Bivalves (Class: Bivalvia) are bilaterally symmetrical mollusca have a laterally compressed body enclosed by a shell of two valves linked dorsally by a hinge. They have a ventral foot which does not have a crawling surface. Bivalves are filter feeders and their shells can vary from delicate to very strong. Some species have the ability to burrow into the sand while others secrete threads with which they bind themselves to rocks.
There are of course many bivalves inhabiting the Turkish coastal waters. Many shells belonging to a wide variety of species can be found on almost every dive and are too numerous to list in this guide. Common live examples of the larger species can also be found on almost every dive and some common examples are described below.
MEDITERRANEAN FAN MUSSEL or PEN SHELL (Pinna nobilis)
This large fan shaped mussel stand upright in muddy sand and gravel areas and is usually attached to sunken stones or rock by byssus threads. Colored red brown green they are often covered with a growth of weeds and other plants. Feeding is by filtration, siphoning water continuously between their partially open valves. If disturbed they quickly close, only opening slowly when they sense no danger. The byssus threads of this species were once used to in the manufacture of Cloth of Gold.
THORNY OYSTER (Spondylus gaederopus)
This species of bivalve is not uncommon but is often more difficult to find because their outer surface is usually encrusted with other invertebrates, algae or weed. They are distinctive, having many variable, blunt spines on their upper valve while the lower valve is attached permanently fused to rock. They are usually only noticeable when they suddenly close, which is usually when even the quietest of divers gets within 3 meters. The inside of the shell is white and they are usually a maximum of 10cms in diameter.
Many examples of burrowing bivalves can be found by sifting through the top surface of sandy bottoms, live specimens should of course after examination, be returned to their natural habitat under the sand.
COMMON OCTOPUS (Octopus vulgaris)
These harmless, (to divers), and intelligent animals can be found on most dives, although during the day they are difficult to find because they hide in rock crevices and among stones. The entrance to their lair is usually camouflaged with an arrangement of stones and shells, and it is the neatness of their work that makes their habitats relatively easy to spot, when you know what to look for. Despite their affinity for rocky areas they can be found in sandy areas where they burrow into the sand forming a funnel shaped lair lined and reinforced with rocks and the shells of their unfortunate former victims.
Unfortunately they are heavily fished to supply the demand of local restaurants. Their strong arms bear two rows of suckers and are usually green/ brown in color depending on their situation and rarely grow to more than 50cms in length in this region. On night dives in torch light the color changes can be quite spectacular flashing from light blue to deep brown. At night they can be seen roaming over the rocks in search of prey instantly changing color and altering their texture to match their surroundings.
During the early part of the season, around May and June, the female octopus builds a specially prepared nest in a hole in the rocks in which to lay her eggs. The entrance is blocked with rocks and it would appears that she does not feed during this time. Although the nurseries are easy to find, it is best to leave the mothers undisturbed.
LESSER OCTOPUS (Eledone cirrhosa)
This species of octopus is relatively rare during the daytime but can be seen on most night dives. They have long slender arms bearing only one row of suckers and they have a very soft texture. Colored coral pink to red brown with white spots, they do not have the same ability as the common octopus to change color or texture.
CUTTLEFISH and SQUID (order: Decapoda)
These cephalopods have cylindrically shaped bodies with lateral fins and have an internal shell or cuttlebone. The mouth is surrounded by 8 short and two longer tentacles.
COMMON CUTTLEFISH (Sepia officinalis)
The common cuttlefish is an intelligent and voracious nocturnal carnivore that can be seen on most night dives and occasionally during the day. They are able to change color and shape to resemble their background. If threatened, they eject ink into the water in order to mask their escape. If observer at night by torchlight the pale underside reflects a myriad of colors.
Because of their similarity there is often a great deal of confusion among divers whether what they have observed is a cuttlefish or a squid. More often than not it will be a cuttlefish that they have seen because most species of squid are pelagic and do not often venture close to the shore.