Platyhelminthes & Nematoda The un-segmented worms

Earland

GENERAL CHARACTERISTICS 18,500 species Simplest animals with bilateral symmetry Exhibit some cephalization Three germ layers (i.e.:triploblastic) Acoelomate: no mesodermal lined cavity 3 classes parasitic, 1 class free-living

Flatworm Organ Systems Biology: Life on Earth (Audesirk) Flatworm Organ Systems Pharynx (a) Digestive System Excretory Canal Gastrovascular Cavity Excretory Pore (b1) Excretory System Flatworms such as planarians have well-developed organ systems. (a) The elaborately branched digestive system, the centrally located ventral pharynx, and eyespots in the head are clearly visible. (b) (Left) The excretory system consists of branching tubes that conduct excess fluid to the outside through numerous pores. Cilia keep the fluid moving. (Right) The nervous system of flatworms shows clear cephalization, with eyes and a brain composed of ganglia cells in a well-defined head. Ladderlike nerve cords carry signals through the rest of the body. (b2) Nervous System Nerve Cord Brain Chapter 22 Chapter 22

ESSENTIAL FUNCTIONS Because they are flat, flatworms have no specialized circulation or respiration. They simply use diffusion across body wall. In addition to diffusion, flatworms use protonephridia (simple kidney-like structure) to osmoregulate (control water balance). Within the protonephridia, there are beating cilia which draws fluid through. Because this looks like a flickering candle, these cells are dubbed flame cells.

Digestion Digestion: 1 way (like us!): Pharynx is on underside of flatworm and sucks food into the gastrovascular cavity. Intestine branches the length of the flatworm, so digested food can be delivered to all body tissues

Reproduction & Movement Reproduction: Most flatworms are simultaneous hermaphrodites. Each individual can function as both male and female. Although a single individual cannot fertilize itself. Movement: Secrete mucus and use cilia on their epidermal cells to glide across bottom, as well as muscle contractions which allows them to twist and turn.

Classes of Flatworms Class Turbellaria-planarians, free-living, non-parasitic, live in moist environments Class Trematoda-flukes, parasites that absorb nutrients from the body of a host harming it, may have more than 1 host Class Cestoidea-tapeworms, parasitic, live inside 1 or more hosts, contain flat segments each with reproductive organs Earland

Class Tubellaria Class Turbellaria 16% of flatworms Most species are free living. Most live in marine environments Diet includes: bacteria, algae and invertebrates Considerable powers of regeneration in some species

Class Cestoda Class Cestoda Endoparasites: Internal parasites Celebrity cestoda: Tapeworm Hosts are primarily vertebrates. Extremely high specialization for parasitic lifestyle. No ciliated epidermis. No mouth, instead has scolex studded with hooks and suckers. Scolex attaches to the intestinal wall

An intermediate host is required, such as a cow, fish or pig. It is estimated that 135 million people are infected with tapeworms. Symptoms include: Nausea, weakness, loss of appetite, abdominal pain, diarrhea and weight loss Most of the body is made up of repeating reproductive segments called proglottids. A single proglottid may contain over 100,000 eggs!  An intermediate host is required, such as a cow, fish or pig.

Class Trematoda Class Trematoda Parasitic worms known as flukes. Some are ectoparasites parasites, living on skin, mouth and gills of host. Celebrity Tremadode: Schistosoma, humans are primary hosts.

Schstoma Life Cycle Schistosoma lay so many eggs in blood vessels of the intestine that blood vessels burst and eggs and blood are released into intestine.

Pseudocoelomates Nematoda Rotifera

How do the Pseudocoelomates fit in? Rotifera Nematoda the pseudocoelomates Platyhelminthes Nemertea Cnidaria Porifera unknown common ancestor

Pseudocoelomates There are 9 different phyla that are classified as pseudocoelomates. We are only covering 2 phyla: Nematoda Rotifera

Pseudocoelomate Characteristics Organ level of organization Tissues are organized to for organs which are used to accomplish physiological functions Triploblastic 3 Germ Layers endoderm mesoderm ectoderm 3 Tissue Layers gastrodermis mesoderm epidermis

Pseudocoelomate Characteristics “false” body cavity ectoderm pseudocoelom mesoderm Gut endoderm the pseudocoelom is lined by mesoderm on ONE side only

Pseudocoelomate Characteristics the pseudocoelom is a closed, fluid filled cavity contains digestive, excretory, and reproductive structures the fluid within acts as a circulatory system the fluid within acts as a hydrostatic skeleton against which the muscles work

Pseudocoelomate Characteristics Bilateral Symmetry with anterior and posterior ends Cephalization concentration of sensory organs in the head of the animal

Pseudocoelomate Characteristics Digestive System complete (they have an anus!) some regional specialization Circulation System no system (or organs) performed by the pseudocoelom fluid

Pseudocoelomate Characteristics Eutely each individual of a species has the same # of cells growth occurs by cells getting bigger rather than dividing

Phylum Nematoda the roundworms 1st phyla we will talk about and what we will cover in the lab today is…

Nematodes Most abundant living animals include the roundworms –closely related to insects than others. Cylindrical and bilateral body, a complete gut and a false coelom filled by reproductive organs. Have flexible cuticle – undergo repetitive molting as it grows. Free living sp that are decomposers and agricultural pests. Others are parasites to humans, dogs and insects.

Roundworms-Phylum Nematoda Roundworms-small, cylindrical worms with pointed heads and tapered tails 3 tissue layers Complete digestive tract with mouth and anus Digestion highly specialized Free-living and non-parasitic roundworms are the most abundant but parasitic types are hookworm, pinworm, threadworm and trichinosis Many are introduced through poorly cooked pork or walk barefoot in infected areas Earland

The Invertebrate Phyla: Nematoda (Round Worms) Advanced gastrovascular cavity Tubular Two openings Advanced sensory "ganglionic brain" Lack circulatory and respiratory systems Depend on diffusion for gas exchange Sexual reproduction Most are harmless - Some parasitic Chapter 22

Physiology Life Style Digestion Free-living parasitic complete system (have an anus) some regional specialization (e.g. an esophagus)

Physiology Skeletal system Cuticle fluid in pseudocoelom acts as a hydrostatic skeleton Cuticle covers body (secreted by epidermis &composed mostly of collagen) functions as a primitive external skeleton

Physiology Movement longitudinal muscles ONLY (results in “whiplike” motion) No external/internal cilia  even sperm don’t have flagella http://www.devgen.com/devpage/largeimage/wild.html

Physiology Circulatory system Excretion Nervous system cephalization, cerebral ganglia dorsal and ventral nerve cords Circulatory system No system (no organs) performed by fluid in pseudocoelom Excretion Renette glands

Physiology Reproduction Sexual usually dioecious often the sexes are sexually dimorphic (males and females look different) Males often have a spicule at the end of their tail used to insert their sperm into the female

Physiology Reproduction Sexual usually dioecious often the sexes are sexually dimorphic internal fertilization males have ameboid sperm

Ecology There are >12,000 species that are found in almost all habitats (marine, freshwater, underground, inside plants and animals, etc…). They are also incredibly abundant. For example: a m² of soil may contain >4 million nematodes a decomposing apple may contain >90,000 nematodes of a single species

parasite of soybean plants parasite of tomato plants Ecology Many nematodes are important parasites of both plants and animals. parasite of soybean plants parasite of tomato plants

Parasites Eye worm (Loa loa): transmitted by fly bites larvae go through bloodstream adults live in subcutaneous tissue

Parasites Intestinal roundworm (Ascaris): transmitted by contaminated food adults live in small intestine it’s estimated that 20% of world’s population is infected (~1.3 billion people) this intestine was completely blocked

Parasites Guinea worm (Dracunculus medinensis): transmitted by infected copepods in drinking water larvae move into the body cavity female adult migrates to the subcutaneous tissue, causes an ulcer/blister, and releases eggs through hole when host comes in contact with water

Guinea worm

Parasites Guinea worm (Dracunculus medinensis): traditionally removed by winding the worm around a matchstick over the course of several days this may be the basis for the Caduceus symbol used in the medical field

Parasites Trichinella spiralis: causes Trichinosis transmitted by eating undercooked pork juveniles encyst within host muscle cells juvenile Host muscle cell

Parasites Heartworms (Dinofilaria immitis):

Ecology The study of the model nematode C. elegans has resulted in important discoveries in genetics and development.

Phylum Rotifera the rotifers 1st phyla we will talk about and what we will cover in the lab today is…

The “wheel” animals

Physiology Feeding have a “crown” of cilia called a corona the corona creates a current to bring food into the mouth

Physiology Feeding have a specialized feeding structure called the: mastax-trophi complex modified jaws within the mastax a modified muscular pharynx

Looking down into the corona….

Physiology Some of the trophi (jaws):

Physiology Life Style Digestion Free-living complete system (have an anus) some regional specialization (e.g. mastax-trophi complex)

Physiology Movement Skeletal system the corona fluid in pseudocoelom acts as a hydrostatic skeleton Movement the corona pedal glands (produce adhesive), as well as foot and toe (spurs) for attachment to substrate

Physiology Circulatory system Excretion Nervous system cephalization, cerebral ganglia dorsal and ventral nerve cords Circulatory system no system (no organs) performed by fluid in pseudocoelom Excretion protonephridia and flame cells cloacal bladder (collects wastes)

Physiology Sexual Reproduction complex life cycle with different types of eggs usually dioecious but in some groups, males are absent (parthenogenesis) Parthenogenesis: unisexual reproduction where females produce offspring from unfertilized eggs (virgin birth)

Physiology Amictic eggs Mictic eggs haploid (meiotically produced) produced after some sort of environmental stimulus (eg. high density, change in temperature) if unfertilized, develop into haploid males if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females diploid (mitotically produced) can’t be fertilized develop into diploid, amictic females

Ecology There are ~1500 species. Although they are found mainly in freshwater habitats, there are a few marine rotifer species and a couple of species are even found in mosses! Because of the reduced role of males in reproduction, most males are incapable of feeding and do not even have a digestive tract (they are just there for sperm delivery!). Males have never been recorded in Bdelloid rotifers. This means they haven’t had sex in millions of years!

Here are some of the other pseudocoelomate phyla

Kinorhyncha Loricifera Nematomorpha Priapulida

Acanthocephala Gastrotricha Entoprocta

How do the Pseudocoelomates fit in? Rotifera Nematoda mastax-trophi no cilia corona longitudinal muscles only pseudocoelom Platyhelminthes Nemertea Cnidaria complete digestive system Porifera organ level of organization triploblastic unknown common ancestor