Biology, Protostomes

Raven Biology 13th edition, Protostomes Ch33

The Clades of Protostomes, All protostomes belong to either

the Lophotrochozoa or the Ecdysozoa

Defining Characteristics of the Lophotrochozoa, Characterized by the presence of

trochophore larva or lophophore feeding structure

Ecdysozoa, Contains animals that molt

have an exoskeleton (hard external skeleton); includes arthropods and nematodes

Phylum Platyhelminthes, Flatworms are ciliated, soft-bodied animals

bodies are solid aside from an incomplete digestive cavity; many parasitic, some free-living

Flatworms (Platyhelminthes), Simple bodies with no circulatory or respiratory systems

have complex reproductive system; includes planarians, flukes, and tapeworms

Additional Flatworm Features, Have only one opening to digestive cavity

muscular contractions in pharynx ingest and tear food; lack circulatory system; cells engulf particles by phagocytosis

Additional Flatworm Features, Tapeworms (parasitic flatworms) lack digestive systems

absorb food directly through body walls

Major Groups of Flatworms, Includes the parasitic flatworms

Trematoda (flukes) attach within host by suckers, anchors, hooks; life cycle may have 2+ hosts

Trematoda, Schistosoma is one of most important trematodes to human health

afflict 200 million people; about 200,000 die each year from schistosomiasis

Cercomeromorpha, Tapeworms hang onto inner wall of host intestine using

a scolex

Phylum Rotifera, Are microscopic animals with a ciliated organ called a corona

creates water currents for feeding and locomotion

Phylum Mollusca, Second in diversity only to arthropods

includes snails, slugs, clams, octopuses; some have shell, some do not

Features of the Phylum Mollusca, Range in size from microscopic to huge

giant clams may weigh 270 kg; evolved in oceans; important human food source

Features of the Phylum Mollusca, Economically significant

pearls from oysters, mother-of-pearl from abalone; pests include zebra mussels

Mollusk Body Plan, Characterized by three main body parts

muscular foot, visceral mass (contains organs), and mantle (secretes shell)

Classes of Mollusks, Four classes discussed are

Polyplacophora (chitons), Gastropoda (limpets, snails, slugs), Bivalvia (clams, oysters), Cephalopoda (squids, octopuses)

Class Polyplacophora (Chitons), Marine mollusks with oval bodies

most are grazing herbivores

Class Gastropoda, Includes limpets, snails, slugs

primarily marine, some freshwater, and only terrestrial mollusks; most have single shell, some lost it

Class Gastropoda, Torsion is unique among animals

mantle cavity and anus moved from posterior to front; should not be confused with coiling (spiral winding of shell)

Class Bivalvia (Bivalves), Includes clams, scallops, mussels, oysters

most marine, some freshwater; have two shells (valves) hinged together

Class Bivalvia (Bivalves), Adductor muscles counter hinge ligament

water enters through inhalant siphon, exits through exhalant siphon

Class Cephalopoda, Includes squids, octopuses, cuttlefishes, chambered nautilus

most intelligent invertebrates; have well-developed eyes and closed circulatory system

Annelids (Annelida), Segmented worms

body built of repeated units allowing for specialization

Annelid Features, Earthworms have 100-175 similar segments

chaetae project from body wall; eat through soil; no eyes but sense light/touch/chemicals; hermaphroditic

Annelid Features, Leeches are annelids that

are often ectoparasites; used in medicine for bloodletting and microsurgery

Phylum Nematoda, Members found everywhere – abundant and diverse

marine, freshwater, parasites, free-living; vinegar eels, eelworms, roundworms

Nematode Reproduction and Composition, Sexual reproduction most gonochoric with internal fertilization

adults consist of fixed number of cells; Caenorhabditis elegans has only 959 cells, important in genetic studies

Nematode Lifestyles, Many are active hunters preying on protists and small animals

others are plant parasites or live within larger animals; largest (9m) parasitizes sperm whale placenta

Nematodes and Human Disease, About 50 species cause human diseases

hookworms cause anemia; Trichinella causes trichinosis from undercooked meat

Arthropod Characteristics, By far the most successful animals

well over 1,200,000 species (2/3 of all named species); affect all aspects of human life

Arthropod Characteristics, Divided into four extant classes

Chelicerata, Crustacea, Hexapoda, Myriapoda

Arthropod Success, Success attributed to

segmentation, exoskeleton, jointed appendages

Arthropod Circulatory and Nervous Systems, Open circulatory system

nervous system has double chain of segmented ganglia; ventral ganglia control most activities

Arthropod Respiratory and Excretory Systems, Aquatic arthropods diffuse waste through gills

terrestrial insects use Malpighian tubules to eliminate nitrogenous wastes as concentrated uric acid/guanine, conserving water

Class Chelicerata, Includes spiders, ticks, mites, scorpions, horseshoe crabs

most anterior appendages called chelicerae (may function as fangs/pincers)

Order Araneae (spiders), About 35,000 species

important predators; catch prey in silk webs or actively hunt; all have poison glands with channels through chelicerae

Order Acari (mites and ticks), Most diverse of chelicerates

predators and parasites; mites small, ticks larger blood-suckers; can carry diseases (Rocky Mountain spotted fever, Lyme disease)

Class Crustacea, Largely marine, some freshwater

includes crabs, shrimps, lobsters, barnacles, crayfish, copepods; have three tagmata (cephalon and thorax fused to cephalothorax)

Class Crustacea, Decapod crustaceans (shrimps, lobsters, crabs) have 10 feet

5 pairs of thoracic appendages; exoskeleton usually reinforced with CaCO₃

Order Cirripedia (Barnacles), Sessile as adults

capture food with feathery legs; hermaphroditic

Class Hexapoda, Insects are by far the largest group of animals

more than half of all named animal species; approximately one billion billion insects alive at any time

Insect Mouthparts, All have the same basic structure

modifications reflect feeding habits

Insect life histories, Many insects undergo metamorphosis

simple metamorphosis (grasshoppers) immature similar to adults; complete metamorphosis (butterflies) with wormlike larva and pupa stage

Class Myriapod Characteristics, Head regions followed by numerous segments

gonochoric, internal fertilization, lay eggs; young add segments as they grow