INTRODUCTION: The animal kingdom is generally thought to have originated in the Archaeozoic oceans long before the earliest fossil records. Each major phylum of animals has at least a few marine representatives; some groups, such as cnidarians and echinoderms, are largely or entirely marine species. Coming from the ancestral marine environment, different groups of animals have invaded fresh waters; some moved to land. There are more than a million described animal species. About 5% of this number are animals with backbones or simply called vertebrates. The rest of the 95% is made up largely of the animal kingdom, namely invertebrates. The spine is the only feature that separates the entire animal kingdom into two groups. However, the most successful animals among all animals are arthropods, which make up 85% of animals. Invertebrates do not have a single positive characteristic in common. Some invertebrates have common phylogenetic origins and others are only loosely related.o INVERTEBRATE GROUPS AND THEIR CHARACTERISTICS1. Domain: EukaryotaKingdom: AnimaliaPhylum: PoriferaPhylum Porifera or sponges are mainly marine animals made up of poorly organized cells. Characteristics of the phylum Porifera include: o Asymmetric or superficially radially symmetric o Three cell types: pinacocytes, mesenchymal cells, and choanocytes o Central cavity or a series of branching chambers, through which water circulates during filter feeding. o No tissues or organs. One of the classes in this phylum is the class Hexactinellida. The general characteristics of this class are spicules composed of silica and six-rayed spicules, often fused into a complex, cup- or vase-shaped lattice, sycon...... middle of paper...... eviana.5. Domain: EukaryotaKingdom: AnimaliaPhylum: NematodaPhylum Nematodes are roundworms that are one of the most abundant animals on earth. Characteristics of the nematode phylum include: o Triploblastic, bilateral, vermiform (worm-like in shape, long and thin), non-segmented, pseudocoelomate o Body round in cross section and covered with a layered elastic cuticle, molting accompanies usually growing in juveniles o Complete digestive tract, mouth usually surrounded by lips bearing sensory organs o Most have a unique excretory system consisting of one or two renette cells or a set of collecting tubules o Body wall n It only has longitudinal muscles. One of the classes in this phylum is the class Adenophorea. The general characteristic of this class is that phasmids are absent, most live freely but some parasitic species are present. Example: Trichinella spiralis.