The dorsal margin of the two valves are usually united by ligament. A chitinous-toothed tongue called the radula is present in most mollusks. In addition to molluscs that are a part of the food industry, pearls made by oysters have a large commercial value. In addition, carbonate of magnesium and trace of silica are also detected. The class Scaphopoda was finally established by Bronn 1862.
It also has internal shell Largest. 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. Octopus can change its colour. The dorso-ventral muscles correspond to the columellar muscles of the gastropods. Dorsal side is covered by transversely placed 7 to 8 shell plates, held together by a surrounding fleshy thick girdle. Anterior part of the shell much wider than the posterior end.
Shells are equal-sized and with a few large cardinal and lateral hinge teeth. Examples: Soft shell clams Mya , Boring clams Pholas, Barnea, Martesia, Xylophaga , Wood borer in shipworms Teredo, Bankia. The shell is circular in outline. How is the nervous system of molluscs organized? In Scaphopoda the kidneys are also paired. The ovary and testis look alike and are distinguishable by colour only. The posterior gills have lamellae usually on one side, while the anterior ones have lamellae on both sides.
Cephalization is evident in molluscs, as they contain neurons concentrates in a ganglial pattern. Visceral mass is enclosed by a thick muscular fold of the body wall, called mantle or pallium, which secretes spicules or shell. What is the ecological role of earthworms? The Acephala includes Tunicata, Brachiopoda and Cirripedia. These three features are seen in every member of this phylum, even humans. If you have not done even one quest, you are gonna have to do them so. Annelids are cylindrical worms with segmented bodies they are metameric.
Notaspidea: i Shell may or may not be present. But the relation of the soft parts with reference to the shell differs in Spirula and Nautilus. In Stylommatophora and Siphonophora the two ducts unite to form a common duct which opens into cloaca. There are present two siphons posteriorly. Females of some species care for the eggs for an extended period of time and may end up dying during that time period. Sexes separate; external sexual dimorphism in some species.
Neopilina lives in mud and feeds mainly on foraminifera. Nuculoida: i Shell small to triangular and equivalve. Generally, the kidneys open externally near the anus into the mantle cavity. Neopilina galatheae is about 3. The margin of the mantle is the main source of deposition of shell matter and the rest of the mantle helps to thicken the innermost layer. While most of the members are relatively unintelligent and rely on sessile filter feeding, many species are very intelligent, competing with organisms like dolphins and pigs.
Bengal , Talsari Odisha and South Indian coasts. Fertilization may be external or internal. Shell may be external e. Most of the Bivalves live on micro-organisms, but the larval forms for some time lead ectoparasitic life in the gills of fishes. Therefore, they play the role as decomposers and fertilizers. Which group of organisms is most closely related? Cuvier 1795 first named Cephalopoda for the cuttle fish. The toxin released, known as conotoxin, is a peptide with internal disulfide linkages.
Note the hatchet shape of the foot used to burrow into mud or sand. Members of this class are found in marine as well as freshwater habitats. The Danish Zoologist, Lemche first collected the species in 1952 from the assorted molluscs collected in Galathea expedition. In monoaulic forms the seminal receptacle opens into the hermaphroditic duct into the oviduct in the dialulic forms but in Doris the seminal receptacle not only opens into the oviduct but also communicates with vagina. Habitat: Most species are burrowers in sand and mud in warm seas.
The clitellum is a special region of the annelid made up of rings metameres with a reproductive function. A ventral muscular foot is present which helps in locomotion and may be secondarily modified in some forms. It is a major group in the animal kingdom as regards the number which occupies next to arthropods. Examples of representative species: earthworms, leeches, lugworms. Foot is not compressed but has a flattened ventral surface upon which the animal creeps. The Questions and Answers of Which is the second largest phylum? Mollusks are predominantly a marine group of animals; however, they are known to inhabit freshwater as well as terrestrial habitats. The prototroch of the Trochophore expands in the veliger larva to form a ciliated disc, called velum Fig.