Download Mollusks-Segmented worms- Arthropods

Mollusks-Segmented wormsArthropods
Mollusks-Segmented wormsArthropods
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Organ systems
Triploblastic
Bilateral
True coelom
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 shell
• All molluscs have a similar body plan with three
main parts:
– Muscular foot
– Visceral mass
– Mantle
• Many molluscs also have a water-filled mantle
cavity, and feed using a rasplike radula
• 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
• There are four major classes of molluscs:
– Polyplacophora (chitons)
– Gastropoda (snails and slugs)
– Bivalvia (clams, oysters, and other bivalves)
– Cephalopoda (squids, octopuses, cuttlefish, and
chambered nautiluses)
Table 33-3
Chitons
• Class Polyplacophora consists of the chitons, ovalshaped marine animals encased in an armor of
eight dorsal plates
Fig. 33-16
Gastropods
• About three-quarters of all living species of
molluscs are gastropods
Fig. 33-17
(a) A land snail
(b) A sea slug
• Most gastropods are marine, but many are
freshwater and terrestrial species
• Most have a single, spiraled shell
• Slugs lack a shell or have a reduced shell
• The most distinctive characteristic of gastropods is
torsion, which causes the animal’s anus and mantle
to end up above its head
Fig. 33-18
Mantle
cavity
Anus
Mouth
Stomach
Intestine
Bivalves
• Molluscs of class Bivalvia include many species of
clams, oysters, mussels, and scallops
• They have a shell divided into two halves
Fig. 33-19
• The mantle cavity of a bivalve contains gills that are
used for feeding as well as gas exchange
Fig. 33-20
Mantle
Hinge area
Coelom
Gut
Heart Adductor
muscle
Digestive
gland
Anus
Mouth
Excurrent
siphon
Shell
Palp
Foot
Mantle
cavity
Gonad
Gill
Water
flow
Incurrent
siphon
Cephalopods
• Class Cephalopoda includes squids and octopuses,
carnivores with beak-like jaws surrounded by
tentacles of their modified foot
• Most octopuses creep along the sea floor in search
of prey
Fig. 33-21
Octopus
Squid
Chambered
nautilus
• Squids use their siphon to fire a jet of water, which
allows them to swim very quickly
• One small group of shelled cephalopods, the
nautiluses, survives today
• Cephalopods have a closed circulatory system, welldeveloped sense organs, and a complex brain
Annelida
• Annelids have bodies composed of a series of fused
rings
• The phylum Annelida is divided into three classes:
– Oligochaeta (earthworms and their relatives)
– Polychaeta (polychaetes)
– Hirudinea (leeches)
Table 33-4
Oligochaetes
• Oligochaetes (class Oligochaeta) are named for
relatively sparse chaetae, bristles made of chitin
• They include the earthworms and a variety of
aquatic species
• Earthworms eat through soil, extracting nutrients
as the soil moves through the alimentary canal
• Earthworms are hermaphrodites but cross-fertilize
Fig. 33-22
Cuticle
Epidermis
Coelom
Circular
muscle
Septum
(partition
between
segments)
Metanephridium
Longitudinal
muscle
Anus
Dorsal vessel
Chaetae
Intestine
Fused
nerve
cords
Ventral
vessel
Nephrostome
Metanephridium
Clitellum
Esophagus
Crop
Pharynx
Giant Australian earthworm
Intestine
Gizzard
Cerebral ganglia
Mouth
Subpharyngeal
ganglion
Blood
vessels
Ventral nerve cord with
segmental ganglia
Polychaetes
• Members of class Polychaetes have paddle-like
parapodia that work as gills and aid in locomotion
Fig. 33-23
Parapodia
Leeches
• Members of class Hirudinea are blood-sucking
parasites, such as leeches
• Leeches secrete a chemical called hirudin to
prevent blood from coagulating
Fig. 33-24
Arthropoda
• Two out of every three known species of animals
are arthropods
• Members of the phylum Arthropoda are found in
nearly all habitats of the biosphere
Arthropod Origins
• The arthropod body plan consists of a segmented
body, hard exoskeleton, and jointed appendages,
and dates to the Cambrian explosion (535–525
million years ago)
• Early arthropods show little variation from segment
to segment
General Characteristics of Arthropods
• The appendages of some living arthropods are
modified for many different functions
Fig. 33-29
Cephalothorax
Antennae
(sensory
reception)
Head
Abdomen
Thorax
Swimming appendages
(one pair located
under each
abdominal segment)
Walking legs
Pincer (defense)
Mouthparts (feeding)
• The body of an arthropod is completely covered by
the cuticle, an exoskeleton made of layers of
protein and the polysaccharide chitin
• When an arthropod grows, it molts its exoskeleton
• Arthropods have an open circulatory system in
which fluid called hemolymph is circulated into the
spaces surrounding the tissues and organs
• A variety of organs specialized for gas exchange
have evolved in arthropods
CLASS ARACHNIDA
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Spiders-Scorpion-Tick
Cephalothorax and Abdomen
4 pairs of legs
Simple eyes
No antennae
Fig. 33-31
50 µm
Scorpion
Dust mite
Web-building spider
Class Crustaceans
• While arachnids and insects thrive on land,
crustaceans, for the most part, have remained in
marine and freshwater environments
• Crustaceans typically have branched appendages
that are extensively specialized for feeding and
locomotion
• Most crustaceans have separate males and females
• Cephalothorax and abdomen-compound eyes-tow
pair of antennae-5 pairs of legs-mostly marine and
freshwater
Fig. 33-38a
(a) Ghost crab
Class Diplopoda
• Millipedes
–terrestrial, and have jaw-like mandibles
– Each trunk segment has two pairs of legs
– Elogate---dorsal convexed body—many segments—
one pair of antennae—simple eyes---terrestrial
– Scavengers
Fig. 33-33
• Centipedes, class Chilopoda, are carnivores
– They have one pair of legs per trunk segment
– Flattened body
– Simple-eyes
– One pair of antennae
Fig. 33-34
Class Insecta
• more species than all other forms of life combined
• They live in almost every terrestrial habitat and in
fresh water
• Head thorax and abdomen
• Three pairs of walking legs
• Often with wins on thorax
• Simple and compound eyes
• One pair of antennae
Fig. 33-35
Abdomen
Thorax Head
Compound eye
Antennae
Heart
Cerebral ganglion
Dorsal
artery Crop
Anus
Vagina
Malpighian
tubules
Ovary
Tracheal tubes
Nerve cords
Mouthparts
• Insects diversified several times following the
evolution of flight, adaptation to feeding on
gymnosperms, and the expansion of angiosperms
• Insect and plant diversity declined during the
Cretaceous extinction, but have been increasing in
the 65 million years since
• Flight is one key to the great success of insects
• An animal that can fly can escape predators, find
food, and disperse to new habitats much faster
than organisms that can only crawl
• Many insects undergo metamorphosis during their
development
• In incomplete metamorphosis, the young, called
nymphs, resemble adults but are smaller and go
through a series of molts until they reach full size
• Insects with complete metamorphosis have larval
stages known by such names as maggot, grub, or
caterpillar
• The larval stage looks entirely different from the
adult stage
• Most insects have separate males and females and
reproduce sexually
• Individuals find and recognize members of their
own species by bright colors, sound, or odors
• Some insects are beneficial as pollinators, while
others are harmful as carriers of diseases, or pests
of crops
• Insects are classified into more than 30 orders