Marine Life


Maybe you think that snails, clams, mussels, squid, and Octopods are very different. Yet, they are all in the same category of animals known as mollusks and are structurally similar. Mollusks are some of the most well known of invertebrate sea creatures (there are over 50,000 species). Some are very rare and are only found in very deep-water.

Mollusks have three body regions.:

  • The head contains the “brain” and sense organs

  • The “visceral mass” contains the internal organs

  • The “foot” is the muscular part of the body

Mollusks usually, but not always, have a shell, which is secreted by a body wall called the mantle. Many mollusks have a tongue of sorts, called a radula. The radula is rough like sandpaper. Mollusks have well developed body organs that are used in the respiratory, circulatory and nervous systems.

The Stomach-Foot
The stomach-foots (class Gastropoda) contains about 70% of all mollusk species. The stomach-foots include snails, limpets and abalones, which have shells. Slugs and nudibranchs are also stomach-foots, but do not have shells. A few stomach-foots are found on land. Some Examples below:-

Pleurobranchus testudinarius: Order: NOTASPIDEA ~ Superfamily: PLEUROBRANCHOIDEA
Family: Pleurobranchidae

Elongate tubercles projecting on dorsum. Pattern of polygonal rings on dorsum either white or pink.


Cymatium: common name the hairy triton, is a species of medium-sized predatory sea snail, a marine gastropod mollusc in the family Ranellidae, the tritons.


The Many-Plated or Chitons
The many-plated or chitons (class Polyplacophora) have eight plates and look like pill-bugs (but pill-bugs are not chitons).  Chitons crawl along rocks looking for food (usually algae).  A chiton uses its radula (tongue) to scrape algae off rocks. It also has very hard teeth that are also used to scrape algae of rocks. These teeth are hard enough to etch glass! Embedded within their shells are primitive "eyes" that can detect light.
Chitons are very, very slow moving. During a year, a chiton may move only ten feet!

How Are Pearls Made?
Pearls are made by most bivalves (not just oysters) and even some snails (such at the conch). When an irritant, such as a grain of sand, becomes embedded in the mantle of a bivalve, the creatures coats the irritant with the same material used to produce the lining of its shell. This makes the irritant smooth and less painful to bivalve. Over time, the irritant gets covered with more of the material, making a pearl!

The Bivalves
The bivalves (class Bivalvia) are very well known. They include clams, mussels, oysters and scallops. All bivalves have two shells (the name means "two shells"), and there are about 15,000 species. Most bivalves are marine, but about 20% are found in fresh waters. Most bivalves do not have radula because they eat by filtering water through their gills to obtain organic particles.

Squid & Octopus
The class cephalopoda, meaning "head-footed," includes squids, octopods, cuttlefish and nautiluses. The feet, or arms, of these creatures are connected to their heads, not their bodies. The rest of the body is in front of the head. That's why they're called, "head-footed." The "feet" of cephalopoda are called "arms," not tentacles.
The cephalopods appear to be very different from other mollusks, but physiologically they are similar. Cephalopods, like most mollusks, have a mantle, a mantle cavity, a radula, and a U-shaped digestive tract. Cephalopods have two kidneys and three hearts, which pump blue blood. They are carnivores that feed on fish, shrimp, crabs and other cephalopods.


Cuttle Fish Eating a Painted Comber...


The most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. Octopuses do not have shells at all, while squids have a small internal shell. (Nautiluses, which are found in the South Pacific and Indian oceans, are the only cephalopods with an external shell. They are also the only cephalopods with four gills instead of two.) Cephalopods have a more developed nervous system than other mollusks. They also have very well developed eyesight that is used in finding prey. Once prey is found, it is grasped firmly and eaten with a mouth located at the base of the arms. Cephalopods also have a parrot-like beak which is used in biting into prey.




Body long, fleshy with a short triangular tail. It is covered with lots of projections and blue spots. It has two pairs of tentacles, oral tentacles and rhinophores about the same size (you have to look carefully among the hairy bits to distinguish the tentacles). The parapodia appears to be a hole in the centre of the body, rather than 'wings' or flaps as in other large sea hares. It may come in different colours but is usually well camouflaged and blends in perfectly with among seaweeds and seagrasses. Like some other sea hares, it produces a purple ink when disturbed. It eats cyanobacteria, in particular, the mat-forming Lyngbya majuscula, which was formerly known as the filamentous blue-green alga Microcoleus lyngbyaceus. Apparently, Bursatella sea hares swallow large amounts of sand in the process of eating, somewhat like earthworms do.




Body black or very dark brown, sometimes with a red border to the parapodia, foot and cephalic tentacles. Sometimes some whitish blotches over body. The parapodial lobes are widely separated both anteriorly and posteriorly. Can grow to 40 cm long.

The sea hares have a small thin internal shell, largely covered by the large wing-like body flaps (parapodial lobes) which also protect their gills. These give it a bat-like appearance when swimming. They vary from bright red to brown in colour, have a clear head, tiny eyes and have two pairs of tentacles, the larger of which look like rabbit's ears. It is these tentacles along with its large size and rounded body shape that give it a rabbit-like look and consequently its common name. When stressed they release a purple ink into the water which is contains the toxin opaline. The animals are said to be mildly toxic but are eaten in some areas of the world.

Most sea slugs feed on other animals including sea anemones, but the sea hares are vegetarians preferring seaweed.  They come inshore to breed, most usually in the Spring. Each sea  hare is both male and female being a simultaneous hermaphrodite.  They are known to form long mating chains each animal being a male
to the one in front of it and female to the one behind. The penis is on the side of the head just below the right anterior (cephalic) tentacle. They then lay a pink to orange chain of eggs forming  large spaghetti-like masses at the bottom of the shore or in shallow water. The young hatch from these, spend some time as a veliger larva in the plankton and them settle on algae as a tiny 1-2 mm sea hare. They grow rapidly reaching full size in a year, before breeding and dying.



Pinna nobilis


PHYLUM: Mollusc – CLASS: Bivalve – SUB CLASS: Pteromorphe – ORDER: Mytiloide – FAMILY: Pinnide


Pinna nobilis is a protected species and listed as endangered. According to European Council Directive 92/43/EEC on the conservation of natural habitats and wild fauna and flora, Pinna Nobilis is under strict protection and all forms of deliberate capture or killing of this bivalve are prohibited. It is strictly prohibited to fish or disturb the shell.
Endemic to the Mediterranean Sea, this bivalve mollusc is noted for its size: over three feet in length. It lives, planted upright on sand-banks at a depth of 3 to 30 meters, where posidoniae weeds prosper. The two halves of the shell are of greyish-brown colour and their rough surface hosts algae, diatomae and other small sedentary sea-creatures. The Pinna nobilis shows little signs of activity but every hour it filters 6 litres of water to feed on plankton. For such purpose, the two half shells are left slightly ajar.

Optimal conditions for maintenance of sufficient density of the Pinna-beds are :
• luminosity
• on polluted water with a slow but steady flow to ensure enough food transit ;
• vitality of the environing prairies of posidoniae weed, actually threatened by various human activities and pollution.

Unlike other members of the Mytilaceae family, who attach themselves to rocks, Pinna nobilis burrows its pointed end into the sand-banks where, if conditions allow, it prospers in great numbers.
It has long been believed that the tuft of fibbers from which Sea-Silk was obtained served as an anchor for the animal, in the way roots do for plants. Yet, it appears that the 25 centimetres of shell imbedded in the ground suffice to the function, to the point of making collecting difficult. Unlike these of other bivalves, the Pinna's fibbers are not equipped with anchoring cups. Ultimately, the tuft might be a by-product of the mollusc's food rejections, and it can be of use to the animal when it floats to a new location.
The fibbers, mostly made of albumin, result from the hardening of froth secreted by a specialised gland - said "sea-silk gland" - located near the pointed end of the shell. It is the ambient salt that turns the froth into fibbers which gather some 20 centimetres above the point of the shell and is naturally renewed every 2 years.


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