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IB-202-4. 3-15-06. Most animals have bilateral symmetry The vast majority of animal species belong to the clade Bilateria Which consists of animals with bilateral symmetry and triploblastic development. Developmental Patterns (Deuterostome and Protostome).

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ib 202 4

IB-202-4

3-15-06

slide2
Most animals have bilateral symmetry
  • The vast majority of animal species belong to the clade Bilateria
    • Which consists of animals with bilateral symmetry and triploblastic development
developmental patterns deuterostome and protostome
Developmental Patterns (Deuterostome andProtostome)
  • Based on certain features seen in early development
    • Many animals can be categorized as having one of two developmental modes: protostome development or deuterostome development
cleavage

Deuterostome development

(examples: echinoderms,

chordates)

Protostome development

(examples: molluscs, annelids,

arthropods)

(a) Cleavage. In general, protostomedevelopment begins with spiral, determinate cleavage.Deuterostome development is characterized by radial, indeterminate cleavage. Means at the 8 cell stage you

can separate out a cell and will develop into a complete individual

Eight-cell stage

Eight-cell stage

Spiral and determinate

Radial and indeterminate

Cleavage
  • In protostome development
    • Cleavage is spiral and determinate
  • In deuterostome development
    • Cleavage is radial and indeterminate

Figure 32.9a

coelom formation

(b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development).

Coelom

Archenteron

Coelom

Mesoderm

Blastopore

Mesoderm

Blastopore

Enterocoelous:

folds of archenteron

form coelom

Schizocoelous: solid

masses of mesoderm

split and form coelom

Figure 32.9b

Coelom Formation
  • In protostome development
    • The splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous development
  • In deuterostome development
    • Formation of the body cavity is described as enterocoelous development. Red represents mesodermal cells.
fate of the blastopore

Mouth

Anus

Digestive tube

Anus

Mouth

Mouth develops

from blastopore

Anus develops

from blastopore

Figure 32.9c

Fate of the Blastopore
  • In protostome development
    • The blastopore becomes the mouth
  • In deuterostome development
    • The blastopore becomes the anus. Note two layers of mesoderm lining body cavity.
flatworms
Flatworms
  • Members of phylum Platyhelminthes
    • Live in marine, freshwater, and damp terrestrial habitats
    • Have a gastrovascular cavity and are flattened dorsoventrally (significance=don’t need

a circulatory system as diffusion is adequate to meet nutrient distribution from the gut, gas exchange and waste disposal needs because of short distance from cell to environment

  • Although flatworms undergo triploblastic development
    • They are acoelomates (body cavity solid)
class turbellaria

Figure 33.9

Class Turbellaria
  • Turbellarians
    • Are nearly all free-living and mostly marine
planaria

Digestion is completed within

the cells lining the gastro-

vascular cavity, which has

three branches, each with

fine subbranches that pro-

vide an extensive surface area.

Pharynx. The mouth is at the

tip of a muscular pharynx that

extends from the animal’s

ventral side. Digestive juices

are spilled onto prey, and the

pharynx sucks small pieces of

food into the gastrovascular

cavity, where digestion continues.

Undigested wastes

are egested

through the mouth.

Gastrovascular

cavity

Eyespots

Ganglia. Located at the anterior end

of the worm, near the main sources

of sensory input, is a pair of ganglia,

dense clusters of nerve cells.

Ventral nerve cords. From

the ganglia, a pair of

ventral nerve cords runs

the length of the body.

Figure 33.10

Planaria
  • The best-known turbellarians, commonly called planarians
    • Have light-sensitive eyespots and centralized nerve nets. Cephalization-concentration of sensory organs and nerve bodies (ganglia) at the anterior end. Allows them to avoid light, seek food etc.
other flatworms are parasites monogenea and trematoda
Other Flatworms are parasitesMonogenea and Trematoda
  • Monogeneans and trematodes
    • Live as parasites in or on other animals
    • Parasitize a wide range of hosts
life cycle of blood fluke schistosoma

Mature flukes live in the blood vessels of the human

intestine. A female fluke fits into a groove running

the length of the larger male’s body, as shown in

the light micrograph at right.

1

Male

Female

1 mm

These larvae penetrate

the skin and blood

vessels of humans

working in irrigated

fields contaminated

with infected human

feces.

5

Blood flukes reproduce

sexually in the human host.

The fertilized eggs break through

blood vessel wall into the digestive

tract and exit the

host in feces.

2

The eggs develop in

water into ciliated

larvae. These larvae

infect snails, the

intermediate hosts.

3

Asexual reproduction

within a snail results in

another type of motile

larva, which escapes from

the snail host.

4

Snail host

Figure 33.11

Life cycle of blood fluke (Schistosoma)
  • Trematodes that parasitize humans
    • Spend part of their lives in snail hosts
slide14
Most monogeneans
    • Are parasites of fish
cestode tapeworm

Proglottids with

reproductive structures

200 µm

Hooks

Scolex

Sucker

(Cestode) Tapeworm
  • Tapeworms (highly specialized for parasitic life)
    • Lack a digestive system—absorb nutrients from intestinal lumen. Specialized head for attachment to gut wall.
rotifers
Rotifers
  • Rotifers, phylum Rotifera
    • Are tiny animals that inhabit fresh water, the ocean, and damp soil and are of interest because of their prolonged asexual reproduction.
slide17

0.1 mm

Figure 33.13

  • Rotifers are smaller than many protists (largest 2 mm)
    • But are truly multicellular and have specialized organ systems (digestive tract with mouth and anus, body cavity but is pseudocoelom-not lined by mesoderm).
rotifer reproduction
Rotifer Reproduction
  • Rotifers reproduce by parthenogenesis (unfertilized eggs develop into adult females) which produce more females from unfertilized eggs.
  • Without sexual reproduction, deleterious mutations should accumulate that would make the organism less fit. However this has been going on for 35 million years and how they flout the general rule against long-lived asexuality is a puzzle.
nemerteans

Figure 33.15

Nemerteans
  • Members of phylum Nemertea
    • Are commonly called proboscis worms or ribbon worms, pseudocoelom)
slide20
The nemerteans unique proboscis
    • Is used for defense and prey capture (some inject toxin into prey)
    • Is extended by a fluid-filled sac
  • Nemerteans also have a closed circulatory system (none of the other phyla we talked about have this).
    • The blood is contained in vessels distinct from fluid in the body cavity but there is no heart. Fluid moved through the system by contraction of body wall. (Antarctic nemerteans can capture a 6 inch long fish and ingest it. Cut them in half and regenerate). Mucous contains tetrodotoxin -a nerve toxin).
the annelids

The Annelids

Segmented worms.

slide22

Table 33.4

  • The phylum Annelida is divided into three classes
oligochaetes
Oligochaetes
  • Oligochaetes (class Oligochaeta)
  • The earth worms (fish bait)
    • Are named for their relatively sparse chaetae, or bristles made of chitin
    • Include the earthworms and a variety of aquatic species
slide24
Earthworms eat their way through the soil, extracting nutrients as the soil moves through the alimentary canal
    • Which helps till the earth, making earthworms valuable to farmers
slide25

Coelom. The coelom

of the earthworm is

partitioned by septa. Allow

Independent movement

of body wall.

Metanephridium. Each

segment of the worm

contains a pair of

excretory tubes, called

metanephridia, with

ciliated funnels, called

nephrostomes. The

metanephridia remove

wastes from the blood

and coelomic fluid

through exterior pores.

Each segment is surrounded by longitudinal muscle, which in

turn is surrounded by circular muscle. Earthworms coordinate

the contraction of these two sets of muscles to move (see

Figure 49.25). These muscles work against the noncompressible

coelomic fluid, which acts as a hydrostatic skeleton.

Cuticle

Epidermis

Septum

(partition

between

segments)

Circular

muscle

Many of the internal

structures are repeated

within each segment of

the earthworm.

Longitudinal

muscle

Anus

Chaetae. Each segment

has four pairs of

chaetae, bristles that

provide traction for

burrowing.

Dorsal

vessel

Intestine

Tiny blood vessels are

abundant in the earthworm’s

skin, which functions as its

respiratory organ. The blood

contains oxygen-carrying

hemoglobin.

Nerve

cords

Ventral

vessel

Cerebral ganglia. The

earthworm nervous system

features a brain-like pair of

cerebral ganglia above and

in front of the pharynx. A ring

of nerves around the pharynx

connects to a subpharyngeal

ganglion, from which a fused

pair of nerve cords runs

posteriorly.

Nephrostome

Clitellum

Pharynx

Esophagus

Metanephridium

Crop

Giant Australian earthworm

Intestine

Gizzard

Mouth

Subpharyngeal

ganglion

Ventral nerve cords with segmental ganglia.

The nerve cords penetrate the septa and run

the length of the animal, as do the digestive

tract and longitudinal blood vessels.

The circulatory system, a network of vessels,

is closed. The dorsal and ventral vessels are linked

by segmental pairs of vessels. The dorsal vessel

and five pairs of vessels that circle the esophagus

of an earthworm are muscular and pump blood

through the circulatory system.

  • Anatomy of an earthworm

Table 33.23

polychaetes

Parapodia

Figure 33.24

Polychaetes
  • Members of class Polychaeta
    • Possess paddlelike parapodia that function as gills and aid in locomotion, bristles and gas exchange.
slide27

Figure 33.1

  • Polychaete Christmas tree worm
  • “Feathers” used to trap food particles which are moved along their base to the mouth--also gas exchange.
leeches

Figure 33.25

Leeches
  • Members of class Hirudinea (1 to 30 cm, tropics)
    • Are blood-sucking parasites, such as leeches. Secrete hirudin (anticoagulant) and drink 10 x their body weight in blood. Medicinal leech used to drain blood from injured finger.
nematoda non segmented round worms
Nematoda (non-segmented round worms)
  • Grouped with arthropods in Ecdysozoa clade because covered with cuticle that it sheds as it grows
slide30

25 µm

Figure 33.26

  • The cylindrical bodies of nematodes (phylum Nematoda)
    • Are covered by a tough coat called a cuticle
slide31
Fluid filled pseudocoelom acts as a hydroskeleton that the circular and longitudinal muscles work against
  • Great numbers of nematodes live in moist soil and lake bottoms. Are agriculture pests (corn root worm) and parasites of animals and humans. These include pinworms and round worms in the intestinal tract.
slide32

Encysted juveniles

Muscle tissue

50 µm

Figure 33.27

Can acquire this parasite from eating uncooked pork of infected swine. The encysted juveniles mature and migrate from your intestine into the intestinal muscle. Produce more juveniles which migrate to the heart where they encyst forming calcium deposits. Avoid the immune system. Make muscle cell bigger to house them and vascularization. Painful inflammation.

  • Trichinosis (Trichinella) a human disease
phylum mollusca
Phylum Mollusca
  • Includes snails and slugs, oysters and clams, and octopuses and squids
  • Most molluscs are marine
    • Though some inhabit fresh water and some are terrestrial
  • Molluscs are soft-bodied animals
    • But most are protected by a hard calcium carbonate shell
  • Molluscs have a muscular foot, a visceral mass, and a mantle
anatomy of molluscs
Anatomy of Molluscs
  • All molluscs have a similar body plan with three main parts
    • A muscular foot
    • A visceral mass
    • A mantle
generalized anatomy of a mollusc

Heart. Most molluscs have an open circulatory

system. The dorsally located heart pumps

circulatory fluid called hemolymph through arteries

into sinuses (body spaces). The organs of the

mollusc are thus continually bathed in hemolymph.

Nephridium. Excretory organs

called nephridia remove metabolic

wastes from the hemolymph.

The long digestive tract is

coiled in the visceral mass.

Visceral mass

Coelom

Intestine

Gonads

Mantle

Stomach

Radula. The mouth

region in many

mollusc species

contains a rasp-like

feeding organ

called a radula. This

belt of backward-

curved teeth slides

back and forth,

scraping and

scooping like a

backhoe.

Mantle

cavity

Shell

Mouth

Radula

Anus

The nervous

system consists

of a nerve ring

around the

esophagus, from

which nerve

cords extend.

Gill

Nerve

cords

Foot

Mouth

Esophagus

Figure 33.16

Generalized Anatomy of a mollusc
slide36
Most molluscs have separate sexes
    • With gonads located in the visceral mass
  • The life cycle of many molluscs
    • Includes a ciliated larval stage called a trochophore
trochophore larva

Apical tuft

of cilia

(a)

An ectoproct, a lophophorate

Mouth

(b)

Structure of trochophore larva

Figure 32.13a, b

Anus

Trochophore Larva
  • Other phyla
    • Go through a distinct larval stage called a trochophore larva
they look very different live in diverse environments and have different life histories

Table 33.3

They look very different, live in diverse environments and have different life histories
  • There are four major classes of molluscs
chitons

Figure 33.17

Chitons
  • Class Polyplacophora is composed of the chitons
    • Oval-shaped marine animals encased in an armor of eight dorsal plates (Firmly attached to rocks in the intertidal region of the ocean). Try and pry off of a rock-home range.
gastropods

A land snail wiith protective

shell

(a)

A sea slug. Nudibranchs, or sea slugs, lost their shell

during their evolution. Gills on dorsal surface.

(b)

Figure 33.18a, b

Gastropods
  • About three-quarters of all living species of molluscs
    • Belong to class Gastropoda
slide41
Most gastropods
    • Are marine, but there are also many freshwater and terrestrial species
    • Possess a single, spiraled shell
  • Slugs lack a shell
    • Or have a reduced shell
torsion in gastropods

Stomach

Mantle

cavity

Intestine

Anus

Mouth

Figure 33.19

Torsion in Gastropods
  • The most distinctive characteristic of this class
    • Is a developmental process known as torsion, which causes the animal’s anus and mantle to end up above its head. To accomodate shell?? Some

have flattened shells (abalone). Head with eye stalks. Modified radula as poisonous dart (marine cone snail toxin can kill humans).

bivalves

Figure 33.20

Bivalves
  • Molluscs of class Bivalvia
    • Include many species of clams, oysters, mussels, and scallops. Were used as food sources by early man as well as today.
    • Have a shell divided into two halves
anatomy of a bivalve

Hinge area

Coelom

Gut

Mantle

Heart

Shell

Adductor

muscle

Mouth

Anus

Excurrent

siphon

Palp

Water

flow

Foot

Incurrent

siphon

Mantle

cavity

Gill

Figure 33.21

Anatomy of a Bivalve
  • The mantle cavity of a bivalve
    • Contains gills that are used for feeding as well as gas exchange
cephalopods
Cephalopods
  • Class Cephalopoda includes squids and octopuses
    • Carnivores with beak-like jaws surrounded by tentacles of their modified foot
    • Closed circulator system
    • Well developed eye similar to vertebrate eye (lens, retina etc)
    • Very active life style. Squid can feed on herring by zipping through a school. Herring capable of rapid swimming.
    • Elaborate sex where male inserts packets of sperm into mantle cavity of female. (Will look at squid in lab).
    • Ink gland for escape.
slide46

(a) Octopuses are considered among the

most intelligent invertebrates.

Figure 33.22a

  • Most octopuses
    • Creep along the sea floor in search of prey
slide47

(b) Squids are speedy carnivores with beaklike jaws and well-developed eyes.

Figure 33.22b

  • Squids use their siphon
    • To fire a jet of water, which allows them to swim very quickly
slide48

(c) Chambered nautiluses are the only living cephalopods with an external shell. Have rudimentary eye without lens like a pin hole camera. Shell is chambered and put less dense ammonium chloride in chamber for flotation. Less dense than seawater.

Figure 33.22c

`
  • One small group of shelled cephalopods
    • The chambered nautiluses, survives today
    • Huge nautilus fossils in northern Africa