Class of mollusca - monoplacophora, Biology

Class of Mollusca - Monoplacophora

Bilaterally symmetrical, with broad flat foot and single shell, mantle cavity has five to six pairs of gills; six pairs of nephridia of which two functions as gonoducts; radula present; sexes separate. Extant species are included in three genera. These are found at great depths in the sea. Also many fossil forms belonging to Cambrian and Devonian times are known. The monoplacophorans can he regarded as the ancestors of all molluscs. Monoplacophorans have following salient characters: The shell varies in shape from a flat shield to short cone: length of the animals ranges from 3 mm to 3 cm.

  • The buccal cavity comprise a radula and a subradular organ. The stomach has a crystalline style. There is a long and coiled intestine.
  • The foot is very broad and flat.
  • Sexes are separate. Two pairs of gonads are situated in the middle of the body. Fertilisation is external. Example Neopilina
  • The mantle cavity comprises 5 or 6 pairs of monopectinate gills.
  • The mouth lies in front of the foot and the anus opens posteriorly in the mantle cavity.
  • 6 pairs of kidneys are present.
  • Heart has two pairs of auricles and a pair of ventricles and is surrounded by paired pericardial coelom.
  • Nervous system is typical along with a pair of cerebral ganglia, circumoral nerve ring, a pair of visceral nerves and a pair of pedal nerves.
  • There is a preoral fold in front of the mouth extending laterally as a larger ciliated palp like structure. Another fold projects behind the mouth on either side as postoral tentacles.
Posted Date: 2/4/2013 12:57:47 AM | Location : United States







Related Discussions:- Class of mollusca - monoplacophora, Assignment Help, Ask Question on Class of mollusca - monoplacophora, Get Answer, Expert's Help, Class of mollusca - monoplacophora Discussions

Write discussion on Class of mollusca - monoplacophora
Your posts are moderated
Related Questions
Express the term in brief - Protonephridia. An osmoregulatory-excretory structure found in some invertebrates. Also known as a flamecell, this tubule is closed at its distal en

State the similarity between Shigella and Salmonella There are many points of similarity between Shigella and Salmonella. They dwell primarily in the gastrointestinal tract, wi

Lentic Ecosystems Lakes are inland, depressions containing standing water. They vary considerably in area and depth. The largest lake in the world, the lake Superior in North

Phylum Ascomycetes 1) Sexual reproduction is by conjugation and is followed by the formation of ascospores inside a sac called ascus. 2) The asci may be grouped together to

Explain Metabolic Requierments For Types Of Exercise ? A relative scale of energy requirements related to heart function necessary for performing various daily activities has b

Features of Amphibian Gastrulation Major features of amphibian gastrulation are: Ectoderm surrounds the embryo by Epiboly. Gastrulation is initiated by a limited i

protoplasmic level of oganisation

The name Joseph Merrick, subject of "The Elephant Man", is generally associated with one disorder, though it now seems likely he actually suffered from a different disorder. Name e

How do placental mammals reproduce? Placental mammals reproduce sexually, they have internal fecundation and they are viviparous, i.e., their embryo creates within the mother's

The fact that some pure solutions of hydrocarbons do not readily evaporate at room temperature is a result of- Select one: a. London dispersion forces. b. The hydrophobic