Glaucilla marginata is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of small, floating, blue sea slug

Slug

Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...

; a pelagic aolid nudibranch

Nudibranch

A nudibranch is a member of what is now a taxonomic clade, and what was previously a suborder, of soft-bodied, marine gastropod mollusks which shed their shell after their larval stage. They are noted for their often extraordinary colors and striking forms...

; a marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

  opisthobranch gastropod mollusk in the family Glaucidae

Glaucidae

Glaucidae is a taxonomic family of colorful sea slugs. These are specifically aeolid nudibranchs. They are marine gastropod molluscs in the superfamily Aeolidioidea.-Genera and species:Genera and species within the family Glaucidae include:...

.

Distribution

This species is pelagic, and like many other pelagic species, it can be found worldwide.

Habitat

These small nudibranchs float upside down on the surface tension

Surface tension

Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 in temperate and tropical seas.

Description

This nudibranch is dark blue, and in many ways it resembles a smaller version of Glaucus atlanticus

Glaucus atlanticus

Glaucus atlanticus is a species of small-sized blue sea slug, a pelagic aeolid nudibranch, a marine gastropod mollusk in the family Glaucidae...

. However, in this species the cerata

Cerata

Cerata are anatomical structures found in nudibranch sea slugs, marine opisthobranch gastropod mollusks.They are dorsal and lateral outgrowths on the upper surfaces of the body....

(saw teeth on the skin) are arranged in a single row in each arch, while in Glaucilla there are multiple rows.