INVERTEBRATES AND THE ORIGIN OF ANIMAL DIVERSITY

Clues to animal phylogeny

Phylogeny = the evolutionary history of a species or group of related species. Based primarily upon clues from comparative anatomy and embryology.

Comparative anatomy and embryology provide clues to animal phylogeny: an overview of animal diversity

The diagram (fig. 32.14) on page 636 in Campbell (see below) is one interpretation of the phylogenetic relationships of the different animal kingdom. You will examine these animal phyla in the lab, however we will examine some of the major anatomical, and embryological evolutionary steps which have accounted for the incredible diversity seen in this phyla.

1. The Parazoa-Eumetazoa split

Subkingdom Parazoa

This contains only the phylum Porifera, (the sponges). Unique development and simple anatomy separates this phylum from the other animals. This group of "animals" lack true tissues. The cells that make up the bodies of these organisms are relatively unspecialised. Sponges are suspension feeders (also known as filter feeders) that collect food particles from the water circulating through the porous body.

PHYLUM PORIFERA. The Sponges.

These organisms represent the simplest animals you will examine. There is speculation that the sponges arose independently of all other animals, and as such, are on their own separate line of evolution. The sponges have the simplest type of multicellular animal construction, existing at the cellular level of organisation. This means they lack true tissues or organs and the division of labour within the animals is confined to a few specialised cell types. There are approximately 5,000 extant species of Poriferans, of which about 120 are freshwater forms. The remainder can be found in almost all marine habitats. The sponges are attached (sessile) or benthic organisms, adhering to all solid substrates including the coverings of other animals such as snails, corals and crabs.

Phylum Characteristics.

1. multicellular animals, body a loose aggregation of cells

2. cellular level of organisation

3. all aquatic, mostly marine

4. body of pores canals and chambers for water passage

5. radial or asymmetrical

6. body of two layers separated by a gelatinous mesohyl

7. skeleton of proteinaceous spongin which may or may not be impregnated with calcium or silica

8. filter feeders with intracellular digestion

9. adults sessile, larvae (amphiblastula) motile

10. reproduction asexual and sexual

Here you see a close up of two live sponges.

Below you see a diagram illustrating the anatomy of a typical sponge.