How do the acoelomates fit in?

Porifera

unknown common ancestor

Cnidaria

triploblastic

organ level of organization

Platyhelminthes

protonephridia

cephalization

Ladder-like nervous system

Nemertea

proboscis

Complete digestive system

Closed circ. systemacoelomate

acoelomate

How do the Pseudocoelomates fit in?

unknown common ancestor

Porifera

Cnidaria

Platyhelminthes Nemertea

the pseudocoelomates

NematodaRotifera

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 cavityectodermectoderm

mesoderm

endoderm

Gut

pseudocoelom

the pseudocoelom is lined by mesoderm on ONE side only

Pseudocoelomate Characteristics

the pseudocoelomectoderm

• 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

• with anterior and posterior ends

Bilateral Symmetry

Cephalization

• concentration of sensory organs in the head of the animal

Pseudocoelomate Characteristics

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

Digestive System

Circulation System

• no system (or organs)• performed by the pseudocoelom fluid

Pseudocoelomate Characteristics

• each individual of a species has the same # of cells

• growth occurs by cells getting bigger rather than dividing

Eutely

Phylum Nematoda

the roundworms

Physiology

Life Style– Free-living– parasitic

Digestion– complete system (have an anus)– some regional specialization (e.g.

an esophagus)

PhysiologySkeletal 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

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

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

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

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

ParasitesTrichinella 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 Rotiferathe rotifers

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

a modified muscular pharynx

modified jaws

within the mastax

Looking down into the corona….

PhysiologySome of the trophi (jaws):

Physiology

Life Style– Free-living

Digestion– complete system (have an anus)– some regional specialization (e.g.

mastax-trophi complex)

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

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)

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)

Physiology

• 2 types of eggs: amictic & mictic

Amictic eggs

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

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

• 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!

Ecology

Here are some of the other pseudocoelomate phyla

Loricifera

Priapulida

Kinorhyncha

Nematomorpha

Acanthocephala

Entoprocta

Gastrotricha

How do the Pseudocoelomates fit in?

unknown common ancestor

Porifera

Cnidaria

Platyhelminthes Nemertea

Nematoda Rotifera

triploblasticorgan level of organization

mastax-trophicorona

pseudocoelomno cilia

longitudinal muscles only

complete digestive system