Phylum Arthropoda It doesn’t get any bigger than this!

Major Features An exoskeleton (external skeleton) made out of chitin. Must molt (shed their skeleton) in order to grow. Have jointed appendages – Serve a variety of roles (walking, swimming, repro, eating, sensing) Three body regions – head, thorax, abdomen.

Features cont’d Well-developed nervous system – Includes a brain and a ventral nerve cord – Includes sense organs (antennae, compound eyes)

Diversity

Classification Broken into subphyla. – Subphylum Crustacea – Subphylum Uniramia – Subphylum Chelicerata

Subphylum Crustacea “Crustaceans” – barnacles, shrimp, lobster, crab, crayfish… marine arthropods. The sow bug is a terrestrial example.

Crustacea cont’d (We’ll use crayfish as our representative) External structure: Cephalothorax – skeleton over head and thorax are fused. Head has compound eyes, antennae, and pairs of mouth appendages. Thorax has 5 pairs of limbs (4 pairs of walking legs, 1 pair of pincers [chelipeds]). Abdomen has swimmerets, uropods and telson.

Crustacea cont’d

Internal structure: Digestive system – 2-chambered stomach, digestive glands, intestine. Green glands for excretion. Cardiovascular system – heart pumps blood into the space surrounding the internal organs (the “hemocoel”). – Blood contains a blue pigment (hemocyanin).

Crustacean circulation

Crustacea cont’d Internal structure cont’d: Nervous system – brain, ventral nerve cord, and ganglia in several segments. – Receptors line antennae – include chemical receptors and force receptors. Reproduction – separate genders. – Sperm transferred by 1 st pair of swimmerets. – Females carry fertilized eggs on their swimmerets.

Crustacea cont’d

Subphylum Uniramia “Insects” – most diverse group on Earth. General structure: Head has compound or simple eyes, antennae, and mouth appendages. Thorax has 3 pairs of legs – Sometimes includes wings. Abdomen stores the internal organs.

Insects cont’d We will use grasshoppers as our representative. External structure: 3 rd pair of legs adapted for jumping. Has two pairs of wings. Females – have a posterior structure called an ovipositor for digging holes to lay eggs in. Has tympanum – a thin membrane – on abdomen for hearing.

Grasshopper Exterior

Insects cont’d Internal Structure: Digestive system – complete, with mouth, stomach, intestine, and anus. Excretion – uses structures called Malpighian tubules that release uric acid into intestines for disposal. Respiration – uses openings in the exoskeleton called spiracles that that lead into a trachea. – Air is pumped by the contraction and relaxation of the body wall.

Spiracles and Malpighian Tubules

Insects cont’d Circulation – a heart pumps hemolymph into the aorta, which empties into a hemocoel (open space around organs). – Hemolymph in insects is NOT used to carry O 2, so it has no pigment. Reproduction – Fertilization is internal. Genders are separate. – Fertilized eggs are ejected into the ground.

Circulation and Reproduction

Insects cont’d Metamorphosis: a change in physiology and anatomy that occurs as an insect matures from a larva to an adult. – (Many insect larvae, including grasshoppers, are called nymphs).

Subphylum Chelicerata Arachnids (spiders, ticks, scorpions, mites). General Features: Cephalothorax – Has 6 pairs of appendages attached to it 4 pairs are walking legs 1 pair are pedipalps – these sense and hold prey 1 pair are fangs (chelicerae) Abdomen – stores internal organs

Arachnid structure

More arachnids!

Arachnids cont’d (Representative organism = spiders) Capable of delivering venom to prey through fangs. Digestion: prey is injected with digestive juices. Juices gradually digest prey. – Spider will “suck up” liquefied prey to complete digestion.

Arachnids cont’d Respiration: Uses “book lungs” – folds of tissue inside the body wall. – The folded surface provides plenty of room for gas exchange.