Crayfish, Lobsters, Spiders, Mites, Scorpions, & Insects Phylum Arthropoda Crayfish, Lobsters, Spiders, Mites, Scorpions, & Insects

Characteristics of the Phylum Arthropoda Largest Phylum in the Animal Kingdom Metameric – dividing the body into sections Tagmatization – each section is based on function Exoskeleton made of chitin Paired, jointed appendages Many go through a molting period called ecdysis Open circulatory system Many go through at least one larval stage

Advantages & Disadvantages of Having an Exoskeletons Prevention of water loss Provides a system of levers for muscle attachment and movement Provides protection Disadvantages: Cannot grow with the arthropod, so must be shed, or molted, in a process called ecdysis. Molting can take a few hours or a couple days and leaves the animal very vulnerable to predators and the environment. This is why many arthropods will hide during this process.

Metamorphosis Changing from a larval form to an adult form. Caterpillar to butterfly Maggot to fly What is the purpose of having two (or more) separate stages of development? Means that the stages do not compete with one another for food or living space.

Metamorphosis Types 1) Incomplete – egg, nymph, adult Egg hatches into a nymph which is a smaller, wingless form of the adult. After wings emerge, it is considered an adult. 2) Complete – egg, larva, pupa, adult Egg hatches into a larva whose job it is to eat voraciously. The larva spins a chrysalis, pupa or cocoon. After enzymes and hormones produce a body change, an adult emerges.

Complete Metamorphosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Complete Metamorphosis From Raven/Johnson, Biology, 3rd ed., Copyright © 1999 The McGraw-Hill Companies.

Incomplete Metamorphosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Incomplete Metamorphosis From Hickman/Roberts/Larson, Integrated Principles of Zoology, 11th ed., Copyright © 2001 The McGraw-Hill Companies.

The Earliest Arthropod Trilobites – similar to today’s wood louse (roly-poly) just MUCH bigger Trilobites went extinct about 345 million years ago, during the time of the dinosaurs.

SubPhylum Chelicerata Spiders, Mites, Ticks, Horseshoe Crabs, Sea Spiders, Water Scorpions, & Scorpions Usually have 2 tagmata The head tagma (cephalothorax) is used for sensory, feeding, and locomotion. Usually has eyes, but no antennae; instead, it has chelicerae and pedipalps. Behind the pedipalps are 4 pairs of walking legs. Chelicerae are usually pincers or fangs used in feeding. Pedipalps are usually sensory, but can also be used for feeding, locomotion, or reproduction. The tail tagma (opisthosoma) contains the digestive, reproductive, excretory, and respiratory organs.

Class Merostomata – Horseshoe Crabs Horseshoe Crabs – have remained virtually unchanged for over 200 million years. Only 4 species remains in existence today. Use book gills to exchange gases between the water and their blood. Called book lungs because they look like the pages of a closed book. Horseshoe crabs are dioecious. The female digs a hole in the sand to lay her eggs and the male then fertilizes them. Fertilized eggs are covered with sand and develop unattended.

Horseshoe Crab Ventral View

Fig. 18.2a

Fig. 18.2b

Class Arachnida – spiders, mites, ticks, and scorpions Dioecious Most arachnids are carnivores. Some hold their food with their chelicerae while enzymes from the gut tract pour over the prey. Partially digested food is then taken into the mouth. Others inject the enzyme directly into the prey through hollow fangs. The excretory system of arachnids is made of either coxal glands or Malpighian tubules that excrete uric acid. Some arachnids exchange gases using book lungs, others use tracheae, similar to our lungs, where oxygen enters through openings called spiracles.

Malpighian Tubules, Spiracles, & Tracheae

Order Aranaea - arachnids The chelicerae are fanglike and bear poison glands; while pedipalps are leglike and adapted for sperm transfer in males. Have 6 to eight eyes. Have spinnerets that produce silk for webs. Some spiders even use their silk to help the move from one location to another, just like Spiderman. All spiders are poisonous to something, but most aren’t poisonous to humans. Black widows and brown recluse spiders are the exception!

Brown Recluse Bite

Order Opiliones – Daddy Long Legs These guys are NOT spiders, therefore they do not have poisonous chelicerae. Therefore, the rumor that daddy long legs are poisonous is COMPLETELY FALSE!

Order Acarina – mites and ticks Many are parasites. Mite example – scabies. A female scabies mite can tunnel into human skin where it will lay about 20 eggs a day. This causes intense itching and can be acquired by contact with an infected individual. Ticks – Feed on blood and can cause several diseases, including Lyme disease.

Dermatophagoides Dust mite Feeds on microscopic food particles in dust. Allergies to fecal products 1 gram of dust holds 250,000 droppings

Order Scorpionida (Scorpions) Common in hot, dry climates. Nocturnal; during the day, they hide under logs and stones. Have fanged chelicerae and modified pincher pedipalps. Only a few species have venom that is toxic to humans, most scorpion stings are equivalent to wasp stings. Scorpion mothers provide care to their young by allowing them to crawl onto her back and remain there for up to a month after birth.

Class Crustacea Includes crabs, lobsters, crayfish, brine shrimp, shrimp, water fleas, barnacles, & wood lice (roly-polys). Most are marine, but some live in freshwater or on land. Dioecious Have 2 pairs of antennae. 5 pairs of legs (4 for walking, 1 for grasping); the claws are called chelipeds Breathe using gills. Many have compound eyes (an eye with more than one lens). The top shell is called the carapace.

Class Diplopoda: Millipedes Have 11 to 100 segments, not 1,000. Each segment has 2 pairs of legs. Round in shape. Herbivores Almost always found under decaying leaves or logs. Can excrete cyanide when threatened or attacked.

Class Chilopoda: Centipedes Have 15 or more segments. Each segment has only one pair of legs. Most are nocturnal. Predators; have poison claws for immobilizing prey; however most centipedes are NOT poisonous to humans. Flattened body.

Class Hexapoda - Insects Single largest class of all animals. Includes bees, flies, grasshoppers, lice, butterflies, moths, ants, and beetles. Has 3 body regions, head, thorax, & abdomen. 3 pairs of legs attached to the thorax. Many have wings and 1 pair of antennae. Have grinding and shearing mouth parts called the mandible and the maxilla.

Insect Flight Insects were the first animals to fly. Wings have thickened, hollow veins for increased strength. Most insects have to reach an internal temperature of about 80 degrees Fahrenheit for their muscles to contract rapidly enough to for flight. Frequencies of up to 1,000 wing beats per second have been recorded in midges!