button Porpita porpita; and the violet snail, Janthina janthina. Occasionally, individuals will attack and eat other individuals in captivity.

G. atlanticus is able to feed on Physalia physalis due to its immunity to the venomous nematocysts. The slug consumes the entire organism and appears to select and store the most venomous nematocysts for its own use. The nematocysts are collected in specialized sacs (cnidosacs) at the tip of the animal's cerata, the thin feather-like "fingers" on its body.Because Glaucus concentrates the venom, it can produce a more powerful and deadly sting than the Man o' War upon which it feeds.

Like almost all heterobranchs, Glaucus is a hermaphrodite, having both male and female reproductive organs. Unlike most nudibranchs, which mate with their right sides facing, sea swallows mate with ventral sides facing. After mating, both animals produce egg strings.