Chapter 30 : Invertebrates (continued)

Phylum Arthropoda

 This is largest phylum in any kingdom : over 1 million species. They have a segmented body with very specialized segments : tagmatization. Normally 3 tagmata : head, thorax, abdomen.

Head : sense organs and mouthparts.
Thorax : legs and wings.
Abdomen : digestive and reproductive organs.

Arthropods have an open circulatory system (blood flows from the heart into large cavities, it is not in blood vessels all the time).

Hard exoskeleton ( chitin ) for protection, muscle attachment and to prevent drying out. Grow by molting ( ecdysis ). So they go through metamorphosis (change) during the life cycle : incomplete metamorphosis : young are like small adults eg termite.
complete metamorphosis : larva look different from adults eg butterfly. Metamorphosis

Subphylum Trilobita (Trilobites)

 Common in the sea 600 million - 300 million years ago. Became extinct 250 million years ago. Flattened body divided into 3 segments. Heavily armored. Trilobites had compound eyes like modern insects. They swam, walked or burrowed. Trilobites

Subphylum Chelicerata

They have chelicerae ( fangs ) as part of their mouthparts. They have 8 legs. Also no antennae, and simple eyes. They are fluid feeders.
Body in two parts : cephalothorax and abdomen. eg : Limulus ( horseshoe crabs )

The largest class of chelicerates is: Class Arachnida. This class has 70,000 species. It includes spiders, scorpions, ticks. Spiders produce silk from spinnerets in the abdomen, and breath through book lungs. Spider web

When male spiders want to mate, they tap on the female spider's web with a particular frequency that tells the female spider that they are not dinner! eg : Latrodectus ( black widow spider ) found in Florida. Females guard their young.

Portia prey on other spider species. They sometimes pretend to be a male spider coming to mate, and then attack the female spider.

Uroctonus ( scorpion ). Males face the females during mating, holding onto their front claws. The male drops a bag of sperm on the ground, then pulls the female over it.

Ixodes ( tick ) sucks blood and accidentally transmits Lyme disease. Lyme disease

Amblyomma (tick) transmits the bacterial disease erhlichiosis. Ticks

Subphylum Uniramia

 1 million species. Appendages end in a single point.

Class Hexapoda ( insects ) 900,000 species. Insects first evolved 300 million years ago. Their body is divided into three tagmata: head, thorax, abdomen. Insects have 6 legs and usually 1 or 2 pairs of wings. Insects breath through tracheal tubes. Excretion is through Malpighian tubules which release waste into the intestine.

Sense organs : compound eyes ( multiple images )
hair organs ( touch, vibration )
chemoreceptors ( smell )
humidity sensors
Tympanic membrane (hearing) usually on the abdomen.

Why are insects so successful?
1) Survive well on land - exoskeleton prevents dehydration and allows movement.
2) Most can fly.
3) Rapid reproduction ( up to 25 generations/year ).
4) Mouthparts and limbs can be modified in many ways.
5) Co-evolved with flowering plants - as pollinators .

Orders of insects

Coleoptera ( beetles )
500,000 species worldwide. Beetles have 2 pairs of wings : the front pair modified into tough elytra. Chewing mouthparts. Pleasing fungus beetle Complete metamorphosis.

Lepidoptera ( butterflies and moths )
150,000 species. Two pairs of wings. Chewing mouthparts in larva (caterpillar), sucking mouthparts ( tube-like tongue ) in adult. Antennae are often large, especially in moths to detect pheromones. Complete metamorphosis. Some butterflies have wing patches that work just like LEDs. Wings

Hymenoptera ( ants, bees )
100,000 species. Wings absent ( ants ) or 2 pairs ( bees ). Social, living in colonies. Chewing or sucking mouthparts. Complete metamorphosis.

Bees (genus Apis): each hive of 50,000 bees has : one queen who lays all the eggs and is the only fertile female. Drones are fertile males, who provide sperm but are only produced occasionally.Workers are all sterile females and do all of the work: collecting food, feeding the queen, feeding the larvae, building the hive, storing honey etc. The queen bee can determine whether an egg grows into a worker or a drone. Fertilized eggs produce females (workers) unfertilized eggs produce drones. The queen mates with several males, killing each one after mating. The difference between a worker female and queen is nutritional: queens are fed "royal jelly".

Diptera ( flies, mosquitoes )
100,000 species. One pair of wings ( rear "wings" modified into halteres which act like gyroscopes ). Piercing and sucking mouthparts. Flies can "taste" with their feet, and spit on food to digest it before sucking up the liquid. Complete metamorphosis. Maggots and flies are often used in forensic entomology.

Subphylum Uniramia (continued)

Class Diplopoda ( millipedes )
Have a total of 24 - 750 legs. They always have 2 pairs of legs per segment of the body. Millipedes are herbivores and feed on leaf litter. Protection from predators: roll into a ball and have stink glands ( produce acid, iodine or chlorine ). eg : Rhinocrisis

Class Chilopoda ( centipedes )
Total of 30 - 100 legs. Always one pair of legs per segment. Total number of segments is always uneven eg 15, 27 etc. Centipedes are predators; front "legs" modified into poison glands. eg : Scutigera

Subphylum Crustacea

Appendages are biramous (end in 2 pincers). Two pairs of antennae. Aquatic, gas exchange using gills. Hard mandibles for grinding food (crustaceans and uniramia are called "mandibulates" beacuse they have jaws, unlike the chelicerates).

Many limbs : often 5 pairs of walking legs ( pereopods ) and 5 pairs of swimming legs ( pleopods ). Usually have a hard shell of calcium carbonate. Green gland for excretion. Compound eyes. Nauplius larva has 3 pairs of appendages and one eye.

Classes of crustacean

Class Malacostraca ( crabs, shrimp, lobster )
Have 14 body segments that have appendages. Front pair of walking legs have large claws ( chelae ). Head and thorax covered with a carapace. Male fiddler crabs (Uca) use one large claw for signaling to their mate outside thier burrow. Female fiddler crabs inspect an average of 23 burrows before mating. Fiddler crabs

Class Cirripedia ( barnacles )
Filter feeders, use modified "feet" ( cirri ) to collect food. Thick shell protects them from predators. Barnacles Males are often small, may be parasitic on females. eg Balanus

Class Copepoda ( copepods )
Small, but very abundant in the sea. They are plankton (they drift with the ocean currents), near the base of the food chain. Copepods have 4 pairs of appendages. Copepods Filter feeders, predators or parasites on fish. eg : Calanus

 Last edited September 2011, by David Byres, dbyres@fscj.edu