The gastropod Aporrhais, a relict from the Mesozoic

The shallow-marine gastropod (snail) family Aporrhaidae [pronounced "a-poor-rye-id-dee"] has a geologic range of Triassic (210 million years ago) to modern day. During the Jurassic and Cretaceous, this family diversified greatly, but the mass-extinction event at the end of the Late Cretaceous (66 million years ago) greatly decimated the family. There are only a few Cenozoic genera and only a few remaining species in the world today. 

The most characteristic shell feature of aporrhaids is the expanded outer lip with its labral digitations or "wing-like" structure present on the lower half or so of the shell and originating from the right side of the aperture (the opening where the snail extends its body, when it crawls about). The shape of a "wing" is very important in the identification of the various genera and species, but finding specimens with the "wing" intact is not common. Juvenile aporrhaid shells (those without a "wing") tend to have similar looking shells. Naming of new species, therefore, requires having mature specimens available.

Aporrhais pespelecani (Linnaeus, 1758), which lives today in waters extending from Norway, the British Isles, and into the Mediterranean Sea, is one of the most common extant (living) aporrhaids. The species name, pespelecani, is based on this gastropod having a forked "wing," shaped like a pelican's webbed foot. The following two pictures are of the same specimen of this species.

Two views, front and back, of a specimen of Aporrhais pespelecani (Linnaeus).
The specimen is 42 mm in height and 31.5 mm in width.

Aporrhais serresianus (Michaud, 1828) is another apporaid that lives in the Mediterranean Sea. This species is uncommon and is found in relatively deep water. The following two pictures are of a specimen of this species.

Two views, front and back, of a specimen of A. serresianus. The specimen is 41.4 mm in height and 22.3 mm in width.

Aporrhais pesgallinae Barnard, 1963 lives in mud, in moderately deep water in southwest Africa. The following two pictures are of a specimen of this uncommon subspecies.

Two views, front and back, of a specimen of A. pesgallinae. The specimen

 is 33.8 mm in height and 31.8 mm in width.

Other Gastropods that Carry Shells

My previous post concerned the "carrier" gastropod Xenophora, the most common example of a marine gastropod that cements foreign objects onto/into its shell.


In this new post, I present a very broad overview of the other main examples of "carrier" gastropods." 

A high-spired Straparollus, approximately 1 cm height, with fragments of shells attached to its whorls.

One of these other "carrier" gastropods is Straparollus, of Ordovician to Devonian age in North America. Whether this gastropod crawled or was stationary (sessile) is unknown. Straparollus has an uncertain classification and evolution. I used the following reference for obtaining information about Straparollus and as the basis for my own sketch of its shell:

Linsley, R.M. and E.L. Yochelson. 1973. Devonian carrier shells (Euomphalidae) from North America and Germany. United States Geological Survey Professional Paper 824, pp. 1–26.
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Scaliola bella, 1.2 mm height, Indonesia.

Another "carrier gastropod," is the minute Scaliola, which ranges from the Cretaceous to modern day. There are only a few species, and specimens are generally less than 1 mm in height. They live predominantly in the Indonesia region of the Indo-Pacific ocean region. This gastropod cements sand grains onto the adult part of its shell. The family placement of Scaliola is quite different from that of Xenophora.

The following reference was used for obtaining information about Scaliola and as the basis for my own sketch of its shell.

Bandel, K. and H. A. El-Nakhal. 1993. The history and relationship of Scaliola, a gastropod that cements particles to its shell. Mittelungen aus dem Geologisch Palaontologische Institut der Universität Hamburg, 73:171–191.

The following two groups of "carriers" are not true "carriers" of shells upon their own shell, buy they do collect foreign objects and glue them onto themselves. Thus, they are of interest, in a comparative way. The first group is the microscopic agglutinated foraminifers, which are amoeba-like, one-cell protists. Their geologic record ranges from the Early Paleozoic (Middle Ordovician).

Agglutinated (also referred to as arenaceous) foraminifers cement sand, mica, or calcareous particles, as well as tests of other micro-organisms (especially sponge spicules), onto themselves. The cement is calcium carbonate, silica, or iron-bearing compounds. The type of material they attach to can be dependent upon the temperature of the surrounding ocean water (e.g., quartz grains in cold water versus calcium-carbonate particles in warm water). Two examples are: 

Sand-grain agglutinated foraminifer Rhadbdammina, 0.1 mm height, Ordovician, Oklahoma. 

Sand-grain aggluinated foraminifer Saccammina, 0.05 mm height, Silurian, Oklahoma.
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The second group of debatable carriers are some amphipods, which are microscopic shrimp-like crustaceans having no carapace (hard "shell-like covering). This type of amphipod "collects" pieces of shells, cuts them, and then cements them onto its sides (thereby forming blisters or tubes). I could not fine any images of them, and I do not believe that they have a known fossil record. 

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."