BIOLOGY

ARTHROPODS

Concepts/Ideas/Facts:

1. ¾ of all animal species
2. the muscles of arthropods occur in bundles

Definitions:

1. Appendages – extensions of the body and include legs and antennae
2. Exoskeleton – three-layered, hard, external covering that provides protection and support.  It is secreted by the epidermis.
3. Chitin – tough carbohydrate that makes up the exoskeleton along with some proteins
4. Molting – the periodic shedding of the exoskeleton allowing the organism to get larger.  Enzymes secreted by the epidermis digest the inner exoskeleton layer and recreates a larger exoskeleton as the outer layer breaks along specific lines and is shed.
5. Green Glands – excretory organs which remove waste from the blood and retain salts
6. Cirri – feathery filtering appendages of barnacles which are actually modified legs
7. Compound Eyes – bundles of light sensitive units grouped in a mosaic
8. Statocysts – a balance organ present in some aquatic invertebrates. It consists of a sac-like structure containing a mineralised mass (statolith) and numerous innervated sensory hairs (setae).
9. Satae – sensory hairs
10. Statolith – calcium granule in statocyst, influenced by gravity whose movement stimulates sensory cells

Characteristics of Arthropods:

1. jointed appendages, a pair of appendages is attached to each segment
2. segmented body
3. exoskeleton – made of chitin
4. bilaterally symmetrical
5. molting – shedding of the exoskeleton

Subphyta of Arthropods:

Trilobita – extinct trilobites

Crustacea – shrimp, lobsters, crabs, barnacles, crayfish, water fleas, copepods, ostracods, and cladocerans.

1. two pair of branched antennae
2. chewing mouth-parts (mandibles)
3. exoskeleton contains calcium carbonate
4. mostly aquatic
5. body divided into two parts
6. isopods (pill bugs) have seven identical pairs of legs
7. gills are attached to each walking leg

Chelicerata – spiders, ticks, scorpions, mites, sea spiders, and horseshoe crabs

1. absence of antennae
2. pincer-like mouthparts (chelicerae)

Uniramia (one-branch)– centipedes, millipedes, and all insects.

1. Have branched antennae and mandibles
2. Unbranched appendages

Body Structure of Crustacean:

1. Cephalothorax – contains fused head and thorax.  It has 13 segments and is covered by a hard carapace
2. Abdomen – posterior to the cephalothorax, it is divided into seven segments
3. Telson – the seventh segment of the abdomen, which forms a flat triangular section at the tail of the animal.  It is for locomotion.
4. Chelipods – claws that capture food and serve as a defensive weapon
5. Antennules – smaller whip-like appendages with receptors for touch, taste, and equilibrium at the very anterior end (front) of the animal.
6. Rostrum – an anatomical structure, part of the carapace, resembling a bird's beak located about the thorax of an arthropod.
7. Carapace – dorsal part of the exoskeleton that covers the cephalothorax of crustaceans.  It functions as a protective cover over the cephalothorax.
8. Antennae – larger whip-like appendages for touch and taste at the very anterior end (front) of the animal.
9. Mandibles – “jaws” which move up and down to crush food at the anterior end of the animal
10. Maxillae – “jaws” which move side to side to tear food
11. Maxillipeds – “jaws” to hold food
12. Walking Legs – appendages for walking
13. Swimmerets – appendages for movement, swimming, which create water currents.  They also function in reproduction.
14. Uropods – posterior flat appendages that propel the animal through the water

Class Arachnida – spiders, mites, scorpions

Body Structure – cephlothorax and abdomen, have unique respiratory system

1. Cephalothorax – contains fused head and thorax. Four pair of legs, a pair of chelicerae, and a pair of pedipalps are attached.
2. Chelicerae – pincer-like mouthparts
3. Pedipalps – appendages that aid in chewing or other functions
4. Spiracles – openings in the cuticle for breathing
5. Book Lungs – paired sacs in the abdomen with page-like components, which provide a large surface area for the exchange of gases.
6. Tracheae – in insects, one of a network of air tubes that connects the pharynx to the lungs
7. Pharynx – open are at the back of the mouth
8. Malpighian Tubules – the main excretory organ consisting of hollow projections of the digestive tract that collect body fluids, remove waste, and carry  waste to the intestines where water is reabsorbed  and solid waste leaves the body.
9. Coxal Glands – in spiders, organs that remove waste and discharge them through an opening at the base of the leg.
10. Spinnerets – in spiders, three pairs of organs, each made up of hundreds of microscopic tubes, at the posterior tip of the abdomen from silk from silk glands flow

Scorpions

1. have greatly enlarged pedipalps which are held in a forward position
2. large stinger on the last segment of the abdomen

Mites and Ticks

1. have fused cephalothorax and abdomen
2. mites are the most specialized and most abundant archnids

Myriapods (many feet) – centipedes and millipedes

Class Diplopoda – Millipedes (thousand feet)

1. terrestrial
2. no waxy cuticle
3. millipedes have two pairs of short legs on each body segment except the last two
4. millipedes are herborvores
5. rounded bodies in cross section

Class Chilopoda – Centipedes (hundred legs)

1. body flattened in cross section
2. one pair of longer legs per section except for the first and last two
3. carnovores
4. first body segment has a pair of claw-like appendages that can inject venom into a prey