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1a. Has no digestive system or organs; loosely-organized
water-filtering animals.
Sponges.......................... Phylum Porifera
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1b. Digestive system uses a single opening that serves as
both mouth and anus.
Usually somewhat small or tiny.................... 2
1c. Not as above; mouth and anus are separate
openings........................ 7
2a. Tiny, usually in fresh water, commonly with a "wheel organ"
of cilia around the mouth; may be anchored with foot-like
graspers or swimming; sometimes colonial.
Rotifers.
....................................................................... Phylum Rotatoria
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2b. Body has circular layout (radially symmetrical); outer
ectoderm, inner endoderm with jellyish layer between;
have tentacles with stinging cells. Phylum Cnidaria..................... 3
2c. Superficially look like jellyfish, but with at most 2 tentacles,
and move using comb-like rows of cilia visible on sides;
no stinging
cells, but have cells that produce glue-like
substance.
Comb Jellies............................... Phylum Ctenophora
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2d. Body very flat, with mirror-image right and left sides (bilaterally
symmetrical); has three definite cell layers and internal
organs.
Flatworms and tapeworms. Phylum Platyhelminthes.. 4
3a. Usually alternate between small sexual jellyfish (medusa)
stage and asexual polyp (tentacles on top) stage; polyps
do not have multichambered body cavity. May exist in
colonies................................................................... Class Hydrozoa
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3b. Jellyfish with no or reduced polyp form; ocean only; have 8
notches on bell margin; includes all large
jellyfish.
....................................................................... Class Scyphozoa
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3c. Polyps only, with no medusa form; body cavities divided
into chambers;
includes many types of corals.... Class Anthozoa
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3d. Live alone or in colonies; may have a skeleton; various
numbers of tentacles, but never 8; includes sea
anemones and some corals................................ Class Zoantharia
INFO LINK (Listed as Subclass of Anthozoa)
4a. Live free in the environment; often have eye spots.
Class Turbellaria.............................................................................. 5
4b. Parasites; bodies are oval or leaf-shaped; have suckers
and/or hooks to help attach them to hosts.
Class Trematoda.............................................................................. 6
4c. Parasites; bodies are series of repeating segments behind
head with attachment structures.
Tapeworms.
............................................................................ Class Cestoda
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5a. Usually have no or two eyes, rarely 1 or 4; have no gut,
excretory, or obvious reproductive
organs................ Order Acoela
INFO LINK (Questions inclusion here)
5b. Usually have no or two eyes, rarely 1 or 4; gut is a simple
sac; have simple excretory and reproductive
systems.
................................................................... Order Rhabdocoela
INFO LINK 5c. Two eyes or eyes in 2 clusters; gut has three limbs, often
with many side branches; adults are 3 mm and
larger.
.......................................................................... Order Tricladida
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5d. Two or more clusters, bands, or rows and clusters of eyes;
gut has many limbs and branches; adults are 1 - 50
mm.
....................................................................... Order Polycladida
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6a. Live on the outside of animal hosts; possess a single organ
of attachment, which has hooks and
suckers. Order Monogenea
6b. Live inside animal hosts; possess two organs of attachment,
usually
suckers........................................................... Order Digenea
7a. Body is long and cylindrical (worm-like), possessing no limbs
or side-attaching fins; body not covered in
scales.......................... 8
7b. Body as in 7a, but covered in scales. Phylum Chordata................ 28
7c. Not as above, or may be worm-like but have limbs or
fins................ 10
8a. Very basic worm shape, often pointed at each end; range of
sizes, but most are tiny; often parasites.
Roundworms.
..................................................................... Phylum Nematoda
8b. Body a series of segments, creating a ringed appearance;
small to moderate size; found in water or soil.
Phylum Annelida.............................................................................. 9
9a. Almost always in salt water environment
(marine); usually
have a pair of paddles and/or bristles on each
segment.
.......MORE
INFO......................................... Class Polychaeta
9b. Often found in fresh water or soil; body with fine bristles or
no outside structure. Includes
earthworms....... Class Oligochaeta
9c. Body is fairly thick and often somewhat flattened, with small-
to moderate-sized suckers; predators and parasites.
Leeches................................................................... Class Hirudinea
10a. Body is laid out in a five-fold circular pattern
(pentaradial
symmetry,
e.g, starfish); support and power comes
mostly from a water-driven system (water vascular
system).
Phylum Echinodermata.............................................. 11
10b. Skin is not rigid, although it may produce and support rigid
structures, such as scales, scale-based shells, hair,
feathers,
etc; muscles are outside of skeleton............................. 14
10c. Body is covered by a rigid or semi-rigid material, a shell or
an
exoskeleton, with muscles inside; includes arthropods
such as spiders and
insects........................................................... 15
11a. Possesses arms that radiate out from a central
disc...................... 12
11b. Not as in 11a....................................................................................... 13
12a. Mouth normally points upwards; arms have small
branches (pinnules);
often supported on stalks.
Sea Lilies & Feather
Stars.................................... Class Crinoidea
12b. Mouth normally points downward; no pinnules; arms
have deep, lengthwise grooves.
Starfish............ Class Asteroidea
12c. As in 12b, but arms lack grooves and are often thinner.
Brittle
Stars......................................................... Class Ophiuroidea
13a. Body wall is solid; may be covered with movable spines.
Sea Urchins and Sand / Sea Dollars................. Class Echinoidea
13b. Body wall is soft; no spines; often have thick cylindrical
bodies. Sea Cucumbers............................... Class Holothuroidea
14a. No skeleton inside body; may be small and snail-like, or
possessing tentacles. Mollusks. Phylum Mollusca.................... 16
14b. Internal skeleton present, of cartilage and/or bone, usually
with backbone (vertebral column); has notochord
sometime during lifetime. Chordates.
Phylum
Chordata........................................................................... 28
15a. If shelled, the shell is a relatively simple covering, hard
and with no more than one hinge; has soft body; may
have tentacles with suckers. Mollusks.
Phylum
Mollusca........................................................................... 16
15b. Outer covering is complex, covering legs, with many
pieces and movable joints. Arthropods.
Phylum
Arthropoda....................................................................... 18
16a. Shell is coiled, or may have no shell; moves on single
broad foot with mucus underneath. Snails and
Slugs.
...................................................................... Class Gastropoda
16b. Has two shells, hinged, that close around soft parts.
Includes Clams, Oysters, Scallops,
Mussels........... Class Bivalvia
16c. Has no shell, simple internal shell, or coiled chambered
shell;
possesses eight to ten arms/tentacles, with suckers.
Cephalopods. Class Cephalopoda............................................. 17
17a. Have coiled shell with flotation chambers; found in Pacific
and Indian Oceans.
Nautilus............................... Order Nautiloidea
17b. Have fins, 8 relatively short arms, and 2 long tentacles.
Squids and
Cuttlefish............................................ Order Teuthidida
17c. Have no fins, 8 arms / tentacles; bottom dwellers,
Octopus................................................................ Order Octopodida
18a. Have four pairs of stumpy legs with short claws; are
usually tiny; have roundish body.
Water Bears, Tardigrades....................... Subphylum Tardigrada
18b. Usually have just 2 body sections and 4 pairs of legs;
do not
have wings or antennae; usually have front
palps, which may have pincers or look like regular
legs.
Subphylum Chelicerata.................................................... 19
18c. Have from 3 to many pairs of legs; one to three body
sections;
have antennae, which may be very small.
Subphylum
Mandibulata.............................................................. 22
19a.
Body covering like a rounded shield; legs hidden
beneath; eyes visible on top; long, pointed tail.
Horseshoe
Crabs.............................................. Class Xiphosurida
19b. Usually fairly small; found in oceans; 4 simple eyes;
4 pairs of walking legs. Sea
Spiders............ Class Pycnogonida
19c. Body has large or long abdomen; predators; may spin
webs.
Arachnids. Class Arachnida............................................ 20
20a. Front palps have pincers; abdomen long, with stinger at end;
found in warm, dry regions. True Scorpions.... Order Scorpiones
20b. Front palps have pincers; abdomen round, without stinger;
fairly small; often live concealed under objects.
Pseudoscorpions.................................. Order Pseudoscorpiones
20c. Front palps have pincers; abdomen ends in long whip-like tail,
without stinger. Whip
Scorpions....................... Order Pedipalpida
20d. Body is oval, often apparently all one section; usually small;
often have reddish coloration; may be parasitic or
scavengers. Mites and
Ticks......................................... Order Acari
20e. Body is oval, apparently all one section; have long, thin legs;
often scavengers. Harvestmen and Daddy Longlegs.
....................................................................... Order
Opiliones
20f. Body has 2 distinct sections joined at narrow "waist;" have
poison fangs; produce webs. Spiders. Order Araneae.............. 21
21a. Fangs point backward; often appear hairy. Tarantulas and
relatives.
............................................. Suborder Mygalomorphae
21b. Fangs point toward middle. True
Spiders.
..................................................... Suborder Araneomorphae
22a. Almost always live in water
(aquatic); both the head and
thorax covered with single covering (carapace); have
two sets of antennae; have many pairs of legs.
Crustaceans. Class Crustacea..................................................... 23
22b. Body is cylinder-shaped; many legs, in 2 pairs per segment;
land-dwelling (terrestrial) herbivores.
Millipedes.
......................................................................... Class Diplopoda
22c. Long, fast predators with several legs, one pair per segment;
large mandibles and poison fangs.
Centipedes.
......................................................................... Class Chilopoda
22d. Body divided into head, thorax, and abdomen; six legs
and usually 2-4 wings (in adults) attached to thorax;
two antennae.
Insects................................................. Class Insecta
23a. Mostly inside a clam-like shell; no more than 3 pairs of
thin legs on thorax; usually small bottom dwellers.
Mussel shrimp, Seed shrimp.
Ostracods..... Subclass Ostracoda
23b. Have flattened dome-shaped shell. External (and
under-
scale) parasites of fish. Fish Lice................ Subclass Branchiura
23c. Long oval body, often with long antennae used for swimming;
one central eye; usually 6 pairs of thin legs; usually small.
Copepods....................................................... Subclass Copepoda
23d. Body encased in plates, roughly pyramid-shaped; adult forms
are not mobile, on objects or parasites on animals.
Barnacles.......................................................... Subclass Cirripedia
23e. May have shell-like carapace over head and thorax; has 4 or
more flat, paddle-like legs; small to tiny; found usually in
fresh water. Subclass Branchiopoda........................................ 24
23f. Small to fairly large; body usually a total of 19 segments,
with 6 to 7 in the abdomen; abdomen usually has
legs
or swimmerets. Many different types.
Subclass
Malacostraca................................................................ 25
24a. Body is a long cylinder with no shell-like carapace; have
eyes on stalks;
small. Fairy Shrimp, Brine Shrimp.
....................................................................... Order Anostraca
24b. Carapace is a low oval shield; tail ends in forked,
whip-
like structure.
Tadpole Shrimp........................... Order Notostraca
24c. Carapace like a clamshell, with body compressed inside;
tail often ends in claws. Clam
Shrimp.......... Order Conchostraca
24d. Carapace like a clamshell, but not around head; tail often
ends in claws;
swims with 2nd antennae; have single eye.
Water Fleas,
including Daphnia.......................... Order Cladocera
25a. No obvious carapace; abdomen of 7 segments. Some
terrestrial forms, including
sowbugs, potato bugs.
........................................................... Superorder Leptostraca
25b. Carapace present but not fused to thorax; abdomen of 6
segments;
claws bend backwards. Mantis Shrimp.
...LINK...................................................... Order Stomatopoda
25c. Body high and narrow, flattened side-to-side.
Amphipods.......................................................... Order Amphipoda
25d. Carapace covers all of thorax; abdomen of 6 segments.
Superorder Eucarida..................................................................
26
26a. Have seven pairs of legs, all very similar. Open ocean
swimmers.
Krill.............................................. Order Euphausiacea
26b. Carapace not fused at back; legs mostly alike; no pincers.
Opossum Shrimp, Mysids.................................... Order Mysidacea
26c. Have five pairs of legs, including front pair used in feeding,
often with pincers. May be large. Order Decapoda.................... 27
27a. Body somewhat narrowed; claws, if present, are small.
Shrimp................................................................. Suborder Natantia
27b. Body may be cylindrical, but often a bit flattened; if pincers,
front set much larger than others. Mostly bottom dwellers.
Includes lobsters, crayfish, and crabs............ Suborder Reptantia
28a. Fish-like but flat and small; no backbones; ocean forms.
Lancelets........................................ Subphylum Cephalochordata
28b. Various shapes, including tadpole-like, cask- or
spindle-
shaped; no backbones; ocean forms; adults usually
not mobile. Includes Sea squirts, Sea grapes, Sea
mushrooms.................................................... Subphylum Tunicata
28c. Have backbones and usually skulls. Subphylum Vertebrata....... 29
29a. Teeth, if there are any, are not in jaws but embedded in the
tissues of the mouth; have no scales; have no limbs; if fins
are present, they run along the midline.
Superclass
Agnatha...................................................................... 30
29b. Have jaws; usually have paired limbs or fins.
Superclass Gnathostomata........................................................ 31
30a. Very primitive, worm-like fish; have a single nostril; tail is
rounded;
have whisker-like tendrils. Hagfishes.
Class
Myxini; Order Myxiniformes............... Family Myxinidae
30b. Eel-like fish; found in salt or fresh water; adults live as
parasites on more advanced fish. Lampreys.
Class
Petromyzones; Order Petromyzoniformes.
........................................................... Family Petromyzontidae
31a. Primitive fish, with skeleton of cartilage; scales poorly
developed.................................................... Class Chondrichthyes
31b. Advanced fish, with bony skeletons; well-developed scales;
gills under operculum
cover........................ . Class
Osteichthyes
31c. Usually live in water and/or moist environments; have skin
which is thin, without scales, and
glandular........ . Class Amphibia
31d. Found in wide range of environments; skin is scaly; may
or may not have
legs................................................. . Class Reptilia
31e. Front limbs are wings; usually capable of flight; covered
with feathers;
warm-blooded....................................... . Class Aves
31f. Covered with fur or hair; young usually born alive; possess
milk glands;
warm-blooded................................ . Class Mammalia
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