ECOL 182R 1st Edition Lecture 12 Outline of Last Lecture I What are they II Body plans III Tissues A Diploblasts Triploblasts IV How they move V Basal Lineages A Porifera Cnidaria Ctenophora Acoelomorpha Outline of Current Lecture I Overview II Evolution III Diversification IV Body plans A Different appendages V Different lineages Current Lecture Overview Molecular phylogenies support that protostomes are a monophyletic group divided into the Lophotrochozoa and the Ecdysozoa Although many have limbless wormlike bodies and live in marine environments the most diverse and species rich lineages Mollusca and Arthropoda have distinctive and complex features What triggered the diversification of protostomes several lineages making the water to land transition and diversification in appendages and mouthparts and the evolution of metamorphosis in marine terrestrial forms Protostomes include some of thhe most familiar and abundant animals on Earth like arthropods insects spiders crustaceans and molluscs snails clams octopuses squids Most animals are protostomes Protostome Evolution Bilateral symmetry Triploblastic coelomates Monophyletic comprising 2 lineages Lophotrochozoa Ecdysozoa Lochotrochozoan The 14 phyla of this include molluscs annelids and flatworms The name Lophotrochozoan comes from the feeding structure called a lophophore rings the mouth and does suspension feeding and a type of larva called a trochophore the type of larva common to several phyla of lophotrochozoa But only some phyla have these traits Ecdysozoa The big difference between this and Lopho is their methods of growth Ecdysozoans grow by molting shedding of the soft cuticle or hard exoskeleton Which serve to protect the animals from predators THe most prominent of the 7 Ecdysozoa are the roundworms Nematoda and the arthropods Arthropoda Diversification of Protostomes Have diverged into the 22 different phyla that are recognized by distinctive body plants mouthparts This diversification was triggered by evolutionary innovations in body plan feeding moving reproducing Basic Body Plan Most have wormlike bodies with a basic tube within a tube design Radical changes happened in coelom as protostomes diversified Ex Platyhelminthes flatworms are acoelomates lacking a body cavity Varying Body Plans Among Phyla The pseudocoelom which forms from an opening between ectoderm and mesoderm arose independently in rotifers and ecdysozoans In Arthropods and Mollusca the coelom is drastically reduced A fully functioning coelom has two roles 1 Providing space for fluids to circulate 2 Providing a hydrostatic skeleton for movement In arthropods and molluscs other structures do these functions Arthropod Body Plan Segmented bodies organized into regions called the head thorax and abdomen They re distinguished by their jointed limbs an exoskeleton made of chitin Locomotion is based on muscles that apply force against exoskeleton to move legs wings Have a spacious body cavity called the hemocoel that provides space for internal organs and fluid circulation The Molluscan Body Plan Three major components Foot large muscles at base of animals and usually used in movement Visceral mass region containing most of the internal organs external gill Mantle tissue layer covering visceral mass secreted a shell in some species The coelom s functions are replaced by the visceral mass the muscular foot Variation Among Body Plans of the Wormlike Phyla Characterized by similar body plans but specialized mouthparts or feeding structures Echiurans have a proboscis an extended structure that forms a gutter leading to mouth Priapulids have a toothed throat that can be turned inside out to trap prey and then retract Nemerteans have a barb tipped proboscis that extends and spears entangles prey and then retracts Water to Land Transition Ability to survive in terrestrial environments evolve independently in arthropods molluscs roundworms and annelids The protostome groups that made the transition already had hydrostatic skeletons exoskeletons appendages and other things for support locomotion that happened to work for land AND water facilitating the transition To make the transition new adaptations allowed them to exchange gases so they wouldn t dry out Adaptations for Moving Variation in movement depends on variation in the presence absence of limbs the type of skeleton present Walking running jumping flying gliding crawling jet propulsion Reproduction Asexually or sexually but sexual is the predominant mostly Asexual is common in lots of wormlike phyla Many crustacean insects can reproduce asexually by parthenogenesis unfertilized eggs develop into offspring Sexual reprod starts with external fertilization in sessile forms internal fertilization in groups that can move 2 unique reproductive innovations 1 The evolution of metamorphosis 2 An egg that wouldn t dry out on land Rotifera Rotifers 1800 species damp soils marine freshwater environments Have a cluster of cilia at their anterior end called a corona used for suspension feeding Most swim by beating cilia in the corona Platyhelminthes Flatworms 20 000 species three major subgroups Turbellarians free living flatworms Cestodes endoparasitic tapeworms Trematodes endo or ectoparasitic flukes Broad flattened body shape w large surface area for gas exchange Lack a lophophore have a digestive tract with only one opening for ingestion of food eliminating wastes Annelida Segmented Worms Segmented body plan a coelom that functions as a hydrostatic skeleton 16 500 species divided into two major lineages Polychaeta Clitellata Polychaeta named for their bristle like extensions called chaetae Mostly marine can range from 1 3 5 mm in size Clitellata Made of oligochaetes leeches Oligochaetes earthworms which burrow in moist soils Leeches freshwater and marine habitats Mollusca molluscs By far the most species rich 93 000 morphologically diverse group in Lophotrochozoa Marine environments but some are terrestrial freshwater Four most important lineages are bivalves gastropods chitons cephalopods Bivalvia clams mussels scallops oysters have two separate shells made of calcium carbonate that are hinged Are suspension feeders Most live in the ocean but some are freshwater forms Only external sexual reproduction Gastropodia snails slugs nudibranchs 70 000 species terrestrial and marine Have a large muscular foot on their ventral side and many lack shells During development torsion rotates the visceral mass Have radula in