Spondylus

Thorny oysters Temporal range: Triassic - Recent PreЄ Є O S D C P T J K Pg N
A shell of S. regius
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Subclass:	Pteriomorphia
Order:	Pectinoida
Suborder:	Pectinina
Superfamily:	Pectinoidea
Family:	Spondylidae Gray, 1826
Genus:	Spondylus Linnaeus, 1758
Species
See text

Spondylus is a genus of bivalve molluscs, the only genus in the family Spondylidae. They are known in English as spiny oysters (though they are not, in fact, oysters).

Description

Spondylus varius in Mayotte.

The many species of Spondylus vary considerably in appearance and range. They are grouped in the same superfamily as the scallops. They are not closely related to true oysters (family Ostreidae); however, they do share some habits such as cementing themselves to rocks rather than attach themselves by a byssus. The two halves of their shells are joined with a ball-and-socket type of hinge rather than with a toothed hinge, as is more common in other bivalves. They also still retain vestigial anterior and posterior auricles ("ears", triangular shell flaps) along the hinge line, a common feature of scallops though not of oysters.

Like all scallops, Spondylus spp. have multiple eyes around the edges of their shells, and have relatively well-developed nervous systems. Their nervous ganglia are concentrated in the visceral region, with recognisable optic lobes connected to the eyes.

Evolutionary history

The genus Spondylus appeared in the Mesozoic era and it is known in the fossil records from the Triassic Cassian beds in Italy (235 to 232 million years ago) on. About 40 extinct species are known.^[1]

Fossil valve of Spondylus crassicosta from the Pliocene of Italy

These molluscs can be found in fossil shells all over the world. They are present in Cretaceaous rocks in the Fort Worth Formation of Texas and in the Trent River Formation of Vancouver as well as in other parts of North America.^[2][3]

Distribution

Spiny oysters are found close in all subtropical and (especially) tropical seas, usually close to the coasts.

Ecology

Spondylus adults are filter feeders that live cemented to hard substrates, a characteristic they share, by convergent evolution, with true oysters and jewel boxes. Like the latter, they are protected by spines and a layer of epibionts and, like the former, they can produce pearls.^[4] The type of substrate depends on the species: many only attach to coral, and the largest diversity of species is found in tropical coral reefs; others, (particularly S. spinosus) however, easily adapt to man-made structures and have become important invasive species. Others still are often found attached to other shells, perhaps the most common belonging to the genus Malleus.

Uses

Archaeological evidence indicates that people in Neolithic Europe were trading the shells of S. gaederopus to make bangles and other ornaments throughout much of the Neolithic period.^[5] The main use period appears to have been from around 5350 to 4200 BC.^[5] The shells were harvested from the Aegean Sea but were transported far into the center of the continent. In the LBK and Lengyel cultures, Spondylus shells from the Aegean Sea were worked into bracelets and belt buckles. Over time styles changed with the middle neolithic favouring generally larger barrel-shaped beads and the late neolithic smaller flatter and disk shaped beads.^[5] Significant finds of jewelry made from Spondylus shells were made at the Varna Necropolis. During the late Neolithic the use of Spondylus in grave goods appears to have been limited to women and children.^[5]

S. crassisquama is found off the coast of Colombia and Ecuador and has been important to Andean peoples since pre-Columbian times, serving as both an offering to the Pachamama and as currency.^[6] In fact, much like in Europe, the Spondylus shells also reached far and wide, as pre-Hispanic Ecuadorian peoples traded them with peoples as far north as present-day Mexico and as far south as the central Andes.^[7] The Moche people of ancient Peru regarded the sea and animals as sacred; they used Spondylus shells in their art and depicted Spondylus in effigy pots.^[8] Spondylus were also harvested from the Gulf of California and traded to tribes through Mexico and the American Southwest.

Even today, there are collectors of Spondylus shells, and a commercial market exists for them. Additionally, some species (especially S. americanus) are sometimes found in the saltwater aquariums.

S. limbatus was commonly ground for mortar in Central America, giving raise to its junior synonym, "S. calcifer".

Some Mediterranean species are edible and, in particular S. gaederopus, is commonly consumed in Sardinia. Tropical species, however, tend to bioaccumulate saxitoxin.^[9]

Species

Spondylidae taxonomy has undergone many revisions,^[10] mostly due to the fact that identification is traditionally based on the shell only, and this is highly variable. To add to this, while some shallow-water species are extremely common, at least two deep-water ones are known from a single specimen, while a third (S. gravis)^[11] was only rediscovered after 77 years. At least another common species (S. regius) has a different shell when it grows in deep water.^[12]

Pacific thorny oyster, S. crassisquama Lamarck, 1819, from the Gulf of California, Mexico

The interior of two fossil valves of Spondylus from the Pliocene of Cyprus

Cat's tongue oyster, Spondylus linguaefelis Sowerby, 1847, from Hawaii

A view of the colorful mantle edges of a live thorny oyster from East Timor: The eyes can be seen on the fringe between the mantle and the shell.

A fossil Spondylus gaederopus from the Pliocene of Cyprus

References

External links

• Spondylidae pictures of the shells of most extant species.
• shells at the Rotterdam Natural History Museum
• Session Abstracts on Spondylus research at the 13th Meeting of the European Association of Archaeologists at Zadar, Croatia, September 2007
• Information about Spondylus from the website of the Gladys Archerd Shell Collection at Washington State University Tri-Cities Natural History Museum
• Article on "notched" Spondylus Neolithic artifacts in Europe

Bibliography

• A full and constantly updated bibliography on Spondylus spp. in Aegean, Balkan, European and American contexts
• Lamprell, Kevin L.: Spondylus: Spiny Oyster Shells of the World, E. J. Brill, Leiden, 1987 ISBN 90 04 0839 4