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Chapter 29 Review
1 List several characteristics of ecdysozoans.
In order to grow, ecdysozoans must shed their protective cuticles, or exoskeletons. Ecdysis, or molting, is
the basis for separation of the ecdysozoans from the lophotrochozoan. Evolutionarily, the development of
ecdysis influenced the further development of respiratory structures such as the trachea, gills, and lungs
as well as internal fertilization and metamorphosis.
2 Explain the taxonomical organization of the ecdysozoans.
The ecdysozoans are represented by eight very different phyla of protostomes: phylum Nematoda
(roundworms) and phylum Nematomorpha (horsehair worms) constitute a group called the
Nematoidea.The following phyla are small and have only a few examples: phylum Kinorhyncha (minute
marine worms), phylum Priapulida (about 16 species of cold-water marine worms), and phylum Loricifera
(fewer than 100 species of tiny marine animals). Clade Panarthropoda consists of three phyla: phylum
Arthropoda (insects and their relatives), phylum Tardigrada (water bears), and phylum Onychophora
(velvet worms).The panarthropodans possess a true coelom (body cavity). The nematodes,
nematomorphans, and kinorhynchs have a pseudocoelom, and the loriciferans can be a
pseudocoelomate or an acoelomate depending upon the species.
3 Name five characteristics of phylum Nematoda.
As a general rule, the bodies of nematodes are long, cylindrical, and tapered at both ends. Nematodes
possess a thick, protective, nonliving cuticle that grows between molts. The epidermis and subepidermal
muscle can be found beneath the cuticle. In nematodes, the fluid-filled pseudocoel is well developed and
serves as a hydroskeleton. The mouth of a nematode opens into a buccal cavity with teeth or a stylet
(spear-like structure). Nematodes have a long, straight intestine that serves as a site of digestion and
absorption. Nematodes lack protonephridia but possess glands and tubules that open through a
midventral pore into the outside environment. The nervous system consists
of a variety of nerve rings. Nematodes have sensory papillae, and nonparasitic species possess amphids
(sensory organs) on each side of the head. Parasitic species have phasmids (sensory organs) near their
posterior end. Most nematode species are dioecious, with the male being smaller than the female.
4 Trace the natural history of three sample nematodes.
Hookworms (Necator americanus) possess hook-like anterior ends (Fig. 29.6). Females can attain a
length of 11 mm and males 9 mm. Hookworms infect a number of mammals, including humans.
Hookworm eggs pass in the feces of the infected host, and the juveniles hatch in the soil. Thus, going
barefooted in an area where animals frequently defecate is not wise. The juveniles feed upon bacteria
until they have the opportunity to burrow through the skin of a new host. The parasite travels to the lungs
and, eventually, the intestine. The hookworm attaches to the intestinal mucosa, where it feeds on blood.
Symptoms of a hookworm infection include anemia and protein deficiency and, in young children, the loss
of proteins and iron. Left untreated, this loss can retard growth.
Vinegar eels (Turbatrix aceti) are free-living nematodes commonly found in fermented fruit juices and
unpasteurized vinegar. Turbatrix actively feed upon bacteria living in these liquids. Fortunately, the
vinegar in your kitchen is pasteurized.
Under the microscope, the 2 mm nematodes are noted for their thrashing movements.
Filarial worms get their name from their young, called microfilariae. In humans, a devastating filarial worm
called Wuchereria bancrofti infects people in tropical countries in Africa and South America. Females can
exceed 10 mm in length and live in the lymphatic system. Females release microfilariae into the lymphatic
system and blood. A mosquito bite causes the infection, which occurs primarily in dogs and is caused by
Dirofilaria immitis. Occasionally, a cat, a sea lion, or a human can acquire the infection. This disease can
be deadly to dogs if left untreated.
Mosquitoes are the vector for heartworms. Wuchereria bancrofti is responsible for the disfiguring disease
elephantiasis.
The most common filarial disease in the United States is heartworm,
5 Name five characteristics of phylum Arthropoda.
One of the most distinguishing characteristics of the arthropods is the presence of a chitinous
exoskeleton.
Arthropods exhibit bilateral symmetry. Typically, they are divided into three body regions: head, thorax,
and abdomen.
Arthropods also exhibit segmentation, metamerism, typically with each somite having a pair of jointed
appendages. Typically, arthropods exhibit a great degree of cephalization. Also, they possess a variety of
sense organs, such as compound eyes and antennae. The digestive system is complete, consisting of a
foregut, midgut, and hindgut. Osmoregulation in arthropods occurs in Malpighian tubes and glands.
Respiration in arthropods takes place through the gills, tracheae, book lungs, and the body surface.
Generally, arthropods are dioecious and undergo internal fertilization.
6 Describe and provide specific examples of the subphylum Chelicerata.
Members of subphylum Chelicerata are easily distinguished from other members of phylum Arthropoda.
They are characterized by six pairs of appendages, including four pairs of walking legs, a pair of
chelicerae (appendages behind the mouth used for feeding), and a pair of pedipalps (appendages that
aid in chewing). Chelicerates have no antennae and no mandibles. The body has two regions: a
cephalothorax and an abdomen. Chelicerates include horseshoe crabs, scorpions, spiders, mites, ticks,
sea spiders, and extinct eurypterids. Three classes of chelicerates have been described: Merostomata
(horseshoe crabs), Pycnogonida (sea spiders), and Arachnida (spiders).
7 Compare and contrast chilopods and diplopods.
Members of class Chilopoda are called centipedes. Of course, most centipedes do not have a hundred
legs, and most species have only 30 pairs of legs. Centipedes feature one pair of legs per segment.
These flattened, elongate arthropods have a chitinous exoskeleton and range in length from 4 mm to 30
cm. Most centipedes are dull brown and can be found in the underbrush, or perhaps visiting your house!
Centipedes use their venom claws, which actually are the first pair of legs, to capture and kill their prey.
Centipedes are dioecious.
Millipedes, a member of class Diplopoda, classically have been called “thousand-leggers” because, as
they busily scoot across the ground, they may look like they have a thousand legs! Approximately 10,000
species have been identified. Usually, millipedes hide under logs and stones. Millipedes are herbivorous,
or detritovores, compared to the carnivorous centipede. When disturbed, millipedes may roll into a ball
and emit a foul-smelling odor. The millipede body is more dome-shaped than the centipede body and
consists of 25 to more than 100 segments. Millipedes have two pairs of legs per segment, with the
exception of some anterior and posterior segments. Millipedes reproduce sexually, although several
parthenogenic species have been described. Initially, larval forms may be mistaken for centipedes
because they have one pair of legs per segment.
8 Label the following diagram.
1. Cheliped
2. Antennule
3. Antenna
4. Rostrum
5. Compound eye
6. Walking legs
7. Carapace
8. Abdomen
9. Telson
10. Uropod
11. Tergum
12. Cephalothorax
9 Explain the organization of the crustaceans.
Biologists recognize six classes of crustaceans. The four large classes are class Branchiopoda: brine
shrimp, tadpole shrimp, and fairy shrimp; class Ostracoda: ostracods and seed shrimp; class Maxillopoda:
barnacles, tongue worms,
fish lice, and copepods; and class Malacostraca: lobsters, crabs, shrimp, isopods, and pill bugs. Classes
Remipedia and Cephalocardia include rather obscure crustaceans.
10 Why are insects successful?
Insects are prolific and have conquered the majority of environments on earth.
11 Label the following diagram.
1. Ocelli
2. Prothorax
3. Metathorax
4. Tibia
5. Cercus
6. Subgenital plate
7. Spiracle
8. Tarsus
9. Femur
10. Mesothorax
11. Compound