The infinite variety: the beginning of life
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- Scientific classification
- The first Multicellular Organisms
- Ctenophores and Cnidarians – first organism with real structure
Protista Diversity There are thousands of species of protistans, some possessing cilia or flagellum, whereas others use pseudopodium for locomotion. Some protistans secrete shells of silica or lime, whereas others have combined individual cells to produce a colony (eg Volvox). The constituent cells of Volvox, however, are co-ordinated, for all the flagellum around the sphere beat in an organized way and give direction to locomotion. 
Volvox is one of the best known genera of green algae, and is the culmination of the evolution of spherical colonies. Each Volvox is composed of on the order of a thousand cells, each a bi-flagellate similar to Chlamydomonas, interconnected and arranged in a hollow sphere (a Coenobia), with a distinct anterior and posterior. Asexual colonies consist of somatic or vegetative cells, which do not reproduce, and gonidia, which reproduce, the reproduction being a process of longitudinal division. Sexual or oogamous colonies contain, as well as somatic cells, ova (non-motile female cells) or spermatozoa (small, motile male cells) or a mixture of the two. These cells, near the back of the colony, develop into new colonies, initially with the flagella directed inwards and held within the parent. Eventually the parent bursts and the daughter colonies evert. Volvox
Volvox
Volvox aureus Scientific classification Kingdom: Plantae Phylum: Chlorophyta Class: Chlorophyceae Order: Volvocales Family: Volvocaceae Genus: Volvox Species
Volvox aureus Volvox carteri (V. nagariensis) Volvox globactor Volvox dissipatrix Volvox tertius The first Multicellular Organisms? Increased co-ordination between colonial cells appeared with the evolution of the sponges (Porifera). Sponges may be formless lumps on the sea floor reaching two metres in size. Their surfaces are covered with tiny pores through which water is drawn into the body by flagella and then expelled through larger vents. The sponges feed by filtering particles from this stream of water passing through its body. Some sponges produce a soft flexible silica-based substance which supports the whole organism, whereas other sponges secrete lime or silica to create a hard "skeleton" for support. Despite the elaborate skeletons that some sponges are able to produce they cannot be considered as an integrated multi-cellular animals since they have no nervous systems nor muscle fibres. 
Sponges are primitive, sessile, mostly marine, waterdwelling filter feeders that pump water through their matrix to filter out particulates of food matter. Sponges are among the simplest of animals, with partially differentiated tissues but without muscles, nerves, or internal organs. In some ways they are closer to being cell-colonies than multicellular organisms. There are over 5,000 modern species of sponges known, and they can be found attached to surfaces anywhere from the intertidal zone to as deep as 8,500 m. Though the fossil record of sponges dates back to the Precambrian era, new species are still commonly discovered. The structure of a sponge is simple: it is shaped like a tube, with one end stuck to a rock or other object and an open end, the osculum, open to the environment. The spongocoel, or interior of the sponge, is composed of walls perforated with microscopic pores that allow water to flow through the spongocoel. Sponges Sponges
Scientific classification Kingdom: Animalia Phylum: Porifera Grant in Todd, 1836 Classes Calcarea Hexactinellida Demospongiae Sclerospongiae Ctenophores and Cnidarians – first organism with real structure The simplest organisms to possess such structures are the Ctenophores which include comb jellies, "sea gooseberries", "sea walnuts" and the "Venus' girdles" and the Cnidarians which are represented by the Anthozoa which are corals and sea anemones, Scyphozoa which are jellyfish, the Cubozoa represented by the box jellyfish (sea wasps) and the and Hydrozoa which includes the Hydroids, hydra-like animals. Chironex fleckeri is a highly venomous species of box jellyfish that inhabits Australian coast and is a very fast swimmer and has very sophisticated eyes. 
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