Order I. Crustacea (Lat., crusta, a crust or shell).—Water-breathing; having gills and more than eight jointed legs; four antennæ. Examples: fairy-shrimp, water-fleas, goose barnacle, acorn barnacle, opossum-shrimp, prawn, lobster, crayfish, cancer-crab, rock-crab, pill-bug, sand-hopper.
Order II. Arachnida (Gr., arachne, spider).—Eight legs; air-breathing. Examples: garden-spider, tarantula, bird-spider, trap-door spider, mite, tick, king-crab or horseshoe crab.
Order III. Insecta (Lat., insectum, cut in, owing to the grooves surrounding the body).—Distinct head, thorax and abdomen; air-breathing. Examples: fishmoth, springtail, cockroach, grasshopper, cricket, katydid, locust, dragon-fly, caddis-fly, may-fly, white ants or termites, ant-lion, water-boatman, water-bug, back-swimmer, chinch-bug, squash-bug, lice, plant-lice, scale-insect, gnat, mosquito, flea, house-fly, stage-beetle, wood-beetle, water-beetle, potato-beetle, ladybug, firefly, moth, butterfly, ants, honey-bees and bumblebees, wasps, hornets, yellow-jackets, centipeds.
Class VII. Mollusca (Lat., mollis. soft),—Soft-bodied, unjointed Metazoa, with muscular skin (“mantle”), generally protected by a calcareous shell; two or three-chambered heart; three main pairs of nerve-ganglia. Examples: Clams, oysters, snails, cuttlefish, devil-fish, nautilus.
Class VIII. Echinodermata (Gr., echinos, a hedgehog; derma, skin).—Radiated Metazoa, with distinct alimentary canal and well developed nervous system; body-walls secreting calcareous plates; parts in multiple of five. Examples: starfish, sea urchins, sea cucumbers, sea lilies, serpent or brittle stars, basket stars.
Class IX. Worms (Lat., vermes).—Bilateral Metazoa, with no jointed legs, nor primitive stripe. Examples: earth worm, leech, tube worm, tape worm, bristle worms, vinegar eel, rotifers.
Class X. Cœlenterata (animals with combined body and stomach cavity).—Radiated Metazoa, with distinct digestive cavity, tentacles and nettling thread-cells. Examples: jellyfish, sea-anemones, coral polyps.
Class XI. Porifera (Lat., porus, pore; fero, to carry).—Sponges, Metazoa, with numerous ingoing openings, one or few outgoing orifices, a skeleton, independent cells. Example: sponges.
Sub-Kingdom PROTOZOA (Gr., protos, first; zoon, animal).—One-celled animals of microscopic size. Simplest forms of animal life. Examples: amœba, bell animalcule (vorticella), euglena.