The fourline nudibranch, Polycera quadrilineata, 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 dorid

Doridacea

Doridacea is a taxonomic grouping of dorid nudibranchs, shell-less marine gastropod mollusks. included in the clade Euctenidiacea of the clade Nudibranchia.- Taxonomy :*Superfamily Doridoidea**Family Dorididae**Family Actinocyclidae...

 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...

. It is 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...

 gastropod mollusc in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Polyceridae

Polyceridae

Polyceridae is a taxonomic family of sea slugs, dorid nudibranchs, marine gastropod mollusks within the Superfamily Polyceroidea.- Taxonomy :...

.

Distribution

This species is found off the South African coast from the Atlantic coast of the Cape Peninsula to Algoa Bay. It is found from the intertidal zone

Intertidal zone

The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...

 to 20 m.

Description

The fourline nudibranch is a smooth-bodied variably coloured nudibranch. The ground colour is white or grey and there are usually black, yellow or orange stripes longitudinally along the notum

Notum

The notum is the dorsal portion of an insect's thoracic segment. It is typically a single large sclerite. It can be further divided into the alinotum which bears the wings and the postnotum which bears the phragma....

, though these can be absent. The head has six yellow projections. The gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s and rhinophore

Rhinophore

A rhinophore is one of a pair of club-shaped structures which are the most prominent part of the external head anatomy of a group of sea slugs, marine gastropod opisthobranch mollusks in the order Nudibranchia, the nudibranchs, specifically the dorid nudibranchs.- Etymology :The name relates to the...

s are black, and may be spotted with yellow. Alongside the gills is a pair of yellow projections. The animal may reach 20mm in total length. It is distinguished from the crowned nudibranch

Crowned nudibranch

The crowned nudibranch, Polycera capensis, is a species of dorid nudibranch. It is a marine gastropod mollusc in the family Polyceridae.-Distribution:...

in having raised yellow spots on the mid-dorsal region.