Spondylus Gaederopus
– Thorny Oyster –
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Bivalvia |
| Order: | Pectinida |
| Family: | Spondylidae |
| Genus: | Spondylus |
| Species: | S. gaederopus |
| Binomial name |
|---|
| Spondylus gaederopus Linnaeus, 1758 |
Description
Spondylus gaederopus is a species of marine bivalve mollusc, a thorny oyster in the family Spondylidae. This species is endemic to the Mediterranean Sea.
The donkey spondyle has an unequal * shell , thick and heavy, oval in shape . Its average size varies between 60 and 125 mm. However, individuals measuring 135 mm in length have already been observed.
Its general appearance is very variable, depending on several exogenous factors: position on the rock, strength of the current, etc. Generally, the upper valve (or left), a kind of movable cover is decorated with a dozen of radial ribs on which stand the calcareous spines shorter or longer forms irregular: pointed, thick, spatula-shaped or tubular. Numerous spikes accumulate in the interstices of the shell giving it a rough appearance.
The lower (or right) valve , hollow and more voluminous, welded firmly to the substrate *, can also bear spines concentrated only on the edges. Specimens without thorns are not uncommon.
The upper valve is always purple , purplish red or violet , rarely orange. The lower one is most often white with sometimes purplish red or orange spots. The interior of the valves is pure white . The hinge has 2 strong teethor buttons on each valve and a sturdy ligament between them. The 2 teeth of the upper valve fit perfectly into the dimples of the lower valve and vice versa. A single, almost centrally positioned adductor muscle leaves a circular imprint inside the shell.
Biotope
This benthic species * lives firmly fixed by its lower valve on rocky bottoms (drop offs, rocks), on wrecks, sometimes on the valves of large molluscs such as the large nacre Pinna nobilis . It can be found from a few meters up to about fifty meters in depth in sites exposed to regular currents.
Similar Species
There is no possible confusion in its distribution zone, Spondylus gaederopus being the only spondylid of our metropolitan coasts. However, young or small individuals may be mistaken for the small spiny oyster Chama gryphoides smaller in size (3 cm) and with short spines arranged in concentric rows.
Food
This species has a microphagous * suspensivore * diet: it feeds exclusively on organic matter and plankton * suspended in seawater which it filters through its gills.
Reproduction
Spondylus gaederopus is like all pectinid bivalves a hermaphrodite * species. The gonads release eggs and sperm into the water column. Fertilization is external. A few days later, the eggs give birth to larvae * trochophores * planktonic *. The latter will metamorphose in a few days (depending on the temperature of the water and the food available) into veliger larvae *. At the end of this larval phase, the young, identical in all points to the adults, will settle on the bottom and undergo a series of transformations up to the juvenile stage.
Associated Life
The upper valve of the donkey spondyle shell is mostly colonized by numerous invertebrate organisms which provide it with camouflage and relative protection. It is the Crambe crambe orange-red encrusting sponge that covers it most often and it is difficult to distinguish the shell from the bivalve in this case.
Various Biology
In the 1980s and then in 2008-2009, along the Mediterranean coasts, episodes of high mortality were observed in Spondylus gaederopus. Whether on the French coasts or on the west coasts of Italy, observed a mortality rate of over 90% during the summers of 1981, 1982 and 1983. All bathymetric sections * of the infralittoral level * ( 0 to 30 m), young and old, small or large, were affected. The causes, although no analysis has been established on individuals on the verge of death, appear to be due to a viral, bacterial or fungal epidemic. The speed and extent of the phenomenon seem to corroborate this hypothesis. These abnormal findings were again reported in 2008 and 2009. It should be noted that during these two periods other bivalve molluscs also died in large numbers: Arca noae (Noah’s ark), Barbatia barbata (bearded ark) andLima lima(scaly lime).
Further Information
Although edible, the flesh of the spondyle is more or less appreciated because of its bitter flavor. Its fishing is occasional and artisanal: bottom trawls, dredges. Catches in scuba diving are rare. Eaten fresh, it rarely appears on the markets of the countries bordering the Adriatic Sea (Italy, Croatia); in Corsica it is only collected and consumed by a few initiates.
This species is also the object of collection for collectors. This attraction is not new since we have found in archaeological excavations in Greece only the remains of upper valves.
Archaeological excavations on the Mediterranean coasts (Aegean Sea in particular) have shown that fossil shells of Spondylus gaederopus had, during the Neolithic period, i.e. around 5,000 years ago, been used to make ornaments, bracelets or belt buckles.
