Nephasoma (Nephasoma) rimicola (Gibbs, 1973)
This species is the only one in the genus with hooks arranged in several rings. The trunk has smooth and lustrous skin without prominent papillae. The oral disk has a circle of flattened tentacles surrounding the mouth, and a lobed nuchal organ. The transition from introvert to trunk is not sharply marked and the introvert tapers gradually towards its tip. A pair of nephridiopores opens anteriorly to the anus.
West Reef, Wembury (Gibbs, 1973).
(From Gibbs, 1973)
A large specimen with 65 mm long is deposited in the British Museum (Natural History) under the registration number 1972.9.1. A series of 25 paratypes specimens, measuring 15-65 mm in length, are deposited in the same Museum under registration number 1972.9.2-26. Additional material has been deposited in the collection of the National Museum of Ireland, Dublin, and the Zoological Museum of the University of Bergen.
Skin smooth without prominent papillae. Hooks arranged in rings behind the tentacles.
(From Gibbs, 1973)
Introvert shorter than the trunk. Transition from introvert to trunk is not sharply marked and the introvert tapers gradually towards its tip.
Hooks arranged in rings. The anterior rings are normally complete but the posterior ones often have many hooks missing. The largest hook measured 75 µm height.
The trunk is 1.5-3.0 mm in width, slender and cylindrical.
Tentacular crown consists of a single circle of slender, flattened tentacles around the mouth. The tentacles are grouped in pairs and arranged. In worms longer than 20 mm, the number of tentacles varies from 12-20, but normally there are 16.
The nuchal organ is divided by shallow longitudinal grooves into five main lobes.
The trunk wall has a continuous longitudinal muscle.
Two ventral retractor muscles are attached to the body wall in the anterior half of the body. In extended worms the point of attachment lies between two-fifths and halfway along the length of the body, and about one-fifth of the distance between the anus, and the posterior end of the trunk.
Spindle muscle extends through the intestinal coil and is not attached to the posterior end.
There are no fixing muscles attaching the gut to the trunk wall.
A small caecum is present on the rectum.
A pair of free nephridia opens posterior to the anus.
A pair of reddish eyespots is embedded in the brain, and they are visible through the introvert wall.
The majority of the worms measure 25-50 mm in total length (introvert extended), and the largest are 65 mm long (Gibbs, 1973).
The array of hooks, the distinct tentacles and the nephridiopores posterior to the anus differentiate N. rimicola from its congener species N. minutum.
Ecology and Distribution
This species was found in intertidal waters in southwestern England, northern Spain, and the southern coast of Florida. Off southern Spain it was collected in deep water (350-720 m).
Habitat and Ecology
In southwestern England and northern Spain this species was found in muddy sand with fine shell gravel filling rock crevices (Gibbs, 1973 and Saiz Salinas, 1986). In deep water off southern Spain it was found in sediment composed of mollusk shells, foraminiferans or pteropods (Saiz Salinas, 1990). In Florida the specimens were found in coquina rubble.
Four miles off Fort Pierce Inlet, Florida, N. rimicola is found in coquina rubble with the following sipunculans species: Aspidosiphon albus, A. parvulus, A. fisheri, A. sp., Nephasoma pellucidum, Antillesoma antillarum.
This species was first described by Gibbs (1973) from southwestern England based on a collection of more than 200 specimens.