When a chamber is abandoned, its fluid is removed and replaced with gas by the siphuncle, helping to compensate for the added mass of the shell and body, thereby maintaining buoyancy. The image above shows the shell of a chambered nautilus that has been cut in half to reveal the arrangement of the internal chambers and septa.
Note the small perforations holes in each septum that permit the passage of the siphuncle. As mentioned previously, squids and cuttlefishes have two tentacles equipped with suckers only at their distal ends as well as eight arms that bear suckers along their length.
In terms of skeletons, squids have only a vestigial shell called a pen and a horny beak. These cephalopods are excellent swimmers that have streamlined bodies. Lateral fins serve as stabilizers, but are held close to the body for rapid swimming. Lab These cephalopods have well developed sense organs, especially eyes and are capable of complex behaviors and learning. They also can change their appearance to match their backgrounds using pigment containing chromatophores in the skin.
This slide shows a stained section of a radula from a snail. The numerous chitinous teeth on this ribbon-like membrane are used to scrape, pierce, tear or cut off small pieces of food that are then directed in a continuous stream toward the digestive tract by conveyor belt like movements of the membrane. This slide shows several stained veliger larvae that are found in many gastropods and bivalves. The larvae which develop from ciliated, free-swimming trochophore larvae have the beginnings of a foot, shell and mantle.
In many molluscs the trochophore larval stage is passed in the egg, and the veliger hatches to become the only free-swimming stage. This slide shows the glochidium larva of a bivalve. In most freshwater bivalves, eggs are fertilized internally by sperm entering with incurrent water flow.
After fertilization, the eggs develop within the gill tubes which serve as temporary brood chambers into the tiny bivalved glochidia larvae. After being discharged, the larvae wait until they contact a passing fish and attach themselves to the gills or skin where they live as parasites for a few weeks before dropping off to begin living independent lives. This larval "hitch hiking" is seen as an adaptation for dispersal among organisms whose powers of locomotion are otherwise very limited.
The image above shows a squid dissection mount. Numbered structures shown on the mount include the funnel, or siphon, 1 ; anterior vena cava 2 ; funnel, or siphon retractor, muscle 3 ; intestine 4 ; ink sac 5 ; gills 6 ; branchial hearts 7 ; posterior vena cava 8 ; intestinal cecum 9 ; mantle 10 and the anus This image and the accompanying close-up view show a specially prepared squid dissection encased in a Lucite block.
During the dissection, a midline incision was made and both sides of the circular mantle 1 were deflected to the side to reveal the internal organs. It is these rings of mantle in the intact squid that are eaten as calamari in many restaurants! The gills 2 and major arteries on this dissected squid have been injected with red latex, while the branchial hearts 3 that supply blood to the gills and major veins have been injected with blue latex.
Note the large funnel, or siphon, 4 through which water is ejected to achieve a form of locomotion by "jet propulsion". A pair of lateral fins 5 helps provide stability during swimming. Squids have eight arms 6 that bear suckers along their length and two tentacles 7 that bear suckers 8 only on their distal ends. Except for a horny beak located inside the mouth 9 , the squid has only a small vestige of an internal skeleton called a pen In terms of circulation, all cephalopods have a closed circulatory system.
Blood is pumped to the body by a centrally located systemic heart After delivering its oxygen to the squid's tissues, poorly oxygenated blood is returned to the gills via an anterior vena cava 12 and two posterior vena cavae 13 to be pumped to the gills 2 by a pair of accessory hearts called branchial hearts 3. Squid are predators that capture prey with their arms 6 and tentacles 7 and dispatch the prey with a powerful beak sometimes containing venom inside of the mouth 9. Prey are detected with large eyes 14 , the sides of one of which is seen on the dissection.
From there, the food passes through the esophagus into the stomach to be digested. Once partially digested, the food is diverted to a blind pouch called the intestinal cecum 15 where the process is completed, after which the remaining wastes are discharged through the anus Running along side the intestine is the ink sac 17 , which can discharge a load of ink through the anus 15 that may help to conceal the squid's escape from potential predators or perhaps startle them into retreating.
Also seen on this dissection of a male squid is the penis 18 through which sperm are inserted into the mantle cavity of the female during a head-to-head mating. This image shows a magnified view of some of the central organs and arteries of the male squid, including the gills 1 ; branchial hearts 2 ; systemic heart 3 ; lateral mantle arteries 4 ; median mantle artery 5 ; anterior vena cava 6 ; posterior vena cava 7 ; penis 8 ; ink sac 9 and the intestinal cecum This image shows a number of anatomical features of a preserved, commercially prepared dissection mount of a freshwater mussel.
Note the large, hatchet-shaped foot 1 that is used for burrowing into the substrate. The heart 5 has been injected with red latex, the gills 4 with blue latex and the intestine 9 with yellow latex. Digestive wastes are discharged from the intestine into the mantle cavity through the anus Bivalves are distinguished from other molluscs by being having laterally compressed bodies encased in two shells valves that are held together by a dorsal hinge ligament 6 that causes the valves to open ventrally.
The valves are drawn together by a pair of anterior 2 and posterior 8 adductor muscles, which are the parts of edible scallops that are eaten. In terms of nutrition, most bivalves are sedentary filter feeders. The posterior edges of the mantle 7 are modified to form a ventral incurrent siphon 11 that brings food and oxygen into the animal and a dorsal excurrent siphon 12 that takes carbon dioxide and wastes out.
Bivalve shells carry out a variety of functions including support for soft tissues, protection from predators, locomotion in scallops and boring tunnels through hard substrates shipworms. The shell is made of three layers: the nacreous layer, an inner iridescent layer of nacre mother-of-pearl composed of calcium carbonate that is continuously secreted by the mantle, the prismatic layer, a middle layer of chalky white crystals of calcium carbonate in a protein matrix and the periostracum, an outer pigmented layer composed of a protein called conchin that protects the prismatic layer from abrasion and dissolution by acids especially important in freshwater forms where decay of leaf materials produce acids.
The image above shows the inside of a freshwater mussel shell with all of its internal organs removed. Observe the iridescent lining of nacre 1. Near the anterior end of the valve is a raised portion called the umbo 2 , which is the oldest part of the shell. The shells are held together dorsally by a spring like hinge ligament 3 that causes them to open.
They are drawn together two muscles, the anterior adductor muscle 6 and the posterior adductor muscle 7. Grooves on the valves called hinge teeth allow the valves to securely interlock. In freshwater mussels there are two sets of hinge teeth, a posterior set of lateral hinge teeth 4 and an anterior set of cardinal hinge teeth 5.
The image above shows a preserved, dissected freshwater mussel. Note the conspicuous fold of tissue called the mantle 1.
In molluscs the mantle is a sheath of skin that hangs down in two folds around the soft body and encloses a mantle cavity, which performs many of the same functions as a coelom in other animals. The outer side of the mantle secretes the shell while the inner side is ciliated, and along with gills 2 , participates in gas exchange.
Note the prominent anterior adductor muscle 3 and posterior adductor muscle 4 that draw the two valves together to enclose and protect the animal from predators. The lateral hinge teeth 5 that help the valves to securely interlock can also be seen in this image.
Observe the heart 6 , which is contained within the pericardial cavity 7 located in a dorsal position just below the lateral hinge teeth 5. In molluscs, this cavity represents the remains of a much-reduced coelom. Note the conspicuous, hatchet-shaped foot 8 that is used for burrowing. In the image shown, a portion of the foot has been removed to reveal the greenish digestive gland 9 and gonad The image above shows another view of a freshwater mussel dissection.
Structures that can be seen on this image include the lateral hinge teeth 3 , cardinal hinge tooth 4 , anterior adductor muscle 6 , posterior adductor muscle 7 , gills 8 , the fleshy mantle 1 , a portion of exposed nacre lining the shell 2 and part of the digestive gland 5 inside what remains of the foot most of which has been removed during the dissection.
Also visible on the above image is one of the two pairs of labial palps 9 , flap-like structures attached to each side of the at the anterior end of the visceral mass near the anterior adductor muscle that help guide food particles toward the mouth. Click on the links below to see images of a plastic model showing the principal internal organs of a typical bivalve mollusc.
Foot; 2. Anterior adductor muscle; 3. Stomach; 4. Mantle; 5. Gills ctenidia ; 6. Posterior adductor muscle; 7. Nephridium; 8. Labial palp; 9. Pericardium coelom. Lab-6 30 1. Nephridiopore; 2. Nephrostome; 3. Pericardium Coelom ; 4. Auricle of the heart; 5. Ventricle of the heart; Gills Ctenidium ; 7. Anterior adductor muscle; 2. Labial palp; 3. Digestive gland; 4. Stomach; 5. Gonad; 6. Plenty of less-common bivalves exist as well, and some are eaten in smaller numbers where they are plentiful enough to catch, cook and consume.
What makes a bivalve a bivalve? The technical answer involves their scientific classification. Bivalves can be eaten in a wide variety of ways, with techniques from raw consumption to deep frying and preparation in chowders all common. Looking for some inspiration? Consider these popular approaches to cooking bivalves:.
Crabs, lobsters, crayfish and shrimp are among the most commonly consumed crustaceans. These animals all live near or in water and are characterized by their hard shells, mostly soft interiors and branching limbs — like the claw of a lobster or crab. Crustaceans also benefit from a number of tried and true preparations and presentations. Here are just a few to consider:. Snails and slugs are the common names for members of the Gastropoda class.
These soft, usually small creatures may or may not have a shell and can live on land or in water depending on species. While most slug types are only emerging as a possible regular food source, snails have long been served as a delicacy. A few recipes to make the most of gastropods include:. Bivalves There are many bivalves regularly eaten around the world, from clams and scallops to mussels and oysters.
Consider these popular approaches to cooking bivalves: The classic New England clambake — which can include lobster and shrimp, both crustaceans — mixes seafood and other ingredients common to the region into a delicious and filling meal.
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