Invertebrates

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Chapter 33

• Invertebrates

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Lets meet the Invertebrates
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Life Without a Backbone

• Invertebrates
• Are animals that lack a backbone
• Account for 95 of known animal species

Xmas Tree Worm
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A review of animal phylogeny
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Invertebrate diversity
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Invertebrate Diversity
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Invertebrate Diversity
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Sponges (Phylum Porifera)

• Sponge characteristics
• Sessile
• Porous body
• Choanocytes flagellated collar cells generate a
  water current through the sponge and ingest
  suspended food by phagocytosis
• Live in both fresh and marine waters
• Lack true tissues (groups of similar cells that
  form a functional unit). All animals except
  sponges belong to the clade Eumetazoa, the
  animals with true tissues
• Most sponges are hermaphrodites (each individual
  functions as both male and female)

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Sponges

• Sponges are suspension feeders
• Capturing food particles suspended in the water
  that passes through their body

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Cnidarians (Phylum Cnidaria)

• A diverse range of both sessile and floating
  organisms including hydras, jellies, sea
  anemones, and corals
• Cnidarian characteristics
• radial symmetry
• gastrovascular cavity (digestive compartment)
• Cnidocytes

movie
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Cnidarian Body Plan

• Relatively simple diploblastic (two germ layers),
  radial body plan
• Basic body plan of a cnidarian is a sac with a
  central digestive compartment, the gastrovascular
  cavity
• A single opening functions as both mouth and anus
• There are two variations on this body plan
• The sessile polyp and the floating medusa

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Cnidarian Feeding

• Cnidarians are carnivores
• That use tentacles to capture prey
• The tentacles are armed with cnidocytes
• Unique cells that function in defense and the
  capture of prey

Threads can inject poison into the prey, or stick
to or entangle the target
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Classes of Phylum Cnidaria
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Hydrozoan Life Cycle
The zygote develops into a solid ciliated
larva called a planula.
The planula eventually settles and develops
into a new polyp.
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Classes Hydrozoa, Scyphozoa, Cubozoa, and
Anthozoa
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Cnidarian Classes

• In the class Hydrozoa
• Most hydrozoans alternate between polyp and
  medusa forms. Freshwater Hydras exist only in the
  polyp form.
• In the class Scyphozoa
• Jellies (medusae) are the prevalent form of the
  life cycle
• In the class Cubozoa, which includes box jellies
  and sea wasps
• The medusa is box-shaped and has complex eyes
• Class Anthozoa includes the corals and sea
  anemones
• Which occur only as polyps

Hydra
Purple coral
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Hydra movie 1
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Hydra movie 2
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Coral reproduction
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Jellyfish movie
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Bilateria

• 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

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Flatworms

• Members of phylum Platyhelminthes
• Live in marine, freshwater, and damp terrestrial
  habitats. Some are parasitic.
• Are flattened dorsoventrally and have bilateral
  symmetry
• Undergo triploblastic development
• Are acoelomates (lack a coelom) with
  gastrovascular cavities.
• Lack a digestive system entirely and absorb
  nutrients across their body surface.

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Flatworm Classes
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Turbellarians

• Are nearly all free-living and mostly marine

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Turbellarians

• Planarians are common examples of turbellarians
• They have light-sensitive eyespots and
  centralized nerve nets

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Monogeneans and Trematodes

• Live as parasites in or on other animals They
  parasitize a wide range of hosts
• Most monogeneans are parasites of fish
• Trematodes (Flukes) that parasitize humans spend
  part of their lives in snail hosts

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Tapeworms (Class Cestoda)

• Are also parasitic and lack a digestive system

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Rotifers (Phylum Rotifera)

• Are tiny animals that inhabit fresh water, the
  ocean, and damp soil
• Rotifers are smaller than many protists
• But are truly multicellular and have specialized
  organ systems
• Rotifers have an alimentary canal
• A digestive tube with a separate mouth and anus
  that lies within a fluid-filled pseudocoelom
• Some species of rotifers reproduce by
  parthenogenesis
• In which females produce more females from
  unfertilized eggs

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Rotifers (Phylum Rotifera)
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Rotifer movie 2
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Three Phyla of Lophophorates Ectoprocts,
Phoronids, and Brachiopods

• Lophophorates have a lophophore
• A horseshoe-shaped, suspension-feeding organ
  bearing ciliated tentacles that trap suspended
  food particles

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Ectoprocts

• Are colonial animals that superficially resemble
  plants

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Phoronids

• Are tube-dwelling marine worms ranging from 1 mm
  to 50 cm in length

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Brachipods

• Superficially resemble clams and other
  hinge-shelled molluscs
• But the two halves of the shell are dorsal and
  ventral rather than lateral, as in clams

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Nemerteans (Phylum Nemertea)

• Commonly called proboscis worms or ribbon worms
• The nemerteans unique proboscis
• Is used for defense and prey capture
• Is extended by a fluid-filled sac
• Nemerteans also have a closed circulatory system
• In which the blood is contained in vessels
  distinct from fluid in the body cavity

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Molluscs (Phylum Mollusca)

• Phylum Mollusca Includes snails and slugs,
  oysters and clams, and octopuses and squids
• Mollusc characteristics
• Body plan muscular foot, visceral mass, and a
  mantle
• Mantle is a fold of tissue that drapes over the
  visceral mass and secretes the shell.
• 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
• 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

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Mollusc anatomy
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Classes of molluscs
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Chitons

• Class Polyplacophora is composed of the chitons
  (Oval-shaped marine animals encased in an armor
  of eight dorsal plates)

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Gastropods

• About three-quarters of all living species of
  molluscs belong to class Gastropoda

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Gastropods

• Gastropod characteristics
• Most 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
• The most distinctive characteristic of this class
  is a developmental process known as torsion,
  which causes the animals anus and mantle to end
  up above its head

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Bivalves (Molluscs of class Bivalvia)

• Include many species of clams, oysters, mussels,
  and scallops
• Have a shell divided into two halves

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Bivalves

• The mantle cavity of a bivalve contains gills
  that are used for feeding as well as gas exchange

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Clam locomotion
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Cephalopods

• Class Cephalopoda includes squids and octopuses
• Carnivores with beak-like jaws surrounded by
  tentacles of their modified foot

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Octopus

• Most octopuses creep along the sea floor in
  search of prey

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Squid

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

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• One small group of shelled cephalopods
• The nautiluses, survives today

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Annelids

• Annelids
• Segmented worms
• Have bodies composed of a series of fused rings
• 3 Classes Oligochaeta, Polychaeta, Hirudinea

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Classes of Annelida
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Oligochaetes

• Oligochaetes (class Oligochaeta)
• Are named for their relatively sparse chaetae
  (bristles made of chitin)
• Include the earthworms and a variety of aquatic
  species
• 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

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Earthworm anatomy
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Polychaetes

• Members of class Polychaeta possess paddlelike
  parapodia that function as gills and aid in
  locomotion

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Leeches

• Members of class Hirudinea are blood-sucking
  parasites, such as leeches

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Nematodes (roundworms)

• Nematodes are nonsegmented pseudocoelomates
  covered by a tough cuticle
• Among the most widespread of all animals,
  nematodes, or roundworms
• Are found in most aquatic habitats, in the soil,
  in moist tissues of plants, and in the body
  fluids and tissues of animals

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Nematode movie
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Nematodes

• The cylindrical bodies of nematodes are covered
  by a tough coat called a cuticle

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Nematodes

• Some species of nematodes are important parasites
  of plants and animals

Trichinella spiralis encysted in human muscle
tissue
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Arthropods

• Arthropods are segmented coelomates that have an
  exoskeleton and jointed appendages
• 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

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Arthropod Characteristics

• The diversity and success of arthropods
• Are largely related to their segmentation, hard
  exoskeleton, and jointed appendages
• 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
• The body of an arthropod is completely covered by
  the cuticle, an exoskeleton made of chitin
• When an arthropod grows it molts its exoskeleton
  in a process called ecdysis

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Segmentation

• Early arthropods, such as trilobites showed
  little variation from segment to segment
• As arthropods evolved the segments fused, and the
  appendages became more specialized
• The appendages of some living arthropods are
  modified for many different functions

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Subphyla of Arthropoda
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Cheliceriforms

• Named for clawlike feeding appendages called
  chelicerae
• Includes spiders, ticks, mites, scorpions, and
  horseshoe crabs
• Most of the marine cheliceriforms are extinct
• But some species survive today, including the
  horseshoe crabs

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Cheliceriforms

• Most modern cheliceriforms are arachnids
• A group that includes spiders, scorpions, ticks,
  and mites

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Arachnids

• Arachnids have an abdomen and a cephalothorax
• Which has six pairs of appendages, the most
  anterior of which are the chelicerae. (4 pairs of
  walking legs)

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Myriapods

• Subphylum Myriapoda
• Includes millipedes and centipedes
• Millipedes, class Diplopoda
• Have a large number of legs
• Each trunk segment has two pairs of legs
• Centipedes, class Chilopoda
• Are carnivores with jaw-like mandibles
• Have one pair of legs per trunk segment

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Insects

• Subphylum Hexapoda, insects and their relatives
• Are more species-rich than all other forms of
  life combined
• Live in almost every terrestrial habitat and in
  fresh water
• The internal anatomy of an insect includes
  several complex organ systems

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Insect anatomy
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Insects

• 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

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Metamorphosis

• 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 (example grasshoppers)
• Insects with complete metamorphosis have larval
  stages specialized for eating and growing that
  are known by such names as maggot, grub, or
  caterpillar
• The larval stage looks entirely different from
  the adult stage
• Metamorphosis from the larval stage to the adult
  stage occurs during a pupal stage

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Metamorphosis
movie
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26 Orders of Insects
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26 Orders of Insects
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Crustaceans

• While arachnids and insects thrive on land
• Crustaceans, for the most part, have remained in
  marine and freshwater environments
• Crustaceans, subphylum Crustacea
• Typically have biramous (branched) appendages
  that are extensively specialized for feeding and
  locomotion

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Decapods

• Decapods are all relatively large crustaceans
• And include lobsters, crabs, crayfish, and shrimp

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Decapod movie
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Planktonic crustaceans

• Planktonic crustaceans include many species of
  copepods
• Which are among the most numerous of all animals

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Barnacles

• Barnacles are a group of mostly sessile
  crustaceans whose cuticle is hardened into a shell

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Deuterostomes

• Echinoderms and chordates are deuterostomes
• Chordates and echinoderms share the
  characteristics of deuterostomes
• Radial cleavage
• Formation of the mouth at the end of the embryo
  opposite the blastopore

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Echinoderms

• Echinoderm characteristics
• Sea stars and most other echinoderms are
  slow-moving or sessile marine animals
• A thin, bumpy or spiny skin covers an
  endoskeleton of hard calcareous plates
• Unique to echinoderms is a water vascular system
• network of hydraulic canals branching into tube
  feet that function in locomotion, feeding, and
  gas exchange

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Echinoderm movie
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Echinoderm anatomy
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Echinoderm classes
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Sea Stars

• Sea stars, class Asteroidea
• Have multiple arms radiating from a central disk
• The undersurfaces of the arms bear tube feet,
  each of which can act like a suction disk

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Brittle Stars

• Brittle stars have a distinct central disk and
  long, flexible arms

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Sea Urchins and Sand Dollars

• Sea urchins and sand dollars have no arms, but
  they do have five rows of tube feet that function
  in movement

Sand Dollar
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Sea Lilies and Feather Stars

• Sea lilies live attached to the substrate by a
  stalk
• Feather stars
• Crawl about using their long, flexible arms

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Sea Cucumbers

• Sea cucumbers do not look much like other
  echinoderms
• They lack spines, and their endoskeleton is much
  reduced

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Sea Daisies

• Sea daisies were discovered in 1986
• And only two species are known

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Chordates (Phylum Chordata)

• Chordates
• Two subphyla of invertebrates as well as the
  hagfishes and the vertebrates
• Share many features of embryonic development with
  echinoderms

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Review of Animal Phyla