Developmental Variations During embryonic development the process of gastrulation forms the digestive cavity Gastrulation varies in the animal kingdom No gastrulation placozoans ID: 710115
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Slide1
The Deuterostomes
Echinoderms and ChordatesSlide2
Developmental Variations
During embryonic development, the process of
gastrulation
forms the digestive cavity.
Gastrulation
varies in the animal kingdom
No
gastrulation
(
placozoans
)
Incomplete
gastrulation
Forms a
gastrovascular
cavity with one opening
Complete
gastrulation
Forms a digestive tract with 2 openingsSlide3
Animals with Complete Gastrulation
Complete
gastrulation
forms a true digestive tract with 2 openings, the mouth and the anus
In
protostome
animals, the first opening of the gastrula forms the mouth
In
deuterostome
animals, the second opening of the gastrula forms the mouthSlide4
Deuterostome Phyla
There are 3 phyla characterized by
deuterostome
development
Echinoderms
Sea Cucumbers, Crinoids, Sea Stars, Brittle Stars and Sea Urchins
Hemichordates
Acorn Worms and
Pterobranchs
Chordates
Tunicates, Lancelets, Jawless fish and VertebratesSlide5
Phylum Echinodermata
The echinoderms are unusual in the animal kingdom in that they have a great deal in common with the chordates and hemichordates, but also differ in ways that do not appear anywhere else in the animal kingdom
It seems unlikely that their similarities with other
deuterostomes
are the result of convergent evolution, so it seems that through the course of evolution the
echinoerms
have lost a number of ancestral characters retained in the other phylaSlide6
Characters retained:
Embryonic development &
Gastrulation
Triploblastic
Complete digestive tract
Body Cavity
Eucoelomate
Symmetry
Bilateral during larval stagesSlide7
Characters lost or diminished:
Segmentation
Cephalization
No head, brain or specialized sense organs
Sensory apparatus are not centralized
Bilateral symmetry in the adult form
The bilateral symmetry in the larvae goes through a dramatic metamorphosis, reorganizing the body into a
Pentaradially
Symmetrical adultSlide8
Metamorphosis
The
coelom
forms as a U shape, which pinches off into 3 distinct cavities, 2 of which will become diminished
The digestive tract becomes reorganized, with the formation of new mouth and anal openings and a new orientation (mouth on the left and anus on the right)
The left and right sides of the larvae undergo differential development, with the left side forming the oral surface and the right side forming the
aboral
surfaceSlide9
Derived characters special to the Echinoderms
Water-vascular system
Consisting of a
madroporite
, a system of canals (stone canal, ring canal, radial canals and lateral canals) and sucker tipped tube feet
Dermal endoskeleton
Consisting of calcified plates called
ossicles
and a variety of spines and
pedicellaria
Hemal
system
Poorly understood, it appears to function for distribution of materials
Pentaradial
symmetry
Organs radiate from a central disc, characteristically in a pattern of fivesSlide10
Water Vascular SystemSlide11
Tube FeetSlide12
Crinoids (Sea Lilies)
https://
www.youtube.com/watch?v=cZcomBnNKXg&feature=related
https://
www.youtube.com/watch?v=hAdEfdyKBHM
https://
www.youtube.com/watch?v=jg_0UdbSRsM&feature=relmfu
https://
www.youtube.com/watch?v=XR4NnmJfEXcSlide13
Sea Stars
https://
www.youtube.com/watch?v=pSo30lRHaAw
https://
www.youtube.com/watch?v=I8as-z-EShc
https://www.youtube.com/watch?v=-
ardrFZuFkU
https://
www.youtube.com/watch?v=qC89SLOXIvs
https://
www.youtube.com/watch?v=TioCree5axI
https://
www.youtube.com/watch?v=Xm2mF2IgLrASlide14
Brittle Stars
https://
www.youtube.com/watch?v=Myhp8ifW6ig
https://
www.youtube.com/watch?v=Chs8Vk-6hooSlide15
Sea Cucumbers
https://
www.youtube.com/watch?v=vsLBOkYLLeI
https://
www.youtube.com/watch?v=iYSbLr-mVkM
https://
www.youtube.com/watch?v=6mx0GDxfjQ4Slide16
Sea Urchins
https://
www.youtube.com/watch?v=eGixkoZwEUs
https://
www.youtube.com/watch?v=oljZbs5haaY
https://
www.youtube.com/watch?v=WI7ZCK8aWoMSlide17
Echinoderms - Video
Sea Stars
https://www.youtube.com/watch?v=A100m5EpfFI
https://www.youtube.com/watch?v=rE8l-KFQlhY
Sea Urchins
https://www.youtube.com/watch?v=nD7_0obUm0o
https://www.youtube.com/watch?v=D3W4OCnHyCs
Sand Dollars
https://www.youtube.com/watch?v=bSsgDhWpPq0
https://www.youtube.com/watch?v=gLK71-vsi2ESlide18
Phylum Hemichordata
Hemichordates are
deuterostomes
, a characteristic they share with both echinoderms and chordates
As the name suggests, hemichordates have some derived characteristics that are ancestral to the phylum
chordata
Dorsal, hollow nerve cord
Gill slits in the pharynx
These traits are shared with all chordates, but are absent in the echinodermsSlide19
Hemichordate Diversity
The phylum
Hemichordata
consists of two classes
The Acorn Worms (
Enteropneusta
)
The
Pterobranchs
The Acorn Worms and the
Pterobranchs
are similar in body form, but vary with regard to feeding structures
Feeding structures in both are ciliated to collect food particles and direct them to the mouthSlide20
Acorn Worms – Feeding
The acorn worms have a muscular proboscis used for food gathering located anterior to the mouth opening
The mouth is ventrally located
A collar is associated with the mouth, and is used both to direct food into the mouth and to redirect particles too large to ingest
Acorn worms are free living and burrow actively to search for foodSlide21
Pterobranchs - Feeding
The proboscis itself is shield shaped
The base of the proboscis bears several tentacles which extend into the water to create a food gathering surface for filter feeding
Pterobranchs
move freely inside of a
collagenous
tube, but are sessile in that they are restricted to life within that tubeSlide22
Gill Slits in the Pharynx
Hemichordates have one or more pairs of gill slits that allow water from the pharynx to pass out of the animal, rather than being ingested
Cilia maintain water flow through the gill pouches
Aside from providing a mechanism for filtering and concentrating food particles, the gill pouches create a surface for gas exchange. Slide23
Central Nervous System
A point of emphasis in our discussion of the evolution of the central nervous system has been the presence in many invertebrate phyla of ventral nerve cords
A ventral nerve cord persists in the hemichordates, but is accompanied by a dorsal nerve cord
The dorsal nerve cord is hollow because it is formed by an
invagination
of
ectodermal
embryonic tissue, as is the “spinal cord” associated with the chordatesSlide24
Phylum Chordata
The chordates are
deuterostomes
– they possess a complete digestive tract with the mouth forming from the 2
nd
opening of the gastrula
Chordates, like the hemichordates, have a dorsal hollow nerve cord. Unlike hemichordates they do not have a persistent ventral nerve cord
All chordates, at some time in their development, have pairs of pharyngeal gill slitsSlide25
The Notochord
The distinguishing characteristic of phylum
Chordata
is an endoskeleton centered around the formation of a notochord
The notochord is a rod of
mesodermal
tissue located on the dorsal side of the animal that extends almost the full length of the body
The notochord lies just ventral to the nerve cord that forms the central nervous systemSlide26
More notochord stuff
In the simplest of the chordates, the notochord is a simple rod of tissue with a fibrous sheath that provides some level of longitudinal rigidity
In other chordates, the notochord may exhibit pronounced segmentation, and may or may not become ossified (impregnated with calcium, forming bone)Slide27
Ancestral and Derived Characters
Aside from the shared ancestral characteristics that Chordates share with their closest relatives
(
deuterostome
development, notochord, dorsal hollow nerve cord & pharyngeal gill slits)
the Chordates share 2 derived characteristic only with other Chordates:
An
endostyle
(from which the thyroid gland is derived)
A post-anal tailSlide28
The Endostyle
The
endostyle
is a specialized organ associated with the pharynx
In some of the invertebrate chordates the
endostyle
functions largely as a filter-feeding apparatus, secreting mucus for trapping food particles in the pharynx
The
endostyle
persists in Chordates that do not filter feed. The thyroid gland is derived from the embryonic
endostyle
, and retains a function related to feeding and metabolismSlide29
Chordate Diversity
The Chordates are a diverse phylum, including both invertebrate and vertebrate classes
The
Protochordates
are invertebrate filter feeders, and consist of the
Urochordates
(tunicates) and the Cephalochordates (lancelets)
The
Agnatha
are the jawless fish. They are the simplest bodied vertebrates, with a cranium and a well developed tripartite brain (three regions: forebrain, midbrain, hindbrain)Slide30
Protochordates: TunicatesSlide31
Tunicate Anatomy
Tunicates are filter feeders
Water enters the mouth, filters through the gill slits in the pharynx, and passes out through the atrial siphon
Food passes through a complete digestive tractSlide32
Protochordates: LanceletsSlide33
Lancelet Anatomy
Lancelets are filter feeders like the tunicates, but they have more fully developed musculature, notochord and dorsal nerve cordSlide34
Vertebrates with Jaws
The most familiar Chordates are the Vertebrates.
Aside from the
Agnatha
, the remaining vertebrate Chordates have jaws derived from the first 2 pairs of gill arches
The ability to process food has evolved independently in many different phyla. Any level of processing has the potential to improve digestion and thus increase the chances of survivalSlide35
Vertebrate Diversity - Fish
Agnatha
– jawless fish (hagfish and lampreys)
Chondrichthyes
– jawed fish with cartilage skeletons (sharks and rays)
The
Chondrichthyes
lack a swim bladder, and maintain
bouyancy
through a large, oily liver
Osteichthyes
– jawed fish with bony, calcified skeletons (most familiar fish)
The bony fish offset the density of their heavy skeleton with an air filled swim bladder on the dorsal side of their body cavitySlide36
Class Agnatha – Jawless FishSlide37
Chondrichthyes – Cartilage FishSlide38
Osteichthyes – Bony FishSlide39
Poikilothermy vs. Homeothermy
Poikilothermic
Temperature varies
“Cold Blooded”
Ectothermic
Body temperature is a function of the outside environment
All invertebrates, as well as fish, amphibians and reptiles
Homeothermic
Temperature is relatively constant
“Warm Blooded”
Endothermic
Body temperature results from within
Body heat derived from metabolism
Dinosaurs (theoretically), birds and mammalsSlide40
Vertebrate Diversity – Poikilothermic
Tetrapods
Class
Amphibia
Includes frogs, toads, salamanders and newts.
Moist, vascular skin functions for gas exchange
The earliest terrestrial vertebrates
Amphibians are tied to moist environments by the need to keep their skin and their eggs moist
Class
Reptilia
Includes lizards, turtles, crocodilians & snakes
Dry, scaly skin is well adapted for life on land
Shelled, amniotic egg frees reptiles from the need to return to the water to lay eggsSlide41
AmphibiansSlide42
ReptilesSlide43
Vertebrate Diversity – Homeothermic
Tetrapods
Class
Mammalia
Mammals are distinguished by a variety of skin gland variations
Hair glands
Milk glands
Class Aves (Birds)
Birds possess a number of adaptations unique to the class Aves, including
Feathers (derived from epidermal scale pouches)
Bipedalism
, with Forelimbs adapted for flight
Sternum with a broad “keel” for pectoral muscle attachmentSlide44
MammalsSlide45
Birds (Class Aves)Slide46
Mammalian Diversity
Class
Mammalia
is divided into 3 groups due to variations in reproductive behavior and anatomy
Monotremes
Include the platypus and the echidna
Marsupials
Include the kangaroo, koala and opossum
Placentals
Include most familiar mammals, including humansSlide47
Monotremes
Monotremes
have reproductive systems and behaviors almost identical to reptiles. They are oviparous (egg layers) and their eggs have leathery shellsSlide48
Marsupials
Marsupials are viviparous. Their young are born live, but immature and poorly developed
Marsupial young continue their development through prolonged lactation within a protective pouchSlide49
Placental Mammals
Placental mammals are live born after a long gestation period
The young are nourished through the placenta, which imbeds in the wall of the uterus and allows exchange of nutrients and wasteSlide50
Marc Kirschner
, Harvard:
How the chordate got its cord
https://www.youtube.com/watch?v=232wtCuLsoI
https://www.youtube.com/watch?v=Y0xfpGdh1_Y
https://www.youtube.com/watch?v=I1yqkSuTwrU