21_WormsW11 - Protostomes 1: Why are there so many worms?...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Protostomes 1: Why are there so many worms? • Coelom • Major clades • The worm lifestyle – Hydrostatic skeleton • Mollusks – Diversity of a shared body plan Flatworm, Platyhelminthes Example: Sponges 1. Flagellated choanocytes (specialized feeding cells) create currents Spicules provide support 2. Water and plankton enters pores into small canals. 3. Choanocytes capture food with “collar” Why have many small pores and canals instead of one big one? Jet propulsion • Eject mass of fluid away from body to create thrust • Fluid density increases, thrust increase • Water can create 830 times thrust of air • Any animal strong enough to create thrust in air would be too heavy for it to work • Jet propelled animals only in water Cavity enclosed by mantle fills with water Jet propulsion in squid (Mollusk) Water is forced out through siphon; animal moves Fig 33.10 Choanoflagellates Cnidaria Multicellularity LOPHOTROCHOZOA Cnidaria Bilateral symmetry ANIMALIA PROTOSTOMES BILATERIA ECDYSOZOA DEUTEROSTOMES Coelom, cephalization, CNS DEUTEROSTOMES Example: Scyphozoans • In Cnidarian Clade – Cnidocytes – Diploblastic – Incomplete gut Medusa Planula Larvae Polyp • Jellyfish or medusa stage dominates complex life cycle – Medusa produces sperm & eggs Mature polyp budding off medusa Example: Scyphozoans • Use jet propulsion to move in water • Still not great at moving against currents • Predators – Use cnidocytes to capture prey Protostomes and Deuterostomes Gastrulation: Blastula invaginates to create mouth or anus Protostome: Mouth 1st Deuterostome: Mouth 2nd Genus Ambystoma Vertebrate Deuterostome Protostomes and Deuterostomes Initial embryo cleavage pattern associated with groups Protostome: spiral Deuterostome: Radial nesting in between, unequal division size even, right on top of parental cells Possibly derived cleavage is determinant ability to produce twins Possibly ancestral Protostomes and Deuterostomes Coelom formation (body cavity lined with mesoderm develops) PROTOSTOMES DEUTEROSTOMES Gut Coelom Gut Mesoderm Block of solid mesoderm splits to form coelom Cross section Mesoderm Mesoderm pockets pinch off of gut to form coelom Figure 32-8c Classic View: Coelom is derived Coelom= body cavity surrounded by mesoderm Ectoderm Mesoderm Endoderm Acoelomate: No enclosed body cavities Pseudocoelomate: Body cavity present, partially lined with mesoderm Coelomate: Body cavity present, fully lined with mesoderm “Progression” reflected in phylogenies Porifera ANIMALS Cnidaria Ctenophora Acoelomorpha Two Major rotostome Groups Bilateral symmetry Protostome development LOPHOTROCHOZOA Rotifera Platyhelminthes Annelida PROTOSTOMES Mollusca loss of coelom ECDYSOZOA Nematoda Tardigrada Coelom Onychophora Arthropoda Echinodermata Chordata Lophotrochozoans • Typically have either – Lophophore (“crest bearing”) feeding apparatus as adults ribbon worm,s, annelids, mollusks – Trochophore (“wheel bearing”) larvae traits seen in most of the clades ectoprocts, brachicopods phoronids Lophophores function in suspension feeding in adults. Food particles Water current Mouth Anus Gut Figure 33-3 Example of Lophophore: Ectoprocts • Also called bryozoans – lace corals, moss animals • Live in colonies • Individuals (zooids) in boxes • Lophophore – Cilia create current – helps capture food Lophotrochozoa>Ectoprocta Trochophore Larvae • Common larval form • Typical of annelids and mollusks • Have band of cilia around center • Part of complex life cycle (only in water) green cilia Worms: The soft life Why is worm morphology common? • Most Recent Common Ancestor of bilateria probably a worm • Maximizes SA/V – Many respire across skin surface worm is not a clade, but a morphological type • Hydrostatic skeleton • Costs unprotected, water loss (desiccation) – Vulnerable to predators (no shell) – Vulnerable to desiccation Hydrostatic skeleton • Water is incompressible fluid • Muscle push and pull against internal fluid – coelom • Does not require hard skeleton • Most common in dense environments – water, sediment/dirt, parasites inside tissue Water – Sediment/dirt – Parasites inside tissue • Note- not exclusive to worms Figure 32-7 Hydrostatic Skeleton Body wall Gut Nematode Fluid-filled pseudocoelom Muscles Muscles relaxed Muscles contracted Muscles contracted Muscles relaxed acoelomate Flatworms • Respire across surface – Flat morphology maximizes SA/V flat morphology incr. SA/V ratio • Move by cilia on surface • Parasitic and Free Living Forms Lophotrochozoa>Platyhelminthes Sex, Conflict, & Cooperation • Simultaneous hermaphrodites –functional male and female reproductive organs in one ind at the same Functional male and female time reproductive organs in one individual at same time • Flatworms can’t typically selffertilize, must outcross • Conflict in hermaphrodite outcrossers – Male fitness enhanced by having multiple partners while acting as male – Female fitness enhanced by being choosy – Coordinated systems – Aggressive systems Defense: Coloration & Poison • Two color strategies for defense – Dull color- match background (“crypsis”) – Bright color- signal predators you taste bad • “aposomatic” coloration • predators learn to avoid Lophotrochozoa>Platyhelminthes Example: Parasitic Flatworm • Flukes-in flatworm clade • Schistosomiasis- caused by flukes in Schistosoma genus • Complex life cycle • Alternates between human and snail host Lophotrochozoa>Platyhelminthes Don’t memorize life stage names Cercariae Sporocyst in snail Schistosomulae in human In bloodstream Become adult in liver Miracidia- in H20 Adults move to blood vessels near bowels or bladder. Produce fertilized eggs Eggs in urine or feces Lophotrochozoa>Platyhelminthes Ribbon Worms • • • • Long, thin worms Complete gut Respire through skin Predators – Eversible proboscis – Single tooth “stylet” on end – Injects toxin into prey • Up to several meters long Lophotrochozoa>Nemertea Lophotrochozoans: The Worms Flatworms Ribbon worms Phoronids Annelids “Worm” is a morphological type, not a clade Coelom: Advantages • Hydrostatic Skeleton – Water is incompressible – Muscles can work against it • Provides space for organ evolution • Protects organs • Disconnects organs from movement Annelids • Segmented Worms – Helped drive development of circulatory system – Specialization of segments • Coelom • Chaeta (plural: chaetae) – Bristles that stick out from segments – May extend from parapodia – Aid in locomotion Nereis grubei Earthworm Locomotion Circular muscles lengthen segment Longitudinal muscles shorten Chaetae provide traction Earthworm Locomotion Alternation of contractions down body results in peristaltic locomotion Annelids:Major groups • Polychaetes – Mostly marine – Complex life cycle (trochophore larvae) and direct development – Possibly paraphyletic – Includes deep sea vent worms • Clitellates – – – – Terrestrial and freshwater Direct development Oligochaetes (earthworms) Leeches Hermodice carunculata Bearded Fireworm ...
View Full Document

This note was uploaded on 02/26/2011 for the course LIFE SCI 1 taught by Professor Halpin during the Winter '11 term at UCLA.

Ask a homework question - tutors are online