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Marine Invertebrates
Chapter 15
Kingdom Animalia
• Two types: Vertebrates and Invertebrates
Invertebrates
• More than 90% of all living and fossil animals are
invertebrates
• Soft bodies animals that lack a rigid internal
skeleton
– Most have hard outer covering
• 33 invertebrate phyla
Phylum Porifera
• Ex. Sponges
• Widely distributed
– Intertidal zone to abyss
• Most primitive true animals
• Found at all latitudes
Porifera Characteristics
• Lack true tissues and organs
– No digestive, circulatory, respiratory or nervous system
– Have digestive cells
– Excretion by diffusion
• Porus- “holes”
• Suspension or filter feeders
– Strain water for plankton and other small organic food
• Motile larvae but sessile adults
• Skeleton made up of spicules of calcium carbonate
or spongin
Porifera fun facts
• Come in different shapes
– Branching, vase-like and encrusting
• A large sponge can filter more than 400
gallons of water in 24 hours
Phylum Cnidaria
• Ex Corals, jellyfish
• Mostly carnivorous
• 2 layers of true tissue
– No circulatory, respiratory or excretory systems
• Radial symmetry
– Body parts radiate from center
• Tentacles bear stinging nematocysts
• Gastro vascular cavity
• 3 classes: Hydrozoa, Scyphozoa and Anthozoa
Cnidaria Interesting facts
• Digested food is absorbed by the cells,
indigestible bones are eliminated through the
mouth
• They have two layers of cells
– Inner: digestion and reproduction
– Outer: capturing prey and protection
• Two forms
– Medusa: swim by rhythmic contractions
– Polyps: attach to a substrate
Class Hydrozoa
• Spend most of their life as polyps
• Solitary or colonial
• Ex: Portuguese man-of-war
– Tentacles up to 165 ft long
– Venomous tentacles
Class Scyphozoa
• Spend life as medusa form
• Reproduce sexually
• Ex: Moon Jelly, Sea Wasp (most lethal jelly fish
in the world)
Class Anthozoa
• Colonial or solitary polyps
• Central body surrounded by tentacles
• Ex: Sea pen, Sea Fan, Sea anemone
Marine worms
• Bilateral symmetry- left and right are mirror
images
• Found on underside of rocks or sharing
burrows
• Some sensory tissue in the head
• 3 phylums
Phylum Platyhelminthes
Ex: Flat worms
• Simplest
• Most primitive with central nervous system
• Free living or parasitic
• Exchange gas and eliminate wastes through
cell diffussion
• 3 layers of tissues
– Endoderm, mesoderm and ectoderm
Phylum Nematoda
Ex: Round worms
• Unsegmented
• Flow through digestive system
• Very abundant
• Live in soft sediments or as parasites
Phylum Annelida
• Most advanced worms
• Bodies divided into segments or rings
– Metamerism- segments
• Each segments can have circulatory, excretory,
muscular, and reproductive systems
• Have 3 classes (we are only doing one!)
Phylum Annelida
• Class Polychaeta
– Many bristles
– Largest, most diverse
– Most important marine worms
– Brightly colored
Phylum Mollusca
• Soft- bodied
• Often have a hard calcified shell or internal
shell
• Have flow through digestive tract and well
developed nervous systems
• Have muscular foot and mantle
• Bilaterally symmetrical
• 3 classes
Class Bivalvia
Ex: Clams, oysters, and scallops
• Shell is hard, made up of calcium carbonate
• Soft bodied animal inside
• Two shells hinged together
• Wedge shaped foot
• Sessile as adults
• Burrow in mud or sand
Class Gastropoda
Ex: Snail, conch, sea slugs
• One shell or no shell (most have spiral shell)
– Animal adds to shell as it grows
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Use broad muscular foot in movement
Distinct head
Most are cross-fertilizing hermaphrodites
Can be predators, suspension feeders or
grazers
Gastropods
Class Cephalopoda
Ex: Squid, octopus
• Most highly evolved
• “head- foot”: head is attached to the single foot
• Foot is divided into tentacles
• Closed circulatory system, highly developed brain
and sense organs
• Move by creeping across the bottom, by
swimming with fins or squirting jets of water
• Catch prey with discs (suction cups) and tear or
bite flesh with horny beaks
• Squid can grow to large sizes (record=59 ft)
• Octopus and squid use ink to confuse
predators
– One produces sparkling luminous ink instead of
black ink
– Some can produce “ dummy” squid from ink
Phylum Arthropoda
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Exoskeleton made of chitin
Jointed appendages
Segmented body
Many undergo metamorphosis
Open circulatory system
Largest phylum
4 subphylums(we are covering 3)
Phylum Arthropoda continued
• 3 evolutionary advances
– Exoskeleton
• Strong, lightweight form- fitted external covering
– Striated muscle
• Quick, strong lightweight form of a muscle that makes
rapid movement and flight possible
– Articulation
• Ability to bend appendages at specific points (joints)
Fascinating facts of Arthropoda
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Cover the greatest variety of habitats
Most successful on Earth
Consume greatest quantity of food
Largest crustacean=king crab
– Can reach leg span of 12 feet
• Heaviest crustacean=lobster
– Can weigh up to 48lbs
Subphylum Trilobita
• Two furrows running from head to tail
• Each appendage divided into two branches- a
gill and a walking leg
• ALL are extinct
Subphylum Chelicerata
Ex: Horseshoe crab
• Most are terrestrial
• First pair of appendages specialize as feeding
structures
Subphylum Crustacea
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Ex: Crabs, barnacles, shrimp
Mostly aquatic
Most live in salt water
Two or three body segments and chewing
mouthparts
• Many have carapace that covers all or part of
the body
Phylum Echinodermata
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Live in salt water
Adults have radial symmetry
Endoskeleton
Tube feet
Water vascular system used in respiration,
excretion, feeding and locomotion
• 5 classes
Class Crinoidea
• Ex: Sea lily, feather star
Class Crinoidea
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Filter feeders
Feathery arms
Mouth and anus on upper surface of body disk
Some are sessile
Class Asteroidea
• Ex: Crown of thorns, sea star, sunstar
Class Asteroidea
• Star shaped
• Carnivorous bottom dwellers
• Mouth on lower surface
Class Ophiuroidea
• Ex: Brittle Star, Basket Star
Class Ophiuroidea
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Small body disk
Long, armored arms
Most have only 5 arms
Lack an anus
Most are filter feeders
Class Echinoidea
• Ex: Sea Urchin, Sand Dollar, Sea Biscuit
Class Echinoidea
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Lack arms
Body incased in rigid, box like covering
Covered with spines
Most are grazing herbivores
Class Holothuroidea
• Ex: Sea Cucumber
Class Holothuroidea
• Cylindrical body with feeding tentacles on one
end
• Lie on their side
• Mostly filter feeders
• Endoskeleton greatly reduced