AP BIOLOGY UNIT 11 (CH. 33)
Invertebrates
Ch. 33
Subkingdom: Parazoa
Phylum Porifera
• Primarily marine; some freshwater species.
• Lack true tissues (apoblastic) and organs but have specialized cells.
• Asymmetric
• Sessile adults, larva may swim.
• Water filtering system; filter water and feed on bacteria. Some harbor symbiotic
algae.
• One family is carnivorous!
• They are supported by a skeleton made up of the protein collagen and spicules,
which may be calcareous or siliceous, depending on the group of sponges (basis
for classification)
• Asexual and sexual reproduction. Most sexually reproducing are hermaphroditic
and produce eggs and sperm at different times.
Subkingdom: Eumetazoa
Radiata
Phylum Cnidaria
• Eg Jellyfish, hydra (freshwater), sea anemones, coral
• Cnidarians are characterized by stinging cells called nematocysts or cnidocysts,
which when disturbed eject a barbed thread and often poison as well.
• Diploblastic (epidermis and gastrodermis), radial symmetry.
• Between the two there is a layer of jelly-like substance called mesogloea, which
may be thin or thick.
• Gastrovascular cavity used for digestion. Has single opening; often surrounded
with tentacles.
• Digestion is intracellular
• Sessile forms are polyp and free-floating called medusa.
• Planula formed after fertilization; ciliated larva that forms polyp.
• Medusa has oral side w/ mouth
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
Three major classes of Cnidarians:
Hydrozoa:
• Exist as either polyps (most common) or medusae.
• A fertilized egg develops into a sessile polyp, which buds asexually and
eventually buds off one or more medusae. The medusa produce eggs and
sperm, reproduce sexually.
• Majority of species are marine and colonial (Obelia), but many species
are solitary and some live in fresh water (Hydra). Other colonial forms
include the Portuguese-Man-of-War (many specialized hydroids)
Scyphozoa: (eg. Jellyfish)
• rim of the bell contains sense organs, including statocysts that sense
balance and orientation and photoreceptors (eyspots) that are sensitive to
light.
• Oral arms surround mouth and are covered with nematocysts (can be up
to 40 meters long.)
• Gonads (sex organs) appear as crescents around mouth on oral side.
Anthozoa: (Reef building corals, sea anemones, sea fans, and sea pens)
• only found as polyps
• secrete calcium carbonate skeleton (that’s the reef)
• many involved in symbiotic relationship with dinoflagellate algae.
Limits their depth of growth to max. depth of light penetration.
• Anemones are carnivorous.
Phylum: Ctenophora
• Comb jellies.
• Ctenophores derive their name (Greek for "comb-bearers") from the eight "comb
rows" of fused cilia arranged along the sides of the animal
• Medusa-like forms.
• At most, two tentacles with sticky material at end to capture prey.
• Bioluminescent
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
Bilateria
Acoelomates
Phylum: Platyhelminthes
• Flatworms, flukes, tapeworms
• Bilateral symmetry
• unsegmented
• First triploblastic organism (possess endo, meso and ectoderm)
• Acoelomate (no body cavity)
Class Turbellaria.
• Flatworms (ex Planarian)
• Free-living, marine and freshwater.
• Rely on diffusion for movement of oxygen, food and nitrogenous wastes.
• Intracellular digestion; food taken in cells by phagocytosis.
• Highly branched to increase surface area.
• “Flame cells” allow diffusion of ammonia into surroundings. Flame cells are
terminal ends of water regulation structure called protonephridia.
• Largest multicellular organism to move using cilia on ventral surface.
• Highly cephalized with ganglion at anterior end, longitudinal nerve cord along
body. Eye spots (ocelli) used to detect light, chemoreceptors, statocysts for
balance.
• Asexual and sexual reproduction. Can regenerate lost parts.
Class Trematoda.
• Blood flukes (Schistosoma sp.), liver flukes
• Feed on veins/organs of vertebrate host.
• All parasitic; usually of vertebrates.
• Hermaphroditic; eggs fertilized in host then shed in feces. Larva continues
development in secondary host (snail)
• Ranks second behind malaria in terms of socio-economic and public health
importance in tropical and subtropical areas. The disease is endemic in 74
developing countries, infecting more than 200 million people in rural
agricultural and peri-urban areas.
Class Cestoda.
• Tapeworms
• Parasites of vertebrates.
• Lack digestive system; usu. attach to inner intestinal wall with scolex (head
with hooks/suckers) and absorb food from host; body has many microvilli.
• Individual proglottids (body units packed with gametes) and eggs shed in feces
of host into water where they enter secondary host to form larva. Embeds in
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
meat of secondary host (beef/pork) and then passed back to humans through
infected meat!
Pseudocoelomates
Phylum: Rotifera “wheel-bearer”
• Primarily freshwater
• Pseudocoelom used for transport of wastes and as “hydrostatic skeleton”
• Complete digestive system. Allows for specialization of regions within system.
• Cilia at anterior end draw food into mouth.
• Very complex for a pseudocoelomate
Phylum: Nematoda.
• Roundworms
• Freshwater, marine, tissues and fluids of plants and animals.
• Causes diseases such as elephantiasis, river blindness
• Function as decomposers, parasites (Trichinella in pork). Caenorhabitis elegans
important in genetic studies (one of first organisms with completed genome)
• Cuticle (tough flexible covering) for protection
• Complete digestive system
• Pseudocoelom mostly filled with an intestine and oviducts/testes
• Longitudinal muscles for movement give it a thrashing motion (back-n-forth)
• Internal fertilization, separate sexes (dioecious)
• Prolific egg producers (100,000/day)
• Nematodes have a fixed number of cells as adults
• Free living forms are important in decomposition and nutrient cycle
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
Coelomates
Protostomes
Phylum Mollusca:
• Eg. snails, slugs, oysters, clams, octopuses, and squids
• Mainly marine, some terrestrial. Grazers, herbivores and predators!
• The molluscan body consists of three primary parts:
 Foot: muscle for locomotion; edible.
 Visceral mass: internal organs.
 Mantle: surrounds the mantle cavity, which houses the gills or lungs if they are
present, and its surface may assist in gas exchange. Secretes shell.
• Soft bodied but mostly are protected by a hard CaCO3 shell, secreted by mantle.
• Open circulatory system (except Cephalopoda) with hemolymph (general body fluid).
Blood bathes the organs, no vessels
• Complicated digestive system, with a mouth in the head and the anus emptying into
the mantle cavity (look out below!)
• Complex nervous system, especially in Cephalopoda.
• Gas exchange is via gills, lungs, or the body surface (diffusion)
• Radula functions as a rasping, scraping, tearing of food. Not present in bivalves.
• Some species are monoecious while most are dioecious (separate sex)
Class Polyplacophora:
• chitons
• marine
• Shell divided into eight dorsal plates
• Use foot to cling to rocks
• single heart
• simple nervous system and sense organs (eyes and chemosensory organs)
• A radula is used to cut and ingest (“graze”) algae
Class Gastropoda: “Stomach-Foot” [Largest molluscan class]
• Snails, slugs, abalone, nudibranch (Mr. Knight’s Favorite!)
• Assymetric
• Mostly marine
• Torsion during embryonic development is a distinctive characteristic: Uneven
growth in the visceral mass causes the visceral mass to rotate 180 degrees,
placing the anus above the head and gills in adults. Twisting of visceral mass
due to muscle contraction
• Some Hermaphroditic; mostly dioecious with internal fert.
• Distinct heads with eyes at the tips of tentacles; Detect change in light intensity
• Movement results from a rippling motion along the elongated foot
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
• Most gastropods are herbivorous.
• Exchange gases via gills; terrestrial forms have lost the gills and utilize a
vascularized lining of the mantle cavity for gas exchange
Class Bivalvia: (aka. Pelecypoda) “Hatchet Foot”
• Eg. Clams, oysters, mussels, and scallops
• Posses a shell divided into two halves; Hinged with elastic ligament and held
together with adductor muscles (scallop meat) to protect the animal.
• Extend the foot for motility or anchorage when the shell is open.
• Mantle cavity (between shells) contains gills that function in gas exchange and
feeding
• “Eyes” of scallop for light detection
• Suspension feeders. Water drawn in through Incurrent siphon, mucus coating
gills traps food, then moved to mouth. Water exits through Excurrent siphon.
• No radula or distinct head is present.
• Open circulatory system
• Bivalves lead sedentary lives. Scallop can clap shells to move rapidly. Sessile
mussels secrete threads (Abyssal thread) that anchor them to rocks, docks or
other hard surfaces for anchoring. recomDNA attempting to replicate for
bone/teeth repair.
Class Cephalopoda: “Head-Foot”
• Squids, Octopus, Cuttlefish, Nautilus (only cephalopod with a shell)
• Highly evolved mollusk
• Agile carnivores; Beak-like jaws to crush prey. Ring of tentacles around mouth
to capture prey.
• Most cephalopods have chromatophores, special pigment cells, in their skins,
which allow them to change color rapidly. Most also have a sac that secretes an
ink-like substance called sepia; this is expelled when the animal is alarmed,
providing concealment as the animal flees.
• Cephalopods are dioecious
• A mantle covers the visceral mass, but the shell is either reduced and internal
(squids) or totally absent (octopuses)
• Squid swim backwards by forcing water out of excurrent siphon
• Octopus usually don’t swim in open water, but move along the sea floor in
search of food
Important for speed and hunting:
• Closed circulatory system in which blood is always contained in vessels
• Well developed nervous systems with complex brains capable of learning
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
Coelomates
The Lophophorate Animals
Phyla: Phoronida, Bryozoa, and Brachiopoda
• Posses a U-shaped digestive tract (the anus lies outside of the tentacles) and have no
distinct head.
• All have a lophophore; suggests a relationship among these phyla
Lophophore: Horseshoe-shaped or circular fold of the body wall bearing ciliated
tentacles that surround the mouth at the anterior end of the animal.
• tentacles are hollow (therefore have a coelom)
• the mouth is always located inside the lophophore ring of tentacles, while the anus lies
outside the ring
Coelomates
Protostomes
Phylum: Annelida.
• Eg. earthworms, polychaete worms, and leeches
• All are segmented to some extent; allows for specialization and increased complexity;
more efficient movement.
• circular and longitudinal muscle act on fluid filled coelom.
• setae (made of chitin) projecting from their cuticle. Sometimes the setae are located
on paddle-like appendages called parapodia. Absent from leeches.
• Closed circulatory system (blood confined to vessels and separate from other fluids);
hemoglobin, aortic arches (hearts) around esophagus.
• Complete digestive system.
• Metanephridia used for excretion (N-wastes) and osmoregulation (homeostasis of
solutes). Produces a dilute urine which is excreted through nephrostome.
• Gas exchanged through skin, or sometimes through specialized gills or modified
parapodia (polychaetes)
• Developed nervous system with two ventral, solid nerve cords running longitudinally
and cerebral ganglia (brain)
• combination of tactile organs (detect vibrations), chemoreceptors, balance receptors,
and photoreceptors.
• Sexual and asexual reproduction, some hermaphroditic. Clitellum contains gonads
and secretes mucus cocoon to protect eggs.
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
Annelida Classes:
Oligochaeta (earthworms)
• all bear setae
• Most are hermaphroditic
• feed primarily on detritus and algae.
• help to aerate soil and cycle nutrients through soil. Form casts at surface.
Hirudinea (leeches)
• Mostly freshwater.
• fixed number of segments (usually 34), flattened body, both an anterior and
posterior sucker (usually), no parapodia, and usually no setae.
• Hermaphroditic.
• Most are either carnivorous or parasitic.
• Historically used medicinally. Anticoagulant (hirudin) used in surgeries where
limbs are reattached.
Polychaeta (lugworms, clam worms, bristleworms, fire worms)
• Largest class; primarily marine.
• parapodia, paddle-like, unjointed fleshy appendages, with stiff bristles (“many
setae”); may be used for locomotion and gas exchange; fire-worms, have
bristles which come equipped with a stinging poison.
• gonads are temporary and appear during the breeding season.
• Some live in tubes (Featherduster worm) and have spirals of feather-like
tentacles for food capture.
Protostome
Coelomates
Phylum: Arthropoda. “jointed foot”
• Segmented. Allows for specialization
• Jointed appendages. Modified as jaws, walking, sensory input, egg depositor, sucking
tubes, swimming.
• Exoskeleton covered with cuticle. Allows for terrestrial life, thinned at segments,
lines tracheal tubes. Provides organism with support on land, protection from
predators, attachment point for muscles. Does not grow so must be molted.
• Highly cephalized. Brain inhibits movement.
• Open circulatory system.
• Respiratory system as gills (crustaceans), book-lungs (stacked plates in spiders) or
trachea (insects).
• Systematics identifies 4 sub-phyla originating from ancestral protostome:
Knight/Invertebrates Notes (Ch. 33)
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AP BIOLOGY UNIT 11 (CH. 33)
Arthropoda
Trilobitomorpha
Trilobites (extinct)
Chelicerata
spiders, scorpions
Uniramians
Crustaceans
insects, milli- & centipedes
lobster,
pillbug, barnacles
Insects and Other Uniramians
Classes: Diplopoda, Chilopoda, and Insecta
•
•
•
•
•
Make up more than ¾ of all known species on earth
Appendages are unbranched (ramus means branched) with several articulating pieces.
Paired antennae and mandibles and two pairs of maxillae
Tracheae and spiracles in adults, young may have gills and be aquatic.
Dioecious
A. Diplopoda:
• Worm-like with a large number of walking legs (2 pair per segment),
• Eat decaying leaves and other plant matter (Detritivore, Saprobe)
• specialized glands that secrete foul-tasting compounds and thus function in defense
B. Chilopoda:
• Carnivorous (eat insects and soft bodied annelids)
• one pair of walking legs per segment.
• first pair of appendages on the trunk are modified into a pair of claws with poison glands
C. Insecta
• Entomology- the study of insects (about 750,000 identified species, about 250,000
beetles)
• Has a greater species diversity than all other forms of life combined: 26 orders of insects,
only a few marine forms exist.
• High number of species due to increased specialization and niche filling.
• A head, thorax, and abdomen.
• Compound eyes.
• A pair of antennae.
• Mouthparts consisting of a labrum and labium (upper and lower lips), a pair of mandibles
(for crushing), a pair of maxillae (move food into mouth)
• One or two pairs of wings, derived from outgrowths of the body wall (unlike any
vertebrate wings) and covered with chitin; Only invertebrate with flight; Veins for
reinforcing.
• Three pairs of walking legs attached to thorax.
Knight/Invertebrates Notes (
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AP BIOLOGY UNIT 11 (CH. 33)
• Excretion of nitrogenous waste takes place through Malpighian tubules. Uric acid/dry for
water conservation.
• Complex nervous system (number of ganglia and a ventral, double nerve cord).
• Open circulatory system.
• Reproduction by insects often involves a male locating a receptive female through
chemicals (pheromones) released by the female. Many females mate only once and rely on
sperm stored during (within spermatheca) that mating for the rest of their lives.
Top Orders:
Coleoptera “shield wing” (beetle)
Diptera “two winged” (fly, gnat, mosquito)
Hymenoptera “membrane wing” (ant, wasp, bee)
Lepidoptera “scale wing” (moth, butterfly)
Orthoptera (cricket, roach, grasshopper)
Flight is the key to the success of insects, enabling them to escape predators, find food and mates, and
disperse more easily than non-flying forms. This is made possible with complex nervous systems and
exoskeleton for muscle attachment.
Many insects undergo metamorphosis during their development (under hormonal control [ecdysone])
Incomplete metamorphosis  young resemble adults but are smaller and have different body
proportions
(i.e. grasshoppers)
• Immature young  nymph
Complete metamorphosis  characterized by larval stages (i.e. Maggot, grub, and caterpillar) which are
very different in appearance from
adults (90% of species)
• Larva eat and grow before becoming
adults (usually live in different
habitats, eat different foods, and
assume a body form completely
different from that of their parents.)
• High maternal care- leads to complex
social behavior (termite, ant, wasp,
bee)
• Embryo/ Egg (non-feeding) 
Larvae (caterpillar, grub, maggot)
feeding  Pupae (non-feeding,
external anatomy remodel,
cocoon/chrysalis)  Adult
Knight/Invertebrates Notes (Ch. 33)
AP BIOLOGY UNIT 11 (CH. 33)
Sensory Structures:
A) Compound eye: numerous, ommatidium with cornea, good motion detection but poor acuity
B) Touch: small hair/setae called sensilla, on antennae, leg, detect direct contact and air vibrations
C) Sound: rubbing legs/wing, courtside, alarm
D) Pheromones: chemical messages, attract males
Phylum Arthropoda, Sub-Phylum:Crustacea
(include lobsters, crabs, crayfish, shrimp, copepods, barnacles, Daphnia, Fairy Shrimp)
• Primarily marine
• All have two pairs of antennae
• a pair of mandibles and two pair of maxillae on their heads to manipulate food.
• Chelipeds (large pinching claw) to capture food
• pair of appendages on each body segment for walking; swimmerets for copulation.
• a pair of compound eyes (usually on stalks)
• respire via gills
• regenerative abilities
Knight/Invertebrates Notes (Ch. 33)
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