Annelida (Segmented Worms)

• Invertebrates are the focus

Phylum Annelida

• Includes segmented worms like earthworms, polychaetes, fan worms, and leeches
• Characterized by having a true coelom and segmented bodies
• Sensory organs are concentrated near the anterior end

Earthworms

• Terrestrial and freshwater segmented worms
• Setae are present for movement
• They are hermaphroditic, possessing both sexes
• They have rudimentary excretory systems known as nephridia
• They utilize hydrostatic skeletons for movement
• They possess a closed circulatory system

Marine Segmented Worms

• Have a well-developed head
• Have parapodia that function in locomotion on each segment
• Most are marine, tube-dwelling, and free-living
• Parapodia are richly supplied with blood vessels and can function as gills

Leeches

• Mostly inhabit fresh water, but some can be found on moist land
• Most feed on invertebrates, some are blood-sucking parasites
• Some use bladelike jaws to slit skin, while others use enzymes to digest a hole in the skin
• Hirudin keeps blood from coagulating
• Leeches can be used for treating bruised tissues and stimulating circulation of blood to fingers or toes that have been sewn back on after accidents

Polychaetes

• Polychaetes have a complete digestive tract
• They reproduce sexually, and sexes are separate

Phylum Nematoda

• Includes roundworms, pinworms, hookworms, and nematodes
• They are non-segmented
• Some are free-living, while others are parasites

General Characteristics

• Exoskeleton composed of chitin
• Have jointed appendages
• Possess an open circulatory system
• Gills for aquatic species, while terrestrial species have tracheal systems

Class Insecta-Insects

• One or two pairs of wings
• Body has three regions (head, thorax and abdomen)
• One pair of antennae, two compound eyes, several pairs of appendages surround the mouth
• On the thorax have 3 pairs of walking legs
• Sexes are separate and sexual reproduction occurs
• Most insects undergo metamorphosis during development
• The nervous system includes two nerves fused into a cerebral ganglion

Incomplete Metamorphosis

• Egg becomes nymph and then adult
• Nymph looks like the adult but lacks wings

Complete Metamorphosis

• Caterpillar (butterfly), maggot (fly) or grub (beetle) looks entirely different from adult
• Egg becomes larva then pupa and then adult

Class: Arachnida

• Includes spiders, scorpions, ticks, and mites
• Body has two main parts
• Six pairs of appendages consisting of 1 pair of chelicerae, 1 pair of pedipalps, and four pairs of walking legs
• Mostly terrestrial
• Spiders have book lungs (stacked plates) abdominal glands and spun by spinnerets
• Spiders produce silk, a protein

Class: Myriapoda

• Includes Millipedes & Centipedes

Millipedes

• Have two pairs of legs per segment
• Live on decaying leaves and other plant matter

Centipedes

• Terrestrial carnivores
• Appendages modified into mouthparts
• Each segment has one pair of walking legs
• Have poison claws on the anterior most end

Class: Crustacea

• Includes Crabs, lobsters, crayfish, shrimp
• Have multiple specialized appendages
• Have two pairs of antennae
• Have three or more pairs of appendages on the mouth
• Walking legs on thorax and abdomen
• Have gills for respiration
• Open circulatory system
• Separate sexes, larvae are planktonic