Kidneys in different Molluscs vary greatly.
Sea butterflies or shelled pteropods (Spiratella, Limacina, Cavolina, Clio, Cymbulia, Corolla, Desmopterus). In some Bivalves like Anodonta and Mytilus, hinge- teeth are absent. There is no separate gonoduct and the sexual products are discharged into the pericardial cavity. [78], However, an analysis in 2009 using both morphological and molecular phylogenetics comparisons concluded the molluscs are not monophyletic; in particular, Scaphopoda and Bivalvia are both separate, monophyletic lineages unrelated to the remaining molluscan classes; the traditional phylum Mollusca is polyphyletic, and it can only be made monophyletic if scaphopods and bivalves are excluded. (i) Shells equivalve, circular, ovate or trapezoidal and moderately compressed and isomyarian.
The shell was originally a simple cone, but due to the increase in size of the visceral hump the shell has become twisted to accommodate whole of the visceral organs. They have recorded since the Lower Cambrian Period and all the members have become extinct during Jurassic Period except Nautilus (Fig. [12], In some forms the shell contains openings. Some bivalves bury themselves on the seabed in sediments, while others lie on the seafloor or attach to rocks or other hard surfaces.
Shells may be planospiral (like a wounded garden hose), commonly seen in snails in the garden, or conispiral (like a spiral staircase), commonly seen in marine conches. The subclass contains a single family Nautilidae and is represented by four extant species: N. macromphalus is found in Western Pacific, New Caledonia and Loyalty Islands. Aplysia California has the largest body of 1 m length. Bivalves include clams, oysters, mussels, scallops, and numerous other families of shells.
Nucula; Malletia, Subclass Pteriomorphia, ex. Good evidence exists for the appearance of gastropods, cephalopods, and bivalves in the Cambrian period, 541–485.4 million years ago. Foot usually flat on the ventral surface, situated behind the head usually used for creeping. The sexes are separate in Polyplacophora. 16.60D), Neorossia. To start with, let me tell you the one thing the scientific community who undertake this task { they are called taxonomists. Mostly extinct (Lower Cambrian to Devonian), a few living species. 2. Marine, found in Australian oceans, from shallow water (200 m) to mostly in deep water (3000 m). Among the members of 7 classes some members of this class have ventured onto land and a few are parasitic. Numerous molluscs also live in freshwater and terrestrial habitats. Subclass Opisthobranchia (=Euthyneura), Ex. The inner surface of the valves shows pallial lines which are actually the impressions produced by the muscular edge of the mantle. For this reason it was called Loven’s larva for many years since its discovery. They are distributed in almost all the parts of the earth and exhibit variety of forms. Mantle and Mantle Cavity 8.
To employ this strategy, the plant has to be large enough for the mollusc to 'sit' on, so smaller macroscopic plants are not as often eaten as their larger counterparts. 16.62C).
The subclass prosobranchia is divided into 3 orders: Order 1.
podos = foot] living species and 40,000 fossil species. 14. Fins are absent.
Reduced mantle cavity shows a tendency to occupy in the posterior side due to detorsion of the visceral hump. In freshwater bivalves, trochophore stage is suppressed and the veliger stage is represented by either Glochidium larva or Lasidium larva or Haustoria larva. Amongst cephalopods the shell varies in form. Gills as well as kidneys are two pairs.
Siphonodentalium, Cadulus, Pulsellum, Entalina. In all Opisthobranchia excepting Acteon and in all Pulmonata excepting Amphibola operculum is absent. It has previously been employed as a basis for classification. [15] Molluscs never use phosphate to construct their hard parts,[28] with the questionable exception of Cobcrephora. (1955). There are numerous gills or ctenidia in the respiratory organs usually provided with osphradium at the base. 18.
Shell and operculum usually reduced or absent. The ligament which unites the two valves consists of two parts, the externally located ligament proper and the internal cartilage. Mollusc species can also represent hazards or pests for human activities. …