how do the acoelomates fit in? porifera unknown common ancestor cnidaria triploblastic organ level...
TRANSCRIPT
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
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