Download Biology Chapter 38 notes Section 38

Biology Chapter 38 notes
Section 38-1 Phylum Arthropoda
Classification of Organisms
Kingdom
Animalia
Phylum
Arthropoda
Class
Chilopoda
Order
Geophilomorpha
Family
Oryidae
Genus
Orya
Species
barbarica (centipede)
Phylum Arthropoda
The phylum Arthropoda includes lobsters, crabs, spiders, millipedes, centipedes, and
insects.
Characteristics of Arthropods
Arthropods are segmented animals.
The body segments have jointed extensions called appendages (legs and antennae).
Arthropod = “jointed foot.”
Exoskeleton - provides protection and support. (made of chitin)
- three layers that are secreted by the epidermis
Appendages around the mouth = sensors and food handlers.
Most arthropods have compound eyes - eyes composed of many individual light
detectors (lens).
Many have simple eyes that sense light intensity.
All have open circulatory systems.
Molting
An arthropod cannot grow without periodically shedding its exoskeleton - molting.
A hormone is produced that induces molting.
In response to the hormone the cells of the epidermis secrete enzymes that digest the
inner layer of the exoskeleton.
At the same time the epidermis begins to make a new exoskeleton.
Eventually the outer layer of the old exoskeleton loosens, breaks along specific lines.
It takes a few days for the new exoskeleton to become hard.
Evolution and Classification
First appeared more than 600 million years ago.
Evolved from a common ancestor.
In most living species the segments are fused into a number of larger structures =
tagmata, (specialized to perform functions such as feeding, locomotion, and
reproduction.)
Arthropods are divided into 4 subphyla on the basis of differences in development,
mouthparts and other appendages.
1. Trilobita - includes extinct animals called trilobites.
2. Crustacea (Crustaceans)- shrimps, lobsters, crabs, crayfish, barnacles, isopods,
copepods, and water fleas. (Mostly aquatic)
- branched antennae and a pair of chewing mouthparts (mandibles).
3. Chelicerata - spiders, scorpions, mites, ticks, sea spiders, and horseshoe crabs.
Lack antennae, but have pincerlike mouthparts = chelicerae.
4. Uniramia - centipedes, millipedes, and insects.
Have antennae and mandibles, but appendages are unbranched.
Only group that seems to have evolved on land.
Section 38-2 Subphylum Crustacea
Characteristics and Diversity of Crustaceans
Only arthropods that have two pairs of appendages on their head - serve as feelers.
Exoskeletons of aquatic crustaceans often contain calcium carbonate = extremely hard.
Some small crustaceans exchange CO2 and O2 through the thin areas of exoskeleton,
Large crustaceans respire with gills.
Embryo = free-swimming larva – nauplius
After many molts it reaches adulthood.
Copepods are an important part of the ocean’s plankton, the collection of small
organisms that drift or swim near the surface.
In freshwater environments, much of the plankton is composed of water fleas (Daphnia).
Barnacles are marine crustaceans that are adapted to a sessile lifestyle as adults.
Free- swimming barnacle larvae attach themselves to any surface.
Develop a very hard shell of calcium carbonate.
Six pairs of long legs – cirri, sweep small organisms and food particles in its mouth.
Sow bugs and pill bugs are terrestrial members of a group of crustaceans called
isopods.
Lose water quickly through their exoskeletons.
Only in moist environments.
Feed on living and decaying vegetation.
The Crayfish
Structurally similar to lobsters.
Decapods = “ten feet” - have five pairs of legs.
External Crawfish
2 major sections: the cephalothorax and the abdomen
Cephalothorax = 2 tagmata: the head, which has 5 segments, and the thorax, which has
8 segments
Dorsal exoskeleton in the cephalothorax is fused into a single, tough covering =
carapace.
The abdomen = tagma next to the cephalothorax - divided into 7 segments.
7th abdominal segment – telson
Antennules - feelers sensitive to touch, taste, and equilibrium.
Antennae - feelers; respond to touch and taste.
Crayfish chew food with their mandibles and manipulate it with their two pairs of
maxillae and three pairs of maxillipeds.
Chelipeds - end in large pincers used for capturing food and for defense.
4 pairs of walking legs
First 2 pairs with small pincers for grasping. The swimmerets, attached to the first five
abdominal segments create water currents and function in reproduction.
Uropods, on the sixth abdominal segment, help propel the crayfish.
Digestion, Respiration, and Excretion
Food passes through the esophagus to the stomach, where teeth made of chitin and
calcium carbonate grind the food into a fine paste.
After the paste is mixed with enzymes secreted by a digestive gland, it enters the
intestine.
Indigestible material leaves through the anus.
Use gills for respiration.
Gills extend from the base of walking legs.
As it walks, its legs circulate water across its gills.
Gills permit gases to diffuse into them.
Dorsal heart pumps hemolymph to different regions of the body.
Hemolymph then passes through the gills, where it exchanges CO2 and O2 with the
water.
From the gills, the hemolymph returns to the dorsal part of the crayfish and enters the
heart.
Live in a hypotonic environment - the concentration of solute molecules is lower than
that in the organism’s cells.
Excess water is eliminated by excretory organs called green glands.
Fluid in the green glands leaves the body through a pore in the antennae.
Neural Control
Brain consists of a pair of ganglia above the esophagus that receive nerve impulses
from the eyes, antennules, and antennae.
Two bundles of nerve fibers extend from the brain and pass around either side of the
esophagus to a ganglion that controls the mandibles, maxillae, and maxillipeds.
Section 38-3
Subphyla Chelicerata and Uniramia
The subphyla Chelicerata and Uniramia are terrestrial.
A major group in Chelicerata is the class Arachnida.
The major groups in Uniramia are classes Diplopoda and Chilopoda.
Class Arachnida
Arachnids include spiders, scorpions, mites, and ticks.
a body that is divided into a cephalothorax and an abdomen.
usually six pairs of jointed appendages: 1 pair of chelicerae; 1 pair of pedipalps, which
aid in holding food and chewing; and 4 pairs of walking legs.
Anatomy of a Spider
- body of a spider is constricted between the cephalothorax and the abdomen.
chelicerae are modified as fangs and are used to inject venom into prey.
Most spiders have eight simple eyes at the anterior end of the cephalothorax.
- tip of the abdomen of many spiders are three pairs of organs called spinnerets composed of hundreds of microscopic tubes that connect to silk glands in the abdomen.
In some spiders, respiration occurs in book lungs, paired sacs in the abdomen with
many parallel folds.
Other spiders have a system of tubes called tracheae that carry air directly to the
tissues from openings in the exoskeleton known as spiracles.
Some spiders have both book lungs and tracheae.
Malpighian tubules - hollow projections of the digestive tract that collect body fluids and
wastes and carry them to the intestine.
Scorpions
Scorpions have large, pincerlike pedipalps, which they hold in a forward position.
They also have a large stinger on the last segment of the abdomen, which is curled over
the body.
Only a few species of scorpions have venom that can be fatal to humans.
Mites and Ticks
Unlike spiders and scorpions, mites and ticks have a completely fused cephalothorax
and abdomen.
They can be found in freshwater, marine, and terrestrial habitats.
Myriapods
millipedes and centipedes
Early myriapods may have been the first animals to appear on land, and all present-day
myriapods are terrestrial.
- do not have a waxy exoskeleton
- they avoid desiccation by living in damp environments under leaves, rocks, and logs.
Class Diplopoda
Most millipedes have two pairs of legs on each body segment except the last two.
- bodies of millipedes are rounded.
- have short antennae and two groups of simple eyes on their head.
poor vision, but a good sense of smell.
When threatened, they coil up and may secrete a noxious fluid that contains cyanide.
Class Chilopoda
Centipedes may have as few as 15 or as many as 175 pairs of legs.
- bodies are more flattened than those of millipedes.
Each body segment behind the head, except the first segment and the last two
segments, has one pair of jointed legs.
The appendages on the first segment are modified into a pair of poison claws.