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• Marine Worms


  • Elongated bodies
  • Lack external skeleton
  • Gain support from fluid in body compartments (hydrostatic skeleton)
• Platyhelminthes (flatworms)


  • Show bilateral symmetry with head and posterior end
  • Have eye spots that allow them to sense differences in light intensity
  • Some are free-living while some are parasitic
• Platyhelminthes


  • Turbellarians (free-living carnivores)
  • Flukes (trematodes, largest group of flatworms with 6,000 species, are parasitic)
  • Tapeworms (cestodes, parasitic flatworms, live in the digestive tract of fish)
• Nemertea (Ribbon worms)


  • Have complete digestive tract (with mouth and anus)
  • Have circulatory system
  • Have proboscis
  • Common in shallow temperate waters
  • Some are nocturnal
  • Longest invertebrate (100ft.)
• Phylum Nematoda (Roundworms)


  • Adapted to live in sediments or the tissues of other organisms
  • Body is cylindrical and elongated, tapered in both ends
  • Can be scavengers, parasites (mostly), predators, or eat algae and bacteria
• Annelids (Segmented worms)


  • Divided internally and externally into repeated segments
  • Body wall has longitudinal and circular muscles for swimming, crawling, and burrowing
  • Skin often has bristles (setae) that can be used for locomotion, digging, or protection
  • Have complete digestive tract (with mouth and anus)
• Annelids


  • Polychaetes (each body segment has a pair of flattened extensions, or parapodia)
  • Beard worms or pogonophorans
  • Oligochaetes (small worms found in mud and sand)
  • Leeches (highly specialized annelids, distinguished by a sucker at each end and no parapodia)
• Sipuncula (Peanut worms)


  • Have small, unsegmented bodies with a coelom
  • Burrow in muddy bottom, rocks, and corals, or hide in empty shells
• Echiura (Echiurans)


  • Look like soft unsegmented sausages buried in the mud or in a coral
  • Similar to peanut worms in shape and size except having a non-retractable, spoon-like or forked proboscis
• Mollusks


  • Have a soft body enclosed in a calcium carbonate shell
  • Body is divided into two major parts: Head-Foot region and Visceral mass
  • Mantle is a thin layer of tissue that produces the shell (in some groups is used in locomotion and gas exchange)
  • All mollusks (except bivalves) have a radula
• Types of Mollusks


  • Gastropods (Class Gastropoda)
  • Bivalves (Class Bivalvia)
  • Cephalopods (Class Cephalopoda)
  • Chitons (Class Polyplacophora)
  • Scaphopods (Class Scaphopoda)
• Gastropods (Class Gastropoda)


  • Largest and most common group of mollusks
  • Have a coiled mass of vital organs enclosed in a dorsal shell
  • Shell rests on a ventral creeping foot and is usually coiled
• Nudibranchs (sea slugs)


  • Gastropods that have lost their shell
  • Most are colorful marine organisms, their bright coloration can be an indication of toxicity
  • Many have cerata on their back
  • Some will feed on cnidarians and retain their nematocysts as protection for themselves
• Nudibranchs


  • Phidiana crassicornis
• Bivalves (Class Bivalvia)


  • Have two (2) valves (shells) attached dorsally by ligaments
  • Body is laterally compressed
  • The valves are closed by adductor muscles and opened as the muscles relax and the weight of the valves pulls it apart
  • No head or radula
  • Their foot is located ventrally and functions in burrowing and locomotion
  • Umbo is the oldest part of a shell
• Cephalopods (Class Cephalopoda)


  • The foot is modified into a head-like structure and have a ring of tentacles that projects from the anterior end to the head
  • Tentacles are used to capture prey, for defense, reproduction, and locomotion
  • Lack shell or have a small internal shell
  • Most can move by jet propulsion
• Cephalopods


  • Hapalochlaena (Blue-ringed octopus)
  • Enteroctopus dofleini (Pacific giant octopus)
  • Illex illecebrosus and Loligo opalescens (both are squids)
• Nautiloid Cephalopods


  • Have a large coiled shell with multiple chambers filled with gas which can regulate buoyancy
  • Have 60 to 90 tentacles
• Coleoid Cephalopods


  • Includes squids, octopus, and cuttlefish
• Chitons (Class Polyplacophora)


  • Have flattened body covered by eight calcareous plates held together by a girdle
  • Common in intertidal zones where they can attach to rocks and scrape off algae
• Chitons


  • Tonicella lineata
• Scaphopods (Class Scaphopoda)


  • Have an elongated shell that's open at the top and tapered like an elephant tusk
  • Lives in sandy and muddy bottoms
• Molluscan gut


  Has a separate mouth and anus
• Digestive gland


  Releases digestive enzymes, which break down food into simpler particles
• Radula


  Rasping structure that removes minute algae from surfaces or cuts through large seaweed
• Molluscan digestive system


  • Can efficiently process large amount of hard-to-digest plant material
  • Involves extracellular digestion in the gut cavity and intracellular digestion in the digestive glands
• Gastropod proboscis


  Where the mouth and radula is found
• Bivalve feeding


  Ingest food particles that are filtered and sorted out by the cilia on the gills
• Crystalline style


  Enzyme secreting rod in the stomach that continually rotates the food to help in its digestion
• All Cephalopods are carnivorous that have to digest large prey
• Nervous System and Behavior

  • Gastropods and Bivalves have several sets of ganglia or "local brain"
  • Cephalopods have the most complex nervous system compared to all invertebrates
  • The strikingly complex eyes of cephalopods reflect the development of their nervous system
• Reproduction and Life History

  • Most molluscs have separate sexes, but some species are hermaphrodites
  • In bivalves, chitons, tusk shells, and some gastropods, sperm and eggs are released into the water and fertilization is external
  • Fertilization is internal in cephalopods and most gastropods
  • Cephalopods use a modified arm to transfer the spermatophore to the female
  • Some molluscs have a trochophore larva like polychaetes
  • The trochophore usually develops into a veliger, a planktonic larvae that has a tiny shell
  • In many gastropods, part or all of development takes place within strings or capsules of eggs
  • Cephalopods lack larvae, and the young develop from large, yolk-filled eggs
  • Female octopuses protect their eggs, which are often attached to crevices or holes in rocks, until they hatch. The female usually dies afterward because she eats little or nothing while guarding the eggs
• Early in the Cambrian period, invertebrates inhabited the Earth's ocean. In order to protect and survive from their prey, animals had protective spikes or armor as well as modified body parts that enabled them to filter and capture food from water.
• Although lacking armor and appendages, this ancient species was closely related to one of the most successful groups of animals ever to swim, walk, slither, or fly: the vertebrates, which derive their name from vertebrae, the series of bones that make up the vertebral column, or backbone.
• For more than 150 million years, vertebrates were restricted to the oceans, but about 365 million years ago, the evolution of limbs in one lineage of vertebrates set the stage for these vertebrates to colonize land. Over time, as the descendants of these early colonists adapted to life on land, they gave rise to the three groups of terrestrial vertebrates alive today: amphibians, reptiles (including birds), and mammals.
• Hemichordates


  Phylum that shares the same basic developmental characteristics of chordates and echinoderms. Some hemichordates also have a larva similar to that of some echinoderms.
• Chordates


  Phylum divided into three major groups, or subphyla. Two of these lack a backbone and are discussed here with the invertebrates. These invertebrate chordates are collectively called protochordates.
• Types of Subphylum


  • Urochordata
  • Cephalochordata
  • Vertebrata
• This phylogenetic hypotheses shows the major clades of chordates in relation to the other main deuterostome clade, Echinodermata. Derived characters are listed for selected clades, for example, only gnathostomes have vertebrates; the notochord is surrounded or replaced by a series of articulating bones, the backbone, or vertebral column.
• Vertebrates (subphylum Vertebrata)


  • Share four fundamental characteristics of the phylum Chordata with protochordates
  • Differ from these other chordates in having a backbone, also called the vertebral column or spine, which is a dorsal row of hollow skeletal elements, usually bone, called vertebrae
  • The vertebrae enclose and protect the nerve cord, also called the spinal cord, which ends in a brain that is protected by a skull made of cartilage or bone
  • Characterized by a bilaterally symmetrical body and the presence of an endoskeleton