Chapter 30 discusses the characteristics of the Arthropods, which include the Crustaceans ( crayfish, lobsters & crabs, the Insects and Uniramians ( the centipedes and milipedes) and the Echinoderms, which include the starfish.

    The Arthropoda phylum is the largest animal phylum largely due to it containing the class Insectivora, which contains all the numbers of insect species. Insects serve several purposes which are listed below.

• Damaging to Agriculture- Even though this is not a good thing it happens and insects cause the greatest agricultural damage in our society.
• Consumption of weeds and other unwanted vegetative material as well as control of other insect populations.
• Fertilization- If it were not for the insect populations, many of our flowering plants would not get pollinated during sexual reproduction.

• Coelom- again a true body cavity , which houses the internal organs.
• Organ Systems- These still occur as in the Annelids, but are more advanced and serve a greater purpose.
• Segmentation-The arthropods show segmentation as did the annelids, but the segmentation is more advanced to the point that there is 3 distinct body parts, the

Characteristics of Arthropods

     There are several characteristics in which the arthropods share, but all arthropods can basically be divided into two large groups.

• Mandibulates- These arthropods have a jaw like structure called a Mandible ( moving jaw) which allows them to be better digest their food. Examples of mandibulates are crustaceans, insects and centipedes and millipedes.
• Chelicerates- Which have fang like mouth parts like the spiders, mites and scorpions. From here we can look at the arthropod characteristics to identify and classify them.

1. 1 Jointed appendages- jointed appendages, which most arthropods have, allow them to have greater flexibility, which increases their range of motion and gives them greater mobility
2. 2- Segmentation- segmentation in the adult arthropods has advanced to the point that there are three distinct body parts.  Head , Thorax and abdomen.
3. 3- Head is distinct with advanced sensory organs to allow them to sense their environment. Sometimes with certain arthropods their head and thorax are fused together which is called a cephalothorax, like the lobsters, and spiders.
4. 4- Exoskeleton- is a shell like covering which protects the arthropods and also helps them from drying out ( dessicaction) . All internal body parts are attatched to the exoskeleton to provide support for the organs.
5. 5- Compound Eyes- is made up of 1,000's of individual  visual units called Ommatida, which have a lens and retina. These structures allow them to see a true image of their environment through each ommatida, which limits vision to responding to movement rather than true recognition. Other arthropods have simple eyes called Ocelli, which do not form images, but rather only respond to light and dark
6. 6- Spiracles- are tubes or openings that allow atmospheric air to enter the body and act as a valve to control the air flow into the body cavity, which helps keep them from drying out. Once the air enters the body cavity, the gases are diffused at the tracheae.
7. 7- Circulation- they have an open circulatory system, which means that blood leaves the blood vessels and pours out over the organs and tissues.
8. 8- Malpighian Tubules- act as the nephridia in annelids, which function to get rid of waste nd conserve water. They excrete their waste in a paste like substance. Valuable material is retained and put back into the system.
9. 9- Wings- In some arthropods wings are present which give them greater ablility form movement and the opportunity to change environments.

Ecdysis- is molting, which many arthropods go through. This process is important, so the organisms can increase in size. Normally the exoskeleton limits how big the arthropod can get, but due to ecdysis the organism can increase in size. This process is controlled by hormones, which are chemicals which bring about physiological changes in the organism. A new shell is produced due to chemical influence. Then water is gathered between the new and old exoskeleton which causes the old shell to split so the organism can emerge with its new shell. It usually takes this new shell 1-2 hours to harden. Terrestrial organisms harden faster than aquatic.
 

    Arthropods are broken down into 3 major sub-phyla the Chelicerata  which include spiders, scorpions and there relatives, Crustacea which includecrabs, lobsters and their relatives, and Uniramia which include the insects and millipedes, and centipedes. Each sub-phyla is broken down into classes and orders as far as classification is concerned.

sub-phyla Chelicerata-  the Arachnida Class is the largest class in this sub-phyla, and includes 3 orders to be discussed below. Arachnids have a pair of chelicerae as their foremost appendage. A second pair of appendages called palps are used to catch and handle prey. They are followed by 4 pair of walking legs.
All arachnids except mites are carnivores( eating other animals.) They have no jaws. In order to digest food they inject powerful enzymes into the prey so to liquify them and then suck up the nutrient material through the pharynx.
The 3 major orders of the arachnid class are Scorpions, Spiders & Mites.
    Scorpions- Their palps are modified into large grasping pincers. They hold their abdomen over their body which ends in a stinger used to stun their prey. The palps are used to rip and tear prey in pieces. Very few scorpions are found around here, but if we do, they probably have came on pipes for oil lines from Oklohoma or Texas.
    Spiders- Their chelicera have been modified into a fang which is used to inject toxins to paralyze the prey. Only two species are kangerous to humans in the U.S. , the black widow, and the Brown Recluse. Spiders have a modified abdomen called a spinneretts which is where the silk material used to form the web is produced and released. Spiders major importance is as an insect preditor and as a part of the food chain.
    Mites- Includes chiggers and ticks  and have a head, thorax and abdomen which are all fused together. Most are predators, although some are herbivores, and even some mites hide in plants and protect them from other herbivorous organsisms.

Sub-Phylum- Crustacea includes crabs, lobsters, crayfish and shrimp. Like insects crustaceans have jaws, and are called mandibulates, but they have many characteristics that are different from the insects.

Crayfish Review
Crayfish
 
 

• Most appendages of crustaceans are branched at the ends, whereas the insects appendages are unbranched.
• All crustaceans have a distinctive larval form call a nauplius, that has three pair of branched appendages.
• Crustacean exoskeletons are hardened by calcium carbonate
• They are the only arthropods with 2 pair of antennae.
• Most crustaceans have 3 pair of chewing appendages while insects only have one pair.
• Crustaceans have legs attached to their abdomen and thorax instead of just the thorax as in insects.
• All crustaceans breath through gills.

    Decapoda is the order for the large marine crustaceans such as shrimps, lobsters and crabs as well as the freshwater crayfish. Decapoda comes from the latin name meaning Deca( Ten) Pod (footed) because these organisms have 5 pair of walking legs. They have a cephalothorax ( head & thorax fused together) . They propel themselves through the water, by forcefully contracting their abdomen.
    Terrestrial Crustaceans.- Only a few species are terrestrial.
 

Honeybee Waggle Dance

Sub-Phylum Uniramia- These include the insects, millipedes and centipedes.

    Uniramians have unbranched appendages, breathe with tracheae and spiracles and excrete waste through malpighian tubules. There are three classes of uniramians;
 

• Diplopoda ( the millipedes) 1,000 footed, each segment, ( usually 15 or so) has  2 pair of legs, millipedes are harmless herbivores that feed on decayed vegitation, they aviod predation by releasing a foul smelling scent.
• Chilopoda ( the centipedes) 100 footed, each segment has only 1 pair of legs and are carnivores, that inject toxins into the prey through fangs.
• Insectivora is the largest group of organisms on earth. This group makes up 50% of all named organisms. There are more kinds of beetles than all the kinds of non-insect animals put together. There are several insect orders on pg. 689 of the text that you need to be familair with. You need to be familiar with examples of insects and the orders they belong to.

Insect structure  and life cycles.

    All insects have 3 distinct body parts, head, thorax and abdomen. They have 3 pairs of legs attatched to the thorax and one pair of antennae. Another feature that stands out in insects is they have one or two pairs of wings. Each wing is solid sheet of chitin.
    The life cycles of insects are complex, often requiring several molts. There are two types of metamorphosis which occur in insects, called complete and incomplete explained below;

    Complete is when there is Egg, Larva, Pupa and Adults stages to the cycle. Each stage is different. The larval stage occurs so the organism can take in as much nutrient as possible to continue metamorphosis. The pupa stage is where the major transformation of metamorphosis takes place. In this stage a caterpillar larvae will go into a Chrysalis( butterfly) or cocoon ( moths) to change into its adult stage either the butterfly or moth.

    Incomplete metamorphosis is when there is only 3 stages, the egg, nymph and adult. The nymph stage looks like a small form of the adult, except there is no wings if present in adult forms and they lack reproductive structures.

    Elaborate social Systems of Insects.

The termites, ants and bees have a fairly complicated social system in that they communicate to others in their colony. Bees do a dance called the waggle dance to communicate where nector of flowers are located. Ants leave a chemical scent called a pheramone which is why ants follow each other in a line or row. There is a social order to ants and bees, like workers, soldiers, male mates for the queen. In a bee colony only one queen bee larva will survive, the rest will be killed by the first queen larvae to  emerge, if two emerge at the same time, they will battle until one is dead.

Phylum Echinodermata  ( Spiny Skinned Animals)

     The echinoderms are familiiar to all of us in the form of sea stars or sandollars. They have a larval form that is bilaterally symmetrical, but an adult form that has radial symmetry. Adult echinoderms have no brain or head, but do have a central ring which serves as a nervous system, each arm acts more or less on its. own. All echinoderms show 4 fundamental characteristics.

• Endoskeleton- This phylum has an endoskeleton composed of individual plates called ossicles. In most echinoderms, the plates extend upwards forming their spiney skin which give this phylum their name.
• Five- Part Radial Symmetry- most echinoderms have 5 arms radiating from a central ring.
• Water- Vascular System- they have a water-filled system of interconnected canals and tube feet. They have a water entrance called a sieve plate in which water enters the water vascular system.
• Coelomic circulation & respiration- circulation & respiration occur through their large internal body cavity. Respiration and waste removal also occur through skin gills in many echinoderms.

    There are 5 classes of echinoderms
 

• Class Asteroidea- includes the sea stars, which are carnivores. They are among the most important marine predators for the ecosystem maintenance.
• Class Crinoidea- includes the sea lilies called feather stars because they look like feather stalks standing upright.
• Class Ophiuroidea- Brittle stars, so named because of their long slender arms which are easlily broken off as attacked. Their arms move in pairs in a rowing fashion to help them move.
• Class Echinoidea- contains the sea urchins and sand dollars, which lack distinct arms but have the same 5 part symmetry.
• Class Holothuroidea- The sea cucumber belongs to this group, their ossicles are spread out and not connected, so their bodies are soft. The tube feet are modified to form tentacles which gather food and force it into the mouth.