Acoelomorpha, Platyzoa and Mesozoa Chapter 8 Acoelomorpha, Platyzoa and Mesozoa

Acoelomate Bilateral Animals Characteristics: bilateral symmetry Marine, freshwater, terrestrial Free-living and parasitic cephalization Triploblastic Ectoderm Mesoderm Endoderm organ level of development no coelom cavity

Pseudocoelomate Bilateral Animals Characteristics: has an internal cavity that surrounds gut But, cavity is not completely lined with mesoderm tissue as in a true coelomate Cavity may be filled with fluid or a type of matrix material Digestive, excretory, reproductive, waste storage, hydrostatic support

Phylum Acoelomorpha “without” “hollow” “form” (350 species) New “contentious” Phylum (used to be in Platyhelminthes as a part of Turbellaria) Characteristics: Entirely Marine living in sediment Small, flat, under 2 mm No gut: mouth, pharynx, vacuole No excretory system Monoecious, but no gonads: gametes formed from mesenchyme cells in the body

Acoelomorpha

Protostome subgroups: Ecdysozoa (“to strip off”) (8 phyla) includes all animals that molt Lophotrochozoa (“crest or tuft”, “wheel”) (17 phyla) Horseshoe-shaped whorl of tentacles Band of cilia found on larvae (trochophore)

Lophotrochozoa Clade Platyzoa Include the following phyla: Platyhelminthes Gastrotricha Gnathostomulida Micrognathozoa Rotifera Acanthocephala

Phylum Platyhelminthes – Flat worms (20,000 species) 1. Class Turbellaria free living – fresh/marine, terrestrial scavengers glandular cells rhabdites (mucous sheath) adhesive (attachment) releaser (dissolver)

Organ Systems Digestion branched tract running down body pharynx chemoreceptors carnivores/herbivores Respiration: no organs – diffusion through body wall Excretion--protonephridia – tubules down each side of body flame cells – enlarged cells with cilia waste released through a nephridiopore

Nervous nerve net – sub-epidermal nerve plexus statocyst – equilibrium cerebral ganglia or nerve cords and neurons Sense organs auricles – sensory lobes on side of head chemoreceptors for finding food ocelli – eye spots or cups orients animal to light (anti-light) through these photoreceptors

Reproduction asexually – transverse fission regeneration of body parts sexually – mostly monoecious male parts: testes run along back side vas deferens – sperm ducts seminal vesicle – store sperm Penis

female parts: ovaries 1- ? pairs oviduct genital chamber genital pore copulatory sac

Copulation usually between two different animals. Sperm deposited in copulatory sac moves to genital chamber to oviducts to ovaries fertilization zygote formed yolk glands cover egg Eggs will be laid outside of body Some will have cocoon. If summer: takes 2-3 weeks to “hatch”. If autumn: wait until spring.

Planaria cs

Planaria

Undergoing transverse fission

Other Turbellarians

Turbellarians

2. Class Monogenea – single host Ectoparasites of fish – attach to gills and feed on epithelial cells Don’t seem to do much harm Opisthaptor – large, posterior attaching device (suction/hooks) Egg—larva--host

Monogenea

Monogenea

3. Class Trematoda – flukes (8,000) All are parasites of vertebrates Tegument over outer body –cells fuse to form a continuous layer of cells known as syncytium Able to form cysts Complicated life cycle

Fluke body plan

Subclass Digenea – two different forms Largest group most medically important group of flukes adhesive organs oral sucker Ventral sucker - acetabulum operculum – lid on egg miracidium – ciliated larvae

Life cycle Egg containing miracidium swims to intermediate host (snail) loses cilia becomes a sporocyst undergoes asexual reproduction producing 100’s of cercaria (“polyembryony”) leaves snail and finds a 2nd I.H. or final host becomes a metacercariae (cyst) eaten by definitive host You are in BIG TROUBLE!

Egg with Operculum

Egg with miracidium

Cercaria

Adult worm

Examples: Chinese liver flukes Blocks bile ducts 50 million people affected raw fish sheep liver fluke Schistosomiasis (blood) 200 million affected Paragonimus (lung) Swimmers itch (skin)

Chinese Liver Fluke

Schistosomiasis

Male and Female worm

Swimmers Itch

4. Class Cestoda – tape worms (3,500 species) long, flat bodies endoparasites no mouth, no digestive system tegument proglottids (strobila) 1 mm to 15 meters in length two hosts required

Body structure: scolex neck strobila – proglottids gravid (full of mature eggs) life cycle of beef tapeworm Taeniarhynchus saginatus proglottid (holding up to 80,000 eggs!) breaks off and is expelled from the small intestine each egg will become a larva having 6 hooks known as a onchosphere

Scolex

Tapeworm Larvae

Beef Tapeworm

cattle grazing on grass eat the larva the onchosphere uses hooks to bore into the intestinal wall to the blood stream then to muscles encysts in the muscle becoming a cysticercus (bladder worm) causing what is known as “measly beef” human eats beef that is improperly cooked, the cysticercus then is released from the meat and starts to live in the intestine the cycle starts over again

Figure 14.19

Other important tapeworms: Taenia solium Pork (can get into the brain) Diphyllobothrium latum fish (Great Lakes)

Moral to the Story: COOK YOUR MEAT!!!!!!!!

Phylum Gastrotricha “stomach” “hair” (460 species) Benthic – found in fresh and marine 65-500 um long bottom sediments bristles and spines forked tail with adhesive glands Monoecious –male system nonfunctional in freshwater

Gastrotrich

Glade or Group Gnathifera Groups of “jaw bearing” tiny, free-living aquatic animals Coeloms: “a-” or “pseudo-” Some protostome and deuterostome characteristics Four phyla Eutely – constancy in the number of nuclei present (epidermis)

Phylum Gnathostomulida “jaw” “mouth” “diminutive” (80 species) Jaw worms (80 species) Characteristics: usually less than 1 mm marine coastlines (sand and silt) live in very low oxygen - Respiration through diffusion Acoelomate pharynx has a pair of lateral jaws to gather food No anus One cilia in each epidermal cell no circulatory system Monoecious - simultaneous

Jaw Worm

Phylum Micrognathozoa Only one species found - Greenland Tiny – less than 142 micro-meters Interstitial in sand Two-part head, thorax, an abdomen and short tail. Dorsal plates Cilia Very complicated jaw with plates and teeth, mouth leads to a simple gut and an anus Only females found so far

Micrognathozoan

Phylum Rotifera “wheel” “to bear” (2000 species) corona – ciliated organ at head freshwater foot with toes pedal glands secrete adhesive external cuticle mastax – pharynx where food is ground

Reproduction – a little strange! If there are no males – females produce amictic (diploid) eggs which develop into females If there are males and females – females will produce amictic and mictic (haploid) eggs. Amictic turn into females. Mictic if left unfertilized turn into males, if fertilized become females So diploids are females, haploids are males Males have an eversible penis that can inject sperm into the pseudocoelom -- known as hypodermic impregnation

Rotifera

Phylum Acanthocephala “spine” “head” (1100 species) Spiny-headed worms 2 mm – 1 m pseudocoelom endoparasites in the intestional tract of vertebrates (mainly fish) two hosts are needed for life cycle juveniles – crustaceans and insects adults – vertebrates proboscis covered with retractable spines glycocalyx covers tegument—protects against host immune defenses no digestive system – absorbs host food like tapeworms

dioecious – fertilization internal life cycle: eggs will be in a shelled larvae which leaves the host must be eaten by an insect or arthropod larvae will emerge called an acanthor the acanthor will burrow through gut of host where it will develop into an acanthella and then into a cystacanth first host will be eaten by a fish, bird (or other vertebrate) the cystacanth will excyst and attach to the intestinal wall. Here we go again!

Spiny Headed Worms

Phylum Mesozoa “middle” “animal” Characteristics : Has no organs or tissues Body possesses no digestive tract Body only has two cell layers in most places Only 20-30 cells Has no nervous system Has some cells develop inside other cells Reproduction quite complex involving both sexual and asexual aspects All are endoparasites on other marine invertebrates