Phylum Annelida
Characteristics

Body metamerically segmented; symmetry bilateral; three germ layers.

Body wall with outer circular and inner longitudinal muscle layers; transparent moist cuticle secreted by columnar epithelium (hypodermis) covers body.

Chitinous setae, often present on fleshy parapodia for appendages; absent in some.

Coelom well developed in most and usually divided by septa; coelomic fluid for turgidity.

Blood system closed and segmentally arranged; respiratory pigments (erythrocruorin and chlorocruorin) with amebocytes in blood plasma.

Digestive system complete and not metamerically arranged.

Respiration by skin or gills.

Excretory system typically a pair of nephridia for each metamere.

Nervous system with a double ventral nerve cord and a pair of ganglia with lateral nerves in each metamere; brain a pair of dorsally located cerebral ganglia.

Sensory system of tactile organs, taste buds, statocysts (in some), photo-receptor cells, and eyes with lenses (in some).

Hermaphroditic or separate sexes; larvae if present are trochophore type; asexual reproduction by budding in some; spiral and determinate cleavage.

Phylum Arthropoda
Characteristics

Body of three clearly defined regions-head, thorax, and abdomen.

Head of six segments, with two antennae and two mandibles and two pairs of maxillae; mouth parts adapted for sucking, chewing, and lapping.

Thorax of three segments, each with a pair of jointed walking legs; thorax may have two pairs, one pair, or no pair of wings.

Abdomen of not more than eleven segments and modified posteriorly as genitalia.

Respiration by a many-branched tracheal system which communicates with the outside by spiracles on the abdomen.

Digestive system of fore-, mid-, and hindgut and provided with salivary glands.

Circulatory system of heart, aorta, and hemocoel; no capillaries or veins.

Excretion by malpighian tubules that empty into the hindgut.

Coelom very much reduced.

Nervous system of a dorsal brain, subesophageal ganglia, and a double ventral nerve cord provided typically with a pair of ganglia to each somite.

Sense organs consisting of simple and compound eyes, receptors for taste about the mouth, receptors for touch on various parts of body, and receptors for sound.

Reproduction by separate sexes; paired gonads with single duct in each sex; fertilization internal; few reproducing by parthenogenesis; most exhibiting metamorphosis.

Mollusca
Characteristics

Symmetry bilateral (viscera and shell coiled in GASTROPODA and some CEPHALOPODA): 3 germ layers

Body usually short, enclosed in a thin dorsal mantle that secretes a shell of 1, 2, or 8 parts (shell in some internal, reduced, or none); head region developed (except SCAPHOPODA, BIVALVIA); a ventral muscular foot variously modified for crawling, burrowing, or swimming.

Digestive tract complete, often U-shaped or coiled; mouth with a radula bearing transverse rows of minute chitinous teeth to rasp food (except BIVALVIA); anus opening in mantle cavity; a large digestive gland and often salivary glands.

Circulatory system includes a dorsal heart with 1 or 2 auricles and ventricles, usually in a pericardial cavity, an anterior aorta, and other vessels.

Respiration by 1 to many gills (ctenidia) or a "lung" in the mantle cavity.

Excretion by kidneys (nephridia), either 1, 2, or 6 pairs or 1, usually connecting to pericardial cavity; coelom reduced.

Nervous system typically of 3 pairs of ganglia (cerebral above mouth, pedal in foot, visceral in body), joined connectives and nerves; many with organs for touch, smell, or taste, eyespots or complex eyes, and statocysts for equilibration.

Sexes usually separate (some monoecious); gonads 4, 2, or 1, with ducts; fertilization external or internal; mostly oviparous; egg cleavage determinate, unequal, and total; a veliger (trochophore) larva, or parasitic stage (UNIONIDAE), or development direct (PULMONATA, CEPHALOPODA); no asexual reproduction.

Echinodermata

Characteristics

Symmetry usually radial and 5-parted in adults, bilateral in larvae; 3 germ layers; most organs ciliated; no head, brain, or segmentation.

Body surface of 5 symmetrical radiating areas or ambulacra, whence the tube feet project, and alternating between these 5 interambulacra (interradii).

Body covered by delicate epidermis over a firm mesodermal endoskeleton of movable or fixed calcareous plates usually in definite pattern; often with spines (skin leathery and plates usually microscopic in HOLOTHURIOIDEA).

Digestive tract simple, usually complete (some lack an anus).

Circulatory (hemal) system radiate, but reduced; coelom lined with ciliated peritoneum, usually large, its fluid containing free amoebocytes; part of larval coelom becomes a water vascular system usually with many tube feet serving for locomotion, food handling, or respiration.

Respiration by minute gills or papulae protruding from the coelom, by tube feet, and in HOLOTHURIOIDEA by cloacal respiratory frees.

Nervous system with circumoral ring and radial nerves.

Sexes separate (rare exceptions), alike externally; gonads large, with simple ducts; ova abundant, usually fertilized in the sea; larvae microscopic, ciliated, transparent, and usually free-swimming, with conspicuous metamorphosis. A few species are viviparous, a few reproduce also asexually by self-division, and many regenerate lost parts readily.

Phylum Hemichordata

Characteristics

Symmetry bilateral , unsegmented, 3 germ layers; body of 3 divisions (protosome, mesosome, metasome), either worm-like (enteropneusts) or vase-like in a case (pterobranchs);

Paired gill slits many, 2, or none.

Body wall of epidermis, nervous tissue, muscle fibers, and peritoneum lining coelom.

A buccal pouch anterior from mouth cavity.

Digestive tract straight and anus terminal (enteropneusts) or u-shaped and anus near mouth (pterobranchs).

Coelom in 3 parts, paired in mesosome and metasome.

Circulatory system open, dorsal and ventral vessels or channels in mesosome, a pulsating vessel in protosome.

Excretion by glomerulus near buccal pouch.

Nervous system diffuse, in epidermis, middorsal and midventral.

Sexes separate, alike; enteropneusts with many paired gonads, development with tornaria larva or direct; pterobranchs with 2 gonads, and a larval stage; adults reproduce by asexual buds.