Biology 102 Chapter 33
The Ecdysoans: The Molting Animals
1. Describe the distinguishing features of ecdysoans.
---possess exoskeleton—a firm, nonliving covering that is
difficult to penetrate
--exoskeleton CANNOT grow as the animal body inside it grows
---solution is to shed (molt) the outgrown exoskeleton and
expand and harden a new, larger one
---cannot use cilia for locomotion so new forms of locomotion
evolved
---hard exoskeletons impede passage of oxygen into animal so new
mechanisms for respiration evolved
---exoskeleton MAY be relatively thin and flexible
--called a cuticle
--provides some protection but does NOT support body
--rely on hydrostatic skeleton
2. List the characteristics of nematodes that distinguish them
from other animal phyla.
---commonly called the roundworms
---have thick, multilayered cuticle secreted by underlying
epidermis
---exchange oxygen and nutrients through both cuticle and
intestine (only one cell layer thick)
---materials moved through gut by contractions of pharynx
--highly muscular organ at worm’s anterior end
---one of most abundant and universally distributed of all
animal groups
---predators, parasites, and free-living
3. List characteristics of arthropods that distinguish them from
the other animal phyla.
---have regional segementation, jointed appendages, and
an exoskeleton (protein and chitin)
---body completely covered by exoskeleton
---body divided into segments
---possess hemocoel
4. Describe the advantages and disadvantages of an exoskeleton.
---advantages include protection and points of attachment
for muscles to move appendages, relatively impermeable
to water
---disadvantage is the old exoskeleton must be shed for
an arthropod to grow (molting)
5. Distinguish among the following arthropod classes and give
an example of each.
a. Arachnida
b. Crustacea
c. Insecta
---Arachnida includes the scorpions, spiders, ticks, and
mites
---have cephalothorax with six pairs of appendages
--chelicarae, pedipalps (sensing or feeling) and
four pair of walking legs
--gas exchange by book lungs (stacked plates in internal
chamber
--ability to make silk
---Crustacea includes the crabs, lobsters, shrimps,
barnacles, and others
--two pair of antenna, 3 or more pairs of mouthparts,
(including mandibles), walking legs on thorax,
appendages present on abdomen
--lost appendages can be regenerated
--gas exchange occurs across thin areas of the cuticle
or by gills
--open circulatory system with hemolymph
--salt balance regulated by pair of specialized antennal
or maxillary glands
--most are dioecious
-some males have specialized pair of appendages to
transfer sperm to female
---Insecta has greater species diversity than all other
forms of life combined
---flight is key to the success of Insecta
--1 or 2 pair of wings emerge from dorsal side of
thorax in most species
--wings are extension of cuticle not modified appendages
--complete digestive system with specialized regions
--open circulatory system with hemolymph
--excretory organs (Malpighian tubules) are outpockets
of the gut
--gas exchange by tracheal system with openings via
spiracles
--dorsal brain and pair of ventral nerve cords
--most undergo some type of metamorphosis
--are dioecious and usually reproduce sexually
6. Distinguish between a hemocoel and a coelom.
---coelom is a fluid-filled body cavity completely lined by
mesodermally derived tissues; inner and outer layers of
tissue that surround the cavity connect dorsally and
ventrally to form mesenteries, which suspend the
internal organs
---hemocoel describes open-circulatory system in which
fluid called hemolymph is propelled by heart through
short arteries and into spaces called sinuses surrounding
the tissues and organs (term “blood” best reserved for
fluid in closed circulatory system)
--body sinuses are collectively called the hemocoel which
is NOT a part of the coelom
--in most arthropods, coelom that forms in embryo
becomes greatly reduced
--hemocoel becomes main body cavity in adults
7. Distinguish between incomplete metamorphosis and complete
metamorphosis.
---incomplete metamorphosis is a type of development during
which the young resemble adults but are smaller and
have different body proportions
--grasshoppers
---complete metamorphosis is a type of development
characterized by larval stages (maggot, grub, or
caterpillar) which are very different in appearance
from adults