Ch 10 Acoelomate Bilateral Animals

Acoelomate Bilateral Animals Consist of phyla: –Phylum Platyhelminthes –Phylum Nemertea –And others

Acoelomate Bilateral Animals Reproductive and osmoregulatory systems 1.Simplest organisms to have bilateral symmetry 2.Triploblastic 3.Lack a coelom 4.Organ-system level of organization 5.Cephalization 6.Elongated, without appendages

Bilateral Symmetry Divided along sagittal plane into two mirror images –sagittal= divides bilateral organisms into right and left halves

Anterior= head end Posterior= tail end Dorsal= back side Ventral= belly side

Bilateral animals Bilateral symmetry = important evolutionary advancement –Important for active, directed movement Anterior, posterior ends –One side of body kept up (dorsal) vs. down (ventral)

Directed movement evolved with anterior sense organs  cephalization Cephalization –specialization of sense organs in head end of animals

Acoelomates lack a true body cavity –Solid body –no cavity b/w the digestive tract and outer body wall

Acoelomates are triploblastic Triploblastic (3 germ layers) –Germ layer= layers in embryo that form the various tissues and organs of an animal body

3 germ layers Ectoderm –Outermost germ layer –Gives rise to outer covering of animal ie. epidermis Endoderm –Innermost germ layer –Gives rise to inner lining of gut tract

Mesoderm –Middle germ layer –b/w ectoderm and endoderm –Gives rise to various tissues/organs (ie. muscles)

Acoelomate animals have an organ-system level of organization

Digestive tract and nervous system Organ-system –Different organs operate together (ie. excretory system, nervous system) –mesodermal tissue gives rise to parenchyma

Polyclad From Red Sea

Phylum Platyhelminthes Flatworms Free living Parasitic

From Atlantic ocean

Phylum Platyhelminthes Flattened dorsoventrally –flatworms 34,000 species Gastrovascular cavity (if present) has only one opening (mouth = anus) Mostly monoecious

Phylum Platyhelminthes First phylum that has an Organ systems present –derived mesodermally (parenchyma): Muscular system Digestive system (incomplete; gastrovascular type) (absent in some) Nervous system Excretory system (absent in some) Reproductive system

Phylum Platyhelminthes Organ systems absent: –Circulatory –Respiratory Rely on diffusion

Phylum Platyhelminthes (cont’d) Hymenolepsis- rat tapeworm Divided into 4 classes: –Class Turbellaria (mostly free-living flatworms) –Class Cestoda (tapeworms) –Class Trematoda (parasitic flukes) –Class Monogenea (parasitic flukes)

Class Turbellaria Mostly free-living flatworms Marine (mostly) or freshwater bottom- dwellers Predators and scavangers First group of bilateral symmetrical animals

Class Turbellaria (cont’d) Move by muscles, ciliated epidermis

Class Turbellaria (cont’d) Freshwater turbellarians adapted osmoregulatory structures –Protonephridia protos= first nephros= kidney network of fine tubules running down sides of organism

Class Turbellaria (cont’d) –Flame cells= branch from tubules Ciliary projections drive fluid down tubule –Tubules open to outside= nephridiopore

Class Turbellaria (cont’d) nervous system with nerve ganglion –ganglion- aggregation of nervous tissue Cephalization- cerebral ganglion= primitive brain

Class Turbellaria (cont’d) Ocelli= light-sensitive eyespots

Turbellarian Reproduction Reproductive and osmoregulatory systems Asexual (fission) –transverse Sexual –Monoecious (mostly) –Cross-fertilization

Other 3 classes: –Class Trematoda –Class Cestoda –Class Monogenea All parasitic lack cilia Have unusual body covering: tegument Outer zone of tegument (glycocalyx) consists of proteins and carbohydrates aids in transport of nutrients, waste, gases Protection against host defenses

Class Trematoda Parasitic flukes Endoparasites –Hooks, suckers, increased reproductive capacity

1mm-6cm long Complex life cycle: 1.Definitive host (primary/final host) – where parasite matures and reproduces (sexually) (eggs released) –vertebrate

2.Intermediate host –Mollusc (ie. snail) –Hosts in which larval stages develop and undergo asexual reproduction – Results in an increase in the number of the individuals

Class Trematoda –Example: Chinese Liver Fluke

Chinese Liver Fluke Infects 30 million people in eastern Asia Lives in ducts of liver –Eats epithelial tissue, blood Definitive host: –Humans, dogs, cats 2 intermediate hosts: –snail –fish

Class Cestoda Tapeworms Endoparasites Vertebrate host –Live in digestive tract 1 mm- 25m long (EWWWW!!) Hymenolepsis- rat tapeworm

Class Cestoda Highly specialized Lack mouth, digestive tract –Absorb nutrients across body wall Hooks and suckers –“head”= scolex Hymenolepsis- rat tapeworm

Adult tapeworms consist of long series of repeating units= proglottids Chain of proglottids= strobila

Tapeworms are monoecious (mostly) –Mostly cross-fertilization No specialized sense organs scolex

Cestodes depend on host digestion –Small molecules in host intestine, liver

Definitive host= human Intermediate host= cattle Beef Tapeworm

Class Monogenea Parasitic flukes Mostly ectoparasites Single host, mostly fish

Phylum Nemertea Triplobastic, acoelamate bilateral symmetry Unsegmented Ciliated epidermis Closed circulatory usually <20cm Marine mud, sand Elongate, flattened worms

Phylum Nemertea (cont’d) Unlike the platyhelminthes, Complete digestive tract, with anus –One-way –More efficient; allows larger growth

Phylum Nemertea (cont’d) Cerebral ganglion, longitudinal nerve cords Long proboscis used in carnivorous species Two lateral blood vessels yet no heart Dioecious –“two” “house” –Male and female organs in separate individuals