Thelepus setosus (Quatrefages, 1865)

Common name(s): Spaghetti worm, shell binder worm

Phylum Annelida
 Class Polychaeta
  Order Terebellida
   Family Terebellidae
Thelepus setosus, about 8 cm long.  The tentacles are white and the gills are red.  The pads on the ventral side of the thoracic segments are visible on the upper side of the first (thoracic) part of the body, and the narrower abdominal segments are coiled to the right.
(Photo by: Dave Cowles, July 2006)
Description:  As with all terebellids, this species is benthic, few if any of the segments are longer than wide, the dorsal surface has no paleae, elytra, or felt, it has no cross-barred capillary setae, it has several long, threadlike, extensile, unbranched filamentlike tentacles closely associated with the mouth and are used in feeding but cannot be retracted into the mouth, the notosetae do not form transverse rows that extend nearly to the dorsal midline, the prostomium does not extend posteriorly as an elongated caruncle, and does not have a distinct caudal region which lacks setae, nor form an operculum.  Terebellids have soft, light-colored pads on the ventral surface of all or most thoracic segments; these secrete the mucus which builds the tube.  The anterior, "thoracic" portion of the body is often larger than the posterior portion.  Thelepus setosus has no proboscislike extension on its peristomium, The uncini, if present in the thoracic segments, are in a single nearly straight row (photo).  The species has 3 pairs of slender, unbranched gills which are not obviously coiled (photo), The capillarynotosetae begin on the 2nd or 3rd gill-bearing segment,  Notosetae are absent from about the last 40 segments.  Length (not including long tentacles) up to 20 cm.

How to Distinguish from Similar Species: Thelepus japonicus has notosetae absent from only about the last 10 segments. Thelepus crispus has uncini on the thoracic segments which curve to form an ellipse.

Geographical Range:  Cosmopolitan:  Pacific, Atlantic, Indian oceans, Mediterranean Sea, Red Sea.  On our area found from British Columbia to southern CA; Japan

Depth Range:  Low intertidal and nearby subtidal.

Habitat:  Lives in a weak tube of encrusted debris under rocks on rocky shores.

Biology/Natural History:  Terebellids build thin, membranous, sand-encrusted tubes in soft mud and sand.  They extend their feeding tentacles from the entrance of the tube like spaghetti over the surface of the nearby sediment.  The tentacles are extended out from the burrow by ciliary creeping and they can be retraced by muscular action.  Mucus and ciliary action on the feeding tentacles transports small organic particles from the sediment to the mouth, especially along a groove along one side (photo).  The tube of Thelepus crispus is usually made of fragments of shell, stone, and other detritus, is nearly 1 cm wide, and is cemented to the undersurface of or between rocks.  It may leave its tube when disturbed and later build a new one.  They circulate water through their burrows.  The major phosphagen in these worms is phosphoarginine; phosphotaurocyamine is also present.  Commensals include the polychaete scaleworms Halosydna brevisetosa, Hololepidella tuta, and Lepidasthenia sp.

There are several genera of terebellids that are difficult to tell apart in the field.  The feeding tentacles of Thelepus has threadlike, unbranched tentacles, and gills of similar length.  Neoamphitrite and Terebella have dark, branching tentacles, which are longer than the gills which are white.  Neoamphitrite has 17 thoracic segments while Terebella has 23 to 28.

Members of Family Terebellidae have special pumping vessels at the base of the gills to actively pump blood through them.

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Dichotomous Keys:
  Kozloff 1987, 1996

General References:
  Morris et al., 1980

Scientific Articles:

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

The tentacles are U-shaped in cross-section, having a large ciliated trough along one side.  Particles can from time to time be seen moving down the trough toward the mouth.

The gillls are curly but not coiled.  The red color is from hemoglobin.

In this closup photo of the thorax, the notopodia with capillarynotosetae can be seen on the left and the neuropodia with the single straight rows of uncini can be seen on the left.
The white filamentous strands are tentacles.  Dorsal is to the left, ventral to the right, anterior is to the top.

Authors and Editors of Page:
Dave Cowles (2006):  Created original page