''Pawsonia saxicola'', the sea gherkin, is a species of

sea cucumber Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothuria ...

in the family

Cucumariidae Cucumariidae is a family of sea cucumbers, marine animals with elongated bodies, leathery skins and tentacles that are found on the sea bed. Description Members of the family Cucumariidae are small to medium-sized sea cucumbers, characterised by ...

. It is found in the northeastern Atlantic Ocean and the Mediterranean Sea.

Description

''Pawsonia saxicola'' has a solid, cylindrical body and can grow to a length of . The mouth is at the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

end and is surrounded by a circle of ten, black and white, mottled, branching, tentacles used for feeding, up to long. The cuticle of the body is smooth with five longitudinal rows of tube feet. The ventral rows are double and clearly visible, while the dorsal rows are largely replaced by low button-shaped protuberances, except near the mouth. The cuticle contains calcareous spicules which are star-shaped. This sea cucumber may be confused with ''

Aslia lefevrei ''Aslia lefevrii'' is a species of sea cucumber belonging to the family Cucumariidae Cucumariidae is a family of sea cucumbers, marine animals with elongated bodies, leathery skins and tentacles that are found on the sea bed. Description Memb ...

''. Both live in crevices with their dark-coloured tentacles projecting; ''P. saxicola'' is white, but may darken somewhat when exposed to light, while ''Aslia lefevrei'' is brown.

Distribution and habitat

This sea cucumber is native to the northeastern Atlantic Ocean and the Mediterranean Sea. Its range extends from the west and south coast of the British Isles to the coasts of France, Spain and Portugal and to the Azores. Its habitat is rocky shores where it conceals itself in crevices and under rocks, from the lower shore down to around .

Ecology

''Pawsonia saxicola'' is a

suspension feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

, consuming

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s and single-cell

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

and also zooplankton, such as

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s, ostracods,

protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

ns,

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

s, jellyfish and larvae, as well as drifting organic particles. The food is gathered by the feeding tentacles which each in turn shrinks and bends and is inserted into the mouth; the two ventral tentacles are short and forked, and are used at the mouth to push particles inside. Although in some related species the short tentacles co-ordinate their activities with the longer tentacles, this is not the case in ''P. saxicola'' where they seem to act independently.

References

{{Taxonbar, from=Q2225950 Cucumariidae Fauna of the Atlantic Ocean Fauna of the Mediterranean Sea Animals described in 1871