''Hermissenda opalescens'' 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 appropriate s ...

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 time ...

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 gastropod mollusc 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 Taxonomy (biology), taxonomic family (biology), family of colorful sea slugs. These are specifically aeolid nudibranchs. They are marine (ocean), marine gastropod molluscs.Bouchet, P. (2012). Facelinidae. Accessed through: W ...

.Lindsay, T. & Valdés, Á. (2016
''The Model Organism ''Hermissenda crassicornis'' (Gastropoda: Heterobranchia) Is a Species Complex.''
PLoS ONE 11(4): e0154265. This species is commonly known as the "opalescent sea slug."

Distribution

This nudibranch was described from

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United State ...

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 ...

, United States. It has been reported from Northern California, to

Punta Eugenia Punta Eugenia is a headland in the Mulegé Municipality. It marks the Western tip of the Vizcaíno Peninsula, thus being the westernmost point on the mainland of the state of Baja California Sur. It belongs to the larger area of El Vizcaíno Bio ...

, Mexico. Its distribution overlaps with ''

Hermissenda crassicornis ''Hermissenda crassicornis'', also known as the opalescent nudibranch or thick-horned nudibranch, is a species of brightly coloured, sea slug or nudibranch, a marine gastropod mollusc in the family Facelinidae.Rosenberg, G. (2011)''Hermissenda cr ...

'' in Northern California and this latter species is found north to

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.S. ...

. These two species were routinely treated as a single species during the last 90 years.O'Donoghue, C. H. 1922. ''Notes on the taxonomy of nudibranchiate Mollusca from the Pacific coast of North America. I. On the identification of ''Cavolina'' (i.e. ''Hermissenda'') ''crassicornis'' of Eschscholtz.'' Nautilus 35(3):74-77. The species has also been observed in

Bahia de los Angeles Bahia ( , , ; meaning "bay") is one of the 26 states of Brazil, located in the Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo, Minas Gerais, and Rio de Janeiro) and the 5th-larges ...

Gulf of California The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja C ...

Habitat

This sea slug 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 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 environmen ...

Description

The species grows to be about 50 mm, or about 2 inches. This slug has been treated as a model organism and used in studies into classical conditioning, memory consolidation and associative learning, the structure of neural circuits and neural physiology. It has also been used to investigate ultrastructure and anatomy, larval and reproductive ecology, behavioral ecology and pharmacology and toxicology including studies into

Beta thymosins Beta thymosins are a family of proteins which have in common a sequence of about 40 amino acids similar to the small protein thymosin β4. They are found almost exclusively in multicellular animals. Thymosin β4 was originally obtained from the ...

. Unfortunately these studies did not differentiate between the three species of ''Hermissenda''.

Life habits

This nudibranch feeds on

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds ...

and other marine organisms such as

ascidian Ascidiacea, commonly known as the ascidians, tunicates (in part), and sea squirts (in part), is a polyphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" m ...

s 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 is host to the ectoparasites '' Halicyclops thysanotus'' Wilson C.B., 1935 and '' Hemicyclops thysanotus ''Wilson C.B., 1935.

References

External links

* {{Taxonbar, from=Q25000955 Facelinidae Western North American coastal fauna Marine fauna of the Gulf of California Gastropods described in 1863