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."