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Mollusks, Echinoderms, and Arthropods

Mollusks, Echinoderms, and Arthropods. Biology 11. Phylum Mollusca pgs 428-432. Examples: snails, clams, oysters, squid Habitat: mostly aquatic and terrestrial 7 classes: Gastropods, Pelecypod, Cephalopods, Polyplacophora, Scaphopod, Aplacophora, Monoplacophora. Body plan Development.

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Mollusks, Echinoderms, and Arthropods

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  1. Mollusks, Echinoderms, and Arthropods Biology 11

  2. Phylum Mollusca pgs 428-432 • Examples: snails, clams, oysters, squid • Habitat: mostly aquatic and terrestrial • 7 classes: Gastropods, Pelecypod, Cephalopods, Polyplacophora, Scaphopod, Aplacophora, Monoplacophora

  3. Body plan Development • Bilateral Symmetry • Three germ layers • True coelom • Protosomes pg 428 • Basic body plan includes: • Foot – for locomotion • Mantle – hanging tissue • Shell – internal or external, calcium carbonate • Gills – respiratory structures (aquatic) • Visceral mass – internal organs

  4. Mollusks Systems • Sexual Reproduction – Hermaphroditic with cross fertilization, or separate sexes. • Circulatory System - Closed Circulatory System • Digestion – Radula (a rough tongue) and filter feeding. A complete digestive tract. • Nervous System – Primitive brain and light receptors or eyes. • Respiration – Gills are covered by the mantle.

  5. Phylum Echinodermata pgs 432-434 • Echinos =spiny or bristly • Derm= skin • Examples:Starfish, sea urchin, sand dollar, sea cucumber • Habitat – aquatic actually means fresh water so they actually live in MARINE environments.

  6. Water Vascular system • The major unifying characteristic of echinoderms is their water vascular system. • Locomotion and feeding are accomplished by this system, which operates much like a hydralic pump.

  7. Echinoderm • Echinoderms are the closest relatives to Chordates. It may not seem so at first, but looking closely at embryological evidence, it is believed that chordates and echinoderms shared a common relative. This relative is believed to have been something along the lines of sea urchin - an orgasnism a bit larger than a golf ball with spines extending radially. Interesting little creatures, they aren't especially intelligent. In fact, they don't do much of anything.

  8. Keep in mind that "close" is a relative term. New York and Sydney are close compared to the distance between the earth and Jupiter. It is all a matter of context. In evolution, the context is a matter of many millions of years.

  9. Body plan Development • Bilateral Symmetry in larvae, • Radial Symmetry in adults (Secondarily derived pentaradial symmetry. What does that mean? It means that echinoderms tend to be pentaradially symmetric. The secondarily derived portion of that means that they switch from being bilaterally symmetric to radially symmetric as they mature. This is of no consequence to taxonomists, they use the symmetry at the larval stage. • Three germ layers • True coelom • Deuterosomes pg. 432

  10. Echinoderm Systems • Water vascular system – unifying systems between all echinoderms. Allows for some locomotion. • Circulatory System – open circulatory system • Digestion – one way digestive tube. Filter feeding and ingestion through the mouth. • Nervous System – oral and radial nerve cords but NO Brain. • Respiration – diffusion • Reproduction- Echinoderms are monoecious, that means that the sexes are separate. Males are males, females are females. There is no ambiguity. However, with echinoderms, the sexes are not readily apparent using the unaided eye.

  11. Phylum Arthropoda Pgs 435-441 • Arthropoda = jointed appendages • Examples: insects, crayfish, spiders • Habitat: ubiquitous (almost everywhere!) • Largest animal phyla • 4 subphyla: • Trilobitomorpha, Chelicerata, Uniramia, Crustacea,

  12. Body Plan development • Bilateral Symmetry • Three germ layers • True coelom • Various stages of metamorphosis • Segemented bodies, all include a head, thorax, abdomen and a chitin exoskeleton. • Developed nervous systems, compound eyes or photoreceptors etc.

  13. Arthropod Systems • Sexual reproduction – separate sexes • Circulatory System – Open circulatory system • Digestion – one way digestive tube, consisting or a foregut, midgut and hind gut. Pg 438 • Nervous System – true brain with two ventral cords • Respiration – tracheal system and gills

  14. Application Questions (to be completed for homework) • Read Pgs 428-434 and do practice questions on Pg 434, Questions #2, 3, 4, 7, 8 • Read Pgs 435-442 and do practice questions on Pg 440, Questions #1, 2, 3, 4 and Pg 442 Question #5

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