These are the major animal phyla that will be discussed in the later chapters, with a brief description and some reproductive and developmental features -
Porifera. The sponges. This group are filter feeders, a common mode of feeding that involves straining food (in this case, microscopic organisms) out of the water. Sponges are sessile, they stay in place. They have two cell layers, an outer epithelium, and an inner layer of mostly choanocytes, filtering cells. Between the layers is a jellyish mesoglea, with structural spicules of various materials and roaming amebocytes, which can replace and become any dead or lost cells. Do not technically have tissues. Various types of symmetry.
Cnidaria. Includes jellyfish, corals, anemones, Hydra, etc. Unique for stinging cells in ectoderm. Have ectoderm and gastroderm around a digestive space, with mesoglea and amebocytes. Also without tissues, although distinction is less clear. Are radially symmetrical, often numeric. Alternation of generations is common, with sessile asexual forms (polyps) and mobile sexual forms (medusas, small jellyfish). May be colonial.
Platyhelminthes, flatworms. Includes free-living planaria, parasitic flukes and tapeworms. Have mesoderm and complex organ systems, no body cavities. Parasitic groups use alternation of generations, with asexual form typically in one host species (intermediate hosts) and sexual form in another (definitive hosts), sometimes with vector hosts between. Typically monoecious.
Nematodes, roundworms. Found in almost every niche usable by a cylindrical worm. Have acoelomate body cavity. Have digestive system with mouth and anus. Typically sexual and dioecious. Adults often have set number of cells. Almost protostomes.
Trochophore larval forms are found in many of these mid-list phyla, as well as minor phyla not listed.
Mollusks. Includes gastropods, the snails and slugs, bivalves, the mussels, and cephalopods, the octopus, squid, and cuttlefish. Protostome group. Body form has foot in different forms, visceral mass with coelom, and mantle, which often generates a shell and surrounds a multi-function mantle cavity. Some appearance of metamerism.
Annelids, the segmented worms. Includes polychaetes, marine worms, oligochaetes, fresh water & earthworms, and hirudinea, leeches. Have definite metamerism, reduced in leeches. Protostomes.
Arthropods, many varied animals with exoskeletons. There are two subgroups: the chelicerates, including spiders, horseshoe crabs, and scorpions; the mandibulates, including crustaceans, insects, millipedes, and centipedes. Most have reduced metamerism. Protostomes.
Echinoderms, including starfish, sea urchins, and sea cucumbers. This is a deuterostome group. Most are pentaradial, although bilateral as early embryos (and sea cucumbers are pentaradial as late embryos but then become largely bilateral).
Chordates, including vertebrates, backboned animals. Technically metameric deuterostomes. Have notochord, structural in primitive forms but an inductive structure in early embryos in most. Sealed eggs with amnions, structures that allow gas exchange with minimal water loss, found in land forms (reptiles, birds, primitive mammals). Umbilicus attaches embryo to yolk (and mother in most mammals).