CAVITURRITELLA: AN INTERESTING GASTROPOD LIVING IN BAJA SUR , MEXICO

The shallow-marine gastropod family Turritellidae  has a long

geologic record ranging from the Early Cretaceous (late early Albian = about 115 million years ago) through modern day. Its shells have a long slender shape, with a sharp apex, and tightly coiled shells with spiral ribs. Fossil specimens can be very common locally and highly useful for differentiating geologic time and ancient-nearshore conditions. Turritellids are vegetarians and feed on detritus. 

Today, there are several species of turritellids living in the warm waters of the Gulf of California. One of these has been long known as Turritella gonostoma Valenciennes, 1832, but recently it has been identified (see Friend and Anderson, 2023) as belonging to genus, Caviturritella.  Unlike specimens of similar looking Turritella, it is possible to extend a needle up through the axis for the entire length of the long spiral shell of Caviturriella gonostoma (Valenciennes, 1832). 

Caviturriella gonostoma, which is found as far south as Ecuador, has a light gray to dark purplish brown shell (up to 115 mm long and 22 mm diameter), and mottled with white. Its sculpture varies from several spiral cords per whorl, with impressed sutures, to almost smooth and flat-sided whorls (Keen, 1971:p. 392, fig. 438).

Two views: apertural view of a shell of C. gonostoma  (length 14.4 cm, diameter 3.3 cm) of C. gonostoma from Mulege, Baja California Sur, Mexico (see map below). The brown circular area in the upper image is the "horny" operculum "trap door" of this shell. The small arrow in the lower image points to the diagnostic hollow central area of the axial area of the shell. 

                                           Map of Baja California Sur, Mexico.

Highway bridge crossing the mouth of the Mulegé River immediately east of the town of Mulegé, Baja California Sur, Mexico (March, 1989). This is the only main river (although small) along the coast of Baja California Sur.

Many years ago, one of my geology major students, Nikki Vaughan, also a scuba-diver, examined a population of this species in very nearshore shallow-marine waters immediately south of the mouth of Mulegé River, at the town of Mulegé, Baja California Sur, Mexico. She discovered this population living in a colony just below the sea floor, in water depths between 7 and 10 feet deep, where the gastropods were crawling around in order to feed. The dominant consensus among biologists at that time was that turritellids are sessile animals (i.e., ones that do not move about)! Nikki was one of the first scientists to provide evidence to dispute that false claim. As part of her study, she also put some of the specimens in an aquarium and watched them move and feed. They even climbed the walls of the aquarium and concentrated around a tube that oxygenated the water. I was one of the first people to watch these movements of gonostoma and confirm her field observations. In 1983, she wrote an abstract about it and, in 1992, co-authored a scientific paper about her important discovery (see below: References Cited).

The C. gonostoma specimens prefer living adjacent to the walled-off outlet of this river into the Gulf of California. They apparently like the brackish water environment and probably migrated there to feed at various times of the year.

References Cited:

Allmon, W.D., D.S. Jones, and N. Vaughan. 1992. Observations on the biology of Turritella gonostoma Valenciennes (Prosobranchia, Turritellidae) from the Gulf of California. The Veliger 35(1):52–63.

Anderson, B. M., D.S. Friend, and W.D. Allmon 2023. Abstract presented at the WSM Meeting June 24, 2023 (50th Annual Meeting, Chapman College, Orange, California).

Keen, A.M. 1971. Sea shells of tropical west America-marine mollusks from Baja California to Peru. 2^nd edition. Stanford University Press, Stanford, CA, 1064 pp.

Vaughan, N. 1983. A study of the ecology of Turritella gonostoma living in the Gulf of California, Mexico. Annual Report (for 1982), Western Society of Malacologists 15:13–14.