Chapter 33 Invertebrates

Parazoa Phylum Porifera:  Sponges   1.  Non-moving (sessile) animals 2.  No nerves or muscles (no tissue differentiation) 3.  Mostly marine 4.  Filter feeders:  Collect food particles from water 5.  Most sponges are hermaphrodites.  Hermaphrodites function as both male and female in sexual reproduction by producing eggs and sperm. **All other animals are in the clade Eumetazoa (true tissues).

Animals probably evolved from colonial, flagellated protists, like this choanoflagellate colony.

Cnidarians Polyp and medusa forms of cnidarians.   Radial symmetry with central digestive (gastrovascular) cavity. One opening in the gastrovascular cavity serves as both mouth and anus.                         Carnivores. Phylum name comes from specialized cells called cnidocytes.  Cnidocytes are stinging cells used for defense and to capture prey.

Purple striped jelly, Pelagia panopyra

Polyps: Sea anemones

Phylum Ctenophora The Comb jellies        Resemble cnidarian medusas.   Use cilia for locomotion.

Protostomia:  Lophotrochozoa Phylum Platyhelminthes:  Flatworms                         Sizes range from microscopic up to 20 meters long (tapeworms).   Many are parasites.

Class Turbellaria (flatworms)                                                 i.  Mostly free-living (non-parasitic) ii.  Feed on small animals, dead animals iii.  Very flat for O2 exchange.  They have no gas exchange organs.                        

Classes Monogenea/Trematoda                                                i.  Live as parasites ii.  Trematodes parasitize vertebrates.  For example, humans but often with intermediate hosts.   

The life history of a blood fluke (Schistosoma mansoni).

Class Cestoidea – Tapeworms                                                 i.  Live as parasites ii.  Head contains suckers and hooks that lock onto the intestinal lining of the host. iii.  The rest of the body is mostly units called proglottids that are sex organs. iv.  Eggs transferred to new hosts by consuming fecal contaminated water.  

Anatomy of a tapeworm

Phylum Mollusca:  Mollusks                         Snails, clams, octopi, squids, oysters   There are at least 150,000 known species All mollusks have similar body plans: a.  Muscular foot b.  Visceral mass with organs            c.  Mantle that secretes the shell

Bivalvia Shells divided into two parts.  Gills are used for feeding and gas exchange. Example:  Clams, oysters

Dreissena polymorpha Zebra mussel

Cephalopoda Rapid movement; well-developed nervous systems.  Example:  Octopus, squid, nautilus  

Phylum Annelida:  Segmented worms                         Sizes range from 1 mm to 3 meters in length.   Each segment contains a pair of excretory tubes called metanephridia. Annelids are hermaphrodites that cross-fertilize. Three classes: a.  Oligochaeta – earthworms            b.  Polychaeta – mostly marine            c.  Hirudinea – leeches

Protostomia:  Ecdysozoa             Phylum Nematoda:  Roundworms Non-segmented Some are important parasites of animals.                                     Pinworms and hookworms, e.g., Trichinella, obtained by eating undercooked pork; juveniles infect all body organs and tissues.  

Nematodes

Phylum Arthropoda:  Arthropods (crustaceans, spiders, insects)             Hard exoskeleton, segmented bodies, jointed appendages Arthropods are the most successful of all animal phyla based on diversity, distribution, and numbers.   Nearly one million species identified so far, mostly insects. The exoskeleton, or cuticle, is composed of protein and chitin. Molting of the cuticle is called ecdysis. Extensive cephalization. Open circulatory systems in which a heart pumps hemolymph through short arteries and into open spaces (sinuses). Aquatic members- gills for gas exchange; terrestrial members- tracheal system of branched tubes leading from surface throughout body.

Four evolutionary arthropod lineages                                     a.  Trilobites – extinct b.  Chelicerates – horseshoe crabs, spiders c.  Uniramians – centipedes, millipedes, insects d.  Crustaceans – crabs, lobsters, barnacles  From these lineages arose five major classes of arthropods.          

Insecta (insects) Outnumber all other forms of animals. Evolved flight during Carboniferous period.  Flight was followed by an explosion of diversity. Coevolution of flowering plants and insects. Wings are extensions of the cuticle. Waste is removed from hemolymph by excretory organs called malpighian tubes.   Nervous system has a pair of ventral nerve chords that join in the head to form a cerebral ganglion (brain) that is close to the sensory organs in the head (cephalization).  

Note: Many insects undergo metamorphosis during their development. Incomplete metamorphosis is a process whereby the young look like the adults, but have different body proportions. Complete metamorphosis is a process where the larval stages (larva, maggot or grub) are specialized for eating. The adult stage is specialized for reproduction and dispersal (e.g. flight). The process of metamorphosis occurs during a pupal stage.

Class Crustacea E.g., crabs, lobsters          Almost all are aquatic. Ca. 40,000 species.             Includes krill eaten by whales, and daphnia, copepods, & amphipods in Lake Erie, pill bugs, etc.

Deuterostomia: Phylum Echinodermata (Echinoderms) Water vascular systems – network of hydraulic canals used for locomotion, feeding, and gas exchange.  It extends into tube feet that are used for locomotion and feeding. Echinoderms appear to be radial, but are bilateral in larval stages.