Download an artificial key to the common aquatic invertebrates of university bay

208
Pickle Jar Aquaria
APPENDIX B
An Artificial Key to the Common Aquatic Invertebrates of University Bay
(Note that Welsch, 1992 is an excellent booklet for identifying aquatic plants)
AN ARTIFICIAL KEY
TO THE
COMMON AQUATIC INVERTEBRATES
OF UNIVERSITY BAY
Prepared for the Biology Core Curriculum
by Kandis Elliot and James W. A. Jaeger, 1991
Pickle Jar Aquaria
209
Helpful terminology for identifying animal groups
1. The presence of branched, jointed appendages is a major feature separating arthropods, the
largest phylum in the animal kingdom, from all other groups. These appendages refer not only to
legs and leg-like structures, but also to antennae, tails, mouthparts, and many other organs that
have been modified from an embryonic or evolutionarily primitive leg-like structure. The
"branches" may be easily seen, as in daphnia antennae and the uropods of a crayfish tail, or the
appendage may appear to be a single, apparently unbranched structure such as a crayfish
antenna. Unfortunately for the novice taxonomist, some juvenile forms of "jointed-appendage"
animals appear to have no appendages whatsoever- the maggots of flies, for example. Most
immature arthropods, however, have very distinctive branched, jointed appendages of all shapes
and sizes.
2. Wings of invertebrate animals are not modified jointed appendages. They are a
developmentally separate and unique feature, and help to further separate subgroups of animals.
Many juveniles of winged invertebrates will possess small wing pads of various shapes.
210
Pickle Jar Aquaria
3. Tentacles are taxomically distinct from whiplike forms of jointed appendages like crayfish
antennae. Tentacles are fleshy structures without hardened internal or external supports and are
highly mobile and contractile. They are almost always placed around an animal's mouth and used
for food gathering. Tentacles are found in many unrelated groups of animals, from tiny bryozoans
to giant squids.
4. As used in this key, a shell refers to a hard, permanent, protective case excreted by an animal's
body. True shells are distinct from exoskeletons and carapaces, which are shed periodically, and
from cases which are constructed by the animal from sand grains, bits of leaf, or other materials.
Shells may be either hinged (thus appearing to be two separate halves) or a single unit. We are
familiar with the shells of clams, snails, and other mollusks, but ostracods and conchostracans,
which are relatives of shrimp and lobsters, also grow very shell-like, modified exoskeletons
called carapaces.
Pickle Jar Aquaria
211
5. Nymphs, larvae and naiads are terms referring to juvenile forms of various invertebrates.
Nymphs resemble the adult form and are easily identifiable. Aquatic insects with nymphs are
mayflies, and bugs such as water-boatmen, backswimmers and water-striders. Larvae, on the
other hand, look very different from the adult animals and are notoriously difficult to identify. For
example, the larvae of crane flies and mosquitoes are legless maggots; larvae of aquatic beetles
and alderflies are often fleshy and wormlike, with small legs, huge mandibles, or rows of
elaborate abdominal gills. The various stages of development of larvae are called instars. Naiad
refers specifically to the juvenile stages of dragonflies and damselflies. Nauplii refer to juvenile
forms of some crustaceans.
212
Pickle Jar Aquaria
1a. Body without visible segments, no jointed appendages .............................................................. 2
1b. Body with visible segments, appendages may be present ........................................................... 7
2a. Animal with a shell ...................................................................................................................... 3
2b. Animal without a shell................................................................................................................. 4
3a. Shell single.......................................................................................................................
3b. Shell double .....................................................................................................................
snails
clams
4a. Body asymmetrical .......................................................................... sponges and moss animals
4b. Body symmetrical........................................................................................................................ 5
5a. Radial symmetry .............................................................................................................. hydras
5b. Bilateral symmetry ...................................................................................................................... 6
Pickle Jar Aquaria
213
6a. Flattened; swim with gliding motion.........................................................................
flatworms
6b. Cylindrical; swim with wiggling motion................................................................... roundworms
7a. Without obvious jointed legs (fleshy prolegs may be present) ................................................... 8
7b. With obvious jointed legs ...........................................................................................................11
8a. With front and rear suckers ............................................................................................. leeches
8b. Without suckers .......................................................................................................................... 9
9a. Without obvious appendages (may be shell) ........................ mosquito larvae and midge larvae
9b. Without obvious appendages or fleshy prolegs...........................................................................10
214
Pickle Jar Aquaria
10a. Transparent with front and rear air sacs ........................................
phantom midge larvae
10b. Not transparent, no air sacs ...............................
freshwater earthworms and cranefly larvae
11a. With 3 pairs of jointed legs........................................................................................................12
11b. With more than 3 pairs of jointed legs ......................................................................................18
10b. No trace of wings.......................................................................................................................13
10b. With external wings or wing pads .............................................................................................14
13a. Living in external case ...............................................................................
13b. Free living, no case ....................................................................................
caddisfly larvae
beetle larvae
14a. With fully developed wings.......................................................................................................15
14b. With wing pads or shortened wings ..........................................................................................16
Pickle Jar Aquaria
15a. Front pair of wings fully hardened; chewing mouthparts .............................................
15b. Front pair of wings partially hardened; piercing mouthparts .......................................
215
beetles
bugs
216
Pickle Jar Aquaria
16a. Without tail appendages ............................................................................
dragonfly naiads
16b. With tail appendages ...............................................................................................................17
17a. Tail appendages long, whip-like ................................................................
17b. Tail appendages blade-like, flattened .........................................................
mayfly nymphs
damselfly naiads
18a. With 4 pairs of legs ....................................................................................
spiders and mites
18b. With more than 4 pairs of legs or other paired appendages ....................................................19
19a. Legs obviously visible; animal large (> 5mm) ........................................................................20
19b. Legs not obviously visible; animal small (< 5mm) .................................................................22
Pickle Jar Aquaria
217
20a. With large pinchers and obvious tail ............................................................................ crayfish
29b. Without large pinchers; no obvious tail..................................................................................... 21
21a. Body flattened from side to side ...................................................................................amphipods
21b. flattened from top to bottom ......................................................................................... isopods
22a. No long visible antenna, animal enclosed in carapace ............... clam shrimp and seed shrimp
22b. With long visible antenna used in swimming............................................................................ 23
23a. Antenna branched, swims in head up position ............................................................. daphnids
23b. Antenna unbranched, swims in horizontal position ..................................................... copepods