Xenophora, the "Carrier"-Shell Gastropod, Recent and Past

This post returns to the subject of family Xenophoridae Philippi, 1853. Its most common genus is Xenophora (usually pronounced as "Zen-off-fer-a"), one of the more unusual gastropods found today in warm-water oceans (for example, Indo-Pacific and Caribbean). Xenophora, which is a Greek word, meaning "foreign bearing," was named by Fischer von Waldheim, in 1807. 

Xenophora is unusual among gastropods because it can attach shells, rock fragments, and other debris to its shell, in order to provide protection and/or camouflage. 

                                                                                        

Xenophora pallidula (Reeve, 1842) dorsal view, one of the more common Xenophora found today in offshore to deep water in the Indo-Pacific Ocean; maximum diameter of entire shell complex (including extended attachments) is 8 cm. This single shell has amassed ("collected") quite a collection of other gastropod shells. 

Same specimen as above, ventral view, showing the smooth aperture, which is also flat. If you look closely on the right-hand side of the image, you will see how the tips of the attached shells have been cemented into the margin of the shell of Xenophora. 

The animal within the shell of Xenophora reaches out of its apertural opening and selects what it wants to attach. It cleans the particles with bites of its mouth and then holds (with the aid of its head) the particles to the margin of the aperture until they are attached firmly by shell secretions from the soft tissue of the mantle (the organ which secretes the shell).

Same specimen as above, side view. Notice how the flat bottom of the actual shell is elevated relative to whatever it is resting upon. This elevation creates a "feeding cage," which enables Xenophora to "hang down" from its shell and feed on the ocean floor. The animal also leaves no trace (smell) of its presence on the floor, thus it helps deter predators.

This is a dorsal view of another specimen of X. pallidula, maximum diameter of entire shell complex 9 cm (including rock attachments), which attached small stones to its shell, rather than other shells. It was a matter of what material was available. A few encrusting annelid-worm tubes attached subsequently to the stones.  This shell is from 30 m depth in waters off of Japan.

Ventral view of same specimen shown immediately above.

The three specimens shown above are of the middle Eocene Xenophora stocki Dickerson, all about the same size in diameter (15 mm), from southern California. The shells are not preserved, but impressions of where shells used to be attached are visible as small depressions (e.g., lower left side).

Like today, fossil Xenophora, ares indicative of warm waters (subtropical to tropical). The geologic range of Xenophora is Late Cretaceous to Recent.

In my posting on October 28, 2018, I mentioned the above-pictured Late Cretaceous species of Xenophora (Endoptygma) hermax Squires and Saul, 2001 from southern California. These specimens could be mistaken for small piles of stones.

For comparison, the above three views of the same specimen (7 cm diameter) show a deep-water, modern-day Stellaria solaris (Linnaeus, 1767) from Taiwan. Stellaria Möller, 132, belongs to the same family as Xenophora, but Stellaria has no attachments. Its species do not need to "carry" shells in order to elevate their shell above the ocean floor. Instead, Stellaria has evolved in such a way as to grow its own "stilts."

Some representative Late Cretaceous Gastropods from the Pacific Coast of North America

There are about 200 reported genera of Late Cretaceous (about 100 to 65 million years ago) shallow-marine gastropods known from the Pacific coast of North America. This post focuses on a few examples of them.

Tessarolax is one of the most "eye-catching" examples. It is an extinct genus characterized by having four long digitations, used to support its shell on soft ocean-floor sediments. The above images are of three different species at oblique views. The specimens range from 70 to 120 mm (max. dimensions). Tessarolax belongs to family Aporrhaidae (pronounced "a-poor-rye-id-dee"). Tessarolax, which is only of Cretaceous age, was widespread in the world.

These two images of Tessarolax are of two different species showing how their shells relate to the ocean floor (substrate). Both specimens are approximately 50 mm, from left to right. Very careful collecting and cleaning are required in order to obtain such high-quality specimens. For the latest information on Tessarolax and also on the details about the species represented by the above-illustrated specimens, see the reference: 

Saul, L.R. and R.L. Squires. 2015. Pacific slope of North America record of the Cretaceous aporrhaid gastropod Tessarolax: Evolutionary trends, mode of life, and paleobiogeography of the genus. Contributions in Science v. 523, pp. 37–65. (pdf available for free---just "Google" the title of the paper.

Anchura is another example of an aporrhaid gastropod having an extension of its shell in order to provide stability on the ocean floor.
For more information on Anchura, see the reference:

Elder, W.P. and L.R. Saul. 1996. Taxonomy and biostratigraphy of Coniacian thorugh Maastrichtian Anchura (Gastropoda: Aporrhaidae) of the North American Pacific slope. Journal of Paleontology 70(3):381–399. (pdf available for free---just "Google" the title of the article).

These two specimens of the gastropod Xenophora look like two small stacks of pebbles. This genus, which is extant, is known as colloquially as the "carrier shell" because it collects and carries pebbles and/or other shells (by cementing them onto its own shell), in order to provide protection/camouflage for itself. In essence, it was the first fossil collector. For more information on this fossil Xenophora, see the reference:

Squires, R.L. and L.R. Saul. 2001. New Late Cretaceous gastropod from the Pacific slope of North America. Journal of Paleontology 75(1):46–65. (pdf available for free---just "Google" the title of the article).

This specimen (height 50 mm) belongs to genus Paosia, formerly known by its junior synonym name of Trajanella. Paosia has a long geologic time range of 75 million years. It is mainly known from Europe, but a lineage became established along the Pacific coast of North America for 25 million years. For more information, see the reference: 

Squires, R.L. and L.R. Saul. 2004. The pseudomelaniid gastropod Paosia from the marine Cretaceous of the Pacific slope of North America and a review of the age and paleobiogeography of the genus. Journal of Paleontology 78(3):484–500.

Trochactaeon (T.) packardi (see my Post 39 of Feb. 3, 2015): An unusual Late Cretaceous gastropod from California. The specimen on the left is 6 cm height and shows the front view. The specimen on the right is 4.6 cm height and shows the back view. This genus, which was restricted to the Cretaceous, was widespread, including California, in warm waters during the Late Cretaceous.

Alamirifica corona genus and species Saul and Squires, 2003; two views, front and back (height 37 mm). Late Cretaceous (Turonian), southern California. This specimen is exceptional because it shows all the exquisite details of its aperture. For more information about this species, see the reference: 

Saul, L.R. and R.L. Squires, 2003, New Cretaceous cerithiform gastropods from the Pacific slope of North America. Journal of Paleontology 77(1):442–453.

Pentzia hilgardi (White, 1889); two views, front and back (height about 10 mm). Late Cretaceous (Campanian to early Maastrichtian). Genus Pentzia consists of only a single species, which is found only in Washington, California, and northern Baja California (Mexico). This species has an usually long geologic time range, which is approximately 13 million years. Most gastropod species last for much shorter time intervals. For more information about this genus and species, see the reference:

Squires, R.L and L.R. Saul, 2003, New Late Cretaceous (Campanian and Maastrichtian) marine gastropods from California. Journal of Paleontology 77(1):50–63.