Return to Marine Biololgy
Chapter 6
Invertebrates

Sponges / Poriferans
  • They have tiny pores instead of mouths
  • Most of their cells line a series of connected chambers and channels
  • They are composed of collar cells, pore cells, and wandering cells which can easily change type
  • Water is drawn into the pores and out the top of the sponge by flagella
  • Collar cells filter food from the water as it passes by.
  • Cells function independently and perform a variety of functions.
  • Spicules and spongin are use for support
http://www.ucmp.berkeley.edu/porifera/porifera.html

Cnidarians/Anemones, Jellyfish, Corals
  • Grouped together because many of the species have a particular type of sting-cell
  • Most have a polyp or sack like stage and a medusa or bell shaped stage.
  • They have not head, no skeleton, and no special organs for respiration or excretion
  • They have:
  • Nematocysts – stinging-cells that eject barbed threads tipped with poison
  • Radial symmetry, where similar body parts encircle a central axis
  • Mouths surround by tenticles
  • Mouth sides (oral surfaces) and sides away from the mouth (aboral surfaces)
  • Blind gut cavities
  • Body walls with two layers of cells
  • Nerve-nets – interconnected neurons lacking a brain http://faculty.washington.edu/chudler/invert.html
http://www.ucmp.berkeley.edu/cnidaria/cnidaria.html

Three Common Groups of Cnidarians:
Hydrozoans
  • Are the most diverse group
  • Some form feathery or bushy colonies
  • Some form drifting colonies
  • Some have specialized floats
  • Unlike true jellyfish they are composed of colonies of individuals, all specialized for various functions
  • Examples: hydra, fire corals, and the "Portuguese man-o'war."
http://www.ucmp.berkeley.edu/cnidaria/hydrozoa.html
Scyphozoans
  • The larger, true, jellyfish
  • The medusa is the dominant stage in most
  • Swim with rhythmic contractions
http://www.ucmp.berkeley.edu/cnidaria/scyphozoa.html
Anthozoans
  • Most lack a medusa stage
  • They exist as solitary or colonial polyps (corals)
  • Some have large muscular polyps (anemones)
  • Some have calcium carbonate skeletons (corals)
  • Some have branching protein skeletons (Sea fans and black corals)
  • Some form fleshy colonies (Soft corals, sea pens, and sea pansies)
http://www.ucmp.berkeley.edu/cnidaria/anthozoa.html

Flat Worms / Platyhelminthes
  • Simplest animals with three cell layers
  • bilaterally symmetrical – could be cut into two similar halves
  • Has a gut, but no anus (Food and wastes move through the same opening)
  • Gut may be branched, so it is close to more cells
  • Respires by diffusion, so a flat shape keeps a surface close to more cells
  • Brain is just a small group of nerve cells in the head
Trematoda, or flukes, are all parasitic (live in lungs and liver tissue)
The Cestoda, or tapeworms, are intestinal parasites in vertebrates
http://www.ucmp.berkeley.edu/platyhelminthes/platyhelminthes.html
http://www.biocrawler.com/encyclopedia/Flatworm__

Ribbon Worms / Nemerteans
  • Gut includes a mouth and anus
  • Blood transports nutrients and oxygen to tissues
  • Proboscis – long fleshy tube to entangle prey
  • Longest animal on earth
http://www.ucmp.berkeley.edu/nemertini/nemertini.html
http://www.biocrawler.com/encyclopedia/Nemertea

Roundworms / Nematodes
Live in sediments or are parasites
They have:
  • Cylindrical bodies with points on both ends
  • A mouth and anus
  • A gut that lies in a fluid filled body that transports nutrients
  • A hydrostatic skeleton made by layer of muscle that pushes and squeezes the fluid filled body aiding movement
http://www.ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html
http://www.biocrawler.com/encyclopedia/Roundworms

Segmented Worms / Annelids
They have:
  • A body consisting of a series of similar compartments
  • A guts that lies in a cavity called a coelom that passes all segments
  • A fluid filled coelom that a long with muscles in the body wall form a hydrostatic skeleton
  • A closed circulatory system with contractions in vessels moving blood
Some have extensions of the body wall that absorb oxygen – gills
Some have specializations to suck blood
http://www.ucmp.berkeley.edu/annelida/annelida.html
http://www.biocrawler.com/encyclopedia/Annelid


Lophophorates
Three groups of marine invertebrates
  • Bilateral filter feeders with a U-shaped gut
  • They have a unique feed structure called a lophophore.
  • Lophophore are a circular or coiled arrangement of ciliated tentacles.

Bryozoans – moss animals
http://www.sms.si.edu/IRLSpec/IntroBryozoa.htm
http://www.ucmp.berkeley.edu/bryozoa/bryozoamm.html
http://www.tolweb.org/Bryozoa
http://www.ucmp.berkeley.edu/bryozoa/bryozoa.html

Phoronids – worm-like and build tubes partially made of sand
http://www.ucmp.berkeley.edu/brachiopoda/phoronida.html
http://www.solaster-mb.org/mb/phoronida.htm

Brachiopods – have a top and bottom shell, but are very different from clams
Many are found in the fossil record.
http://en.wikipedia.org/wiki/Brachiopod
http://www.ucmp.berkeley.edu/brachiopoda/brachiopoda.html

Mollusks / Snails, sea slugs, clams, octopuses, and chitons
Features common to some species:
  • Shell secreted by a thin tissue layer
  • Muscular ventral foot
  • Head with eyes
  • Radula – a rasping tongue
  • Gills
  • Salivary and digestive glands
  • Both closed and open circulatory system

Gastropods
Snails, nudibranchs and sea hares
http://en.wikipedia.org/wiki/Nudibranch

Bivalves
http://en.wikipedia.org/wiki/Bivalves
http://www.solaster-mb.org/mb/bivalvia.htm

Cephalopods
http://www.tolweb.org/Cephalopoda
http://en.wikipedia.org/wiki/Cephalopod

Crustaceans

General characteristics:
  • Segmented bodies
  • Jointed legs
  • Chitinous exoskeleton
Special share characteristics of some:
  • Two pairs of antenna
  • Mandibles for chewing
  • A pair of appendages on each body segment
  • Teardrop-shaped larvae
  • Molting
  • Compound eyes
  • Small simple brains

Barnacles/ Class Cirripedia
  • Begin as free-swimming larvae
  • Cements its back to a suitable surface
  • Catches or filters food with its feet
  • Forms a calcium carbonate shell
  • Hermaphrodite

Copepods
  • Abundant in plankton and a major food for plankton feeders
  • Filter or capture food with mouthparts
  • Swim with antenna

Decapods and Krill__ / Malacostraca
Includes lobsters, crab, and shrimp
Characteristics:
  • Ten legs
  • Claws
  • Carapace that encloses the gills
The large nets used to catch shrimp often kill many other kinds of animals