Phascolopsis gouldii
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| Phascolopsis gouldii | |
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| Species: | P. gouldii |
| Binomial name | |
| Phascolopsis gouldii Pourtalés, 1851 | |
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Phascolopsis gouldii is a species of unsegmented benthic marine worm, also known as a peanut worm or star worm.[2] It lives in burrows in muddy sand in shallow waters off North America.
Phascolopsis gouldii can reach thirty centimetres long and is a smooth slender cylindrical shape. The body is pinkish and divided into an anterior introvert and a posterior trunk. The introvert is about one quarter of the length of the body and can be retracted inside it by turning outside in. This is done by the contraction of two pairs of large introvert retractor muscles which extend from the body wall of the trunk to near the mouth which is at the tip of the introvert in the centre of the oral disc. This is surrounded by a ring of short tentacles that are used for feeding and in gas exchange. They are pink inside due to the presence of the pigment hemerythrin used in oxygen transport. The anus is on a small mound where the trunk and introvert join. The trunk is covered by a thick integument and is largely composed of bands of longitudinal muscles which can be seen through the cuticle. The anterior part of the trunk, into which the introvert retracts, is broader than the posterior part.[2]