Laboratory Notes for BIO 1003
© 30 August 1999, John H. Wahlert & Mary Jean Holland
Superkingdom Eukaryota
Kingdom Animalia
PHYLUM ARTHROPODA
Members of the Phylum Arthropoda may be aquatic, terrestrial (including flying), and parasitic. The body is coelomate and has bilateral symmetry. The skeleton is on the outside and is called an exoskeleton (an internal one, as in humans, is an endoskeleton); it is made of chitin. The appendages are jointed (this is the meaning of arthro-pod). The body is divided into three regions--head (cephalum), thorax, and abdomen. Portions of the body are segmented. In most species the sexes are separate. Hatchlings are larvae that undergo metamorphosis into the adult form. In order for growth to occur, the confining exoskeleton must be shed and a new one formed around the now larger individual; each growth stage is called an instar. A strong, hard skeleton and well developed organ systems permit some of these animals to attain considerable size. The invention of specialized respiratory structures for breathing air have permitted stunning success in colonizing land by a few groups. Use a dissecting microscope to observe details in the examples below.
Class Crustacea
The crustaceans include crabs, lobsters, shrimp, and barnacles. You will be examining the external features and internal anatomy of a crayfish, genus Cambarus. Identify the following features of the external anatomy:
Three body regions: Cephalothorax, abdomen, tail (consisting of telson in the middle and uropods lateral to it.
Head with compound eyes, antennules, and antennae
Mouth parts with mandibles, maxillae, and maxillipeds
Locomotory appendages: Chelipeds with claws, walking legs, and swimmerets on abdominal segments. Be sure you can tell the difference between male and female
Dissection: Make a dorsal, longitudinal cut along the carapace of the cephalothorax, and remove one side to uncover the gill region. Identify the feathery gills and the abdominal flexor muscles, the dorsal heart in a pericardial sinus probably filled with yellow stuff and abdominal aorta, (circulatory system is an open one), green gland, esophagus, digestive gland, stomach, intestine. You may even see the brain in the head and the connective branches of the ventral nerve cord around the esophagus.
Class Insecta
Preserved specimens of the grasshopper Romalea is our example. Find the following external features:
Body regions: head, thorax, abdomen which terminates bluntly (male) or with a pair of digging claws, the ovipositor of the female.
Mouth parts: maxilla with maxillary palps, labrum, labium with labial palps, mandibles
Compound eyes and antennae.
Legs for walking and jumping; tarsi have claws and pads for grasping.
Segments of the body are perforated by respiratory holes called spiracles.
Two pairs of wings, forewings protect fragile hindwings that are for flying.
The large, oval tympanic membrane is for hearing.
Dissection of a preserved specimen with dissecting microscope: make a mid-dorsal and mid-ventral longitudinal cut with the scissors. Remove the exoskeleton form one side of the specimen. Observe the digestive system with gastric ceca. The female will have a mass of rice-shaped eggs in the abdomen.
Class Chilopoda
The centipedes have a dorsoventrally flattened body and one pair of legs on each segment. The first body segment has poison claws.
Class Diplopoda
The millipedes have a cylindrical body and segments bear two pairs of legs. There are no poison claws. When disturbed they curl up, and some secrete a noxious fluid.
Class Arachnida
Spiders and scorpions have a body that consists of cephalothorax and abdomen. The two parts are fused in ticks and mites, which are parasitic. There are no true mandibles or antennae, and the eyes are simple. Arachnids have four pairs of walking legs in contrast to other arthropods.
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Last updated 6 May 1999 (JHW)
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