Spondylus Violacescens

''Spondylus'' is a genus of bivalve molluscs, the only genus in the family Spondylidae.MolluscaBase (2019). MolluscaBase. Spondylus Linnaeus, 1758. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=138518 on 2019-03-04 They are known in English as spiny oysters or thorny oysters (though they are not, in fact, true oysters).

Description

The many species of ''Spondylus'' vary considerably in appearance. 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 attaching 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 characteristic feature of scallops, though not of oysters.

As is the case in all scallops, ''Spondylus'' spp. have multiple eyes around the edges of their mantle, and they 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 is known in the fossil records from the Triassic Cassian beds in Italy (235 to 232 million years ago) onwards. About 40 extinct species are known.

Fossils of these molluscs can be found in fossiliferous marine strata all over the world. For example, they are present in Cretaceaous rocks in the Fort Worth Formation of Texas, and in the Trent River Formation of Vancouver Island, as well as in other parts of North America.Finsley, Chalres. 1999. A Field Guide to the Fossils of Texas. Gulf Publishing. Lanham, Maryland. plate 55.Ludvigsen, Rolf & Beard, Graham. 1997. West Coast Fossils: A Guide to the Ancient Life of Vancouver Island. pg. 104

Distribution

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

Ecology

Spondylus are filter feeders. The adults 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. The type of substrate they use 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. The main use period appears to have been from around 5350 to 4200 BC. 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. 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.

''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. 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. 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. Spondylus were also harvested from the Gulf of California and traded to tribes through Mexico and the American Southwest.

Spondylus shells were the driving factor of trade within the Central Andes and were used in a similar manner to gold nuggets, copper hatches, coca, salt, red pepper, and cotton cloth.

The use of Spondylus shells is what led to an economy of sorts in the Central Andes and led to the development of a merchant class, "mercardes", in different cultures within the Central Andes. This caused the development of different styles of trade that went through evolutionary changes throughout pre-Columbian times. These are reciprocity (home based), reciprocity (boundary), down-the-line trade, central place (redistribution), central place (market exchange), emissary trading, and port of trade. These modes of trade dictate the way that the Spondylus shells are traded, as well as who is benefiting the most from the trades. Modes such as central place (redistribution) require the entity that is the central place to be the one that gains the most benefit from the trade, and modes such as emissary trading and port of trade are the modes that started the "mercardes" class within the Central Andes.

The value of Spondylus shells in the Cent