Zoology: Arthropoda, Insecta and Arachnida

• The notes cover Life Sciences II, specifically zoology and laboratory animals.
• It focuses on the phylum Arthropoda, and classes Insecta and Arachnida.

Arthropoda

• Subphylums include: Branchiata, Tracheata and Chelicerata
• Branchiata includes the class Crustacea
• Crustacea includes the subclasses Malacostrata and Branchiopoda
• Tracheata includes class Insecta
• Chelicerata includes class Arachnida

Mollusks and Arthropods

• Bivalves include mussels, clams, oysters and scallops
• Gastropoda includes snails, limpets, slugs and whelks
• Cephalopoda includes squids, octopus, Devil fish and cuttle fish
• Crustaceans include crabs, lobsters, shrimp and crayfish
• Arachnids include spiders, ticks , clovemites, and house dust mites
• Insects include Bees, butterflies, Ants, Beetles, and Grasshoppers

Arachnida

• Arachnida tagmata consists of a cephalothorax and an abdomen.
• The cephalothorax has a pair of chelicerae, a pair of pedipalps, and four pairs of walking legs.
• Arachnids lack antennae and mandibles.
• Most Arachnids are predaceous and possess claws, fangs, poison glands, or stingers.
• They have sucking mouthparts or a strong sucking pharynx.
• Spiders have spinning glands.
• There are more than 100,000 described species of Arachnids.

Spiders (Aranei)

• Spiders make up a large group of 35,000 species.
• Spiders have a compact body: with cephalothorax and abdomen, both unsegmented and joined by slender pedicel.
• Anterior appendages include a pair of chelicerae with terminal fangs with ducts from poison glands.
• Fourth pairs of walking legs terminate in claws.
• Spiders digest food outside their bodies.
• Expel digestive enzymes from their intestinal tract onto their prey.
• These enzymes break down the prey's body tissues and, after a few seconds, the spider sucks up the predigested, liquid tissues.
• They have a sucking stomach that is the primary pump for drawing food into the body.
• The gut is directly behind the stomach, and parts of it extend into the front portions of the spider's legs.
• Branches of the midgut extend into the abdomen and surround other bodily structures. Spiders have an excretory system of Malpighian tubules

Spiders – Circulatory and Respiratory System

• Spiders have an open circulatory system, without true blood or veins.
• Bodies are filled with haemolymph, pumped through arteries by a heart into sinuses around internal organs.
• They breathe through book lungs.
• Book lungs have parallel air pockets extending into a blood-filled chamber.
•  Air enters the chamber through a slit in the body wall.

Spiders – Nervous and Reproductive system

• The central nervous system consists of a pair of nerve cords running below the gut.
• Paired ganglia act as local control centers; brain formed by fusion of the ganglia, encircling the esophagus.
• Spiders have four pairs of eyes arranged in family-specific patterns.
• Joint slit sensillae detect force and vibrations.
• Web-building spiders rely more on mechanical and chemical sensors than eyes.
• Hunting spiders rely more on eyes.
• Sexes are separate: male and female.
• They reproduce sexually with internal but indirect fertilization involving pedipalps.
• The life cycle has three stages: egg, spiderling, and adult.
• Spiders can lay up to 3,000 eggs, usually in one or more silk sacs.

Ticks and Mites (Acari)

• Acarines differ from arachnids by having a complete fusion of the cephalothorax and abdomen, lacking external division.
• Ticks are efficient disease carriers because they attach firmly when sucking blood.
• They feed slowly and may go unnoticed for a considerable time.
• Ticks take several days to complete feeding.
• Ticks have four life stages: egg, six-legged larva, eight-legged nymph, and adult.
• Ticks have a two year life cycle.
• Gravid females drop off the second host to lay eggs in the fall.
• Larvae hatch into six-legged larvae and over winter.
• Larvae seek out the first host in the spring.
• Larvae molt into nymphs on first host.
• Engorged nymphs drop off the first host, usually in the late summer or fall.
• They over winter in the nymphal stage
• Nymphs molt into adults the following spring, seeking out the second host.
• Adults feed on the second host during the summer and subsequently drop to continue the cycle.
• Females may reattach and feed multiple times, and humans may serve as hosts.
• The second host may not necessarily be a separate species.
• Types of mites are clover mites, house dust mites, itch mites, rodent and bird mites, chicken mite, chiggers and scabies mites.
• Mites parasitize animals, scavengers, and/or prey on insects and other arthropods.
• Mites pass through four stages of development, egg to larva to nymph to adult.
• All stages have eight legs except the six-legged larva.

Insects (Insecta)

• Insects are the largest group of organisms on earth.
• Insects live in every conceivable habitat and some have even invaded the sea.
• Insects have three body sections: head, thorax, and abdomen.
• Insects have three pairs of legs.
• Insects may have one or two pairs of wings.
• Respiration: trachea, or branched tubes, commence at the surface of the body by lateral apertures called "stigmata" or "spiracles".
• Insects have open circulatory system with a dorsal heart.
• Liquid waste gets excreted through Malpighian tubes.
• The sexes are separate.
• Reproduction is usually sexual.
• Some insect groups sometimes develop eggs without fertilization by sperm which is referred to as parthenogenesis
• Chewing mouthparts are typical for beetles, grasshoppers, acrididae, dragonflies, wasps, and cockroaches.
• Chewing-sucking parts are typical for bees, bumblebees.
• Piercing and sucking mouthparts are typical for female mosquitoes, louses, and bugs.
• Sucking mouthparts are found in butterflies.
• Lapping mouthparts are typical for flies.

Insect Life Cycles

• There are typically separate sexes
• Most insects undergo metamorphosis during development.
• Holometabolous/Complete metamorphosis- larvae and adults are very different woth a pupae stage
• Insects with complete metamorphosis are beetles, flies, bees, lacewings, butterflies, ants, and caddis flies.
• Incomplete/Simple Metamorphosis the nymph more or less resembles the adult without a pupal stage
• Some insects with incomplete metamorphosis are crickets, true bugs, termites, grasshoppers, and cockroaches.

Notes on Arthropoda, Insecta, and Arachnida. Covers subphylums such as Branchiata, Tracheata, and Chelicerata. Also covers crustaceans, arachnids and insects, bivalves, gastropoda and cephalopoda.