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Bio 103
Lake Tahoe Community College
Winter Qtr.
Instructor: Sue Kloss
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Chapter 33: Invertebrates
I. Intro to Animal Diversity
A. Characteristics of animals
1. nutritional mode – ingestion
2. cell structure
a. no cell walls
b. cells held together by collagen –protein found only in animals
c. only animals have muscle/nerve cells
3. Repro and development
a. most animals reproduce sexually, diploid condition dominates
b. blastula (hollow ball of cells), gastrula (infolding of blastula)
B. Animal Body Plans - symmetry
1. radial –organized around central axis. Plane thru center divides animal into mirror images.
2. bilateral –organized so that only one plane longitudinally divides into mirror images
a. animal has right and left side
b. accompanied by cephalization
C. Tissue Organization
1. Ectoderm becomes outer layer of animal, and in some, cns
2. Endoderm becomes lining of digestive tract
3. Mesoderm becomes muscles and most organs
4. Diploblasts have Ecto and Endo, Triploblasts have Ecto, Endo and Mesoderm
D. Body cavities – coelom – air or fluid filled space separating digestive tract from outer body wall
1. value of a coelom
a. flexibility
b. cusions suspended organs
c. organs can grow and develop independently, and specialize
d. can act as hydrostatic skeleton
e. fluids help circulate O2, waste and nutrients - amoeboid cells help in these functions
2. coelom condition
a. coelomate- coelom lined with mesoderm – helps digestion, suspension of organs
b. pseudocoelomate – no mesoderm surrounding digestive tract
c. acoelomate – no body cavity aside from digestive tract
E. Protostomes vs. Deuterostomes
1. Protostomes have spiral cleavage, coelom forms from split mesoderm, blastopore becomes mouth
2. Deuterostomes have radial cleavage, coelom forms from outpockets, blastopore becomes anus
F. Phylogenetic Tree
CALCAREA & SILICEA
ANCESTRAL
PROTIST
o
CNIDARIA
LOPHOTRHOCHOZOA
ECDYSOZOA
DEUTEROSTOMIA
II. Most animals are invertebrates, no vertebral column (backbone). 95% of known animal species are invertebrates.
A. Phyla Calcarea and Silicea– Sponges - 5500 spp.
1. Ecology
a. most marine (oceanic), but some freshwater
b. most live singly or in clusters formed by budding. Many can regenerate if fragmented
c. Vase- shaped or cylindrical sponges have radial symmetry
2 . Structure/function - simple animals - generally, 3 loosely associated layers of cells
a. pinacocytes - outside layer of flattened cells provides protection
b. middle body layer has motile cells called amoebocytes and skeletal components
composed of a flexible protein called spongin or mineral containing particles.
c. third cell layer consisting of flagellated cells called choanocytes or collar cells,
have collar like structure surrounding base of flagella. Aided by the flagella on
choanocyte, water flows throughout the pores into the central cavity and then out
of the sponge through its one large opening.
3. Phylogeny -biologists believe sponges arose very early in animal evolution, from multicelled organisms
a. lack digestive tract
b. lack gastrula stage
c. 3 cell layers are not homologous to body layers of other animals
d. lack nerves and muscles
e. no true tissues
B. Phylum Cnidaria: hydras, jellies, sea anemones and corals. All have radial symmetry and cnidocytes
1. Ecology
a. some cnidarians have life cycles with both polyps and medusas
b. carnivores - use tentacles -capture small animals and protists, to push prey into mouth
2. Structure/Function
a. Radial symmetry is a hallmark of this phylum; any vertical cut thru center will produce mirror
images. Body forms:
b. polyps - columnar with radiating arms called tentacles mouth at top of column, at hub of
radiating tentacles
c. medusas - umbrella like, mouth in center of underside of umbrella; fringe of tentacles around
umbrella - motile
d. in both body plans, mouth leads to digestive cavity called gastrovascular cavity
1. undigested food exits thru mouth, no anus; digestive system is said to be
incomplete
2. cavity circulates body fluid that services internal cells
3. fluid in cavity provides body structure and support, like water in a balloon
e. All cnidarians have cnidocytes- specialized cells, found on surface of tentacles of polyps
and medusas- fine thread coiled within a capsule. When discharged, thread can sting or
capture prey; some big enough to catch fish
1. defense
2. prey capture
3. Phylogeny
a. several features absent in sponges, present in other phyla:
1. digestive cavity
2. gastrula stage of development
3. presence of tissues. eg sea anemone has well developed nerve and muscle
tissue, it can creep, swim, roll, burrow or somersault away from danger.
4. tissue animals - though some have organs, most cnidarians have tissues that
perform vital functions.
b. 4 classes of Cnidarians
1. Hydrozoa - - hydras – can be freshwater, medusa and polyp form
2. Scyhphozoa – mostly medusa – the jellies
3. Cubozoans - sea wasps – cube shaped medusa
4. anthozoans – sea anemones and corals – “flower animals” – only as polyps
III. Lophotrochozoans – some have lophophore, trochozoans. Some have neither. Most animals are bilaterally symmetrical can be divided equally by a single cut into mirror image right and left side. Lophotrochozoans are bilateral
A. Intro to Lophotrochozoans
1. widest range of body forms of any of the major animal groups
2. lophophore, trochophore
a. some possess both, some one of these traits, some neither
B. Anatomical terminology
1. head end - anterior
a. head is prominent part of bilateral animals
1. sensory structures
2. brain
3. mouth
b. brain and sensory structures along with nerves = organ system = nervous system
2. tail end - posterior
3. dorsal side - back
4. ventral side - front or underside
5. lateral- side surfaces
6. Radial animals lack forward orientation, sit on surface of seafloor or drift, waiting for action to come to them.
Bilateral animals - generally quite active and travel head first through environment. crawl, swim, run, walk, or
fly. Sense organs contact environment first and help animal respond. Humans are bilateral. Why don’t we
move head first through the environment?
C. Phylum Platyhelminthes- flatworms are simplest bilateral animals. Leaf or ribbonlike animals.
1. Ecology – parasites and free-livers
2. Structure/function
a. unusually simple bodies for bilaterals
b. incomplete digestive tract - no anus
c. flatworms lack an internal cavity; digestive cavity is only space in body, similar to cnidarians it
is a gastrovascular cavity; most bilateral animals have coelom
d. structure related to function - small size of flatworms - don't need body cavity, all nutrients and
O2 can diffuse in and waste out. Even long ones, like tapeworms, are very thin.
3. phylogenetics - 3 major groups of flatworms - classes
a. Turbellarians- freeliving (nonparasitic) flatworms - planaria
1. nervous system - dense clusters of nervous tissue (brain), eyespots, small nerves
2. digestive system - highly branched. mouth located not in head, but ventral surface;
muscular tube protrudes through mouth and pulls food in. Planaria live on undersurfaces
of rocks in ponds and streams. Using cilia, they crawl in search of food. Have muscle tis.
b. Trematodes - flukes - parasites. e.g. Schistosoma - female spends much of time in a groove in the
male’s body; they copulate frequently producing over 1000 eggs/day. Females and males have
suckers to attach to the inside of the blood vessels near the host’s intestines. Blood flukes infect
humans and cause schistosomiasis. Complex life cycle, often > 1 host.
c. Cestodes -tapeworms are 3rd type of flatworms, also parasitic. Inhabit the digestive tracts of
vertebrates, including reptiles, birds and mammals.
1. Long, ribbon like bodies with repeated parts.
2. no digestive tracts themselves - absorb partially digested nutrients directly
3. head is armed with suckers and teeth to attach to host.
4. behind head, a short neck generates the repeated parts;
5. youngest repeated part is behind the neck, oldest posterior
6. parts at posterior end filled with eggs; break off, pass from body in feces.
7. Like flukes, complex life cycle- may have more than one host.
8. Humans can become infected by a large tapeworm (20 m) Taeniarhynchus
D. Rotifera – rotifers
1. Ecology - freshwater, ocean, moist soil; smaller than many protists
2. Structure/Function
a. alimentary canal
b. pseudocoelom serves as hydrostatic skeleton
c. mostly reproduce thru parthenogenesis
d. wheel-bearers
3. Appear to be most closely related to flat worms
E. Lophophorates – all have ciliated crown for feeding – three phyla
1. Ectoprocts –bryozoans- moss animals
a. colonial animals encased in exoskeleton
b. mostly marine, widespread and sessile
2. Phoronids – tube worms with cilia crown
3. Brachiopods – lamp shells – resemble mollusks, but 2 shells are dorsal/ventral, not lateral
a. all marine
b. attached to seafloor by stalk
c. huge during the Paleozoic and Mesozoic- 30 k species
F. Phylum Mollusca - snails, slugs, oysters, clams, octopus and squids are examples of great variety - body
structure NOT conservative in this group!
1. Ecology – incredibly diverse – land, freshwater, marine; molluscus in latin means “soft”
2. Structure/function
a. most have soft bodies protected by hard shell
b. basic body plan – mantle, foot, visceral mass
1. muscular “foot” - locomotion
2. mantle - outgrowth of body surface that protects animal; produces shell in clams, snails
a also: mantle -respiration, waste disposal and sensory reception.
3. many molluscs have radula- a rasping tongue for scraping
c. true coelom - 3 small cavities
1. for heart
2. for reproductive organs
3. one forms part of kidney
3. Phylogenetics - Different body features in different groups (Classes)
a. gastropods - fresh water, salt water, terrestrial. In fact, this group has the only
molluscs that live on land; 75,000 species
1. terrestrial snails, slugs lack gills; mantle cavity has evolved into a huge lung
2. most are marine; sea slugs are unusual mollusks, lacking a mantle, mantle
cavity and shell
b. bivalves - (bi = double, valva = leaf of folding door); include clams, oysters, mussels,
scallops.
1. have shells divided into 2 halves, hinged together
2. sedentary, live in sand or mud
3. muscular foot used for digging/anchoring
4. mucus coated gills to trap fine food particles
5. scallop - many eyes around mantle edges. can clap its shell shut and squirt
water from its mantle cavity, jetting itself a short distance away
c. cephalopods (greek - kephale = head, pous = foot) - built for speed and agility
1. a few have large, heavy shells, but most have small internal shell (squid), or
lack it all together (octopus)
2. marine predators - beaklike jaws and radula to crush or rip prey apart
3. mouth at base of foot, which is divided into numerous tentacles for prey capture/use
4. squids a). draws water into mantle cavity, fires it out - fast sreamlined animal
b). large complex brain
c). among most complex sense organs in animal kingdom - lens (focus
light) and retina (images)
5. all cephalopods have complex brains and sense organs, contribute to success
6. Octopuses have larger, more complex brains, proportionate to body size
than almost any animal. good learners!
d. polyplacophora – chitons – 8 plates; foot used for locomotion; no head; radula
G. Phylum Annelida – (annelus = ring) - segmented worms; 15000 species Earthworms, Christmas tree worms.
1. Introduction -Earthworms are segmented -subdivisions of the body along its length; played a major role
in evolution of many complex animals
a. Advantages of segmented bodies- great bodily flexibility, mobility; probably adaptation for
movement
2. Ecology -Terrestrial (damp soil), freshwater and marine (some swim, most are bottom dwelling
scavengers) habitats; separate head and tail; body segments all very similar
3. Structure/function – segmented, bilateral coelomates
4. Phylogenetics - 3 classes –
a. Oligochaetes - earthworms one of 3 large annelid groups (current classes)
1. eats its way through soil extracting nutrients as soil passes thru digestive tube.
Undigested material passes through anus at posterior end.
2. earthworms are incredibly valuablea. they till the soil and enrich it
b. they improve the texture; Darwin estimated that an acre of land (Britain) had
about 50,000 earthworms that produced about 18 tons of feces/yr.
3. coelom is partitioned by walls
4. nervous system has a cluster of cells in each segment; excretory organs repeated also
5. digestive tract is not segmented; it passes through the segment walls from mouth to the anus.
6. circulatory system - dorsal and ventral blood vessels; main and accessory hearts
b. Polychaetes (gk- poly = many, chaeta = hair) most live on the seafloor; some freshwater or
estuaries. Most annelids are polychaetes.
1. segmented appendages help worms wriggle
2. segmented appendages increase surface area for taking up O2 and dispose of wastes
3. many marine species live in tubes; extend feathery appendages- trap suspended food particles
4. tubes formed by sticky proteins secreted near mouth
c. Hirudinea - Leeches are 3rd group of annelids; blood suckers, some are freeliving, eating snails and
insects. Most leeches are fresh water; a few terrestrial species inhabit moist vegetation in tropics
1. until this century, leeches were used to remove “bad blood” from patients
2. razor-like jaws cut through skin
3. saliva contains strong anesthetic and strong anticoagulant - prevent heart attacks
4. leeches used on burn victims and in reattachments
IV. Ecdysozoans – the most species-rich of the major groups; includes animals that shed tough external covering (ecdysis)
A. Nematodes - roundworms -pseudocoelom and complete digestive tract
1. Ecology – ubiquitous, all niches
a. important decomposers, live wherever there is rotting organic matter - soil, lakes, rivers, oceans
b. also parasites of plants and in body fluids of animals.
c. 25,000 species are known and likely that 10x exist; freeliving worms are most
abundant
d. humans are host to at least 50 parasite species, many of which cause major health problems
1). hookworms
2). heartworms in dogs
3). trichinella - trichinosis (NASTY!! worms may infect heart or brains)undercooked pork may contain juveniles - cook meat until no longer pink
e. conservation of body form among nematodes
2. Structure/function
a. cylindrical worms with a finely tapered tail; head is more blunt.
b. tough, nonliving skin called cuticle, resists drying or crushing
c. complete digestive tract; mouth near head, anus near tail. food travels one way;
d. molecular toolkits to make hosts accommodate them – act live viruses
B. Arthropoda –
1. Intro
a. a million spp. - includes crayfish, lobsters, crabs, barnacles, spiders, ticks and insects.
b. segmentation, metamerism – specialization of segments- hox genes
c. arthropod population of earth is about a billion billion 1018 !
2. Ecology – all niches – most successful phylum of animals ever, in terms of diversity, distribution, number
d. Arthro = jointed, pod = foot; jointed appendages in this phylum. Appendages in lobsterwalking, feeding, swimming, sensory reception and defense.
3. Structure/function
a. exoskeleton - hard external skeleton- chitin: polysaccharide, w/proteins
1. protection, attachment for muscles to move appendages
2. thick in some places thin in others
3. molting- periodic shedding of exoskeleton, secretion of new one
b. annelids have similar segments; most arthropods have distinct groups
lobster, e.g.
1. head- sensory parts: antennae, eyes and mouthparts
2. thorax-pincers for defense and 4 prs. legs for walking
3. abdomen- swimming appendages
4. Phylogenetics – Subphyla a. Malacostraca - horseshoe crab - living fossil - survived w/ little change for hundreds of millions of
yrs. Only survivor of spiderlike arthros abundant in seas 300 mya
b. Arachnids closest living relative of horseshoe crabs -spiders, ticks, mites, scorpions. Most
arachnids live on land.
1. Scorpions are nocturnal hunters. eat mainly insects and spiders
2. mites- thousands can live in a few square centimeters of carpet or in a dust bunny;
not disease carriers; many people are allergic
3. spiders – chelicerae - moving mouthparts with poison glands; cephalothorax w/ 4 pr of
legs; use silk glands to spin webs,
c. Crustaceans - nearly all aquatic- lobster, crayfish, shrimps, crabs, barnacles.
1. barnacles live in limestone shell; jointed appendages protrude from shell to catch
small invertebrates and suspended particles. body and appendages covered with chitin
d. Myriapoda - centipedes and millipedes- jointed legs identify them as arthropods
1. millipedes- plant eaters
2. centipedes - carnivores with poison claws used in defense and to paralyze prey like
cockroaches and flies.
e. these 4 groups make up 170,000 living species. Insect numbers dwarf all other groups
f. Hexapoda - Insects- more total insects than all other animal species combined. prominent on
land for 400 my. fewer in water, especially salt water
.
1. common features: 3 part body- head, thorax, abdomen
2. head- sensory antennae, eyes
3. several prs of mouthparts adapted for particular kinds of eating
a. biting and chewing plants - grasshopper
b. lapping up fluids- houseflies
c. piercing skin and sucking blood- mosquito
4. adults- 3 prs legs, 1 or 2 prs wings.
5. ability to fly- evolutionary success
6. metamorphosis- part of development. life stages may look like adult (incomplete) or
not (complete metamorphosis)
V. Deuterostomia – Echinoderms and Chordates
A. Phylum Echinodermata- spiny skin, endoskeleton, water vascular system
1. Ecology – most marine
a. sea urchins -spherical and have no arms; algae eaters and sea stars- predators
2. Structure/function
a. lack segments
b. radially symmetrical as adults; larval stage bilaterally symmetrical. not closely related to cnidarians.
c. spiny or rough skin, spines embedded
d. spines part of endoskeleton
e. vascular water system- network of water filled canals, that branch into tube feet
3. Phylogenetics
a. Asteroidea – sea stars
1. sea stars grab bivalve with tube feet and push stomach through mouth, into bivalve.
digests soft parts of prey.
2. strong powers of regeneration- regrow feet and arms
b. Ophiuroidea – brittle stars
c. Echinoidea- sand dollars and sea urchins
d. Holothuroidea – sea cucumbers – tube feet; elongated in oral/aboral axis
B. Phylum Chordata- our phylum. 4 distinctive features in embryos
1. dorsal hollow nerve cord
2. notochord - flexible longitudinal nod btn digestive tract and nerve cord
3. gill structures- in pharynx, region of digestive tube behind mouth
4. post anal tail (posterior to anus).
a. vertebrates
b. invertebrates
1. tunicates- large gill apparatus; adhere to rocks and boats. tunicate larvae
exhibit the above 4. Eat fine organic matter caught by mucus around gills
2. lancelets- marine invertebrate chordates- feed on suspended particles; segmented
muscles to flex body side to side. Gill apparatus traps food.
Lesson Objectives Ch. 33
1. Describe defining characteristics of animals.
2. Describe and draw alternate forms of animal body symmetry.
3. Describe tissue layers in diploblasts and triploblasts, and describe the fate of each tissue layer.
4. List the ways a coelom is important to you, as a coelomate animal.
5. Provide examples of how pseudocoelomates and acoelomates function without a true coelom.
6. Distinguish between the following pairs of terms:
a. diploblastic and triploblastic
b. spiral and radial cleavage
c. determinate and indeterminate cleavage
d. schizocoelous and enterocoelous development
7. Compare the developmental differences between protostomes and deuterostomes, including:
a. pattern of cleavage
b. fate of the blastopore
c. coelom formation
8. Distinguish among the acoelomate, pseudocoelomate, and coelomate grades. Explain functions of a body cavity.
9. Distinguish between protostomes and deuterostomes. Why does it matter whether an animal is one or the other?
10. Draw a phylogenetic tree containing the current hypothesis of relationships of important animal groups.
11. Describe basic symmetry, structure and function of sponges.
12. What trait separates sponges from all other animals?
13. Construct a table for major animal groupings, symmetry, coelom condition, example animal and basic descriptions for
the following phyla: (see p. 696)
a. Calcarea, Silicea
b. Cnidaria
c. Platyhelminthes
d. Rotifera
e. Bryozoa
f. Mollusca
g. Annelida
h. Nematoda
i. Arthropoda
j. Echinodermata
k. Chordata