Carrier Shells of the Xenophoridae Family
One Carrier Shell of the Xenophoridae Family can be found in this website:
Robust Carrier Shell, Xenophora robusta. A representative of the Xenophoridae Family of Carrier Shells.
Phylogeny: Carriers Shells of the Xenophoridae Family are gastropod mollusks in the order Littorinimorpha. This order is large and very diverse in shape including snail-like, cowry shaped, and limpet-like. Most are marine species but some are found in freshwater or on land. They all have a twisted shell and a muscular foot that is used for movement. The key characteristic is that they all exhibit torsion, which is a process where the body twists so that the anus, gills, mantle cavity, and reproductive organs all point forward. There are sixteen superfamilies in this large order. The Xenophoridae Family is in the Stromoidea superfamily, along with Conch Shells. Xenophoridae consists of six genera – Aspidophoreas – with four species, Austrophora – with one species, Onustus – with four species, Ponderiana with three species, Stellaria – with one species, and Xenophora – with fifteen species. These shells are also commonly called Xenophorids.
Description: Carrier Shells are small to large-sized, thin, circular in outline, and conical in profile. The shells are wider than they are tall. The whorls are flat-sided and overhang the suture. The body whorl is flared at the base and sometimes marked with spines. They have a flat or concave base. Many species have an umbilicus in the center of their base. The surface sculpting may be fine radial lines, wavy ridges, spines, or smooth. The base is marked with spiral lines. The aperture is oblique and may be porcelaneous but not nacreous. The operculum is corneous (horn like). These shells are generally white, but some species may have rose, brown, or yellow tints, especially towards the top of the shell. The periostracum is often thin or absent. The most obvious feature of these shells is the shells, pebbles, and other foreign matter that are glued to the upper surface of these shells. At least one-third of the shell will be covered. Carrier Shells reach a maximum of 16 cm (6.25 inches) in diameter, not counting the glued-on pieces.
Habitat and Distribution: Carriers reside in sand or mud substrates. They may live in shallow water, though most are found deeper. They reach a maximum depth of 1,400 m (4,600 feet). Carrier Shells are found worldwide in subtropical to tropical seas. At least two species in this family are found in Mexican waters, one along the Atlantic Coast and one along the Pacific Coast.
Natural History: Carriers can be grazers, feeding on algal film, or deposit feeders, feeding on detritus laying on the substrate surface. They are gonochoric and reproduce sexually through broadcast spawning. The Latin name Xenophoridae means “bearing foreigners”. This is a reference to their behavior of gluing other sea shells, small pebbles, or coral rubble to the outside of the growth whorl of their shell. As the shell grows, it accumulates additional shells. The end result is a shell that looks like a pile of debris. In some cases, the glued on shells exceed the weight of the Carrier Shell’s shell. There are few schools of thought as to why they do this. Some speculate that it is merely a form of camouflage. Some say it is to increase the difficulty a predator would have in attacking or swallowing the shell. Gluing on shells is more energy efficient than growing your own shell. Others speculate that it increases the basal surface area to facilitate staying on top of soft muck. Finally, aquarium observations indicate, at least for some species, that the animal uses the glued-on shells for cover while feeding as the animal keeps its head under the attached shells throughout the feeding process. This makes it more difficult for a predator to attack the otherwise exposed head.
Other forms of marine life, such as sponges, also find Carrier Shells to be convenient location to attach, adding to the load of foreign material. Some species in the Family only glue on a few small shells, leaving most of the shell surface exposed. With other species, the great majority of the shell is covered. Individual Carrier Shells tend to be covered with shells that are similar in size and shape i.e. all clams or all elongate snails. This could indicate either preference or availability. Attachment position does not appear to be random. Bivalves are always attached interior side up; gastropods are always aperture up. Selecting, cleaning, positioning, and attaching shells to yourself is not an easy process for an animal that has no hands or arms. Carrier Shells can spend up to 90 minutes just selecting, cleaning and positioning the desired object. They use the anatomical structures of their head, their muscular foot, and the surrounding substrate to manipulate and hold the object in place. They secrete a cement from their mantle and use fine sand particles to fill in gaps. The animal may hold the object in place for up to ten hours while the cement cures. During this time, it occasionally shakes its body to ensure that the new attachment is firmly in place.