BSC 201 General Zoology Flatworms

Flatworms present what two evolutionary advances?

Cephalization and primary bilateral symmetry

Around 350 species; less than five mm in length; live in marine sediments; a few are pelagic; most symbiotic, but some are parasitic; asexual or sexual; monoecious; no excretory or respiratory system; digestion direct to cells; nerves are in radial pattern

Phylum Acoelomorpha

Spiral cleavage; mosaic embryo; blastopore becomes mouth; coelom forms by splitting

Superphylum Protostomia

May be filled with fluid or gelatinous material; space for development of digestive, excretory, and reproductive systems

Pseudocoelom

Larvae with whorl of tentacles

Lophotrochozoas

Flatworms; 1 mm to man meters long; found in all habitats; contains free-living and parasitic members; epidermis is not ciliated; have gut, most with mouth, pharynx, and intestine that ends blindly; most metabolic wastes are removed by diffusion across cell membrane; most are monecious but cross-fertilize; if head and tail are cut off, each end grows missing part

Phylum Platyhelminthes

The epidermis of Platyhelminthes contains

Synctial tegument/neodermis

The epidermis of Platyhelminthes is made up of these rod-shaped cells that swell and form a protective mucous sheath

Rhabdites

Flame cells; used by Platyhelminthes for osmoregulation

Protonephridia

The Platyhelminthes nerve system; like nerve net of cnidarians, but with longitudinal nerve cords lying under muscle layer and specialization of sensory and muscular neuron types

Subepidermal nerve plexus

Platyhelminthes sense organs

Ocelli, statocysts, and rheoreceptors

Platyhelminthes sense organs that sense direction of water current

Rheoreceptors

Turbellarians constrict behind pharynx and separate; each half generates missing parts; rapid population growth

Platyhelminthes reproduction through fission

Mostly free-swimming; 5 mm to 50 cm long; simple gut or no gut; simple pharynx; freshwater planarians; brain is bulbed ganglion; swim or move by cilia or glide over slime track; after copulation, eggs and yolk cells enclosed in small cocoon; embryos resemble little adults

Class Turbellaria

Feeding tube in turbellarians

Pharynx

Some turbellarians glide over slime track using adhesive

Dual-glands

Food trapped in mucous from glands and rhabdites; wrap themselves around prey; extend proboscis to suck up bits of food

Planaria

Used by Planarians to detect food

Chemoreceptors

All parasitic flukes; most endoparasites of vertebrates; have quite a few specific adaptations for parasitism; sense organs poorly developed; feed on host cells, cellular debris, or body fluids; non-extendable pharynx; penetrate snail or eaten by host

Class Trematoda

Adaptations for parasitism in Trematoda:

Penetration glands
Glands to produce cyst material
Hooks and suckers for adhesion
Increased reproductive capacity

Indirect life cycle in most; first host is mollusk; final host is vetebrate; second or third host may be required in life cycle; some serious parasites of humans and domestic animals are part of this group; in general life cycle, egg from definitive host in excreta to water, cercariae emerge from snail and penetrate second intermediate host or encyst, and metacariae develop into adults when eaten by definitive host

Subclass Digenea

Free-swimming ciliated larvae; penetrates tissues of snail and transforms into sporocyst

Miracidium/MI

Final host of digenea; vertebrate; digenea sexually reproduce in this host

Definitive host

Second or third host in some digeneans life cycle

Intermediate host

Miracidium transforms into this; reproduces asexually and forms more of same phase or rediae

Sporocyst/SP

Formed by asexually reproduction of sporocyst; reproduce asexually and form more of same phase or cercariae

Rediae/RE

Formed by asexual reproduction of rediae; emerge from snail; penetrate second intermediate host or encyst; develop into metacercariae

Cercariae/CE

Develop from cercariae; develop into adults when eaten by definitive host

Metacercariae/ME

Human Liver Fluke; common in Southeast Asia; also infects dogs, cats and pigs; adult fluke (10-20 mm) with oral and ventral suckers; adults inhabit bile passageways of humans; eggs shed into water with feces; eggs hatch only when eaten by certain snails; bore into fish muscles or under scales; mammals are infected by eating raw fish; heavy infection can destroy liver and result in death

Clonorchis sinensis

Part of Clonorchis sinensis' life cycle in snail
(Blank) transforms into sporocyst after entering snail
(Blank) produces rediae
(Blank) passes into snail liver
(Blank) develop and enter water

Miracidium; Sporocyst; Rediae; Cercariae

In fish, Clonorchis sinensis encysts as

Metacercariae

Sheep liver fluke; adult fluke lives in Nile passageways of sheep and other ruminants; cercariae encyst on vegetation and await being eaten by sheep

Fasciola hepatica

Blood Flukes; More thane 200 million people across world contain this parasite; three species account for most human infections; causes swimmers itch when cercariae penetrate human skin

Schistosoma

One of three main Schistosoma species responsible for schistosomiasis; found in venules of large intestine

Schistosoma mansoni

One of three main Schistosoma species responsible for schistosomiasis; found in venules of small intestine

Schistosoma japonicum

One of three main Schistosoma species responsible for schistosomiasis; found in venules of urinary bladder

Schistosoma haemotobium

Produces colorful sporocysts in snails' heads; attract birds to eat snails and continue life cycle

Leucochloridium

External parasites of fish or endoparasites pf bladders of fish and turtles; direct life cycle with single host; economic importance for fish farmers; mouth opens near anterior end

Class Monogenea

Attaches to host by posterior by posterior hooks; found in monogeneans

Oncomiracidium

Hooks, suckers, and/or clamps; vary widely; found in monogeneans

Opisthaptors

Tapeworms; more than 1000 species; long, flat bodies with scolex; no digestive system, as they use hosts digestive tract; muscles, excretory, and nervous systems similar to other flatworms; eggs hatch only after being consumed by host; nearly all species require two hosts

Class Cestoda

Holdfast structure with suckers and/or hooks

Scolex

Reproductive units of Cestoda

Proglottids

Larvae have 6 hooks on scolex; mostly consist of chain of proglottids; adults found in vertebrates; most species do little harm

Eucestoda

Chain of proglottids

Strobila

Whale tapeworm; found in arctic water in toothed whales; can reach 130 ft long; highly fecund (muchos babies)

Tetragonoporus calyptocephalus

Beef Tapeworm; lives as adult in humans; juvenile found in muscle of cattle; mature adults can get 10 meters long and produce more than 2000 proglottids; Gravid proglottids pass in feces, crawl out, and rupture as they dry; proglottids or larvae are viable for five months and are ingested by grazing

Taenia suginata

Pork Tapeworm; can cause cysticercosis if they get in human eyes or brain, causing blindness, serious neurological symptoms, or death

Taenia solium