Diversity and Phylogeny The rapld diverslfication of animals during the Cambrian
ID: 135224 • Letter: D
Question
Diversity and Phylogeny The rapld diverslfication of animals during the Cambrian era resulted in a number of different body plans. Traditionally, these different designs have been used to classify animals. In particular, the following features have been used: 1. Level of organization. Does the animal have true tissues, or is It a collection of cells? 2. Body symmetry (Fig. 27.3). Is the animal radially or bilaterally symmetrical? 3. Number of germ layers. Does the developing embryo form two layers of cells (diploblastic: endoderm and ectoderm) or three layers (triploblastic: endoderm, ectoderm and mesoderm)? mesoderm (pseudocoelomate) or a cavity completely lined with mesoderm (coelomate)? animal show spiral, determinate cleavage or radial, indeterminate cleavage? Does it have schizocoelous or enterocoelous coelom 4. Body cavity presence and lining (Fig. 27.4). Does the animal have no body cavity (acoelomate), a cavity only partially lined with 5. Embryonic development (Fig. 27.5). Is the animal a protostome or a deuterostome? During embryonic development, does the development? Does the mouth or the anus develop from the blastopore? Recently, new evidence from molecular studies has led to a revision of the animal phylogenetic tree (Fig, 27.6). Information about body plans is still important in this new classification, and we will refer to the newer tree for the rest of this course. Segmentation LophophoreExplanation / Answer
1. Phylum Cnidaria - It has true tissues mainly used in capturing of the prey.These species are mainly found in mainwater and marine environment.
Body Symmetry- These organisms are bilaterally symmetrical with mouth surrounded by tentacles
Number of germ layers- They are diploblastic
Cnidarians have no true body cavity, that is they are acoelomates as they do not possess a mesoderm tissue and are diploblastic.
Cnidarians are protostomes as the first opening the blastospore becomes the mouth. It undergoes spiral, determinate cleavage.It has schizocoelus development wherein the mouth develops from the blastopore.
Platyhelminthes- They do not have true tissue rather they are colection of cells.
They are bilaterally symmetrical, unsegemented and are soft bodied invertebrates. Though they have three distinct layers, ectoderm, mesoderm, endoderm.
They have no body cavity ie they are acoelomates.
Platyhelminthes are protostomes and they show spiral cleavage, with split mesoderm to develop coelom.They are unsegmented schizocoelus organisms with mouth developing first.