MARS2014 Lecture Notes - Lecture 4: Arthropod Leg, Sooty Oystercatcher, Oceanic Dolphin
Unit 3: Marine Zoology
o What are the key invertebrate phyla on coral reefs?
▪ Porifera (sponges)
▪ Cnidaria (coral, jellyfish, anemones)
▪ Platyhelminthes (flatworms)
▪ Nemertea (ribbon worms)
▪ Annelida (polychaetes, marine worms)
▪ Sipuncula (peanut worms)
▪ Ectoprocta (bryozoans, lace colonies)
▪ Arthropods (crustaceans)
▪ Molluscs (bivalves, snails, nudibranchs, Cephalopoda)
▪ Echinodermata (sea stars, sea urchins, sea cucumbers)
▪ Hemichordata (acorn worms)
▪ Chordata (Urochordata, sea squirt)
o Porifera (sponges)
▪ What are their key characteristics?
• Multicellularity
• No true tissues
• No body symmetry, although some appear to have it
• Simple body plan
• Filter feeders (will filter large quantities in a day)
▪ What is their distribution and diversity?
• Ubiquitous (found everywhere)
➢ All latitudes, poles to tropics
➢ All depths, intertidal to abyss
➢ All habitats, reefs to barren sea floor
• Often the dominant animal despite simplicity
• On coral reefs, their abundance is second only to corals
▪ What is their body organisation?
• Organised at the cellular level
• Most are sessile, although some are capable of slow movement
• Generally asymmetrical
• Cells are in a loose aggregation around the water canal system
• No head end, mouth or gut
• No muscle or nerve cells
• Little distance cellular coordination
• They have cells with different functions (cellular specialisation),
although their dot futio together as a ohesie uit o
coordination)
▪ How do they feed and respire?
• Choanocytes (within spongocoel) use their flagella to create a
current and move water through the sponge
➢ They prevent water stagnation
➢ Draw in microscopic food particles
➢ Draw in high-oxygen water
➢ Remove waste water from cells
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▪ How do the choanocytes function?
• The ollar has stiky threads of uus hih trap food
• The food moves via ciliated movement (via hairs) into choanocyte
body
• Where it is taken up by phagocytosis in the cells
• Mobile amoebocytes take food particles and deliver the digested
nutrients around cells via diffusion
▪ What are the levels of sponge complexity, and what determines complexity?
• Asconoid (simplest and most ancient) → Syconoid → Leuconoid
(most complex, more choanocytes to prevent water stagnation in
the sponge)
• Complexity is related to size and the water flow pathway
▪ How do the water conditions affect the sponge formation?
• In calm waters, sponges are formed differently than in flowing
waters
• In calm waters they are vase-shaped and draw water in
• In flowing waters they are flattened to intercept the flow
▪ What are the different taxa of sponges and their complexities?
• Calcarea (made of CaCO3 spicules) have a range of complexity
• Demospongiae (protenaceous spongin fibres and siliceous spicules)
are quite complex
• Hexactinellida (have siliceous spicules) are quite complex and
fragile, made of glass
▪ What are their predators?
• Hawksbill turtles
• Angelfish, leatherjackets, wrasses
• Some molluscs (sea slugs, cowries)
▪ How are sponges important – ecologically, economically, medically and
phylogenetically?
• Ecologically
➢ Are encrusting organisms
➢ Smother other organisms
➢ Erode reef structures (as boring sponges)
➢ Build sediment
➢ Form habitat
• Economically
➢ Spongin skeleton used as bath sponges
➢ Encrust and foul ship hulls and industrial pipes, very
expensive
• Medically
➢ Produce biotoxins
➢ In drug development
• Phylogenetically
➢ Oldest multicellular animal
➢ Former reef builder
▪ What are Hexactinellid sponge reefs?
• Glass sponges
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• Globally rare
• Found
➢ In glacier-made troughs on continental shelves
➢ 70-80 km from coast
➢ 200m deep
➢ Cover over 700km2
➢ Also in Antarctica, 33m deep
• Long-lived (up to 19,000 years)
• In the deep areas are threatened by fisheries by trawling, and oil
and gas by drilling and dredging
o Cnidaria (corals, anemone, jellyfish)
▪ What are their defining characteristics?
• Stinging cells called cnidocytes
• Mostly marine
• Radial symmetry
• Polarity (have a head end)
• Have functional and structural diversity
• Are dimorphic (have two body types)
➢ Polyp (a stem with the mouth at the top)
➢ Medusa (A mouth opening on the underside)
• Cells are organised into tissues (have tissue level of organisation)
▪ What is the polyp form?
• It may or may not be sessile, some are sedentary (capable of
movement)
• All are either attached or sedentary
• They have a mouth at the top surrounded by tentacles
▪ What is the medusa form?
• A upside do polyp
• Free-living
• Mouth opening underneath, surrounded by tentacles
▪ What is the Cnidaria body plan?
• A distinct mouth opens into the gastrovascular cavity (GVC)
• Cells are interconnected with basement membranes
• Have two cell layers or tissues, known as diploblasty
• There is not much difference between the two body forms
• Specialised cells act in a highly coordinated way
▪ What are their cellular specialisations?
• They have a nerve net to coordinate activities
➢ This is important for mobility in the medusa
• Have tentacles to capture prey and transport to mouth
• Have no vascular system – blood flow or arteries
• The GVC acts as a sac for digestion, circulation and respiration
▪ What are their main cells?
• The cnidocyte
➢ In the epidermis
➢ A large stinging cell, the defining feature of Cnidaria
• The epidermis (contains)
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Document Summary
Little distance cellular coordination although their do(cid:374)(cid:859)t fu(cid:374)(cid:272)tio(cid:374) together as a (cid:272)ohesi(cid:448)e u(cid:374)it (cid:894)(cid:374)o coordination: how do they feed and respire, choanocytes (within spongocoel) use their flagella to create a current and move water through the sponge. In calm waters, sponges are formed differently than in flowing waters. In calm waters they are vase-shaped and draw water in. Encrust and foul ship hulls and industrial pipes, very expensive: medically. Former reef builder: what are hexactinellid sponge reefs, glass sponges. In glacier-made troughs on continental shelves: globally rare, found. Polyp (a stem with the mouth at the top) A large stinging cell, the defining feature of cnidaria: the epidermis (contains) Receptor cells feel changes in water pressure. The epidermis is used for movement in sedentary animals: the gastrodermis (contains) Circular muscle fibrils beside the mesoglea: how do cnidarians feed, are carnivores, use cnidocytes (specialised stinging cells) Can be all over the epidermis, but mostly on the tentacles.
