''Hermissenda crassicornis'', also known as the opalescent nudibranch or thick-horned nudibranch, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of brightly coloured,

sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary tim ...

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...

, a

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Facelinidae The Facelinidae are a taxonomic family of colorful sea slugs. These are specifically aeolid nudibranchs. They are marine gastropod molluscs.Bouchet, P. (2012). Facelinidae. Accessed through: World Register of Marine Species at http://www.marines ...

.Rosenberg, G. (2011)
''Hermissenda crassicornis'' (Eschscholtz, 1831).
Accessed through: World Register of Marine Species on 2012-06-03

Distribution

This nudibranch lives from Kodiak Island,

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...

, to Northern

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

. It is replaced by '' Hermissenda opalescens'' to the south of Northern California.

Habitat

This species is found in various

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s, including the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species ...

of rocky shores, but also in bays and

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...

Description

The species grows to be about 50 mm, or about 2 inches. The colour of this nudibranch varies from one locality to another, but it is always easily recognizable by the orange stripe along its head area and the white stripes on the cerata.Thomas, C., 2007 (Apr 4
''Colour variation in ''Hermissenda crassicornis''.''
essage inSea Slug Forum. Australian Museum, Sydney.

Life habits

This nudibranch feeds on hydroids and other marine organisms such as ascidians and

sea anemones Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, ...

. It sometimes attacks other nudibranchs, and will eat smaller specimens of its own species. It's also been known to eat sea pens, small crustaceans, and stranded jellies.

References

* {{Taxonbar, from=Q522625 Facelinidae Western North American coastal fauna Molluscs of North America Gastropods described in 1831 Taxa named by Johann Friedrich von Eschscholtz