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
Q. How are nutrients distributed through the digestive system in planarias? Planarias have single opening digestive system incomplete with ramifications that transport nutrient

Q. What is the difference between diastoleSystole and systole and diastole are the two stages into which the cardiac cycle is divided Diastole is the stage of the cardiac cycle

How does the amoeboid movement occur? What are examples of beings and cells that use such movements for locomotion? Amoeboid movements are formed by cytoplasmic movements and p

Cell structure and function All organisms, whether simple or complex, plants or animals. are composed of cells. For example, a bacterium or an amoeba is made up of just one cel

general characteristics of phylum chordata

Q. Why is the uricotelic excretion essential for reptile and avian embryos? In birds and reptiles the excretory system is uricotelic since uric acid is less toxic, insoluble an

Define Procedure for Determination of Blood Glucose by Nelson Somogyi Method? 1. Label a series of Folins tubes with blank (B), standard (S1-S5) and sample (SA 1-2) and place

MODIFICATION OF MITOSIS 1 .      CRYPTOMITOSIS OR PROMITOSIS : Primitive type of mitosis. In this mitosis nuclear membrane not disappear (remain intact throughout the div

Excretory organ for protozoa

Why is the occurrence of eyelids in amphibians in comparison to their absence in fishes and adaptation to terrestrial life? Eyelids associated to lacrimal glands protect and ke