Metazoa

Basics

-Multicellular, mobile heterotrophs with an internal chamber for digestion, and without rigid cell walls.
-Mostly with tissue differentiation and collagen in the extracellular matrix.
-Meiosis produces gametes, not spores.
-Development includes a blastula

Placozoa

-A single species discovered in an aquarium in Australia in 1883.
-Marine, soft-bodied, microscopic.
-Distinct dorsal and ventral layers of ciliated cells, no organs.
-External digestion of detritus and algae.

Sponge body plans

-Ascon
-Sycon
-Leucon

Desmospongiae

-"Leucon" type sponges, present in all aquatic habitats, from fresh water to polar, to deep ocean.
-Feed on detritus and microscopic organisms (bacteria and dinoflagellates in particular). -Food acquired by choanocytes with intracellular digestion.
-Comme

Hexactinellida

-The "glass sponges", marine, mostly deep water.
-Silica construction of spicules not always requiring protein matrix. Without continuous layer of choanocytes.
-Famous commensals with shrimp that spend their entire lives within the sponge.

Calcarea

-The only sponges with spicules made of calcium carbonate.
-Shallow (mostly tropical) marine waters where calcium carbonate is less soluble; hard substrates required.
-All of the sponge body types are here.

Cnidaria

-The hydras, anemones, corals and jellyfish. Predators. Mostly marine.
-Includes the "true" or stony corals that form reefs with dinoflagellate symbionts.
-Radially symmetric, with two germ layers (diploblastic).
-Single orifice surrounded by tentacles, n

Ctenophora

-The comb-jellies: marine, planktonic predators without a sessile stage.
-Specialized adhesive cells on tentacles.
-Like Cnidarians, nerves are a network lacking centralization.

Myxozoa

-Aquatic parasites of annelids and ectothermic vertebrates.
-Expulsive filaments that might be derived from cnidocytes.

Bilateria

-Bilateral symmetry, with anterior-posterior and dorsal-ventral axes.
-A third germ layer, the mesoderm, and a coelomic cavity.
-Central nervous system organized around cephalic ganglion and nerve cord.

Mesozoa

-Small, vermiform parasites of marine invertebrates.
-Dorso-ventrally flattened with bilateral symmetry but no organs.