Lecture 3 - Phyla Platyhelminthes, Nematoda, Rotifera, Nematomorphia, and Acanthocephala

Learning Objectives

  • Know the taxonomic groups discussed, their relevant distinguishing features, unique anatomical features, and other life history traits (e.g., how to these organisms eat, move, reproduce, etc.)
  • Be able to compare and contrast protostomes and deuterostomes and identify which groups of animals are in these groups
  • Recognize the site of infection and diseased caused by parasitic “worms” throughout this lecture
  • Describe how the animals presented this week demonstrate more organization or appear more complex than ones that we have already studied

Kingdom Animalia

Phylum Platyhelminthes - “Flatworms”

Distinguishing Characteristics

Body Organization: Organs

  • ==Triploblastic==:
    • Three germ layers that develop into three tissue layers
    • Ectoderm - Epidermis
    • Endoderm - Gastrodermis
    • Mesoderm - Mesoderm
    • Acoelomate

Symmetry: ==Bilateral==

First Animals to ==Cephalize== (develop a head region)

Flat bodies allow for simple diffusion of nutrients and waste in/out of body

Digestion: ==gastrovascular cavity==

  • Incomplete digestive system

Excretion: ==flame cells== for fluid balance and nitrogenous waste removal when simple diffusion won’t work

Reproduction: most monoecious

Germ Layers and Protostomes

Remember last week we talked about two development layers

  • Ectoderm and endoderm

There is a later (mesoderm) that develops in the middle of the other two layers

  • Mesoderm gives rise to many internal structures and lining

Blastopore (the hole formed when the blastula is pushed in) has unique development paths

  • ==Protostomes==: blastopore becomes the mouth

Coelom Types

As the mesoderm develops, a fluid-filled cavity called coelom (sometimes) forms

  • ==Acoelomate==: No coelom
  • ==Pseudocoelomate==: A fake coelom forms between the mesoderm and endoderm
  • ==Coelomate==: A true coelom forms and is lined by mesoderm on both sides

The coelom is a cavity that protects internal organs and sometimes acts as a hydrostatic skeleton for some taxa

Class Turbellaria

Commonly referred to as “planarians”

Found in aquatic habitats (freshwater and marine) and moist terrestrial environments

Primarily ==carnivorous== (consume other animals)

  • Consume by sucking food into their retractable pharynx

Dugesia

Found in freshwater environments

Good example for many primitive organs

==Sensory structures==

  • ==Auricle==: sense environment via touch (thigmotaxis) and olfaction (chemotaxis)
  • ==Eyespots==: sense light (phototaxis)
  • ==Cephalization!==

Locomotion

  • ==Cilia== located ventrally
  • ==Rhabdites==: secrete mucus for movement
  • ==Circular, longitudinal, and dorso-ventral muscles in body==

==Digestion:==

  • Highly branched ==gastrovascular cavity== for digestion and nutrient transport
    • Main chambers = trunks
    • Smaller branches = diverticula
  • Retractable ==pharnyx==
  • Incomplete digestive system (no anus) so food has to come back out the same hole

==Reproduction:==

  • ==Monoecious== but reproduction is often sexual
  • Can undergo transverse fission and regenerate

==Excretion==

  • Protonephridia (primitive kidney-like tissue) for osmoregulation
    • ==Flame cells== reside here

==Nervous tissues:==

  • Cerebral ganglion
  • Transverse nerve cords

Class Trematoda

Also called “flukes”

All trematodes (members of this class) are ==parasitic==

  • Internal parasites of molluscs and vertebrates

Use ==suckers== to attach to host tissues from where they drain nutrients

==Cuticle== layer covers body to protect from host’s digestive enzymes

Built to reproduce

  • Some have complex life cycles
  • Some monoecious

Clonorchis

==Digestion==

  • Feed on host tissues
  • ==Oral sucker== anteriorly and ==ventral sucker== on the ventral side to attach to host
  • Mouth - Pharynx - Esophagus - Intestine
  • Incomplete system - no anus

==Excretion==

  • ==Flame cells== gather waste and drain it into the ==excretory bladder== then out from there via the ==excretory pore==

Reproduction

  • Monoecious

Male Organs

  • Testes - Vas Efferens - Vas Deferens - Seminal Vesicle - Genital Pore

Female Organs

  • Ovary: produces eggs
  • Uterus: transports eggs to genital pore as they develop
  • Yolk Sac: provides yolk (full of nutrients for growth) to eggs

Schistosoma - Human Blood Flukes

Infects > 200 million people

  • Only malaria affects more people globally

Various species each infecting different blood vessel regions

Cause the disease ==schistosomiasis== (aka snail fever)

Reproduction

  • Dioecious - strong sexual dimorphism

Class Cestoda

Tapeworms

Most specialized ==endoparasitic== flatworms

  • Infects lower GI tract

No mouth or digestive cavity

  • Nutrients are directly absorbed from the host’s tissues via diffusion

Protective ==cuticle==

==Scolex== (head region) has ==hooks== ==and suckers== for attachment

Body made up of repeating reproductive segments called ==proglottids==

  • As proglottids mature and enlarge, they move towards the end of the tapeworm’s body
  • All proglottids connected by excretory canals and longitudinal nerves

Reproduction

  • Monoecious, but cross-fertilization is preferred
  • Immature proglottids towards the scolex
  • ==Gravid== proglottids with fertilized eggs towards end of body (so eggs can be released into host’s feces)

Taenia

  • Beef tapeworm
  • Infects human and cattle

Dipylidium

  • Double - pored Dog tapeworm
  • Infects dogs and cats

Phylum Rotifera

Most live in freshwater

Symmetry: ==bilateral==

==Pseudocoloemate==

  • Fluid inside serves as hydrostatic skeleton

Complete digestive system

Dioecious

  • Sexual reproduction with internal fertilization
  • ==Parthenogenesis==

Cilia ==corona== (anterior head structure) used for locomotion and feeding

Mouth with pharyngeal apparatus (==mastax==) and jaws for chewing prey for food particles

==Phylum Acanthocephala==

“Spiny-headed worms”

==Parasite== guts of many vertebrate groups

Attach to host tissues using recurved hooks on proboscis

Lack of mouth and digestive canal

  • Nutrient absorbtion

Symmetry: ==bilateral==

==Dioecious==

==Pseudocoelomate==

Example: Roundworms

Phylum Nematoda

Distinguishing Characteristics

==Pseudocoelomates==

  • Serves as hydrostatic skeleton

Symmetry: ==bilateral==

Complete digestive system

Body covered in ==cuticle== external to epidermis

Body Organization: Organ Systems

Nervous system: pharyngeal nerve ring

Various diets

  • Many are endoparasites

Sexual Reproduction

Ascaris

Human intestinal parasite

Dioecious

Cuticle composed of collagen

Complete digestive system

We will perform a dissection of this worm

Estimated to infect 1/4 of humans worldwide

Trichinella

Trichina worms or ‘pork worm’

Mammalian parasite

Causes disease ==trichinosis==

  • Passed via raw pork consumption
  • Pregnant female burrow into intestine
  • After birth, live young travel to muscle tissues to form dormant cysts which can survive for years

Pinworms

Intestinal parasite

Females lay eggs around the host’s anus

Free-living Nematodes

Vinegar eels

  • Consume microbes in unfiltered vinegar

Soil nematodes

  • Consume microbes and small soil animals (other nematodes, etc.)
  • Can cause plant diseases

Phylum Nematomorpha

Horsehair worms

==Parasites== of arthropods (many insects and crustaceans) when immature; adults free-living

Freshwater-dwelling

External cuticle for protection

Simple nerve ring and mucles

No other body systems

==Pseudocoelomate==

==Dioecious==

Protostome Clades

Lophotrochozoa

  1. Feed apparatus called a lophophore (ciliated crown of tentacles surrounding a mouth)
  2. Trochophore larval stage as part of development

Includes:

  • Platyhelminthes, Rotifera, Acanthocephala
  • Mollusca and Annelida

Exdysozoa

All animals in this clade grow via ecdysis (molting their exoskeleton)

Includes:

  • Nemtoda and Nemmatomorpha
  • Arthropoda

In class

Phylum Platyhelminthes Flatworms

  • Triploblastic
  • Acoelomate
  • Bilateral
  • Developed a head region (first)
  • Gastrovascular cavity
  • Flame cells

Germ Layers and Protostomes

  • Protostomes - Blastophore becomes mouth
    • Blastophore - hole formed when the blastula is pushed in

Coelom Types

Acoelomate - No coelom

Pseudocoelomate - Fake coelom

Coelomate - true coelom

Class Turbellaria “Planarians”

  • Carnivorous (Consume other animals)

Dugesia Genus

Sensory structures

  • Auricle: sense environment via touch
  • Eyespots: sense light
  • Cephalization

Locomotion

  • Cilia
  • Rhabdites: secrete mucus
  • Circular, longitudinal, and dorsa-ventral muscles in body

Digestion

  • Gastrovascular cavity
  • Retractable pharynx

Reproduction

  • Monoecious
  • Reproduction is often sexual

Excretion

  • Flame cells reside in protonephridia

Nervous Tissues

  • Cerebral ganglion
  • Transverse nerve cords

Class Trematoda

  • Parasitic
  • Suckers
  • Cuticle

Digestion

  • Oral sucker and ventral sucker

Excretion

  • Flame cells → Excretory bladder → Excretory pore

Reproduction

  • Monoecious

Male and Female Organs

Schistosoma

  • Causes the disease schistosomiasis (aka snail fever)

Class Cestoda

  • Tapeworms
  • Endoparasite
  • Protective cuticle
  • Scolex has hooks and suckers for attachment
  • Have proglottids (repeating reproductive segments)

Reproduction

  • Gravid proglottids with fertilized eggs towards end of body

Phylum Rotifera

  • Bilateral
  • Pseudocoelomate
  • Pathogenesis - Can fertilize themselves
  • Cilia corona - Used for locomotion and feeding
  • Mastax - Chewing food

Phylum Aconthocephala

  • Spiny-headed worms
  • Parasite
  • Bilateral
  • Dioecious
  • Pseudocoelomate

Phylum Nematoda

  • Pseudocoelomate
  • Bilateral
  • Protective cuticle

Trichinella

  • Causes trichinosis - ingested through consumption via raw pork

Phylum Nematomorpha

  • Horsehair worms
  • Parasites
  • Pseudocoelomate
  • Dioecious

Prostostome Clades

Lophotrochozoa

  • Lophophore
  • Trochophore life stage

Acdysozoa

  • Exdysis - shedding of exoskeleton