Coelomate Invertebrates

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Coelomate Invertebrates

• Chapter 33

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Coelomates

• Coelomates have a new body design that allows for
  the development of complex tissues and organs.
• allows wider array of body architectures and
  increased body size

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Mollusks

• Mollusks (Mollusca)
• extremely diverse
• characterized by a coelom
• great economic significance
• pearls
• mother of pearl
• economic / environmental costs
• zebra mussel invasion
• intermediate hosts for parasites

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Body Plan of the Mollusks

• Distinct bilateral symmetry
• Digestive, excretory, and reproductive organs are
  all concentrated in a visceral mass and a
  muscular foot.
• May have differentiated head
• Folds constituting a mantle
• gills - increased surface area for gas exchange

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Body Plan of the Mollusks

• Shells serve primarily for protection
• Radula - rasping tongue-like organ used for
  feeding
• Circulatory system (except cephalopods) consists
  of a heart and an open circulatory system.
• Nitrogenous wasted removed by nephridia

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Mollusk Body Plans
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Body Plan of the Mollusks

• Reproduction in mollusks
• most have distinct male and female individuals
• most engage in external fertilization
• many have free-swimming larvae (trochophores)
  which closely resemble larval stage of many
  marine annelids

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Classes of Mollusks

• Polyplacophora chitons
• oval bodies with eight overlapping calcareous
  plates
• Gastropoda snails and slugs
• heads of most have pair of tentacles with eyes at
  the ends
• undergo torsion during embryological
  development.

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Classes of Mollusks

• Bivalvia bivalves
• clams, scallops, mussels and oysters
• two lateral shells hinged together dorsally
• mantle secretes shell and ligaments
• most are sessile filter-feeders

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Classes of Mollusks

• Cephalopoda octopuses, squids, nautilus
• most intelligent of the invertebrates
• active marine predators
• foot evolved into a series of tentacles equipped
  with structures to capture prey
• highly developed nervous systems

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Segmented Animals

• Segmentation - building of body from series of
  similar segments
• Annelids
• three characteristics
• repeated segments divided by septa each
  segment can move independently
• specialized segments brain and eyes
• connections segments connected by blood vessels
  and nerve cord

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Segmented Animals

• Body plan of the annelid
• tube within a tube
• each segment typically possesses setae, that help
  anchor during locomotion
• most have closed circulatory system oxygen
  diffuses through skin and into blood vessels
• nephridia collect and transport wastes

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Classes of Annelids

• Polychaeta polychaetes
• well developed head with specialized sense organs
• parapodia on most segments used in locomotion
  and gas exchange
• usually lack permanent gonads with external
  fertilization

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Classes of Annelids

• Oligochaeta earthworms
• Aerate and enrich soil
• No eyes
• Hermaphroditic
• Worms join at the clitellum
• Exchange sperm cells
• Eggs deposited in clitellum as it moves down
  worms body

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Classes of Annelids

• Hirudinea leeches
• occur mostly in fresh water
• hermaphroditic
• develop clitellum during breeding season
• unable to self-fertilize
• secrete anticoagulant into wounds

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Lophophorates

• Lophophore - circular or U-shaped ridge around
  the mouth bearing one or two rows of ciliated,
  hollow tentacles
• functions as surface for gas exchange and as
  food-collection organs
• Attached to ocean floor or move very slowly

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Lophophorates

• phoronids

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Lophophorates

• bryozoans

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Lophophorates

• brachiopods

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Jointed Appendages and Exoskeleton

• All arthropods have jointed appendages.
• Rigid external skeleton (exoskeleton)
• protects animal and provides sites for muscle
  attachment
• brittle, thus arthropod body size limited due to
  exoskeleton thickness
• Must molt (ecdysis) to grow
• estimates of a quintillion insects alive at any
  one time
• 1,000,000 species

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Arthropod Body Plan

• Compound eye
• composed of many ommatidia
• each covered with a lens and linked to a complex
  of eight retinal cells and a light sensitive core
• Simple eyes (ocelli) have single lenses.
• function in distinguishing light from darkness

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The Compound Eye
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General Characteristics of Arthropods

• Circulatory system
• open circulatory system
• Nervous system
• double chain of segmented ganglia running along
  the animals ventral surface

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General Characteristics of Arthropods

• Respiratory system
• no single major respiratory organ
• small branched air ducts tracheae
• Gills
• Book lungs
• Exoskeleton
• Excretory system
• Malpighian tubules

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Crustaceans

• Most crustaceans have two pairs of antennae,
  three types of chewing appendages, and various
  numbers of leg pairs.
• all pass through nauplius larval stage
• Includes crabs, lobsters, shrimp, copepods

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Crustaceans

• Decapod crustaceans
• ten footed
• exoskeleton usually reinforced with calcium
  carbonate
• most body segments are fused into cephalothorax
  covered by carapace
• Lobsters and crayfish have swimmerets and uropods
  to aid in swimming

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Decapod Crustacean
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Crustaceans

• Terrestrial and freshwater crustaceans
• about half of estimated 4,500 species are
  terrestrial and live in moist habitats
• pillbugs
• sowbugs
• isopods
• Sessile crustaceans
• barnacles
• free-swimming larvae

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Class Arachnida

• Largest of three classes
• have a pair of chelicerae, a pair of pedipalps,
  and four pairs of walking legs
• most are carnivorous, except for mites
• many spiders have book lungs

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Class Arachnida

• Order Araneae spiders
• about 35,000 named species of spiders
• many do not spin webs, but actively hunt
• have poison glands leading through their
  chelicerae
• used to bite and paralyze prey

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Class Arachnida

• Order Acari mites and ticks
• largest in terms of number of species and most
  diverse of arachnids
• about 30,000 named species
• diverse in structure and habitat
• found in virtually every habitat known
• ticks can carry many diseases

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Class Chilopoda and Diplopoda

• Centipedes and millipedes
• both have bodies that consist of a head region
  followed by numerous segments
• centipedes have 30 legs
• carnivorous
• millipedes have 60 legs
• herbivorous

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Class Insecta

• Largest group of organisms on earth
• More than half of all named species on earth are
  insects.
• hectare of lowland tropical rainforest is
  estimated to be inhabited by as many as 41,000
  insect species

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Class Insecta

• External features
• three body segments
• head, thorax, and abdomen
• three pairs of legs
• one pair of antennae
• modified mouthparts
• solid wings

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Class Insecta

• Internal organization
• tubular digestive system
• dilute digestive enzymes
• trachea extends throughout body
• fat body for food storage
• Sense receptors
• sensory hairs - linked to nerve cells
• tympanum - found with tracheal air sacs
• pheromones communication signals

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Insect Life Histories

• Metamorphosis
• simple
• immature stages
• complete
• larvae
• pupa (chrysalis)

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Deuterostome Development

• Echinoderms
• ancient group of marine animals consisting of
  about 6,000 living species
• name refers to hard, calcium-rich endoskeleton
  beneath the skin
• unique water-vascular system is a fluid-filled
  system used to aid in movement and feeding

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Echinoderm Body Plan

• Secondary radial symmetry
• bilaterally symmetrical during larval
  development, but become radially symmetrical as
  adults.
• Five part body plan

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Echinoderm Water-Vascular System
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Echinoderm Body Plan

• Reproduction
• many echinoderms have the ability to regenerate
• most reproduction is sexual and external

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Major Classes of Echinoderms

• Living classes
• Crinoidea - sea lilies and feather stars
• Asteroidea - sea stars
• Ophiuroidea - brittle stars
• Echinoidea - sea urchins and sand dollars
• Holothuroidea - sea cucumbers

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Class Asteroidea

• Sea stars
• abundant in intertidal zone
• important marine predators
• body composed of central disc that merges
  gradually with the arms

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Class Ophiuroidea

• Brittle stars
• largest and probably most abundant class
• slender branched arms
• groove running down each arm is closed and
  covered with ossicles
• tube feet lack ampullae and are used for feeding,
  not locomotion

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Class Echinoidea

• Sea urchins and sand dollars
• lack distinct arms, but still have five-part body
  plan
• walk on tube feet or movable spines

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