''Themiste pyroides'' is a

species In biology, a species is the basic unit of Taxonomy (biology), 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 ...

of unsegmented benthic marine worm in the phylum

Sipuncula The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of unsegmented marine annelid worms. The name ''Sipuncula'' is from the genus name '' Sipunculus'', and comes from the Latin ...

, the peanut worms. It occurs in the intertidal zone and shallow water in the western Atlantic Ocean and the northeastern Pacific Ocean. It lives in crevices and under rocks, extending its "crown" of branching tentacles into the surrounding water to feed.

Description

''Themiste pyroides'' is a large peanut worm. It has a cylindrical or spindle-shaped body and an extensible introvert at the tip of which is an elaborate "crown" of branching

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s. The cuticle is covered by tiny papillae but seems smooth. The introvert is longer than the body and is fully retractable into the body. The crown consists of six dichotomously branching tentacles surrounding the mouth, the branches bearing pinnules, used by the worm for

filter feeding 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 feedi ...

(most sipunculids are deposit feeders). The body is yellowish-brown to dark brown, the collar (region of the introvert just below the crown) is smooth and blotched with violet, the tentacles are similarly coloured and the pinnules contain specks of purple pigment. In its fully retracted state, this sipunculid resembles the shape of a

peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible Seed, seeds. It is widely grown in the tropics and subtropics, important to both small ...

kernel, giving the peanut worms their common name.

Distribution and habitat

''Themiste pyroides'' is found in the northeastern Pacific Ocean, in the waters around Japan, Alaska, the United States and Mexico, and in the western Atlantic Ocean. It conceals itself, living in cracks in the rock, under stones and boulders, in clusters of

bivalve molluscs Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biva ...

and among the rhizomes of ''

Phyllospadix iwatensis ''Phyllospadix iwatensis'' is a plant species found along the seacoasts of Japan, Korea, China (Hebei, Liaoning, Shandong), and the Russian Far East (Sakhalin, Primorye and the Kuril Islands). It was first discovered in 1929 near on the Miyak ...

''. It occurs from 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 ...

down to about .

Ecology

The breeding behaviour in this species is unusual in that

swarming Swarm behaviour, or swarming, is a collective behaviour exhibited by entities, particularly animals, of similar size which aggregate together, perhaps milling about the same spot or perhaps moving ''en masse'' or migrating in some direction. ...

occurs; adult males and females congregate among the rocks forming dense masses before releasing their

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

s into the water. After fertilisation, the embryos develop into

trochophore A trochophore (; also spelled trocophore) is a type of free-swimming planktonic marine larva with several bands of cilia. By moving their cilia rapidly, they make a water eddy, to control their movement, and to bring their food closer, to captur ...

larvae. These drift in the

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

, before settling on the seabed and undergoing metamorphosis into juvenile worms.

References

{{Taxonbar, from=Q2262460 Sipunculans Fauna of the Atlantic Ocean Fauna of the Pacific Ocean Animals described in 1919