Rhabdus rectius (Carpenter, 1864) Common name(s):  Western straight tuskshell, Straight tuskshell, Tusk shell, Tooth shell
Synonyms: Dentalium rectus, Dentalium dalli, Dentalium watsoni, Fustiaria rectius, Laevidentalium rectius
Phylum Mollusca Class Scaphopoda Order Dentaliida  Family Dentaliidae
	Rhabdus rectius, 4.5 cm long, found in sediment brought up from the bottom of Burrows Bay by Kirt Onthank. The dorsal side is down and the anterior end is to the left, with the foot projecting.
	(Photo by: Dave Cowles, August 2017 )

Description:  Shell smooth, fragile, usually greater than 2 cm long; without a narrow slit extending from the narrow (posterior) end.  Foot conical. The testis of the male is white and the ovary of the female is yellow, visible through the thin shell. Length to 13 cm, diameter to 6 mm.

How to Distinguish from Similar Species:Dentalium agassizi has fine ribs or lines on the shell. Antalis. pretiosum has a thicker shell and a narrow slit extending from the posterior aperture, plus it lives in shelly hash/gravel. Most other species are < 2 cm long and have a wormlike foot.

Geographical Range:  Alaska to Peru

Depth Range:  Nearly always subtidal.

Habitat:  Mud, silt, or sand

Biology/Natural History:  Scaphopods are small, predatory mollusks which live within the sediment with the anterior (large) end of their shell down into the sediment and the posterior (small) end of the shell also buried or occasionally exposed at the surface. The shell curves, with the dorsal side concave. Members of Order Dentaliida have the largest diameter of the shell at the anterior end, while the other order (Gadilida) is widest somewhat back from the anterior end. The foot extends from the anterior end, or can be folded back into the shell. It has a pair of lateral lobes just behind the front of the foot, leading to the name Scaphopoda which means 'plow-foot'. They extend their foot into the sediment, then extend 'captacula' (club-ended feeding tentacles) to the sediment near the foot to capture prey such as foraminiferans (movie). Rhabdus rectius also eats the sediment and fecal pellets.

Predators include fish and crabs.  Sexes are separate, and a single egg is laid at a time.

Empty tusk shells sometimes wash up on the beach. Some Vancouver Island Indians dredged them up, especially the thicker-shelled Antalis (formerly Dentalium) pretiosum, with wooden rakes from shallow water, strung them on leather strings, and used them for money or ornamentation.

References:

General References:
  Harbo, 1997
  Lamb and Hanby, 2005

Scientific Articles:

Gainey, L.F., Jr., 1972. The use of the foot and the captacula in the feeding in Dentalium. Veliger 15: pp 29-34

Shimek, R.L., 1998. Scaphopoda.  In: Taxonomic atlas of the benthic fauna of the Santa Maria Basin and Western Santa Barbara Channel, Vol. 9: Mollusca.  J.A. Blake, A.L. Lissner, and P.H. Scott, editors.  Santa Barbara Natural History Museum, Santa Barbara, CA.

Web sites:

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

The anterior end, with the foot protruding. The shelf behind the tip of the foot is partly visible, as are several of the captacula tentacles. You can view a video of the captacula tentacles moving here. Photo by Dave Cowles, August 2017

The posterior end, at the same magnification as the anterior end. Note that most of the shell is fragile. There is a white concretion on a portion of the shell visible here.

Another view of the whole animal. Since I see no prominent yellow organs inside the shell, I presume that this is a male.

Authors and Editors of Page:
Dave Cowles (2017):  Created original page
CSS coding for page developed by Jonathan Cowles

Salish Sea Invertebrates web site provided courtesy of Walla Walla University