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Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion , about 542 million years ago. Contents 1 Etymology 2 Characteristics 2.1 Structure 2.2 Reproduction and development 2.3 Food and energy sourcing 3 Origin and fossil

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The Ecdysozoa (pronounced /ˌɛkdɪsɵˈzoʊ.ə/ ) are a grouping of protostome animals, [ 1 ] including the Arthropoda ( insects , chelicerata , crustaceans , and myriapods ), Nematoda , and several smaller phyla . They were first defined by Aguinaldo et al. in 1997, based mainly on trees

The narrative is structured as a pilgrimage , with all modern animals following their own path through history to the origin of life . Humans meet their evolutionary cousins at rendezvous points along the way, the points at which the lineage diverged. At each point Dawkins attempts to infer

have been put forward, and discriminating between them is difficult because the relationships of animal phyla are not completely resolved. Animals are generally considered to have evolved from a flagellated eukaryote. Their closest known living relatives are the choanoflagellates , collared

The Cambrian explosion or Cambrian radiation was the relatively rapid appearance, over a period of many million years, of most major Phyla around 530 million years ago , as found in the fossil record . [ 1 ] [ 2 ] This was accompanied by a major diversification of other organisms, including

Ectoprocta (Nitsche, 1869 [ 4 ] ) The Bryozoa , also known as Ectoprocta or commonly as moss animals , are a phylum of aquatic invertebrate animals . Typically about 0.5 millimetres (0.020 in) long, they are filter feeders that sieve food particles out of the water using a retractable

pedicle projects from an opening in the hinge or from a hole in the larger valve, attaching the animal to the seabed but clear of silt that would obstruct the opening. Brachiopods have a mantle that secretes and lines the shell, and encloses the internal organs. The body occupies typically

Class Polychaeta ( paraphyletic ?) Class Clitellata (see below )     Oligochaeta - earthworms , etc.     Branchiobdellida     Hirudinea - leeches Class Myzostomida Class Archiannelida ( polyphyletic ) The annelids (also called "ringed worms"), formally called Annelida

Cnidarians were for a long time grouped with Ctenophores in the phylum Coelenterata , but increasing awareness of their differences caused them to be placed in separate phyla. Cnidarians are classified into four main groups: sessile Anthozoa ( sea anemones , corals , sea pens ); swimming