Chapter 23 Animal Diversity I Invertebrates 23 1 What Are the Key Features of Animals Animals possess all of the following characteristics Multi cellular No cell wall Obtain energy by consuming other organisms Most reproduce sexually They are motile at some point in the life cycle They are able to respond rapidly to external stimuli 23 2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree Include The appearance of tissues The appearance of body symmetry Lack of tissues separates sponges from all other animals Tissues are groups of similar cells that carry out a specific function e g muscle Sponges are the only modern day animals that lack tissues Individual cells in sponges may be specialized but they act independently and are not organized into true tissues Animals with tissues exhibit either radial or bilateral symmetry Symmetrical animals have an upper dorsal surface and a lower ventral surface Symmetrical animals are divided into two groups Those that exhibit radial symmetry Those that exhibit bilateral symmetry Animals with radial symmetry can be divided into roughly equal halves by any plane that passes through the central axis Animals with bilateral symmetry can be divided into mirror image halves only along one plane that runs down the midline Body Symmetry central axis plane of symmetry anterior a Radial symmetry b Bilateral symmetry plane of symmetry posterior Fig 23 2 23 3 What Are the Major Animal Phyla Animals probably originated from ancestral protists Present day biologists recognize about 27 phyla of animals Most animals are invertebrates lack a vertebral column Less than 3 of all known animals are vertebrates possess a vertebral column Phylum Porifera Sponges have a simple body plan Sponges belong to the phylum Porifera and are found in most marine environments Immobile They may reproduce asexually by budding where the adult produces miniature versions of itself that drop off and assume an independent existence They may reproduce sexually through fusion of sperm and eggs The Diversity of Sponges Fig 23 4 Porifera Sponges have no true tissues and organs The sponge body is perforated by tiny pores through which water passes and by fewer large openings through which water is expelled As water passes through the sponge oxygen is extracted and microorganisms are filtered out and digested by individual cells Porifera Some sponges contain chemicals useful to humans A number of chemicals within sponges have proved to be valuable medicines The drug spongistatin is an emerging treatment for the fungal infections that sicken AIDS patients Some medicines derived from sponges include some promising new cancer drugs Phylum Cnidarian Cnidarians are well armed predators Includes Sea jellies sea anemones corals and hydrozoans These animals are mostly marine and are all carnivorous predators Most cnidarians lack true organs and have no brain but rather a network of nerves that controls movement and feeding behavior Cnidarian Diversity Fig 23 6 Cnidarian Have stinging cells called cnidocytes that are used to capture prey and for defense Cnidocytes contain a finely coiled filament that is explosively expelled when the trigger is touched Some filaments inject poison into the prey Others either stick to or entangle small prey The venom of some can cause extreme pain or death in humans Cnidarian Weaponry The Cnidocyte trigger filament trigger nuclei b Cnidocytes Fig 23 8 Jellyfish Stings Contrary to urban legend urinating on a jellyfish sting will NOT help ease the pain and may even make it worse Rinse the stings with seawater or vinegar and baking soda to deactivate the tentacles Then apply shaving cream to the sting area and shave the skin to remove excess tentacles If you re without a razor a credit card will work The Box Jellyfish One of the 10 most venomous creatures on the planet Found mainly in ocean waters between Australia and Hawaii Stinging cells are ejected at an amazing speed Accelerates at a rate of over 1 million times the force of gravity Rocket launches are about 5 times Sting is painful enough to induce shock or cardiac arrest in a human Over 100 people killed Phylum Ctenophora Comb jellies belong to the phylum Ctenophora Appear similar to cnidarian but use cilia to move All comb jellies are carnivorous eating tiny invertebrate animals that they capture with sticky tentacles Most comb jellies are hermaphroditic and can release both eggs and sperm into seawater fertilized eggs gradually develop into larvae and then adults Phylum Platyhelminthes May be parasitic or free living Include flatworms Many species are parasites and live within the body of another organism Non parasitic free living flatworms inhabit aquatic and moist terrestrial habitats Can reproduce both sexually and asexually most are hermaphrodites Platyhelminthes Have organs but no respiratory and circulatory systems Have a distinct head with sensory organs Their nervous system consist of clusters of nerve cells called ganglia in the head forming a simple brain In the absence of a respiratory system gas exchange is accomplished by diffusion between body cells and the environment Platyhelminthes Some flatworms are harmful to humans Tapeworms can infect people who eat improperly cooked beef pork or fish that has been infected by the worms Tapeworms attach themselves to the lining of the intestine Can grow up to 20 feet in length by absorbing nutrients in the intestine Flatworm Diversity Fig 23 9 Phylum Annelida Includes segmented worms Body is divided into a series of repeating units segmentation Each segment is identical to the others allows for complex movement Most reproduce sexually Annelida Some species are hermaphroditic others have separate sexes During copulation sperm are transferred from one individual to the other In hermaphroditic species sperm transfer may be mutual with each partner donating and receiving sperm Some annelids reproduce asexually by fragmentation The body breaks into two pieces each of which regenerates the missing part Phylum Mollusca Most mollusks have shells Includes clams snails and cephalopods Mollusks reproduce sexually Some species have separate sexes Others are hermaphroditic Mollusca The three classes of mollusks are Gastropods Bivalves Cephalopods Mollusca Gastropods are one footed crawlers Includes snails and slugs They have a muscular foot for locomotion They may possess a shell but not all gastropods are shelled They feed using a radula a
View Full Document
Unlocking...