CHAPTER 33 INVERTEBRATES 35 animal phyla 1 300 000 extant species known Most familiar with Chordates 5 of total species 95 of all living species lack a backbone Collectively called invertebrates PARAZOA Phylum Porifera Sponges Body resembles sac perforated with holes Filter feeders 1 cm 2 m 9 000 species most marine No muscle or nervous tissue indiv cells react to stimuli Hermaphrodites individual both male female Capable of regeneration asexual reproduction Lining inside of body are flagellated choanocytes collar cells Flagella generate water current and collar traps food Water enters through pores into central cavity spongocoel out through osculum EUMETAZOA Phylum Cnidaria an ancient phylum of eumeatzoa Hydras jellyfishes sea anemones and corals Diploblastic condition radial symmetry suggest they arose very early from eumetazoa line No mesoderm 10 000 species most marine Body plan sac with gastrovascular cavity and single opening Two variations 1 Sessile polyp Hydras sea anemones and corals 2 Floating medusae Jellyfishes Some species exist only as polyps some as medusae and some pass through both stages Carnivores use tentacles to capture prey and push food into gastrovascular cavity Tentacles lined with cnidocytes which contain stinging capsules nematocysts No true muscle tissue Nerve net rudimentary contractile fibers microfilaments No brain Sensory receptors distributed radially around body Four major classes 1 Hydrazoa Hydra freshwater Only polyp form Most Hydrazoans alternate polyp and medusa forms 2 Scyphozoa Jellyfishes Medusa prevails 3 Cubozoa box shaped medusa stage complex eyes embedded in fringe of their medusae 4 Anthozoa Sea anemones and corals Occur only as polyps Corals excrete hard exoskeleton Scyphozoan Video Phylum Ctenophora Comb bearers Resemble small Cnidarian medusae 150 species all marine 1 10 cm in diameter Named for eight rows of comb like plates composed of fused cilia Largest animals to use cilia for locomotion Most have pair of long retractable tentacles used to capture food Ctenophore Vide o Lophotrochozoans Bilateral Acoelomates Phylum Platyhelminthes Flatworms Triploblastic acoelomate bilateria 20 000 species nearly microscopic 20 m Marine fresh water and damp terrestrial habitats many parasitic Flattened dorsoventrally moderate cephalization Have mesoderm true muscle tissue Gut remains gastrovascular cavity with one opening Major classes 1 Turbellaria turbellarians free living Nearly all free living and mostly marine Planarians Fresh water Carnivores Lack specialized organs for gas exchange circulation Have simple excretory apparatus flame cells Allows animals to excrete dilute urine Reproduction sexual or asexual regeneration Hermaphrodites copulating mates cross fertilize 2 Tremetoda Trematodes Flukes parasites on other animals Suckers for attachment tough outer covering Like most parasites flukes have complex life cycles Alternation of sexual and asexual stages May require intermediate host where larval form lives before infecting final adult host 200 X 106 individuals infected with blood flukes 3 Cestoda Tapeworms parasitic Worm attaches to intestinal lining of host mostly vertebrates Extensively modified due to parasitic life style Lacks mouth and gastrovascular cavity Contains sacs of sex organs loaded with thousands of eggs Human tapeworm 1 Human feces contaminate food or water of intermediate host cattle or swine 2 Eggs develop in muscle of host to larval stage 3 Humans acquire larva by eating undercooked meat contaminated with cysts Large tapeworm 20 m intestinal blockage Phylum Nemertea ribbon or proboscis worms Body structurally acoelomate but contains small fluid sac reduced version of coelom Sac is used in hydraulically operating an extensible proboscis Proboscis used for capturing prey 1m 30 m 900 species almost all marine Some active swimmers some burrow in sand Probably evolved from flat worms Echinoderms and Nemertean Worms Additional synapomorphic characteristics not found in flatworms 1 Have a simple closed circulatory system blood vessels blood cells 2 Complete digestive tract with mouth anus Pseudocoelomates Body cavity not completely lined with mesoderm This body plan has evolved in several species of small animals Evolutionary relationships unclear Probably arose independently several times Phylum Rotifera 800 species mainly fw some marine or soil 0 05 2 0 mm smaller than many protozoa Complete digestive tract and specialized organs Reproduction Some species only produce females that produce more females from unfertilized eggs Parthenogenesis Other species produce 2 types of eggs that develop by parthenogenesis Females degenerate male Males produce sperm fertilized eggs form resistant zygotes that can survive unfavorable conditions Lophophorates 3 phyla 1 Phoronida 2 Ectoprocta Bryozoa 3 Brachiopoda All share lophophore horseshoe shaped or circular fold of body wall with ciliated tentacles that surrounds mouth Tentacles draw and trap food particles Phoronids tube dwelling marine worms 1 mm 50 cm 12 species Bryozoans moss animals Tiny colonial animals that resemble mosses Usually have hard exoskeleton important reef builders Plumetella puntata Brachiopods lamp shells Superficially resemble bivalve mollusks 2 shells or valves Attaches to substrate by stalk All are marine 330 species Changed little in 400 million years Phylum Mollusca Chitons snails slugs clams octopi and squids 150 000 species most marine some fw soil Soft bodied but most protected by shell Despite differences all have similar body plans Three main parts 1 Muscular foot usually used for movement 2 Visceral mass contains most internal organs 3 Mantle tissue fold draped over the visceral mass usually secretes shell Mantle extends from visceral mass to form mantle cavity Contains gills anus and excretory pores Many feed using straplike rasping organ radula Many have separate sexes Many snails are hermaphrodites Life cycle usually includes ciliated larval stage Trochophore Mollusks probably arose before segmentation characteristic of annelids Eight Classes Look at four 1 Class Polyplacophora Chitons marine oval shells divided into 8 dorsal plates Adheres to substrate using muscular foot 2 Class Gastrapoda Largest class 40 000 most marine One side of visceral mass grows faster torsion Places mantle cavity anus above head Most protected by single spiral shell some no shell Most use radula to graze on plants Some use modified radula for boring holes in shells of