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METAZOA=ANIMALIA.
Key characteristic features that permitted amazing diversity:
a) multicellularity
b) ability to move
c) possession of collagen
d) heterotrophy in feeding( advanced digestive systems)
PHYLUM PORIFERA
 - are sessile
 - primitive; they show the least cellular differentiation & integration of all Metazoa
 - with no true tissues
 - no mouth or gut
 - no muscles or reproductive, digestive, respiratory, sensory or excretory organs
 - no circulatory system
 - cells are remarkably autonomous
 - many show no clear axes of symmetry
 - sometimes put in separate sub-kingdom Parazoa
 Defining sponge traits include:
a) water-canal system
b) Colony form varies from simple to complex
Referred to as ascon type ,sycon type and leucon type
c) Specialized cell types include:
o pinacocytes
o archaeocytes
o contractile cells
o choanocytes
o porocyte
d) Reproduction: budding and fragmentation are common ,most sponges are hermaphroditic and
fertilization is internal
e) Typesof digestion: Food capture - several levels of filtration: ostia = external filter to
exclude big stuff, although porocytes/pinacocytes can phagocytize food that gets stuck
Asconoid Syconoid Leucanoid

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outside. Pinacocytes lining channel walls can do same. If channel gets clogged by oversize
particles, it can reorganize.
Predation - One group of sponges (Cladorhizidae) is predatory and has lost its choanoderm as
well as aquiferous system! Instead uses long filaments extended from the body and armed
with hooked spicules (Vacelet & Boury-Esnault, 1995), a fundamental abberation to the body
plan of Porifera.
Trophic symbioses - In addition to filter feeding, many sponges, like many other sessile
organisms on reefs, have microscopic algal symbionts, that may provide nourishment for the
host.
f) Three classes of Porifera to note (a fourth class is not covered):
CALCARAE,DEMOSPONGIAE and HEXACTINELLIDA that can be grouped into glass
and chalk sponges depending on the type of spicules.
Phylum Cnidaria
 Predatory species divided into three main classes
 Two body forms predominate: polyp and medusae
 The basic body plan of all cnidarians is similar:
o a) radially symmetrical
o b) the gut has one opening (mouth only, no anus)
o c) tentacles (hollow or solid) surround the end bearing the mouth
o d) the gastric cavity has associated canals
 Cnidarians exhibit a true, three-layered, tissue level of organization
o a) epidermis and gastrodermis are true tissues
o b) the middle layer (mesoglea) mostly non-cellular
 This diverse phylum is united by a unique and complex cell type:
o a) a cnidocyte -a cell that bears two important organelles:
 nematocyst
 cnidocil
 Nematocysts come in 30 forms
 Only a few other cell types exist; most are in epidermis and gastrodermis:
o a) epithilio-muscular
o b) interstitial
o c) receptor
o d) nerve
o e) gland
o f) amoeboid
 Life cycle: asexual reproduction and coloniality are widespread
o a) a distinctive ciliated planula larva forms after gastrulation
o b) the planula larva may be the ancestral form of the Bilateria

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Classes:
(a) HYDROZOA
a) Hydroids
 two orders: polyps thecate or naked
 polyps show division of labor in colonial forms
 most possess a medusa stage
b) Trachyline medusae
c) Hydrocorals
(b) SCYPHOZOA
a) new medusae are produced from a polyp
b) some polyp stages possess septae in the gastrovascular cavity
c) ANTHOZOA The class is all polyps and there is no medusa stage
a) Octocorals
b) Hexacorals
Phylum Ctenophora
 all marine, most pelagic; common members of the "gelatinous zooplankton"
o can be significant predators in mid-ocean environment
o body length can reach 2m; some have up to 70cm tentacles
 share 3 features with Cnidaria which they resemble superficially:
o diploblastic organization
o possess only a mouth
o gastrovascular cavity with radiating canals
 exhibit some curious differences from Cnidaria:
o asexual reproduction not well-developed
o all are hermaphroditic
o highly determinate, bi-radial cleavage
o lack cnidocytes
 four distinctive features:
o unique rows of ciliated comb plates: possess 8 vertical "comb rows"
(comb cilia are the largest cilia known in Metazoa)
o two long, branching tentacles covered with colloblasts
o exhibit conspicuous biradial symmetry
o Do not exhibit polymorphism
o Lack the characteristic stinging organelles called nnematocysts
Figure 13.09

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 evolutionarily enigmatic
o middle layer exhibits some tissue-like characters
o middle layer develops from mesenchyme cells
o wide variety of body forms
BilateralAnimals
The Bilateria includes all remaining phyla. Key innovations include:
 Bilateral symmetry that adapts the to forward movement
 Third tissue layer : Triploblastic (ectoderm, mesoderm, endoderm) –tissues defined and
organized into complex functional organs.
 Compartmentation – nervous tissue highly organized and concentrated at the anterior
end of the animal.(Cephalization)
o Most Bilateria exhibit a well-developed coelom
o A pseudocoelom is simply a blood-vascular system lacking a heart
 Excretory organs – no longer depend on simple diffusion
o An excretory system includes 3 steps: i) ultrafiltration, ii) resorption , and iii)
transport
o Plame cell and tubules for Platyhelminthes
o Nephridial systems come in two general forms:
 protonephridia
 metanephridia
 Complete gut (mouth and anus) in the ribbonworms and separated from the circulatory
system.
Platyhelminthes
- Worm-like forms occur in 12 different phyla
1) Ph. PLATYHELMINTHES includes the flatworms, flukes, and tapeworms

o generally small in size
o have a blind gut: mouth but no anus
o no circulatory system or coelom
o depend on a network of protonephridia
o have a simple ladder-like nervous system with anterior brain
o tremendous capacity for regeneration and asexual reproduction
o most are hermaphroditic
o classification is a problem
o the most primitive taxon within the Protostomia:
 has some protostome characteristics
 lacks others (coelom, circulatory system, anus, trochophore larvae)
2) Class TURBELLARIA- mostly free-living flatworms
a) have an extensively ciliated, glandular epidermis
b) vary body shape with circular, longitudinal and dorsoventral muscles
c) gut may be absent, complex, tripartite, or unbranched
d) 3 forms of pharynx: simple, plicate, bulbous
e) gonads may be absent, few, or many; those with gonads are hermaphroditic;
3) Cl. TREMATODA (digenic flukes)

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a) definitive host nearly always a vertebrate
b) oral (and often ventral) sucker, bulbous pharynx, gut has two branches ,Chinese liver fluke has
2 intermediate hosts
4) Cl. CESTOIDEA (tapeworms)
a) common gut parasites of all vertebrate classes
b) distinctive head end; no mouth and no gut
c) produce many segments
d) encyst in intermediate host
Nemertea
NEMERTEA (ribbon worms; 1,150 spp); predatory, mostly marine
a) can reach quite large size
b) share many traits with flatworms
c) differ from flatworms: body is circular in cross-section, complete gut; unique blood-vascular
system lined with endothelium; spectacular proboscis housed in a rhynchocoel
PSEUDOCOELOMATE ANIMALS Aschelminthes
A grouping of convenience whose origins and membership remain controversial
General Adaptive Features:
a) triploblastic organization
b) complete gut
c) small size
d) odd determinate cleavage
e) retractile or eversible spiny head end
f) an acellular outer-body covering
 Larger aschelminthes posses a fluid-filled pseudocoelom
a) it differs little from a hemocoel anatomically
b) it develops like a hemocoel in other protostomes except the gut is often free of mesodermal
tissue
c) it is not associated with a pumping heart
 Most have a collagen or chitin cuticle that has many functions:
a) as a skeleton
b) it lines the pharynx
c) in some groups it must be molted to grow
THE PHYLUM NEMATODA (round worms)
a) most are free living, but many are also parasitic
b) they are a group of many paradoxes:
- may be the most diverse phylum but only 22,000 named spp.
- may be the most numerous metazoans on earth
- most are tiny
- though rarely seen, some are serious human parasites
- although few have seen them, one species (Caenorhabditis elegans) is one of the most
intensively studied 'model' animals
c) surprisingly little morphological diversity

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- cylindrical or spindle-shaped bodies surrounded by tough cuticle
- have a mouth, straight gut and terminal anus
- body wall muscles are exclusively longitudinal
- 4 nerve cords: dorsal and ventral (locomotory), 2 lateral (sensory)
d) large forms have an extensive pseudocoelom
e) many exhibit chromosome diminution
2) Ph. ROTIFERA ("wheel bearer" worms)
a) are among the smallest of metazoans b) exhibit a huge variety of body forms and life cycles
c) often have a 3-part body d) most are suspension feeders e) some are predatory
f) some prey rotifers exhibit dramatic changes in body form
3) Three other aschelminth phyla worth mentioning include:
a) Ph. NEMATOMORPHA (horsehair worms; 325 sp.)
- extremely long, slender worms resembling nematodes
- single large pseudocoelom - like nematodes, they lack circular muscles
- larvae are parasitic in terrestrial insects - only the larvae have a spiny, eversible head end
b) Ph. PRIAPULIDA (penis worms; 18 spp.)
- thick-bodied (0.5 - 40 cm long), typically predatory worms- distinctive, plumose caudal
appendages in some - single large pseudocoelom
- although few living species persist, they were a common invertebrate of Cambrian seas
c) Ph. ACANTHOCEPHELA (spiny-headed worms; 1150 spp.)
- small-bodied (typically 1-2cm), exclusively endoparasitic
- require two hosts - no mouth or gut - single large pseudocoelom
- spiny, eversible head end to anchor in the gut lining - related to rotifers
d) The Aschelminthes may also include the newest animal phylum (1995): CYCLIOPHORA
Protostomes and Deuterostomes
Two major divisions of the Bilateria (Protostomia and Deuterostomia) exhibit many differences:
1) Origin of mesoderm is from very different cell types:
o mesenchyme cells ( protostomes)
o epithelial cells inpocket from archenteron ( Deutero)
2) Origin of coelom is via two different mechanisms:
o schizocoely ( splitting of the mesoderm)
o enterocoely ( as outpocketing of primitive gut- Deutero)
3) Origins of mouth and anus differ. The blastopore gives rise to the:
o mouth; the anus arises secondarily (Protostomia)
o anus; the mouth arises secondarily (Deuterostomia)
4) Other differences include:
PROTOSTOMIA: spiral and determinate cleavage –TRONCHOPHORE LARVA
 multiciliated cells
DEUTEROSTOMIA: radial and indeterminate cleavage-DIPLUERA LARVA
monociliated cells, deuterostomes may only include echinoderms, hemichordates and chordates