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How do the acoelomates fit in?. Nemertea. Platyhelminthes. acoelomate. Complete digestive system. acoelomate. Closed circ. system. Ladder-like nervous system. Cnidaria. proboscis. Porifera. cephalization. protonephridia. organ level of organization. triploblastic. unknown

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how do the acoelomates fit in
How do the acoelomates fit in?

Nemertea

Platyhelminthes

acoelomate

Complete digestive system

acoelomate

Closed circ. system

Ladder-like nervous system

Cnidaria

proboscis

Porifera

cephalization

protonephridia

organ level of organization

triploblastic

unknown

common ancestor

how do the pseudocoelomates fit in
How do the Pseudocoelomates fit in?

Rotifera

Nematoda

the pseudocoelomates

Platyhelminthes

Nemertea

Cnidaria

Porifera

unknown

common ancestor

pseudocoelomates
Pseudocoelomates

There are 9 different phyla that are classified as pseudocoelomates.

We are only covering 2 phyla:

Nematoda

Rotifera

pseudocoelomate characteristics
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 characteristics1
Pseudocoelomate Characteristics

“false” body cavity

ectoderm

ectoderm

pseudocoelom

mesoderm

Gut

endoderm

the pseudocoelom is lined by mesoderm

on ONE side only

pseudocoelomate characteristics2
Pseudocoelomate Characteristics

the pseudocoelom

ectoderm

  • 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 characteristics3
Pseudocoelomate Characteristics

Bilateral Symmetry

  • with anterior and posterior ends

Cephalization

  • concentration of sensory organs in the head of the animal
pseudocoelomate characteristics4
Pseudocoelomate Characteristics

Digestive System

  • complete (they have an anus!)
  • some regional specialization

Circulation System

  • no system (or organs)
  • performed by the pseudocoelom fluid
pseudocoelomate characteristics5
Pseudocoelomate Characteristics

Eutely

  • each individual of a species has the same # of cells
  • growth occurs by cells getting bigger rather than dividing
phylum nematoda

Phylum Nematoda

the roundworms

physiology
Physiology

Life Style

  • Free-living
  • parasitic

Digestion

  • complete system (have an anus)
  • some regional specialization (e.g. an esophagus)
physiology1
Physiology

Skeletal system

  • fluid in pseudocoelom acts as a hydrostatic skeleton

Cuticle

  • covers body (secreted by epidermis + composed mostly of collagen)
  • functions as a primitive external skeleton
physiology2
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

physiology3
Physiology

Nervous system

  • cephalization, cerebral ganglia
  • dorsal and ventral nerve cords

Circulatory system

  • No system (no organs)
  • performed by fluid in pseudocoelom

Excretion

  • Renette glands
physiology4
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

physiology5
Physiology

Reproduction

Sexual

  • usually dioecious
  • often the sexes are sexually dimorphic
  • internal fertilization
  • males have ameboid sperm
ecology
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
ecology1
Ecology
  • Many nematodes are important parasites of both plants and animals.

parasite of soybean plants

parasite of tomato plants

parasites
Parasites
  • Eye worm (Loa loa):
  • transmitted by fly bites
  • larvae go through bloodstream
  • adults live in subcutaneous tissue
parasites1
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

parasites2
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
parasites3
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
parasites4
Parasites
  • Trichinella spiralis:
  • causes Trichinosis
  • transmitted by eating undercooked pork
  • juveniles encyst within host muscle cells

juvenile

Host muscle cell

slide24

Parasites

Heartworms (Dinofilaria immitis):

ecology2
Ecology
  • The study of the model nematode C. elegans has resulted in important discoveries in genetics and development.
phylum rotifera

Phylum Rotifera

the rotifers

physiology6
Physiology

Feeding

  • have a “crown” of cilia called a corona
  • the corona creates a

current to bring food into

the mouth

physiology7
Physiology

Feeding

  • have a specialized feeding structure called the:

mastax-trophi complex

modified jaws

within the mastax

a modified

muscular pharynx

physiology8
Physiology

Some of the trophi (jaws):

physiology9
Physiology

Life Style

  • Free-living

Digestion

  • complete system (have an anus)
  • some regional specialization (e.g. mastax-trophi complex)
physiology10
Physiology

Skeletal system

  • 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
physiology11
Physiology

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)
physiology12
Physiology

Reproduction

Sexual

  • 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)

physiology13
Physiology
  • 2 types of eggs: amictic & mictic

Amictic eggs

  • diploid (mitotically produced)
  • can’t be fertilized
  • develop into diploid, amictic females
physiology14
Physiology

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
ecology3
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!
slide40

Kinorhyncha

Loricifera

Nematomorpha

Priapulida

slide41

Acanthocephala

Gastrotricha

Entoprocta

how do the pseudocoelomates fit in1
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