BIOL 227 Lecture Notes - Lecture 7: Suction Cup, Aplacophora, Hydrostatic Skeleton
3 May 2016
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Biol 227 tut 7 notes arthropods, molluscs & their classification. Arthropoda and mollusca are the most species-rich animal phyla, although the number of cryptic nematode species remains to be established. In particular, molluscs have a common ancestor with: a characteristic foot, a shell, a radula, a mantle, a reduced coelom and a large gill cavity. Hard bodied organisms mainly molluscs are used to flag geologic time periods of rock strata. Molluscs and arthropods are the most diverse protostome clades. Start with the characters important for (morphological) classification: (1) body cavity modifications (2) segmentation and appendage gain, loss or transformation. Morphological diversification of appendages in molluscs and arthropods have long been key indicators of taxonomic diversifications within each phyla (head projections, shell elaboration, leg number, tentacle development, mouthpart variation, etc. ) Segmentation is homoplasic, it has evolved independently in annelids, arthropods and vertebrates, although similar genes appear to be involved in these 3 taxa.
