Return to Marine Biololgy
Chapter 6

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

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

Three Common Groups of Cnidarians:
  • 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."
  • The larger, true, jellyfish
  • The medusa is the dominant stage in most
  • Swim with rhythmic contractions
  • 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)

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

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

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

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

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

Phoronids – worm-like and build tubes partially made of sand

Brachiopods – have a top and bottom shell, but are very different from clams
Many are found in the fossil record.

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

Snails, nudibranchs and sea hares




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

  • 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
  • Ten legs
  • Claws
  • Carapace that encloses the gills
The large nets used to catch shrimp often kill many other kinds of animals