Guam Shell Club - Terebellum terebellum (Linné, 1758)

GASTROPODA : SERAPHSIDAE

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Terebellum terebellum Linné, 1758

Above: Color form lineatum. Length: 29.3mm, Width: 8.4mm, Height: 7.2mm. Scuba, approximately 90 ft, buried in sand. Agat Bay, Guam. Collected by Steve Norby in April 2005.

Left: An unusual color form. Length: 30.2mm, Width: 8.6mm, Height: 7.5mm. Found while fanning inside a sand pit, at 80 ft. Agana Bay, Guam. Collected by Bob Abela on 22 May 06.

Right: Color form punctulorum. I believe this specimen was also from relatively deep water, again buried in sand. Pago Bay, Guam. Collected by Steve Norby in September 2003.

Distribution: Indo-West Pacific.
Habitat: Cryptic, buried, either in sand pockets along the reef or over open sandy expanses.
Availability: Common on Guam.
Size: Guam specimens typically between 25 - 40 mm
Comments: The genus has traditionally been placed within the family Strombidae, though it has been reassigned to the family Seraphsidae. T. terebellum is the only living member.

Discussion:

Of the Guam specimens observed: The foot is creamy white; probiscus and eyestalk markings tend to vary in shades of brown or red, pattern varying as mottling, spotting, or banding. The eye pattern appears constant with a black center, outlined by a yellow ring, outlined by a red 'star.' The shell is typically the color form nebulosum; lineatum is not at all common, and punctulorum appears to be rare.

This species has the uncanny ability to escape danger by using its powerful foot to kick and swiftly propel itself backwards, over several feet, and then quickly bury themselves again. If sweeping over sandy areas, keep an attentive eye out for these guys. As you handle them, they'll kick to get away and, considering how slick they are, can easily slip through your fingers.

They make for a fascinating addition to a small aquarium. Most of the time they remain buried and are easily overlooked, though their eyestalks and probiscus are usually protruding above the surface. The eyestalks are barely noticeable. The probiscus, though more prominant, appears detached and independant, as though it were a small worm. When clear of danger, it'll stretch out and probe about over any surface for bits food. It appears to feed on detritus and algae.

As the animal moves itself forward through the sand, the leading eyestalk will remain stationary above the surface while the rear eyestalk retracts. The probiscus will poke a new hole through which the retracted eyestalk reappears as the lead. This "leap frog" stealth movement through the medium will continue as long as it senses no danger. If disturbed, the animal completely conceals itself in the sand.

References:

Abbott, R. Tucker & S. Peter Dance. Compendium of Seashells. p. 83.

Cernohorsky, Walter O. 1972. Marine Shells of the Pacific. p. 83. pl. 20, fig. 5-5a.

Habe, Tadashige. 1968. Shells of the Western Pacific in Color, Vol II. p. 58. pl. 17, fig. 1.

Hinton, Alan. 1972. Shells of New Guinea and the Central Indo-Pacific. p. 10. pl. 5, fig. 27-30.

Jung, Peter & R. Tucker Abbott. 1967. The Genus Terebellum (Gastropoda:Strombidae). Indo-Pacific Mollusca 1(7):445-454.

Kira, Tetsuaki. 1965. Shells of the Western Pacific in Color, Vol I. p. 34. pl. 16, fig. 1.

Kreipl, Kurt & Guido T. Poppe. 2000. Family Strombidae. p. 19. pl. 8, fig. 1-11; pl. 125, fig. 2

Springsteen, F. J. & F. M. Leobrera. 1986. Shells of the Philippines. p. 68. pl. 15, fig 6 a-d.

Walls, Jerry G. 1980. Conchs, Tibias, and Harps. p. 55-56.