Coelomate Invertebrates

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Coelomate Invertebrates

• Chapter 34

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Introduction

• Coelomates have a body design that
• 1. Repositions the bodys fluid
• 2. Allows complex tissues/organs to develop
• 3. Allows for a larger body size
• Coeloms evolved multiple times during animal
  evolution

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Phylum Mollusca

• Mollusks are second in diversity only to
  arthropods
• Exhibit a wide variety of sizes and body forms
• Live in many different environments
• Include snails, slugs, clams, octopuses and others

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Phylum Mollusca
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Phylum Mollusca

• Mollusks evolved in the oceans and most groups
  have remained there
• They are an important source of human food
• They are economically significant in other ways
• Pearls are produced in oysters
• Mother-of-pearl is produced in the shells of
  abalone
• Mollusks can also be pests
• Zebra mussel (Dreissena polymorpha)

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Mollusk Body Plan

• Mollusks are bilaterally symmetrical
• Characterized by a reduced coelom surrounding the
  heart and excretory organs
• The digestive, excretory and reproductive organs
  are concentrated in a visceral mass
• Mollusks may have a differentiated head at the
  anterior end of the body

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Mollusk Body Plan

• Mantle A thick epidermis that covers the dorsal
  side of the body
• Forms a cavity which houses the respiratory
  organs (ctenidia, or gills) and the openings of
  excretory, reproductive digestive organs
• The muscular foot of a mollusk is adapted for
  locomotion, attachment, food capture
• Or a combination of the above

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Mollusk Body Plan
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Mollusk Body Plan

• Most mollusks produce an external calcium
  carbonate-rich shell
• Used for protection
• Some species have internalized or reduced shells
• Most mollusks have a rasping tongue-like organ
  called the radula
• Used for feeding

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Mollusk Body Plan
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Mollusk Body Plan

• Nephridia Special excretory structures that
  remove nitrogenous wastes
• Consist of cilia-lined openings called
  nephrostomes
• Except for cephalopods, all mollusks have an open
  circulatory system
• Cephalopods have a closed circulatory system

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Mollusk Reproduction

• Most mollusks have distinct male and female
  individuals
• Most engage in external fertilization
• In marine mollusks, embryos develop through
  spiral cleavage
• Trochophores Free-swimming larval stage
• Veliger Second free-swimming larval stage
• Only in bivalves and snails

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Mollusk Reproduction
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Classes of Mollusks

• There are eight recognized classes
• Four are representatives of the phylum
• 1. Polyplacophora
• 2. Gastropoda
• 3. Bivalvia
• 4. Cephalopoda

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Classes of Mollusks

• Class Polyplacophora (Chitons)
• Marine mollusks that have oval bodies with eight
  overlapping dorsal calcareous plates

• Body is not segmented under the plates
• Most chitons are grazing herbivores

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Classes of Mollusks

• Class Gastropoda (Snails and slugs)
• A primarily marine group
• Heads typically have pairs of tentacles with eyes
  at the ends
• During embryological development, gastropods
  undergo
• 1. Torsion Mantle cavity and anus are moved
  from the posterior to the front
• 2. Coiling Spiral winding of the shell

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Classes of Mollusks
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Classes of Mollusks

• Class Bivalvia (Bivalves)
• Includes clams, scallops, mussels, oysters and
  others
• Have two lateral (right and left) shells (valves)
  hinged together dorsally
• Most are sessile filter-feeders
• Water circulation is mediated by siphons and
  rhythmic beating of cilia on gills

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Classes of Mollusks
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Classes of Mollusks

• Class Cephalopoda
• Active marine predators
• Foot has evolved into a series of arms equipped
  with suction cups
• Squids have 10 octopuses, 8 and nautiluses, 80
  to 90
• Have highly developed nervous systems
• Exhibit complex patterns of behavior and a high
  level of intelligence

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Classes of Mollusks
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Classes of Mollusks

• Class Cephalopoda
• -Many have an ink sac and are capable of
  expelling ink to confuse predators

-Octopuses and squids can change color using
pouches of pigment called chromatophores
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Phylum Annelida

• Annelid worms exhibit segmentation (building of
  body from repeated units)
• -Allows for specialization

• Members of this phylum are not monophyletic

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Phylum Annelida

• An annelid consists of a series of ring-like
  elements running the length of the body
• Divided internally by septa
• The anterior (front) segments contain specialized
  sensory organs
• A ventral nerve cord connects the ganglia in each
  segment with each other and the brain

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Phylum Annelida
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Phylum Annelida

• Annelids move using their hydrostatic skeleton
• Each segment contains chitin bristles (chaetae)
  that help anchor the worms
• Most have a closed circulatory system
• They exchange O2 and CO2 through their body
  surfaces
• Excretory system consists of a pair of ciliated,
  funnel-shaped nephridia per segment

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Phylum Annelida

• Annelids have traditionally been classified into
  three classes
• 1. Class Polychaeta
• 2. Class Oligochaeta
• 3. Class Hirudinea
• Hirudinea is now considered a sub-class of
  Oligochaeta

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Phylum Annelida

• Class Polychaeta (Polychaetes)
• Mostly marine worms, such as tubeworms
• Unusual forms and iridescent colors
• Have a differentiated head
• Have paired parapodia on most segments
• Used in swimming, burrowing, crawling
• Sexes are usually separate
• Typically lack permanent gonads

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Phylum Annelida
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Phylum Annelida

• Class Oligochaeta (Earthworms and leeches)
• Mostly terrestrial
• Earthworms
• Consist of 100-175 segments, with a mouth on the
  first and an anus on the last
• Lack eyes, parapodia and head
• Have fewer setae than polychaetes

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Phylum Annelida

• Earthworms are hermaphroditic
• -Clitellum secretes mucus that holds the worms
  together during copulation

-Also secretes a mucus cocoon, in which the
fertilized egg develops
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Phylum Annelida

• Leeches
• -Occur mostly in freshwater
• -Usually flattened dorsoventrally
• -Cross-fertilization is obligatory
• -Have no chaetae (except for one species)

-Medicinal leech, Hirudo medicinalis -Secretes
anticoagulant
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Phylum Arthropoda

• Arthropods are the most successful animals
• 1,000,000 species (2/3rd of all species)
• About 80 are insects
• For each human, 200 million insects are alive at
  any one time
• Athropods affect all aspects of human life
• Are divided into four major classes
• Arachnids, myriapods, crustaceans and insects

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Arthropod Morphology

• All arthropods have jointed appendages
• Modifications antennae, mouthparts, legs
• Arthropods also have an exoskeleton made of
  secreted chitin and protein
• Functions protection muscle attachment
• Its thickness limits arthropod body size
• Arthropod bodies are segmented
• Some segments are specialized into functional
  groups, or tagmata

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Arthropod Morphology
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Arthropod Morphology

• Arthropods have an open circulatory system
• Compound eyes are found in many arthropods
• Composed of independent visual units called
  ommatidia
• Other arthropods have simple eyes, or ocelli
• Have single lenses
• Distinguish light from darkness

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Arthropod Morphology
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Arthropod Morphology

• Nervous system consists of a double chain of
  segmented ganglia on ventral surface
• Brain seems to be an inhibitor, rather than as a
  stimulator, as it is in vertebrates
• Respiratory system consists of tracheae and
  tracheoles
• Connected to the exterior by spiracles

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Arthropod Morphology
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Arthropod Morphology

• Arthropods have a unique excretory system
  consisting of Malpighian tubules
• Eliminates nitrogenous wastes as concentrated
  uric acid or guanine
• Arthropods periodically undergo ecdysis or
  molting
• Shedding the outer cuticular layer

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Arthropod Morphology
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Class Arachnida

• Arachnids are largely terrestrial organisms
• Spiders, ticks, mites, scorpions, and others
• The most anterior appendages, chelicerae, often
  function as fangs or pincers
• Body is divided into two main tagmata
• Prosoma (anterior) Bears all appendages
• Opisthosoma (posterior) Contains the
  reproductive organs

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Class Arachnida

• Pedipalps (palps) are posterior to chelicerae
• Resemble legs, but have one less segment
• Used as copulatory organs, pincers, or sensors
• Most arachnids are carnivorous
• Mites are largely herbivorous

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Class Arachnida

• Order Araneae (spiders)
• About 35,000 species
• Many spiders catch their prey in silk webs
• Silk protein forced out of spinnerets found on
  the posterior of the abdomen
• Other spiders actively hunt their prey
• All spiders have poison glands leading through
  their chelicerae

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Class Arachnida
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Class Arachnida

• Order Acari (mites and ticks)
• Largest and most diverse arachnid order
• Most mites are small
• Cephalothorax and abdomen are fused into an
  unsegmented ovoid body
• Ticks are larger than mites
• Are blood-eating parasites
• Can carry many diseases (spotted fevers, Lyme
  disease)

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Centipedes and Millipedes

• Centipedes (class Chilopoda) and Millipedes
  (class Diplopoda) have bodies with a head
  followed by numerous segments
• Centipedes are all carnivores (eat insects)
• Millipedes are largely herbivores
• In both fertilization is internal
• The sexes are separate

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Centipedes and Millipedes

• Centipedes have fewer legs than millipedes
• -Centipedes one leg pair on each segment
• -Millipedes two on some or all segments

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Class Crustacea

• Crustaceans are primarily aquatic organisms
• Crabs, shrimps, lobsters, barnacles, others
• Have three tagmata
• The two most anterior fuse to form a
  cephalothorax
• Have two pairs of antennae, three pairs of
  appendages, and various pairs of legs
• Most appendages are biramous

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Class Crustacea

• Mandibles (biting jaws) likely evolved from a
  pair of limbs that took on a chewing function

• Most crustaceans have separate sexes
• Majority develop through a nauplius stage

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Class Crustacea

• Decapod crustaceans include shrimps, lobsters,
  crabs and crayfish
• Have ten feet
• Exoskeleton usually enforced with CaCO3
• Most body segments are fused into a cephalothorax
• Lobsters and crayfish have appendages that aid in
  swimming
• Swimmerets and uropods

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Class Crustacea
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Class Crustacea

• Order Cirripedia
• -Barnacles are crustaceans that are sessile as
  adults

-Free-swimming larvae -Are hermaphroditic -Some
have stalks
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Class Hexapoda

• Insects are by far the largest group of animals
• More than half of all named animal species
• Insects are primarily a terrestrial group
• Approximately one billion billion (1018) insects
  are alive at any one time

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Class Hexapoda
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Class Hexapoda

• External features
• Three body regions
• 1. Head Has pair of antennae and modified
  mouthparts
• 2. Thorax Has three segments, each with a pair
  of legs
• -May have one or two pairs of wings
• 3. Abdomen
• Most insects have compound eyes

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Class Hexapoda

• Internal organization
• The digestive tract is a coiled tube
• Lined with cuticle on anterior and posterior
  regions
• Digestion takes place in stomach (midgut)
• Excretion tales place through Malpighian tubules
• Tracheae permeate all tissues

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Class Hexapoda

• Sensory receptors
• Sensory setae are hair-like structures
• Detect chemical and mechanical signals
• Tympanal organs are composed of a thin membrane,
  the tympanum
• Detect sound
• In addition, insects can communicate by means of
  pheromones

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Class Hexapoda

• Insect life histories
• Many insects undergo metamorphosis
• Simple metamorphosis (grasshopers)
• Immature stages similar to adults
• Complete metamorphosis (butterflies)
• Immature larva are wormlike
• A resting stage, pupa or chrysalis, precedes the
  final molt into adult form

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Phylum Echinodermata

• Echinoderms are an ancient group of marine
  animals, with about 6000 living species
• Characterized by deuterostome development and an
  endoskeleton

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Echinoderm Body Plan

• The echinoderm body plan undergoes a fundamental
  shift during development
• Larvae bilateral symmetry
• Adults pentaradial symmetry
• Body structure is discussed in reference to their
  mouths, which define the oral surface

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Echinoderm Body Plan

• Endoskeleton
• Found internal to a delicate epidermis which
  contains thousands of neurosensory cells
• Composed of either movable or fixed calcium-rich
  (calcite) plates called ossicles
• Perforated by pores to allow extension of tube
  feet
• Contains mutable collagenous tissue
• Provides ability to autotomize body parts

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Echinoderm Body Plan

• Water-vascular system
• A hydraulic system that aids in movement and
  feeding
• Composed of a central ring canal from which five
  radial canals extend into each of the bodys five
  parts
• Madreporite Opening for water entry
• Ampulla Muscular sac for tube feet control

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Echinoderm Body Plan
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Echinoderm Body Plan

• Echinoderms have a large coelom which connects
  with a complicated tub system
• Helps provide circulation and respiration through
  extensions called papulae

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Echinoderm Body Plan

• Reproduction
• In some echinoderms, asexual reproduction takes
  place by splitting
• Broken parts can regenerate the whole animal
• Most reproduction in the phylum is sexual and
  external

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Classes of Echinoderms

• There are more than 20 extinct classes
• In addition, there are five extant classes
• 1. Asteroidea (sea stars and sea daisies)
• 2. Crinoidea (sea lilies and feather stars)
• 3. Echinoidea (sea urchins sand dollars)
• 4. Holothuroidea (sea cucumbers)
• 5. Ophiuroidea (brittle stars)

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Classes of Echinoderms