Exam 6 chapter 33

Question 2

Chapter 33: An Introduction to Invertebrates

Question 3

Noncoelomate Invertebrates

Answer 3

Basal animals (Parazoans) are animals that
      do not have
 1) tissues and organs 
 2) a definite symmetry.

Answer 4

• Phylum Porifera (sponges) is a major
group of basal animals (parazoans).
There is only one species in phylum Placozoa.

Question 5

Phylum Placozoa – only one species

Answer 5

• Trichoplax adhaerens looks like a “hairy pita bread.” It is a bilayer of a few thousand cells. They reproduce by dividing into two individuals or by budding off many multicellular individuals.

Question 6

Phylum Porifera – general information

Answer 6

a. marine and freshwater forms
b. size ranges from a few millimeters to
2 meters in diameter
c. most are asymmetrical, but a few small
sponges have radial symmetry
d. larval sponges are free-swimming
e. adult sponges remain attached to the
substrate for the remainder of their life
f. sponges defend themselves by producing chemicals that repel predators

Question 7

Cell Types and Structures Found in Sponges

Answer 7

a. choanocytes = collar cells; function is
water circulation through sponge and
capturing, engulfing, and digesting
food particles

b. amoebocytes – distribute nutrients
throughout the sponge to other cells;
these are totipotent cells that can
become other types of cells

c. pinacoderm – made of flattened cells
that make up the outer epithelium

d. porocytes – flattened cells that line the pores of the ostia (openings where water enters the sponge)
e. osculum (plural, oscula) = larger openings where water exits the sponge body

f. mesohyl = gelatinous, protein-rich
matrix located between the inner and
outer layer of cells

g. spicules = needlelike structures made
of calcium carbonate or silica

h. spongin = tough protein fibers that
make up the skeleton of some
sponges

Question 8

Sponges reproduce both asexually and
sexually.

Answer 8

a. asexual reproduction occurs by
fragmentation
b. sexual reproduction involves fusion of sperm and egg
c. sponges are hermaphroditic and have both male and female parts

Question 9

Eumetazoa: Animals with True Tissues

Question 10

All cnidarians (Phylum Cnidaria) are
carnivores. Most of the 10,000 species are
marine, but a very few live in fresh water.

Answer 10

• diploblastic (no mesoderm)
• have tissues, but no organs
• no reproductive, circulatory, digestive,
or excretory systems
• have a nerve net
• nematocysts are unique to this phylum

Question 11

Basic Body Plans of Cnidarians

Answer 11

a) polyp – typically sessile
b) medusa – swims freely in water

• In both forms, the mouth opens into a
gastrovascular cavity (GVC) and is
surrounded by tentacles.
• The GVC is used for digestion, most gas
exchange, waste expulsion, and
(in many) the formation of gametes.
• Two-layered body wall made up of
epidermis and gastrodermis with an
acellular mesoglea (“middle glue”)
between these.
• GVC serves as hydrostatic skeleton
• Some polyps will build an exoskeleton
of chitin or calcium carbonate for extra
support.
• Sea anemones have no skeleton nor do
medusae. Medusa forms are solitary
while polyps can be colonial.

Question 12

Life cycles of cnidarians – Some have:

Answer 12

1) polyp only
2) medusa only
3) both polyp and medusa; sexes are
separate = gonorchism

egg + sperm  zygote  planula larva  polyp

In some, but not all species, the polyp can
produce other polyps asexually by
dividing, budding, or breaking off bits that
regenerate.

Question 13

Digestion – major evolutionary innovation

Answer 13

Extracellular digestion of food inside
animal in the gastrovascular cavity allows
cnidarian to take in larger prey items than
a sponge can. (Once partial digestion
occurs in the GVC, other cells take up
food fragments by phagocytosis.)

Question 14

Nematocysts = microscopic stinging
capsules (See Fig. 33.6 on p. 672)

Answer 14

• Capsule everts upon proper stimulation
• Releases barbs (some have venom too)
that immobilize or kill prey
• Nematocysts only discharged once
(can’t be reused)

Question 15

Cnidarians are grouped into four (or five)
classes.

Answer 15

1) Class Anthozoa (“flower animals”)
• include sea anemones and corals that
exist as solitary or colonial polyps
• form economically important coral
reefs

2) Class Cubozoa = box jellies
• medusa stage dominant; polyp is reduced or unknown in many cases
• strong swimmers and voracious
predators of fish
• has poison stronger than cobra venom
• some have image-forming eyes

3) Class Hydrozoa = the hydroids
• both polyp and medusa stages in life
cycle (with some exceptions)
• only class with freshwater members
• some marine hydroids and medusae
are bioluminescent
• Portuguese man-of-war = floating
colony of highly integrated polypoid
and medusoid individuals the stings
of which can kill a human

4) Class Scyphozoa = the jellyfish or
“cup animals”
• medusa more prominent and
conspicuous that polyp stage
• propel through ocean by jetting
water from GVC

5) Class Staurozoa = the star jellies
• used to be included in Class Scyphozoa
• resembles a medusa but is attached
to substrate by a stalk-like structure
• planula larva creeps rather than
swims or drifts

Question 16

Phylum Ctenophora: The Comb Jellies

Answer 16

• live in open ocean
• have 8 rows of comblike plates of
fused cilia along with two long
retractable tentacles used for prey
capture
• colloblasts are cells that release a
strong adhesive used in capturing
prey (colloblasts are on tentacles)
• ctenophores are largest animals to
use cilia for locomotion
• many are bioluminescent
• may be triploblastic and have partial
bilateral symmetry

Question 17

The Bilaterian Acoelomates

Answer 17

• key feature is bilateral symmetry
• exhibit functional specializations such
as having anteriorly located nerve
receptors

Question 18

Phylum Platyhelminthes: The Flatworms

Answer 18

1) flattened and solid body (aside
from incomplete digestive cavity)
2) free-living flatworms live in marine,
freshwater, and moist terrestrial
habitats; scavengers or carnivores;
move with ciliated epithelial cells
and also well-developed muscles
3) parasitic flatworms live inside
bodies of other animals; range in
size from 1 mm to many meters

° Digestion in flatworms
• incomplete gut that is branched;
functions in both digestion and distribution of food

° Excretion and Osmoregulation
• primary function of excretory system
is water balance
• wastes diffuse into gut and are
expelled through the mouth
• flame cells with “flickering” flagella
move water and excretory substances

° Nervous System and Sensory Organs
• anterior cerebral ganglion
• nerve cords and cross connections
that have ladder-like appearance
• eyespots distinguish light from dark

° Flatworm Reproduction
• most are hermaphroditic
• cross-fertilization is internal
• can regenerate missing parts

Question 19

Three Classes of Platyhelminthes

Answer 19

• no digestive cavity – absorbs
nutrients through outer surface from
host’s intestine
• body portions are
a) scolex for attachment,
b) neck, and
c) proglottids = repetitive
sections that are largely reproductive

Question 20

The Pseudocoelomates have a body cavity that lies between tissues derived from endoderm and tissues derived from mesoderm. Pseudocoelom serves as hydrostatic skeleton.

Answer 20

.

Question 21

Phylum Nematoda = roundworms

Answer 21

• ecdysozoans that molt their cuticles
• 20,000 recognized species, but may be
100 times that many
• marine and freshwater forms
• many are parasites of animals or plants
• abundant in soil (one spadeful of fertile
soil may contain, on average, a million
nematodes)
° Nematode structure
• bilateral, unsegmented worms
• flexible cuticle is molted as they
grow
• oxygen and carbon dioxide exchange occurs through cuticle
• have longitudinal muscles, but no
circular muscles so can lengthen or
shorten but can’t change diameter

° Nematode reproduction / development
• sexual reproduction
• gonochoric (separate sexes)
• sexual dimorphism (male and female look different)
• internal fertilization
• indirect development

° Nematode lifestyles
• hunters
• parasites of plants or animals

° Nematode-caused human diseases
• Genus Necator found in southern
states causes anemia
• Genus Trichinella causes trichinosis;
mature worms form highly resistant
calcified cysts in muscle tissue;
(don’t eat undercooked or raw pork
or bear meat)

• Enterobius vermicularis = pinworms;
infect 30% of children and 16% adults in U.S.; adult pinworms live in human rectum and cause much itching

• Ascaris lumbricoides infects 1 in 6 people worldwide, but is less common in areas with modern plumbing. Lives in human intestine.

• Wuchereria bancrofti = filarial worms
that cause elephantiasis; mainly seen in tropical areas; transmitted by an intermediate bloodsucking host such as a mosquito

Question 22

Phylum Rotifera = the rotifers

Answer 22

• commonly called “wheel animals” for
the corona (ring of cilia) at anterior end
• bilateral symmetry and unsegmented
• classified as spiralian Platyzoa
• complex internal organs (Fig 33.13)
• adhesive toes help to cling to surfaces
• most live in freshwater and survive 1-2 weeks
• corona used for locomotion and food
gathering; food is crushed by complex
jaw in pharynx

Question 23

The Lophophorates: Bryozoa and Brachiopoda

Answer 23

° Both groups have a lophophore =
U-shaped ridge around mouth bearing
ciliated tentacles used for gas exchange and guiding food to the mouth

Question 24

Phylum Brachiopoda: Lampshells

Answer 24

° Note that these look superficially like a
clam, but their shells are dorsal/ventral
and not lateral as in the bivalves.

° brachiopods and phoronids = solitary
lophophorates

• brachiopod characteristics:
– deuterostomes
– attach to rocks by pedicel or one shell (valve) is cemented to rock
– lophophore located between shells
– U-shaped gut in some; others have
no anus
• phoronid (tube worm) characteristics:
– protostomes
– worm secretes chitinous tube
– withdraws into tube when disturbed
– some buried in sand; others attached to rocks

Question 25

Coelomate Invertebrates

Question 26

Phylum Mollusca:

Answer 26

The Mollusks
• 93,000+ describes species (second
only to the arthropods)
• occupy every habitat on Earth
• includes snails, slugs, clams, scallops,
octopus, cuttlefish, oysters, mussels,
squid, chambered nautilus, etc.

Mollusks are extremely diverse and
important to humans.

• size ranges from a few millimeters to
that of the giant squid which can grow
to 15 meters long and 250 kg
• mollusks evolved in the ocean; some
slugs and snails are adapted to life on
land or in freshwater
• economic importance includes: food,
mother-of-pearl for jewelry
• mollusks can do damage to boats, docks, pilings, and wood exposed to the sea; zebra mussels are invading freshwater ecosystems
• some slugs and snails damage flowers,
vegetables, and other crops
• some snails are intermediate hosts to
larval stages of parasites such as flukes

Question 27

Phylum Mollusca:

Answer 27

• size ranges from a few millimeters to
that of the giant squid which can grow
to 15 meters long and 250 kg
• mollusks evolved in the ocean; some
slugs and snails are adapted to life on
land or in freshwater
• economic importance includes: food,
mother-of-pearl for jewelry
• mollusks can do damage to boats, docks, pilings, and wood exposed to the sea; zebra mussels are invading freshwater ecosystems
• some slugs and snails damage flowers,
vegetables, and other crops
• some snails are intermediate hosts to
larval stages of parasites such as flukes

Question 28

Mollusk body plan is complex and varied

Answer 28

• bilateral symmetry

• mantle = thick epidermal sheet surrounding the mantle cavity; secretes calcium carbonate shell (for those mollusks that have a shell)

• foot = primary means of locomotion
(except for octopus, chambered nautilus, and squid); can also be used for attachment, capturing food, digging

• head may be well-developed or not

° Internal Organs
• coelom is very reduced in size
• visceral mass contains digestive, excretory, and reproductive organs
• ctenidia = gills (in aquatic mollusks)
have much surface area for gas exchange; gills of bivalves also
filter out food

° Shells
• secreted by mantle; protects against
predators and adverse environmental conditions
• some mollusks have reduced, internalized, or no shell at all (squids, octopus, and cuttlefish; and slugs)
• shell has two layers of calcium carbonate; inner layer is pearlescent (mother-of-pearl or nacre); pearls form when a grain of sand or other irritant lodges between inner shell layer and mantle – layers of nacre reduce the irritation

° Feeding and Prey Capture
• radula = rasplike structure with rows
of chitinous teeth used to scrape food off surfaces
• some radular structures are modified for drilling; others work like a harpoon along with a venom gland
• bivalves are only mollusks without a
radula

° Removal of Wastes
• nephridium = removes nitrogenous waste; works somewhat like a kidney
• wastes dumped into mantle cavity
• sugars, salts, water, other materials
are reabsorbed by nephridial walls
and returned to animal’s body to
maintain osmotic balance

° Circulatory Sysytem
• hemocoel = made of several sinuses
and vessel network in gills (All mollusks except for cephalopods have an open circulatory system.)
• hemolymph = equivalent of blood
• heart – most mollusks have three-
chambered heart

° Reproduction
• most mollusks have separate sexes
• a few bivalves and many freshwater
and terrestrial gastropods are
hermaphroditic
• some oysters can change sex
• marine mollusks have external fertilization
• most gastropods have internal fertilization
• trochophore larva is free-swimming
• veliger larva is 2nd free-swimming stage

Question 29

Four (of the 7 or 8) Classes of Mollusks

Answer 29

° Class Polyplacophora: Chitons
• marine only
• 8 overlapping dorsal plates
• body is not segmented
• most are grazing herbivores living
in shallow marine habitats

° Class Gastropoda: Snails and Slugs
• primarily marine (40,000 species)
• there are freshwater species also
• the only terrestrial mollusks are
gastropods

a) most gastropods have single shell,
but some have lost their shell

b) most gastropods creep on their
foot, but in some, the foot is
modified for swimming

c) head has pair of tentacles used for
chemo- or mechanoreception; eyes
are located at base of tentacles;
some have second set of tentacles
with eyes on end of tentacles

d) unique feature of gastropods is
torsion – twisting of body during
larval growth so mantle cavity and
anus are moved to front of body

e) gastropods are predators

f) mantle cavity serves as a lung in
terrestrial gastropods

° Class Bivalvia: Clams, Mussels, Cockles
• most of 10,000 species are marine
• some are freshwater species

a) no radula; no head
b) wedge-shaped foot for digging
c) have two shells (valves)

d) inhalant siphon is where water
enters bringing food and oxygen

e) exhalant siphon is where water exits

f) see additional anatomy on p. 679,
Fig. 33.20

° Class Cephalopoda: Octopuses, Squids, Nautiluses
• more than 600 species
• marine only
• very active predators

a) only mollusks with closed circulatory system

b) foot evolved into arms with suction
cups, adhesive devices, and hooks
for capturing prey

c) strong beak-like jaws; radula;
salivary glands

d) largest relative brain size among
invertebrates

e) highly developed nervous system

f) complex behavior patterns and
highly intelligent

g) cephalopod eyes similar to vertebrate eyes, but evolved separately

h) no external shell, except for
chambered nautiluses; cuttlefish
and squids have internal shell;
octopuses have no shell

i) move by jet propulsion when water
that entered mantle is forced out
through siphon

j) ink sac – used as defense

k) chromatophores in skin allow
cephalopod to change colors for
camouflage or communication

l) cephalopods have direct development; that is, no larval stage

Question 30

Phylum Nemertea: Ribbon Worms
• cylindrical to flattened and very long
• most are marine; a few are freshwater
or live in humid terrestrial habitats
• most range from 10 to 20 cm in length
• Lineus longissimus reported to reach
60 meters in length

Answer 30

a) nemertean body plan resembles that of
a flatworm
b) some cephalization with two lateral
nerve cords
c) complete gut with both mouth and anus
d) rhynchocoel = fluid-filled sac that serves as hydraulic power source for proboscis
e) gonochoric
f) sexual reproduction; but some can reproduce asexually by fragmentation
but many fragments die and don’t form
a new animal

Question 31

Phylum Annelida: The Annelids

Answer 31

• segmented worms
• advantage of segmentation = development and function of individual segments or groups of segments can differ

° The annelid body has ringlike segments
a) brain or cerebral ganglion and
sensory organs at anterior
b) many species have eyes
c) head and tail develop first and then
segments form between them
d) segments divided by septa
e) each segment has pair of excretory organs, a ganglion, and locomotory structure (marine annelid segments
also have reproductive organs)
f) closed circulatory system
g) ventral nerve cord connects ganglia in each segment with one another and the brain

° Annelids move by contracting circular
and longitudinal muscles against the hydrostatic skeleton

° Chaetae (setae) = bristles that help
anchor annelid in substrate so they
don’t slip when they move

Question 32

Class Polychaeta: Polychaetes

Answer 32

• marine worms
• parapodia = fleshy, paddle-like lateral
projections used for swimming,
burrowing, or crawling
• parapodia also have important role in
gas exchange; in some species, they
are modified into gill-like structures
• predatory polychaetes have powerful
jaws
• sedentary tube worms have feathery
tentacles for filter feeding as well as
gas exchange
• most polychaetes are gonochoric and
fertilization is external
• Palolo worms – gamete-filled terminal
parts considered a delicacy by some
South Pacific natives
• fertilization  spiral cleavage  ciliated
mobile trochophore larvae growth to
adult

Question 33

Class Clitellata: Earthworms and Leeches
(Note: The earthworms were formerly
in Class Oligochaeta and leeches were
formerly in Class Hirudinea)

Answer 33

° The merge was because both groups have a clitellum – a thickened band on body that secretes mucus to hold worms together during copulation and to form a cocoon for fertilized eggs to develop.

° Earthworm characteristics
• head is not well-developed
• no parapodia
• few chaetae & project directly from
body wall
• eat their way through soil
• no eyes, but do have light-, chemo-,
and touch-sensitive cells
• hermaphroditic
• cross-fertilization
• eggs develop into young worms
similar to adults

° Leech characteristics
• most are freshwater; few are marine;
some live in tropical terrestrial areas
• dorsoventrally flattened
• hermaphroditic
• cross-fertilization
• clitellum only develops during mating season
• suckers at both ends of body
• coelom reduced and not segmented
• no chaetae (except for one species)
• eat detritus or devour small animals
• some suck blood – secrete anesthetics and hirudin (anticoagulant)
• Hirudo medicinalis = medicinal leech

Question 34

Phylum Arthropoda:

Answer 34

The Arthropods
◊ The most successful of all animals
◊ Two-thirds of all animals are arthropods

◊ Great economic importance
a) pollinate crops
b) food for humans and other animals
c) damage to crops; insects are voracious herbivores
d) carriers or spreaders of disease to
plants and animals including humans

◊ Four extant classes plus one that is extinct:
a) Class Chelicerata (spiders, mites,
ticks, horseshoe crabs)
b) Class Crustacea (crabs, shrimp,
lobsters, barnacles, pill bugs)
c) Class Hexapoda (insects)
d) Class Myriapoda (centipedes,
millipedes)
e) Class Trilobita (trilobites) is extinct.

◊ Arthropod Key Features & Organ Systems

a) mouthparts –
• chelicerae (pincers) in chelicerates
• mandibles (biting jaws) in hexapods, crustaceans, and myriapods

b) segmentation –
• body segments look alike in some
arthropods
• tagmatization = the fusion of segments into specialized functional
groups
- tagmata include:
head
thorax
abdomen
- in some arthropods, head and
thorax are fused to form a
cephalothorax

c) exoskeleton –
• made of chitin and protein; this
combination is strong and flexible
• provides antagonism for muscles,
support for body, protection against
physical forces
• can protect against water loss
• limitations of exoskeleton include:
- size (weight gets too great with
increased size)
- rigidity (arthropods must undergo
ecdysis or molting)

d) jointed appendages –
• may be modified into antennae, various kinds of mouthparts, legs
• can bend to extend or retract
• joints serve as a fulcrum for appendage movement so leverage is possible

e) circulatory system –
• open circulatory system
• heart pumps blood anteriorly; blood
flows toward posterior through spaces between tissues; when heart relaxes, blood returns to posterior region of heart through one-way
valves

f) nervous system –
• double chain of segmented ganglia
along ventral surface
• three fused ganglia form brain
• functions such as eating, moving,
and copulating can be carried out
even when brain is removed
• compound eyes composed of
ommatidia (individual visual units)
• ocelli = simple eyes present in some
arthropods

g) respiratory system –
• gills – in marine crustaceans
• book gills – in horseshoe crabs
• outer epithelium or gut for gas exchange – in some tiny arthropods
• tracheae – in terrestrial arthropods;
tracheae branch into tracheoles;
• spiracles = openings in exoskeleton
where air enters; they can be closed
to prevent water loss
• book lungs – in many spiders

h) excretory system –
• in aquatic arthropods, waste diffuses from blood in gills
• Malpighian tubules occur in terrestrial insects, myriapods, and chelicerates.
- slender projections from digestive tract
- attached at junction of midgut and hindgut
- tubules contain fluid, and nitro-
genous wastes from blood that
bathes tubules are precipitated
as uric acid or guanine that are
then emptied into hindgut for
elimination
- water and salts are reabsorbed by hindgut and returned to arthropod’s body
- Key adaptation to life on land

Question 35

Class Chelicerata = spiders, mites, ticks,
scorpions, daddy long-legs, horseshoe crabs

Answer 35

◊ Chelicerate characteristics:
• two tagmata = anterior prosoma which bears all appendages and opisthosoma which contains reproductive organs
• pair of chelicerae (fangs or pincers)
• pair of pedipalps
- copulatory organs in male spiders
- large pincers in scorpions
- sensorial in most other chelicerates
• four pairs of walking legs
° mostly carnivorous, but mites are mostly herbivorous

1) Order Araneae: Spiders
• important as predators of insects
• produce silk that is forced out of
spinnerets
• wolf spiders and tarantulas hunt rather than spin webs
• all spiders have poison glands with channels through their chelicerae
• poison/venom paralyzes prey
• bites of black widow and brown recluse can be fatal to humans and large mammals

2) Order Acari: Mites and Ticks
• found in every habitat
• predators and parasites of variety of organisms
• most mites less than 1 mm long
• in mites, cephalothorax and abdomen fused into ovoid body
• respiration using tracheae or directly through body surface
• ticks are blood-sucking parasites of humans and other animals
• some ticks carry disease-causing agents such as Rocky Mountain spotted fever, Lyme disease, and red-water fever (affects cattle, horses, sheep, dogs)

Question 36

Class Crustacea = crabs, shrimps, lobsters, barnacles, pill bugs

Answer 36

° about 35,000 species of mostly marine organisms, but some such as crayfish live in freshwater; still others are terrestrial (pill bugs) or semiterrestrial (sand fleas and beach fleas)

◊ Crustacean characteristics:
• three tagmata = cephalon and thorax
(may fuse to form cephalothorax) and abdomen
• two pairs of antennae (crustaceans are only arthropods to have this)
• three pairs of appendages for chewing and manipulating food
• various pairs of legs (located on abdomen and thorax)
• crustacean appendages (with possible exception of first pair of antennae) are biramous (“two- branched”)
• large crustaceans have feathery gills
for respiration
• gas exchange in smaller crustaceans occurs directly through thin regions of cuticle or through entire body

a) crustacean reproduction
• gonochoric (except for barnacles)
• characteristic nauplius larva with three pairs of appendages
• nauplius is evidence for single common ancestor

b) decapod crustaceans = shrimp, lobster, crab, crayfish
• five pairs of thoracic appendages
• calcium carbonate reinforces exoskeleton
• cephalothorax covered by carapace
• pincers used for obtaining food
• swimmerets on ventral surface of abdomen in lobsters and crayfish
• uropods are paired flattened appendages at posterior that form a paddle
• telson = tail spine
• uropods and telson push water anteriorly, thus propelling animal posteriorly

c) sessile crustaceans = barnacles
• sessile adults, but nauplius larva is mobile
• adults are filter-feeders; sweep legs through water in order to gather small food particles
• hermaphroditic condition is thought to be related to their sessile lifestyle
• barnacles have longest penis relative to their size; allows sessile animals to cross-fertilize

Question 37

Class Hexapoda = the insects

Answer 37

° largest group of animals in terms of number of species and number of individuals
° found in every habitat on land and in fresh water, but few found in sea

◊ External characteristics of insects:
• primarily terrestrial
• size range is 0.1 mm to 30 cm in length or wingspan
• mouthparts modified piercing, sucking, or sopping up liquids
• most with compound eyes; some with ocelli
• head, thorax, and abdomen
• thorax has three segments, each segment with a pair of legs
• many insects have one or two pair of
wings
• wings are saclike outgrowths of body wall

◊ Internal organization of insects:
• digestive tract is tube about same length as body in many; but in those insects that feed on juices, digestive system is coiled and may be several times longer that body
• digestion occurs in stomach or midgut
• Malpighian tubules for excretion
• tracheae for gas exchange
• spiracles are openings between segments along side of abdomen and thorax where air enters

◊ Sensory receptors of insects:
• eyes
• sensory setae sensitive to mechanical and chemical stimuli; numerous on antennae and legs
• tympanum = thin membrane that acts like eardrum; detects sound waves and vibrations
• pheromones are chemicals released by insects for communicating mating signals, trail markers, etc.

◊ Insect life histories:
• metamorphosis = change in form
• simple metamorphosis = egg  nymph stages  adult
• complete metamorphosis = egg  larva  pupa (chrysalis)  final molt into adult or imago

Question 38

Class Myriapoda: Centipedes & Millipedes

Answer 38

° both have head followed by numerous similar segments
° both are gonochoric
° fertilization is internal
° all lay eggs

◊ Subclass Chilopoda = centipedes
• one pair of legs per segment
• some centipedes hatch with a final number of legs; others add legs after hatching
• those centipedes that do not add legs tend to care for their young; a rather uncommon behavior among invertebrates
• carnivorous
• poison fangs

◊ Subclass Diplopoda = millipedes
• two pairs of legs per segment
• herbivorous
• roll into flat coil or sphere for defense
• glands produce foul-smelling fluid
• some produce cyanide gas

Question 39

Phylum Echinodermata: The Echinoderms

Answer 39

◊ General characteristics:
• exclusively marine
• deuterostome development
• endoskeleton of calcium carbonate
plates
• pentaradial symmetry
• water-vascular system aids in movement and feeding
• larvae have bilateral symmetry;
therefore, echinoderms thought to have evolved from bilaterally symmetrical ancestors
• oral surface faces substrate in the
asteroids, ophiuroids, and echinoids
• oral surface faces away from substrate in the crinoids
• holothuroids have horizontal axis and oral surface that faces forward

◊ Endoskeleton:
• ossicles = calcium carbonate plates that make up the endoskeleton
• depending on the class, ossicles may be more loosely arranged, tightly fit together to form a test (shell), or scattered throughout body

• mutable collagenous tissue can change texture from tough and rubbery to fluid in seconds if the animal is disturbed
• echinoderms can autotomize (cast off) body parts

◊ Water-vascular system (WVS):
• radially organized
• madreporite = structure on aboral surface where water enters
• WVS extends out into each arm of a sea star; ampulla (bulb) allows tube foot to extend or contract
• gas exchange occurs across body surface and the tube feet
• holothuroidians also have respiratory trees that branch off the hindgut; water enters and exits through anus
◊ Regeneration and Reproduction

• many echinoderms can regenerate
body parts
- asteroids and ophiuroids autotomize arms
- holothuroidians can eviscerate
their digestive system

• some echinoderms can reproduce
asexually by splitting
• sexual reproduction is the norm
• echinoderms are gonochoric
• fertilization is external
• larvae are bilateral and each class of
echinoderms has a characteristic larva

Question 40

Five extant classes of echinoderms
(more than 20 others have gone extinct)

Answer 40

a) Class Asteroidea: Sea stars
• organized in parts of five or multiples of five
• predators
b) Class Ophiuroidea: Brittle stars
• arms are slender and “snake-like”
• arms join central disk very abruptly
• tube feet for feeding, not locomotion
• brittle stars have no anus

c) Class Echinoidea: Sea urchins and Sand dollars
• no arms
• five double rows of tube feet extend through calcareous test (shell)
• spines are moveable and have a ball- and-socket joint

d) Class Holothuroidea: Sea cucumbers
• oriented horizontally to substrate
• parts of five
• filter feeders
• have respiratory trees
• if skin is rubbed, can go from rigid to
liquid in a couple minutes

e) Class Crinoidea: Sea lilies & Feather stars
• oral surface faces up, filter feeders