The phylum Mollusca contains over 100,000 species with a variety of body forms and lifestyles. In mollusks, the coelom is reduced and limited to the region around the heart. The Mollusk body first appeared during the Cambrian Period. All mollusks have: 1. A visceral mass containing internal organs, including the digestive tract, paired kidneys, and reproductive organs. 2. A mantle [...]
In this article we will discuss about:- 1. Description of Torsion 2. Course of Torsion 3. Ways 4. Effect 5. Significance. Description of Torsion: 180° anticlockwise twisting of the visceropallium on the head-foot long axis during early development in gastropod molluscs is torsion. It is an early and fundamental event in gastropod ontogeny (the event in phylogeny, which brought the [...]
The following points highlight the six main classes of phylum mollusca. The classes are: 1. Monoplacophora 2. Amphineura 3. Gastropoda 4. Scaphopoda 5. Pelecypoda or Bivalvia or Lamellibranchiata 6. Cephalopoda. Class # 1. Monoplacophora: 1. The body is bilaterally symmetrical and covered by a mantle. 2. The single dorsal shell is thin and sub circular. 3. The metamerism is apparent [...]