marine bio

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🧪 Marine Biology Study Guide




📌 1. Introduction to Marine Invertebrates




🔹 Major Groups:



  • Vertebrates: Have a backbone.

  • Invertebrates: No backbone; majority of marine life.






🪸 2. Porifera (Sponges)



  • Sessile (non-moving), filter feeders.

  • Multicellular but no true tissues or organs.

  • Have pores (ostia) through which water flows.

  • Skeleton made of spicules (silica or calcium carbonate).

  • Asexual reproduction: Budding.

  • Sexual reproduction: Hermaphroditic (can produce both eggs and sperm).






🥩 3. Cnidaria (Jellyfish, Corals, Anemones)



  • Radial symmetry.

  • Have stinging cells (cnidocytes).

  • Two body forms: Polyp (sessile) and Medusa (free-swimming).

  • Digestive system: Incomplete (one opening).

  • Classes include:

    • Hydrozoa (Hydras)

    • Scyphozoa (Jellyfish)

    • Anthozoa (Corals, Anemones)







🐚 4. Mollusks



  • Soft-bodied with a hard shell (in many).

  • Bilateral symmetry.

  • True coelom.

  • Complete digestive system.

  • Classes:

    • Gastropoda: Snails, slugs

    • Bivalvia: Clams, oysters, mussels

    • Cephalopoda: Octopus, squid – have advanced nervous systems and tentacles.







🦐 5. Arthropods (Crustaceans)



  • Jointed appendages, segmented body, exoskeleton.

  • Must molt to grow (ecdysis).

  • Bilateral symmetry.

  • Classes:

    • Crustacea: Crabs, lobsters, shrimp


  • Open circulatory system.

  • Compound eyes and well-developed sensory systems.






🐟 6. Fish Overview




🔹 3 Main Types:



  1. Agnatha – Jawless fish (e.g. lampreys, hagfish)

  2. Chondrichthyes – Cartilaginous fish (e.g. sharks, rays)

  3. Osteichthyes – Bony fish




🔹 Key Features:



  • Fins, gills, scales, lateral line system

  • Swim bladder (in bony fish) for buoyancy

  • Most have a two-chambered heart

  • External fertilization in many species






🧠 7. Additional Notes



  • Many marine organisms are filter feeders, predators, or detritivores.

  • Bioluminescence in some species for defense, mating, or hunting.

  • Sessile = attached and non-moving (e.g. corals, sponges)

  • Most marine invertebrates exhibit radial or bilateral symmetry.