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INVERTEBRATES - DOC

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									INVERTEBRATES

No backbone, so not vertebrates
 of about 30 animal phyla, only one contains vertebrates (and some chordates are
   inverts!)
 97% of all species are vertebrates (40,000 verts. vs. about 1.3 million inverts)
 85% of all species are arthropods (mostly insects)
 2 most successful marine phyla are arthropods and molluscs (over 90,000 species
   combined)
 about 40,000 species are marine crustaceans (comparable to total number of verts.)
 around 12,000 species of nematodes - could form living layer to planet

Taxonomic classification by morphology:
 Acoelomates - porifera, cnidaria, ctenophores, platyhelminthes (flatworms/flukes)
 Pseudocoelomates - Cavity between endoderm and mesoderm
    nematodes
 Coelomates (cavity within mesoderm)
    Protostomes (just know examples and that it is based on embryological
      differences)
           coelom forms from split in mesoderm,
           spiral cleavage during early development
           blastopore becomes mouth
       Annelids and other worm phyla
       Bryozoa, brachiopoda, etc.
       Mollusca and Arthropoda
    Deuterostomes (same)
           coelom forms from pouching of endoderm, forming mesoderm with an
              already open center
           radial cleavage during early development
           blastopore becomes anus
       Echinoderms
       Chordates and hemichordates

Other classification tools:
 Segmentation (most obvious in annelids, arthropods, and some molluscs)
 Symmetry (asymmetrical, radial, bilateral, pentamerous or pentaradial)

Phyla review
READ YOUR BOOK - presented differently than I will, and I think you need it BOTH
WAYS
 Porifera
 Cnidaria
    Cl. Hydrozoa (hydroids and siphonophores)
    Cl. Scyphozoa (jellyfish)
    Cl. Anthozoa (corals and anemones)
   Ctenophores
   Worms
     Platyhelminthes (flatworms)
        Cl. Turbellarians
        Cl. Flukes (trematodes) and cestodes (tapeworms) - parasites
     Nematoda (roundworms)
     Nemertea (ribbon worms)
     Sipuncula (peanut worms)
     Echiura
     Pogonophorans (beard worms)
     Annelida
        Cl. Polychaeta (most marine segmented worms)
        Cl. Oligochaeta (mostly terrestrial - earthworms)
        Cl. Hirudinea (leeches)
   Chaetognatha (arrow worms)
   Lophophorates
     Bryozoa ("moss" animals)
     Brachiopoda
     Phoronids
   Obscure Meiofauna groups
     Gnathostomulida
     Gastrotricha
     Nematomorpha
     Kinorhyncha
     Loricifera
   Mollusca
     Cl. Monoplacophora
     Cl. Polyplacophora (chitons)
     Cl. Scaphopoda (tusk shells)
     Cl. Gastropoda (snails and slugs)
     Cl. Bivalvia (bivalves)
     Cl. Cephalopoda (octopi and squid)
   Arthropoda
     Subphylum Chelicerata (includes spiders)
        Cl. Merostomata (horseshoe crabs)
        Cl. Pycnogonida (sea spiders)
     Subphylum Crustacea
        Cl. Copepoda
        Cl. Cirripedia (barnacles)
        Cl. Malacostraca (many orders, I'll just name some major ones)
            Or. Stomatopoda (mantis shrimps)
            Or. Isopoda
            Or. Amphipoda
            Or. Euphausiacea (krill)
              Or. Decapoda (many suborders and families, includes shrimps, crabs,
               lobsters, mole crabs…)
   Echinodermata
     Cl. Crinoidea (crinoids, sea lillies)
     Cl. Stelleroidea (sea stars)
     Cl. Ophiuroidea (brittle stars) (sometimes sea stars and brittle stars are both
       classified as subclasses under the class Asteroidea)
     Cl. Echinoidea (urchins)
     Cl. Holothuroidea (sea cucumbers)
   Hemichordata (acorn worms)
   Chordata
     Subphylum Urochordata (tunicates, including sea squirts, salps, larvaceans)
     Subphylum Cephalochordata (lancelets)
     Subphylum Vertebrata



Invertebrate "Themes"



Structural Support:

For protection and locomotion:



Shells (CaCO3):

   Molluscs, corals, brachiopods, sponge spicules (silica also), echinoderms, some
    annelid tubes
   More complex than simply inorganic calcium carbonate:
     Various forms and even layers (mother of pearl, ….)
     Different crystal structures and various combinations of proteins and
       polysaccharides (structural carbohydrates)
     Periostracum - outer proteinaceous layer for shell protection and watertight seal



Exoskeletons (chitin):

   Crustaceans - Primarily polysaccharide, bound with proteins and inorganic salts
    (mostly CaCO3)
     When put that way, not so different from seashells after all!
   Insects - less calcium carbonate and more sclerotin protein in chitin
Internal skeletons

   Squid pen - actually more chitinous than carbonate
   Cuttlefish cuttle - chalky calcium carbonate porous rod - change air content for
    buoyancy (much like nautilus)



"Naked" species

   free-living forms not so defenseless
     still toughened outer skin ("cuticle") (i.e. free-living polychaete worm)
     much collagen, keratin, sclerotin (fibrous proteins)
   or, abandon cuticle, but borrow a defense:
     tube worms, hermit crabs



Growth

   Shells - keep adding on bigger sections
   Cuticles - limited stretching, but can add new segments
   Corals - don't grow, bud!
   Crustaceans (and nematodes) - molt (= "ecdysis")
     In response to growth and environmental cues
     Cuticle under shell (epidermis, or hypodermis for crustaceans), secretes pro-
       enzyme
     Epidermis seperates from cuticle, secretes new thin cuticle beneath old one
     Old cuticle "digested" by enzymes (salts reabsorbed)
     Old shell splits, new one emerges (soft)
     Body absorbs water and swells (about 1/3 bigger in crabs) and then hardens
     Rusty vs. ivory crabs, red-line peelers….



Locomotion:

Mode of locomotion is related to size of organism and necessary speed



Ciliary action:
      Common in protists, but also in some larger inverts
      Hair-like projections imbedded in cell membrane
          o Same structure as flagella, only shorter and more numerous
      Long rows of breaststrokers
          o Effective and recovery stroke, produce rhythmic sections of beating cilia
          o Used for locomotion as well as to establish filter feeding currents
      Ctenophores
          o 8 rows of cilia or “combs”
          o spectrum of shimmering color as cilia beats
      Turbellarians (flatworms)
          o Use cilia to swim and glide on surface
          o Mucus provides traction and glide



Polychaetes – parapodia and setae

      Analogous to ciliary action, only bigger scale (see diagram)
      Quite different than earthworm locomotion
      Useful for tube worms also



Cnidaria – pulsating

      Band of muscle fibers contract against gelatinous bell and its water volume
      When relax, elastic mesoglea (gelatinous inner layer) springs back



Echinoderms – the water vascular system

      Example: Starfish
      System of canals with one connection to the outside (Madreporite) and ending in
       tube feet at the other end (see diagram)
      Filled basically with seawater, but with small amounts of protein and higher K+
       content
      Tube foot has muscles and ends in a sucker
      Movement:
           o bulb (ampulla) associated with each tube foot (podium) compresses, which
               elongates the tube foot.
           o Sucker secretes sticky mucus for adhesion, and tube foot sucker “sucks”
               on as bulb expands
           o Muscles in tube foot allow it to bend and move
           o To release, another chemical breaks down the sticky secretion
           o Waves of tube feet movement move the animal
Crustaceans – walking and swimming

      No rotational joints – must have joints in alternate planes for full range of
       movement
      Many swim – pleopods (abdominal swimming appendages)
          o even antennae for some small species (copepods)



Molluscs – the versatile muscular foot

      Digging (Bivalves)
           o Anchor or expand – hydrostatic muscular action, swollen with blood
      Gliding
           o Contractile waves of entire gastropod (and close relatives) foot
           o Mucus for traction and glide, just as with turbellarians
      Clawing along – conch shells, use operculum as a piton
      Swimming
           o Pteropods with foot modified into wings, pelagic gastropods undulate
      Jet propulsion
           o Cephalopods
                   Take in water under mantle cavity, then seal off mantle lip with
                      cartilaginous valves around head
                   Expel water via siphon – directed forward or back
           o Scallops – open and close shell to jet propel around bottom



Feeding:

Filter feeders/suspension feeders

      Sponges
          o System of water canals around central atrium (various complexity)
          o Flagellated Choanocytes (collar cells) set up water currents, in through
              porocytes, out through osculum
          o Food particles engulfed (phagocytosis) by amoeboid cells, which move
              around within sponge (no true “tissue”), digest, and release wastes
      Tunicates and salps
          o Inhalent (buccal) and exhalent (atrial) siphons
          o Water current established by cilia
          o Filter through mucus net of pharyngeal basket
          o Mucus conveyor belt ever moving toward mouth at bottom
      Tube worms (Feather dusters, spaghetti worms, U-shaped tubes, etc.)
          o Palps modified for elaborate feeding appendages, or extra tentacles
          o Feathers (radioles) lined with cilia/mucus – establish currents and
              transport materials to mouth
          o Tentacles – creep along with cilia – retract and “wipe” tentacles on mouth
      Bryozoa
          o Lophophore (u-shaped, so bilaterally symmetrical)
          o Ciliary action establishes currents and moves particles toward mouth
      Cucumbers and crinoids (also, basket stars)
          o Some sea cucumbers are filter feeders
          o Particles collect on sticky papillae on surface of tentacles
          o When tentacles are full, brought to mouth, stuck in, and slurped clean
          o Similar plan for crinoids
      Bivalves
          o Modified gills – much larger than required for oxygen exchange
          o Filter out particles, and cilia/mucus moves them toward mouth
                   Size-selective
          o If too clogged up, will eject unwanted material as “pseudofaeces”
      Barnacles
          o Filter basket is actually jointed arthropod legs (“Cirri”)
          o Open scutes (plates), wave particles in and into the mouth
          o Notice – an arthropod that secretes a calcium carbonate shelter
      Crustacean zooplankton (copepods, etc.)
          o Establish feeding currents with multiple appendages
      Lancelets (Chordata, subphylum hemicordata)
          o Benthic suspension feeders (pharyngeal gill slits)

Deposit Feeders

      Worms
      Cucumbers
      Many infauna

Grazers

      Gastropods
      urchins

Predators (hunters, particulate feeders) / Scavengers

      Cnidaria (nematocysts) – all classes of cnidaria
      Ctenophores (??)
      Many zooplankton (or filter feed)
      Crustaceans
          o Decapods
                   Chelipeds (chelae if big) catch/pick up food, passed to maxillipeds
                     (typically 3 pair) which work with maxillae (typically 3 pair) and
                        mandibles (hold food in place) to manipulate and shred food for
                        eating
                     All are good scavengers
                     Dimorphic chelipeds (crushing claw and cutting claw) usually =
                        gastropod or bivalve specialist, but will eat anything, catch small
                        fish, etc.
                     Attack predators – mantis shrimp, snapping shrimp
           o Particulate feeders – caprellid amphipods, amphipods/isopods, etc. (some
               filter feed, too)
      Starfish
           o Evert stomach and digest prey in place, then slurp up the “soup”
           o Eat corals, bivalves, urchins, etc…
      Cephalopods
           o Tentacles and arms – just suckers in octopi, but squid have stalked suckers
               sometimes with hooks and usually with toothed ridges
           o Beaks in addition to radula, octopi inject poison
           o Squid eat fish, octopi eat decapods, gastropods, bivalves, fish…
           o Giant squids are largest invertebrate predators
      Gastropods
           o Drillers - moon snails, oyster
           o drills, etc. (queen conch fishermen use similar technique with a hammer
               and knife)
           o Pryers - whelks, tulip snails, etc, use shell and operculum to pry open
               bivalves
           o Poison darts - cone shells
           o Many nudibranchs feed on cnidarians and encorporate nematocysts (some
               ctenophores do that, too…)



Defense:

      Poisons and spines
          o Nudibranchs (as mentioned above)
          o Bristle worms (painful silica spines + toxin)
          o Urchins – tube feet and toxin-bearing pedicellaria, in addition to spines
          o some bryozoa have toxins
          o Feeding toxins also good for defense (cnidaria, octopi, cone shells…)
      Decoys and diversions
          o Holothurians (sea cucumbers)
                  Evisceration – expel respiratory trees, digestive tract, gonads (then
                     regenerate from remnant tissues)
                  Some species can eject sticky white threads (Cuvierian tubules)
                     with a toxin (holothurin) – immobilizes small crabs, lobsters, fish
          o Sacrifice a limb – starfish, crabs (will regenerate for both, but slow)
          o Ink ejection – cephalopods (just visual? bioluminescent in deep sea)
      Camaflouge
          o Fixed color for background (slow change of color)
          o Dramatic rapid color change – cephalopods
                  Chromatophores under nervous control (rapid change, even used
                     for communication)
                  Octopus skin even assumes texture of surroundings
      The obvious stuff:
          o Shells and exoskeletons
          o Stay in shelter (nocturnal activity increases – reef “haloes”)
          o Run away – essentially covered under locomotion (swim, run, dig, hop…)

Symbiosis:

      Generally related to feeding or defense or dispersal/movement
      3 types: mutualism, commensalism, parasitism (under some classifications,
       mutualism=symbiosis)
      Parasitism
        easier for larvae to spread in marine environment (don’t need host)
        examples:
           o Barnacles
                   on whales/turtles (almost commensal?)
                   “Infectious” barnacles on crabs, corals, echinoderms – only
                      recognized by larvae, adults look like fungal infection more than a
                      barnacle – cause so much stress, crabs don’t grow or molt
           o Copepods – very different looking, attach to fish gills and tissues
                   Some endoparasites live inside polychaetes, bivalves,
                      echinoderms, salps…
           o Gill louse – parasitic amphipods
           o Internal parasites – protists, nematodes, flukes, cestodes…
      Commensalism:
        Examples:
           o Juvenile fish among jellyfish tentacles
           o Crabs riding on top of jellyfish bells
           o Anemone fish (mutualism?)
           o Worms living on/associated with clams, gastropods, hermit crabs, shrimps,
               echinoderms, crustaceans…
           o Worms/crabs/shrimp, etc. living in sponges, tunicates, bivalves, worm
               tubes…
           o Venus flower basket and shrimp
           o Pea crabs in oysters (females don’t have a hard exoskeleton)
           o Pearlfish in sea cucumbers
      Mutualism
        Examples:
           o Anemone fish (commensal?)
           o Cleaning stations (shrimp and fish)
           o Zooxanthellae
                        With corals
                             94-98% of all organic C produced passes into host cells,
                                mostly as glycerol
                             facilitiate CaCO3 deposition (3 times faster during daylight)
                        With other cnidaria (Cassiopeia, the upside down jellyfish), giant
                         clams, various gastropods



Sensory abilities:

      Radial nervous system (nerve net in cnidaria) in cindaria and echinoderms
      eventually getting more complicated, compartmentalized, and bilateral as move
       through various worm phyla, developing more complicated ganglia and
       eventually “brains”
      Primitive sensory organs in even most primitive cnidaria and on up
           o Ocelli – light-detecting organs (not image forming)
           o Statocysts – orientation organs (usually calcium sulfate crystals knocking
              against sensory hairs)
      Eyes
           o of a ophiuroid (brittle star)
           o Some polychaete eyes start to have crystalline lens (image forming, but
              primitive)
           o Arthropod compound eyes
                   in crustaceans can only focus up to 20 cm away, but advantage
                      with up to 270º vision.
           o Eyes on bivalves (primitive ocelli or blue eyes with tepetum on scallops)
              and gastropods (even a lens and retina in murexes)
      Chemo and mechanoreceptors often concentrated near head (antennae, sensory
       hairs…), but can be all over.
           o Underappreciated senses due to our human bias
      Cepahlopods
           o very advance CNS (encephalization)
           o eye like vertebrate eye (convergent evolution)
           o giant squid axons get wider as move away from cell body, to deliver
              impulse at a distance at same time as close – produce simultaneous
              contraction of mantle muscle for rapid movement
           o nervous control of coloration.



Reproduction:

Asexual (one alternative, never the only choice for inverts)

      Fragmentation
          o Sponges – pieces can reassemble
          o Starfish/brittlestars/sea cucumbers
                   Stars – break off an arm with part of central disc, regenerate
                   Cucumbers – split and regrow either head or tail
      Budding
          o Colonial tunicates
                   Ex./ constellation tunicate – star-shaped, multiple individuals
                      sharing common excurrent siphon
          o Anthozoans (corals and anemones)
                   Pedal laceration (leave a piece behind which grows into new
                      polyp)
                   Pinch off disc wall – new piece grows out of base of old
          o Hydroids and scyphozoans (jellyfish)
                   Alternate sessile poly and pelagic medusa (or hydromedusa) stage
                           Ciliated planula larval stage produced by sexual
                               reproduction, will settle and grow into polyp stage
                           Normall, polyp stage is dominant for hydroids and medusa
                               stage is dominant for jellyfish – some species skip this
                               alternation, but most don’t
                   Some colonial hydroids have true division of labor:
                           Siphonophores (Portuguese man-of-war) – gonozooids
                               (reproductive), gastrozooids (digestive), dactylozooids
                               (stinging)
      Asexual fission (splitting)
          o Coral and anemones – split laterally down the middle and replicate
          o Brain corals keep growing this way, elongating the mouth rather than
             defining a new one, forming long winding convolutions of the “brain”



Sexual reproduction

      External fertilizers
          o General pattern
                    Disperse eggs and sperm into environment via siphons, osculums,
                       mantles, anus, mouth…
                    In may species, sperm taken in via filter-feeding currents and
                       “external fertilization” is technically internal, but not copulation
                       event
          o Anthozoans – reproduce sexually as well as asexually (they do everything,
              it seems)
                    Release eggs and sperm into water, filling water column
                    Timed for night release over a few consecutive nights each year
                    Pheromones and photoperiod help synchronize release
          o Other external fertilizers: sponges, tunicates, bivalves, most echinoderms,
              bryozoans…
       o Hermaphroditism
             Includes most inverts we have mentioned here
             Usually simultaneous hermaphrodites with inverts
       o Polychaete variations on theme of egg and sperm release:
             Some fairly typical – released through gonoducts or anus into
                water
             Some hermaphroditic fan worms produce eggs in anterior
                segments and sperm in posterior segments
             Some species become pelagic at sexual maturation – when reach
                surface, body wall ruptures to release eggs and sperm, killing adult
             Some species (including many Nereids and Eunicids) produce an
                “epitoke”
                     Posterior segments (often majority of worm) filled with
                       gametes, break off and writhe to surface at night where
                       they release gametes (often bursting apart)



   Internal fertilizers (copulations)
        o Flatworms
                 Simultaneous hermaphrodites
                 Generall reciprocal copulations – both inject their own penis into
                     the other
                 Penis rammed through body wall, injecting sperm into interstitial
                     cells
                 Eggs develop directly into young worms (no larval stage)
        o Gastropods
                 Many hermaphrodites, but not simultaneous generally
                 Males have penis, deposit sperm
                 Slipper shells – interesting variation and common local species
                          Protandrous hermaphrodites (male first, then female)
                          Stack of mating groups (Crepidula fornicata)
                          Largest on bottom (female), but if removed, next biggest
                             male will change sex
                          Generally a size advantage in terms of egg production
                 Once eggs fertilized, females lay eggs in large masses
                          Jelly gland secretes eggs in gelatinous mass
                          In some species, eggs get a chitinous leathery covering
                             (whelks, tulip snails…)
        o Cephalopods
                 Sperm bundled in packets called “spermatophores”
                 Deposited by specialized arm in the mantle of female
                 Various coloration patterns and behaviors for courtship (squid in
                     large aggregations, octopi and cuttlefish not)
                 Females lay benthic eggs generally
                      Octopi and cuttlefish females guard and ventilate eggs, then
                       die once hatched
                     Exception: Argonaut (paper nautilus) is pelagic octopus,
                       spends entire life secreting paper nautilus shell as egg
                       chamber, then dies after hatching of young. Male Argonaut
                       is tiny an breaks off and leaves a partial of one are to
                       fertilize – once thought to be a species of headless worm.
                     Squid leave eggs on their own in flowery anemone-like
                       clusters, then die
             Eggs hatch as planktonic larval forms similar to adults
       o Crustaceans
             Pheromones advertise terminal molt of female – time to copulate
             When molt, males deposit spermatophores with pair of copulatory
                pleopods
                     Guarding behavior by male of soft female (“doublers”
                       among blue crabs)
             Some species release eggs directly into water but most familiar
                forms carry them on abdomen (“sponge”) until hatching, then
                become pelagic larvae
       o Barnacles
             Extend penis to neighbor (routinely >1 cm away)
                     Chemotactic larvae settle close together to allow this
             Brood eggs and release nauplii to plankton



   Brooding vs. pelagic larvae
        o Some species brood initial larval stages (numerous examples in most
           phyla)
        o Greater effort, fewer eggs, greater odds of survival, decreased dispersal
        o Most species opt for total planktonic stages
   Larvae and larval stages
        o Some larvae are common, distinctive, and well-known in the plankton:
        o Trochophore larvae of polychaetes, related worm phyla, and some
           molluscs
                Cilia girdle and apical tuft of cilia
        o Velliger of many molluscs (esp. bivalves and gastropods)
                Ciliated winged larvae, like a mini-pteropod
        o Various echinoderm forms (many varieties)
                Ex./ final stalked larval form of some starfish – starfish bends over
                   and breaks off and becomes fee-living
        o Crustacean nauplius – can have several stages each more complex than the
           next
                Exs./ barnicale nauplii, crab zoea and megalops,…
   Settlement of larvae
o Non-random – chemoreception, currents, tidal/diel timing, directed
  movements…
o Attachment to substrate for sessile species
      Ex./ metamorphosis of larval sea squirt:
            Tadpole-like larvae attaches
            Anterior region expands to make sea squirt (pharyngeal gill
                slits expand into pharyngeal basket)
            Notochord disappears

								
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