''Aspidosiphon muelleri'' is a species of unsegmented benthic marine worm in the class

Sipuncula The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of marine annelid worms, that have secondarily lost their segmentation. Sipuncula was once considered a phylum of unsegmented ...

, the peanut worms. This worm is found in the eastern Atlantic Ocean, the Mediterranean Sea and in various locations in the Indo-Pacific region at depths down to about .

Description

''Aspidosiphon muelleri'' has a cylindrical trunk and a narrower, cylindrical introvert at the front end which can retract back into the trunk. The oral disc is at the tip of the introvert; this has a terminal mouth and a cluster of ten to twelve short

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 arranged in a crescent surrounding a nuchal organ. The introvert bears rings of tiny hooks at the front, and larger, more irregularly-placed hooks at the rear. At the front of the trunk is an anal shield and this acts as an operculum when the introvert is retracted. At the posterior of the trunk is the caudal shield; both it and the anal shield are rough and

chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...

ised, with radial grooves and edged by wart-like papillae. This worm can grow to a length of . The shields are dark in colour while the trunk is pale in small individuals, darkening to dark brown or blackish as they grow.

Distribution and habitat

''Aspidosiphon muelleri'' occurs in the Mediterranean Sea and the eastern Atlantic Ocean, its range extending from the Shetland Islands to West Africa. It is also found in scattered locations in the Indo-Pacific. Its depth range is from the lower part of the

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

down to about . It often occupies empty

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

tusk shell Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class (biology), class of shelled Marine life, marine inve ...

s, or resides in serpulid tubes, holes or crevices, or among the branches of

coralline algae Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of re ...

or the deepwater coral '' Lophelia pertusa''. In Australia it is reported as being an obligate

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

inside solitary, free-living corals such as '' Heterocyathus aequicostatus'' and ''

Heteropsammia cochlea ''Heteropsammia cochlea'', also known as walking dendro, is a species of small solitary coral in the family Dendrophylliidae that is native to the Indo-Pacific area. Description This small solitary free-living coral, not more than 2.5 cm a ...

''.

Ecology

This peanut worm reproduces sexually, females becoming mature when about long. In the western Mediterranean Sea, the number of individuals build up over the summer months, with spawning taking place in August and September, when the sea temperature is nearing its maximum. After that, the number of individuals reduce again, likely because of the energy put into reproduction. When these worms occupy the tubes of polychaete worms, a small bivalve mollusc '' Epilepton clarkiae'' is often found living in association with them.

References

{{Taxonbar, from=Q2805576 Sipunculans Animals described in 1851