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)
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.
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).
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.
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.
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.
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.
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