Phylum Mollusca includes a group of soft-bodied invertebrates with bilateral symmetry. Molluscs have a shell. They also have a mantle, which is a thin layer of tissue covering their body organs. Moreover, they have a muscular foot underside of the body. The three groups of molluscs are gastropods, cephalopods, and bivalves. Cephalopods are marine animals. Gastropods are mainly terrestrial.
Some gastropods are aquatic: salt and freshwater animals. Overview and Key Difference 2. What is Cephalopods 3. What is Gastropods 4. Similarities Between Cephalopods and Gastropods 5. Cephalopods are a group of molluscs comprising of marine animals such as octopi, cuttlefish, and nautili, etc. They are strictly marine molluscs. Cephalopods are the most intelligent invertebrates. They have a highly developed nervous system with a complex brain. Moreover, they show rapid movements in the water.
They can swim fast. Furthermore, they have a closed circulatory system. They have a rudimentary mantle cavity and lack eyes, tentacles, and nephridia excretory organs. The morphology of the shell and the underlying animal can vary from circular to ovate.
A looped digestive system, multiple pairs of excretory organs, many gills, and a pair of gonads are present in these animals.
The monoplacophorans were believed extinct and only known via fossil records until the discovery of Neopilina galathaea in Today, scientists have identified nearly two dozen extant species. These animals have a broad, ventral foot that is adapted for suction to rocks and other substrates, and a mantle that extends beyond the shell in the form of a girdle.
Calcareous spines may be present on the girdle to offer protection from predators. Chitons live worldwide, in cold water, warm water, and the tropics. Most chiton species inhabit intertidal or subtidal zones, and do not extend beyond the photic zone.
Some species live quite high in the intertidal zone and are exposed to the air and light for long periods. Bivalvia is a class of marine and freshwater molluscs with laterally compressed bodies enclosed by a shell in two hinged parts. Bivalves include clams, oysters, mussels, scallops, and numerous other families of shells.
The majority are filter feeders and have no head or radula. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment on the seabed, while others lie on the sea floor or attach themselves to rocks or other hard surfaces.
The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. Gastropoda includes shell-bearing species as well as species with a reduced shell. These animals are asymmetrical and usually present a coiled shell.
Shells may be planospiral like a garden hose wound up , commonly seen in garden snails, or conispiral like a spiral staircase , commonly seen in marine conches. The visceral mass in the shelled species displays torsion around the perpendicular axis on the center of the foot, which is the key characteristic of this group, along with a foot that is modified for crawling. No cephalopods -- with the exception of species belonging to the taxonomic subclass Nautiloidea -- have external shells.
It's thought that cephalopods evolved from certain types of shelled gastropods, which may be why some species -- such as cuttlefish -- still retain an internal shell. Gastropods and cephalopods have very different anatomical structures. The name cephalopod translates to "head-foot. Gastropod means "stomach-foot. By using the site, you agree to the uses of cookies and other technology as outlined in our Policy, and to our Terms of Use. Habitat Among the most obvious differences between gastropods and cephalopods are the habitats in which they live.
Diet Cephalopods have much more specific diets than gastropods.
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