Acoelomate Bilateral Animals

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

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

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

Review 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) Cephalization and bilateral symmetry evolved together

Directed movement evolved with anterior sense organs 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 Acoelomate Phylum Platyhelminths Or not shown here Nemerterean This is a round worm Different Phylum

Architectural patterns of animals Architectural patterns of animals. These basic body plans have been variously modivied during evolutoinary descent to fit aimals to a great variety of habitats. Ectoderm is shown in gray, mesoderm in red, and endoderm in yellow

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 Endoderm 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

Acoelomate animals have an organ-system level of organization Different organs operate together (ie. excretory system, nervous system) mesodermal tissue gives rise to parenchyma Digestive tract and nervous system Organ= different tissues assembled into functional unit Visceral- internal organs

Polyclad From Red Sea http://www.rzuser.uni-heidelberg.de/~bu6/

Phylum Platyhelminthes Free living Flatworms Parasitic

From Atlantic ocean http://www.rzuser.uni-heidelberg.de/~bu6/

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) Divided into 4 classes: Class Turbellaria (mostly free-living flatworms) Class Trematoda (parasitic flukes) Class Monogenea (ectoparasitic flukes) Class Cestoda (tapeworms) Hymenolepsis- rat tapeworm

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

The best-known turbellarians, commonly called planarians Have light-sensitive eyespots and centralized nerve nets Pharynx. The mouth is at the tip of a muscular pharynx that extends from the animal’s ventral side. Digestive juices are spilled onto prey, and the pharynx sucks small pieces of food into the gastrovascular cavity, where digestion continues. Digestion is completed within the cells lining the gastro- vascular cavity, which has three branches, each with fine subbranches that pro- vide an extensive surface area. Undigested wastes are egested through the mouth. Ganglia. Located at the anterior end of the worm, near the main sources of sensory input, is a pair of ganglia, dense clusters of nerve cells. Ventral nerve cords. From the ganglia, a pair of ventral nerve cords runs the length of the body. Gastrovascular cavity Eyespots Figure 33.10

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

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 Monogenea All parasitic Class Cestoda 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 Tegument= external covering for epithelium

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

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

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

Trematodes that parasitize humans Spend part of their lives in snail hosts These larvae penetrate the skin and blood vessels of humans working in irrigated fields contaminated with infected human feces. Asexual reproduction within a snail results in another type of motile larva, which escapes from the snail host. Blood flukes reproduce sexually in the human host. The fertilized eggs exit the host in feces. The eggs develop in water into ciliated larvae. These larvae infect snails, the intermediate hosts. Snail host 1 mm Female Male 5 2 3 4 Figure 33.11 Mature flukes live in the blood vessels of the human intestine. A female fluke fits into a groove running the length of the larger male’s body, as shown in the light micrograph at right. 1

Chinese Liver Fluke Definitive host: 2 intermediate hosts: 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 Adult worm is 10-25mm long and 1-5mm wide

Class Monogenea Parasitic flukes Mostly ectoparasites Single host, mostly fish

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

Tapeworm Tapeworms Are also parasitic and lack a digestive system Proglottids with reproductive structures 200 µm Hooks Sucker Scolex Figure 33.12

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) No specialized sense organs Mostly cross-fertilization No specialized sense organs scolex

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

Beef Tapeworm Definitive host= human Intermediate host= cattle

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