Lecture #11

Worms, Worms & WormsPhylum Platyhelminthes

Phylum NematodaPhylum Annelida

Current Molecular Classification

• Clade Lophotrochozoa:– Phylum Platyhelminthes - worms– Phylum Annelida - worms– Phylum Mollusca – clams, scallops, squids, snails

etc…• Clade Ecdysozoa:

– Phylum Nematoda - worms– Phylum Arthropoda – crustaceans, spiders &

insects

Phylum Platyhelminthes• flatworms – 20,000 species• “platy” – flat• “helminth” = worm• unsegmented flatworms• novel developments (vs. Sponges and Cnidarians):

– development of bilateral symmetry and three embryonic (triploblastic) tissues in these worms

– development of a head-like region = cephalization– development of an excretory system = protonephridia

Phylum Platyhelminthes

• flatworms are divided into two lineages– A. Non Parasitic– Class Turbelleria (free-living)– B. Parasitic:– Class Monogenea (ectoparasitic)– Class Trematoda (parasitic) = flukes– Class Cestoidea (parasitic) = tapeworms

Features common to Phylum Platyhelminthes

• 1. triploblastic– three germ layers: ectoderm, mesoderm and endoderm– mesoderm muscle

• 2. bilateral• 3. flattened body plan

– thin

• 4. acoelomate• 5. protonephridia for an excretory system• 6. no circulatory or respiratory system

– exchange by diffusion

• 7. incomplete digestive system– mouth, no anus

• 8. most are hermaphroditic (monoecious)

Features common to all flatworms

• protonephridia for osmoregulation (water balance) • for the flatworms – influx of

water into their bodies from their environment

• this excess water is removed through protonephridia

• comprised of flame cells or flame bulbs that draw the water in and expel it back to the outside

Class Turbellaria• free-living flatworms – e.g. Planaria & Dugesia

• marine and freshwater• bottom dwellers• over 4,500 species to date• less than 1 cm long in most species• free-living species are shades of black, brown

and gray• larger species can be brightly colored

https://www.youtube.com/watch?v=wn3xluIRh1Y

• incomplete digestive system– most turbellarians are carnivorous and feed

on small invertebrates or scavenge dead animals

– both extracellular and intracellular– food enters the pharynx – enzymes secreted

into the pharnyx for extracellular digestion– food enters the intestine where cells

phagocytose smaller food particles and complete digestion intracellularly

Class Turbellaria

• tubellarians have net-like nervous system (like most flatworms)• nerve trunks that run the length of the body

– neurons organized as sensory and motor and association – seen in higher order animals like humans

• accumulation of neurons near the head – function as a brain• also have two auricles – have neurons for detecting chemicals• two eyespots called ocelli at the head for detecting light

• Asexual reproduction: reproduce asexually via transverse or longitudinal fission– regenerate the missing body regions once they separate

Class Turbellaria

head regeneration:https://www.youtube.com/watch?v=kndPpqC6-78

Class Trematoda• 8,000 species• parasitic flatworms called flukes• wide, flat shape to oval or elongate• body plan: like the turbellarians in structure

– large intestine that splits into two tubes– hermaphroditic– outside is covered with an organic layer of proteins + carbohydrates =

glycocalyx• can help evade the host’s immune system

• Flukes:– attachment through an oral sucker that

surrounds the mouth– a second sucker – acetebulum – located

ventrally in the middle of the body

• e.g Clonorchis sinensis – liver flukes– infects 30 million people annually – mostly in

Asia– adult flukes live in the human liver – definitive

host– life cycle also requires an intermediate host –

usually a mollusc

e.g. Schistosoma – blood flukese.g. Paragonimus – lung flukee.g Clonorchis sinensis – liver flukes

• Schistosoma – blood flukes• adult flukes live in the human

bloodstream• dioecious – males are shorter and thicker• female is long and slender – carried in a

ventral canal on the male• life cycle

– 1. copulation is continuous – constantly mating pairs of worms (female, smaller & thinner)

– 2. eggs are released in feces and releases miracidia into freshwater

– 3. penetrates a snail to continue it life cycle

– 4. larval form leave the snail and penetrate human flesh (creates a rash)

– 5. once in humans the larvae form adults

Class Cestoidea• tapeworms• 3,500 species• endoparasites – vertebrate digestive system• 1 mm to 25m in length• nearly all monoecious• lack a mouth and digestive tract

– absorb nutrients by diffusion• consist of a long series of repeating units called

proglottids (repeating reproductive segments)• attachment by a scolex – holdfast that attaches the

worm to its host• live in a very stable environment – intestinal tract has

few variations

– proglottids are filled with reproductive structures (male and female)

• devoted to making eggs• BUT the male organs mature before the

female – no self fertilization• fertilized eggs accumulate in the uterus

(black under the microscope)• the further back in the tapeworm – the more

mature the proglottid and the more eggs• the oldest proglottids filled with eggs = gravid

proglottid • gravid proglottid breaks off from the worm

and breaks open to release the fertilized eggs• the lost proglottid is remade up near the

neck

• beef tapeworm – Taenia saginata– adults live in small intestine – may reach lengths of 25 meters!!– 80,000 eggs per proglottid– eggs released in human feces– egg develops and forms a 6 hooked larva

called the onchosphere– intermediate host – cattle– onchospheres travel from the gut to the

skeletal muscle where they encyst over long periods of time

– when eaten by humans releases the worm into the human bloodstream – scolex attaches to the intestine wall of the human

oncospheres

https://www.youtube.com/watch?v=EEBbtwGqPEs

Phylum Annelida

• characteristics:– 1. segmented – into metamers– 2. bilaterally symmetrical– 3. coelomate – 4. closed circulatory system

• large vessels that function as hearts • series of vessels closed off from the tissues• circulatory fluid = blood• gas exchange by capillary beds

– 5. complete digestive system• mouth --> storage crop grinding gizzard absorptive intestine anus

– 6. excretory system – pairs of nephridia in each segment– 7. well developed longitudinal and circular muscles

• for locomotion = https://www.youtube.com/watch?v=0Texxu3p7I8

• excretion by nephridia– filters body fluid– minerals and water reclaimed

and put back into the bloodstream

– wastes expelled to the outside– very similar to the vertebrate

nephron

Phylum Arthropoda• characteristics:

– 1. metamerism – segmentation PLUS specialization of body segments for specific functions

– 2. chitinous exoskeleton for support and protection• growth achieved through molting• number one reason for arthropod success

– 3. paired, jointed appendages– 4. open circulatory system & complete digestive tract– 5. metamorphosis often seen to achieve sexual maturity

Phylum Arthropoda

• 4 subphyla– 1. Subphylum Chelicerata

• Class Merostomata – horseshoe crabs• Class Arachnida - spiders• Class Pycnogonida – sea spiders

– 2. Subphylum Crustacea – 6 classes• Class Branchipoda – brine shrimp• Class Malacostraca – shrimp, lobsters, crab, crayfish• Class Maxillopoda – copepods and barnacles

– 3. Subphylum Hexapoda• insects

– 4. Subphylum Myriapoda• millipedes and centipedes

Subphylum Chelicerata

chelicerae

• includes the spiders, mites, ticks, horseshoe carbs and sea spiders

• two specialized body segments– 1. cephalothorax – for sensory, feeding

and locomotion• first pair of paired appendages =

chelicerae (feeding)• second pair = pedipalps (feeding)• followed by paired walking legs

– 2. abdomen• contains digestive, reproductive,

excretory and respiratory organs

Subphylum Crustacea

• crayfish, shrimp, lobsters and crabs• plus the copepods, fairy shrimp, isopods

(pillbugs), amphipods and barnacles

copepod isopod

barnacle

• crayfish: known as a Decapod– at least ten pairs of jointed appendages– body plan: cephalothorax and abdomen– exoskeleton extends all the way around the body = carapace– abdomen takes the form of the “tail”

Class Malacostraca

Decapod Appendages

• 10 pairs of appendages used for feeding and walking

• Head - sensory– 1. antennae– 2. antennules

• Thorax – feeding and walking– 1 3. Maxillopeds (feeding)– 4 8. Periopods (walking legs)

• Abdomen - swimming– 1 5. Pleopods (Swimmerets)– 6. Uropod (part of telson)

• feeding and digestion: prey on other invertebrates, eat plant matter and scavenge dead and dying animals– 1st 8 pairs of appendages are for food detection and handling– enlargened stomach – part of which is specialized for grinding– digestive gland called a hepatopancreatic gland - secretes digestive enzymes into the

stomach– intestine extends from the stomach– intestine ends in an anus – important role in water and salt regulation

Class Malacostraca

• circulation: similar in all arthropods – open system– tissues are bathed in body

fluids containing oxygen binding pigments

– do have a heart

• respiratory: feathery gills attach to the bases of the walking appendages– water is moved over the gills

for the exchange of gases between the oxygenated water and the body fluids

gills

Class Malacostraca

• 2 classes: Entognatha and Insecta• insect body plan:

– body is divided into: head, thorax and abdomen– head bears a single pair of antennae, mouthparts (maxillae,

mandibles), compound eyes and ocelli– thorax bears three pairs of legs & wings (in some insects)

Subphylum Hexapoda- Class Insecta

locomotion: varied methods from crawling to flying

• feeding and digestion: – head bears mouthparts for food

handling and sensory• mandibles for chewing• maxillae for cutting

– digestive tract - long, straight tube of foregut, midgut and hindgut

Class Insecta

The Insect Eye

• ocelli + several compound eyes• ocelli = 500 – 1000 receptor cells beneath a single circular

lens• compound eyes found in many adult insects

– better suited for detecting movement rather than for forming an image

• compound eyes consists of a few to 28,000 receptors called ommatidia – fuse into a multifaceted eye

• ommatidia –light-gathering structure– covered with a cornea, contains a cone (lens)– base is a rhabdom – converts light energy into a nerve impulse

ocelli

compound eye

• excretion: Malphigian tubules– open into the junction of the midgut and hindgut– ions, water and other critical materials are reabsorbed from the rectum

back into the body fluid– nitrogenous wastes move into hindgut– main excretory product - uric acid

• gas exchange : tracheae– tubes that open to the air via the spiracles along the body

• spiracles lead to tracheal tubules that carry air to the muscles – gas exhange

• inspiration through the thoracic spiracles and expiration through the abdominal spiracles

Features common to Phylum Echinodermata

• 1. triploblastic• 2. pentaradial symmetry in adults; bilateral symmetry in

larvae• 3. coelomate• 4. internal endoskeleton made of calcerous (bony) plates

called ossicles• 5. water vascular system for locomotion

Phylum Echinodermata

• approximately 7,000 species• all are marine• living echinoderms are classified into 6 classes

– 1. Asteroidea – sea stars– 2. Ophiuroidea – brittle stars and basket stars– 3. Echinodea – sea urchins and sand dollars– 4. Holothuroidea – sea cucumbers– 5. Crinoidea – sea lilies and feather stars– 6. Cocnentricycloidea – sea daises

• sea stars• about 1,500 species• live on hard substrates in marine environments• five arms radiating from a central disc• central disc has a mouth on its ventral side (oral surface)• opposite surface is the aboral surface with an anus

Class Asteroidea

Water vascular system• water-filled canals for locomotion• water enters into a ring canal through a

stone canal and a sieve-like pore called the madreporite

• five radial canals (or multiples) branch from the ring canal and run down each arm

• extensions off of the radial canals are called tube feet

madreporite

-tube feet • extensions off the ring canals • project to the outside & have suction

cups at its end• inside the body they end as a bulblike,

muscular ampulla• when the ampulla contracts- forces water

into the tube which then extends • contraction of tube feet back into

body pulls sea star forward: locomotion

https://www.youtube.com/watch?v=2DFXGafpGkQ