This page covers both protozoa (single-celled animal-like organisms) and invertebrate animals.

By the way, "invertebrata" is not a real scientific term, of course. It will be the title of my first section of my animal stories collection. And so it's the title of this page too, because this classification section is meant to mirror my story collection; both reflect the diversity of the animal kingdom.

My main source was Brusca & Brusca's Invertebrates (1990) (see their 2nd ed., 2003), along with several other sources. For the species numbers, I followed Margulis & Schwartz's Five Kingdoms, 3rd ed., (1998).

To decide the order of the phyla, I consulted almost ten sources and tried to reconcile the conflicting views of all of them. This was difficult and maybe foolish, but I hope not completely unsuccessful.

				Described living species		Stories
	KINGDOM ANIMALIA. Animals. Animals are defined as "multicellular heterotrophs"—that is, many-celled organisms that gain nourishment by ingesting organic food.				Roughly 1,287,541
		Phylum Mesozoa. Mesozoans. Simple, microscopic parasites of marine invertebrates.			85
		Phylum Porifera. Sponges. Sessile animals, mostly ocean-dwelling, whose cells are not organized into tissues or organs. They feed by filtering large amounts of water through their bodies and sifting out plankton and organic debris.			9,000	Sponge
		Phylum Placozoa. A single primitive, microscopic species, Trichoplax adhaerens.			1
		Phylum Cnidaria. Cnidarians. Simple, aquatic animals, mostly marine, usually soft-bodied, shaped either like a polyp (such as corals) or like a medusa (such as jellyfishes), or even shaped as both during the course of a life cycle. they often sting prey, which includes invertebrates, protists, and fish. Examples include jellyfish, hydras, sea anenomes, and corals.			9,400	Jellyfish
		Phylum Ctenophora. Comb jellies, or sea walnuts. Small marine invertebrates, usually spherical, transparent, and possessing tentacles.			100
		Phylum Platyhelminthes. Flatworms. Ribbon-shaped, soft-bodied invetebrates. Some of them (the turbellarians) are free-living; the rest are parasitic, feeding on a wide variety of animals. They range in size from microscopic (flukes) to 10 m (30 ft.) long (some tapeworms). Examples include tapeworms, flukes, and turbellarians.			20,000	Tape- worm
		Phylum Nemertea. Nemertine worms, proboscis worms, or ribbon worms. Flat, soft worms with an extensible tongue-like proboscis.			900
		Phylum Gnathostomulida. Gnathostomulids, or jaw worms. Microscopic worms that have a jaw-like apparats on their pharynx, inhabiting ocean sands.			80
		Phylum Rotifera. Rotifers. Tiny aquatic animals, ranging from microscopic to a few millimeters long, usually inhabiting fresh water, eating microorganisms and organic debris, and having a distinctive ciliated corona on the top of their heads.			2,000
		Phylum Acanthocephala. Acanthocephalans, or spiny-headed worms. Small parasites, inhabiting two species in their lifespan, and possessing a spiny-tongue-like proboscis.			1,000
		Phylum Cycliophora. Symbion pandora, a single unique species of lobster parasite that was discovered in 1995.			1
		Phylum Gastrotricha. Gastrotrichs. Free-living worms, less than 5 mm long, inhabiting watery sediment.			400
		Phylum Kinorhyncha. Kinorhynchs. Tiny, free-living worms that burrow through ocean sediment.			150
		Phylum Loricifera. Loriciferans. Microscopic animals, inhabiting watery sediment, and having a lorica, or tiny shell, and an introvert, or spiny head.			25
		Phylum Priapulida. Priapulids. Tiny, wormlike animals with a retractable, tongue-like proboscis, inhabiting oceanic sediment.			17
		Phylum Nematoda. Roundworms, or nematodes. Worms in this large phylum range in size from microscopic to several meters long; in behavior from free-living to parasitic; and in habitat from ocean water to fresh water to the soil to the insides of animals. Free-living roundworms provide such benefits as soil aeration and fertilization; parasitic roundworms cause such diseases as heartworm disease (in dogs), trichinosis, and elephantiasis.			80,000
		Phylum Nematomorpha. Horsehair worms, Gordian worms, or nematomorphs. Long worms, almost as thin as a hair, which are parasitic as juveniles but free-living as adults.			250
		Phylum Onychophora. Velvet worms, walking worms, or onychophorans. Small, terrestrial worms of humid, tropical climates, with many pairs of short, unjointed, pincer-bearing legs.			80
		Phylum Tardigrada. Tardigrades, or water bears. Microscopic animals shaped like many-legged bears, and capable of entering into cryptobiosis, a state of suspended animation in which they can survive for decades; can survive X-rays 1,000 times strong enough to kill a human; and can endure temperatures from 3°K to 151°C (-454°F to 304°F).			750
		Phylum Arthropoda. Arthropods. Arthropods comprise by far the largest phylum of life on Earth, with almost a million described species and anywhere from 1 to 50 million yet undescribed. Arthropods are characterized by a jointed exoskeleton, a segmented body, and segmented limbs.			1,033,160
			Subphylum Chelicerata. Chelicerates. Arthropods having two body segments, and having appendages for pinching or piercing. Examples include horseshoe crabs, sea spiders, and arachnids. Arachnids include spiders, scorpions, ticks, mites, daddy longlegs (harvestmen), and others.		75,000
			Subphylum Crustacea. Crustaceans. Crustaceans are arthropods with two-branched appendages, two pairs of antennae, a pair of mandables for chewing, and two pairs of maxillae for handling food. The largest group includes shrimp, crabs, lobsters, krill, hermit crabs, isopods, amphipods, and others. Members of other groups include barnacles, copepods, and ostracods; fairy shrimp, brine shrimp, clam shrimp, and water fleas; cephalocarids; and remipedes.		45,000
			Subphylum Uniramia. Uniramians. Arthropods having unbranched appendages, and having either two or three body parts.		913,160
				Class Diplopoda. Millipedes. Many-legged uniramians with 11 to 100 segments, and two pairs of legs on each segment.	10,000
				Class Chilopoda. Centipedes. Many-legged uniramians with 15 or more segments, and one pair of legs on each segment.	2,500
				Class Pauropoda. Pauropods. Uniramians with 11 segments and 9 pairs of legs, feeding on decaying organic matter.	500
				Class Symphyla. Symphylans, or "garden centipedes." Centipede-like uniramians with 10 to 12 pairs of legs.	160
				Class Hexapoda (Insecta). Insects. XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX.	900,000	Butterfly; Ant or bee
		Phylum Mollusca. Mollusks. Soft-bodied invertebrates, possessing a body part called a head-foot; possessing a visceral mass containing the organs; usually possessing a membrane called the mantle; and often possessing a shell secreted by the mantle. Included are cephalopods such as octopuses (octopi), squid, cuttlefish, and nautiluses (nautili); gastropods such as snails, limpets, and slugs; bivalves such as clams, oysters, mussels, and scallops; and a host of others, including chitons, tusk shells (tooth shells), solenogasters, caudofoveates, and monoplacophorans.			50,000	Octopus or squid
		Phylum Sipuncula. Peanut worms, or sipunculans. Worms with bushy tentacles around their mouths, living in ocean-floor sediment.			150
		Phylum Echiura. Echiurans, spoon worms, or gutter worms. Plump marine worms with a large, tongue-like proboscis.			140
		Phylum Annelida. Segmented worms, or annelids. This phylum includes many of the most familiar kinds of worms. Segmented worms live worldwide in soil, sea, and fresh water, mostly as free-living predators. Examples include earthworms, leeches, and numerous marine worms.			15,000	Earth- worm
		Phylum Pogonophora. Pogonophorans, or beard worms. Long, very thin, tube-dwelling, deep-sea worms with characteristic long, beard-like tentacles.			120
		Phylum Entoprocta. Entoprocts. Tiny, goblet-shaped, tentacle-bearing animals, living in colonies on the ocean floor.			150
		Phylum Ectoprocta (Bryozoa). Moss animals, ectoprocts, or bryozoans. Animals that have a lophophore, a tentacle-bearing organ that surrounds the mouth. Though microscopic, they often live in colonies that are easily visible to the naked eye, colonies which sometimes look like moss to the casual observer.			4,000
		Phylum Phoronida. Phoronids. Small marine animals that have a lophophore of many tentacles and live in colonies on the ocean bottom.			14
		Phylum Brachiopoda. Brachiopods, or lampshells. Small marine invertebrates that look like clams or scallops, having two-sided shells.			335
		Phylum Chaetognatha. Arrow worms. Short, thin worms with a rigid trunk and a series of moveable hooks for catching prey.			70
		Phylum Echinodermata. Echinoderms. Invertebrate animals having an internal skeleton covered by skin, and having pentaradial symmetry (turn them a fifth of a revolution and they look the same). They feed on a variety of invetebrates, and live only in the ocean, from shallow beaches to the deep sea. The numerous examples include starfish (sea stars), brittle stars, sea urchins, sand dollars, sea cucumbers, sea daisies, sea lilies, feather stars, and others.			7,000	Starfish
		Phylum Hemichordata. Hemichordates. Cylindrical marine animals with a trunk, collar, and tongue-like proboscis. Acorn worms and pterobranchs.			90
		Phylum Chordata. Chordates. Animals that possess, during at least some point in their development, a rod-like notocord, a nerve cord, throat-side gill slits, and a tail.			53,073
			Subphylum Urochordata. Tunicates, or urochordates. By far the biggest group of these are the sea squirts, sessile filter-feeders rooted to the ocean floor, possessing only as larvae all the characteristics of chordates. The others are small, free-floating creatures of the open sea: thaliaceans (such as salps) and larvaceans (or appendicularians).		1,400
			Subphylum Cephalochordata. Lancelets (amphioxus). Tiny fish- or tadpole-shaped chordates, living in ocean sand and filtering out plankton from the water.		45
			(Subphylum Vertebrata. Vertebrates—concerning which see my pages on fishes, amphibians, reptiles, birds, and mammals.)		51,628

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