the deuterostomes
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The Deuterostomes. Echinoderms and Chordates. Developmental Variations. During embryonic development, the process of gastrulation forms the digestive cavity. Gastrulation varies in the animal kingdom No gastrulation ( placozoans ) Incomplete gastrulation - PowerPoint PPT PresentationTRANSCRIPT
The DeuterostomesEchinoderms and Chordates
Developmental VariationsDuring 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 openings
Animals with Complete GastrulationComplete 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 mouth
Deuterostome PhylaThere 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
Vertebrates
Phylum EchinodermataThe 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 phyla
Characters retained:Embryonic development &
Gastrulation◦Triploblastic◦Complete digestive tract
Body Cavity◦Eucoelomate
Symmetry◦Bilateral during larval stages
Characters lost or diminished:SegmentationCephalization
◦No head, brain or specialized sense organs
◦Sensory apparatus are not centralizedBilateral symmetry in the adult form
◦The bilateral symmetry in the larvae goes through a dramatic metamorphosis, reorganizing the body into a Pentaradially Symmetrical adult
MetamorphosisThe 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 surface
Derived characters special to the EchinodermsWater-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 pedicellariaHemal system
◦ Poorly understood, it appears to function for distribution of materials
Pentaradial symmetry◦ Organs radiate from a central disc,
characteristically in a pattern of fives
Water Vascular System
Tube Feet
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=XR4NnmJfEXc
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=Xm2mF2IgLrA
Brittle Stars
• https://www.youtube.com/watch?v=Myhp8ifW6ig
• https://www.youtube.com/watch?v=Chs8Vk-6hoo
Sea Cucumbers
• https://www.youtube.com/watch?v=vsLBOkYLLeI
• https://www.youtube.com/watch?v=iYSbLr-mVkM
https://www.youtube.com/watch?v=6mx0GDxfjQ4
Sea Urchins• https://
www.youtube.com/watch?v=eGixkoZwEUs
• https://www.youtube.com/watch?v=oljZbs5haaY
• https://www.youtube.com/watch?v=WI7ZCK8aWoM
Echinoderms - VideoSea Starso https://www.youtube.com/watch?v=A100m
5EpfFIo https://www.youtube.com/watch?v=rE8l-KF
QlhYSea Urchins
◦ https://www.youtube.com/watch?v=nD7_0obUm0o
◦ https://www.youtube.com/watch?v=D3W4OCnHyCs
Sand Dollars◦ https://www.youtube.com/watch?v=bSsgD
hWpPq0◦ https://www.youtube.com/watch?v=gLK71-
vsi2E
Phylum HemichordataHemichordates 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 echinoderms
Hemichordate DiversityThe 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 mouth
Acorn Worms – Feeding The acorn worms have a muscular
proboscis used for food gathering located anterior to the mouth opening
The mouth is ventrally locatedA 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 food
Pterobranchs - FeedingThe proboscis itself is shield
shapedThe 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 tube
Gill Slits in the PharynxHemichordates 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.
Central Nervous SystemA 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 chordates
Phylum ChordataThe chordates are deuterostomes –
they possess a complete digestive tract with the mouth forming from the 2nd 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 slits
The NotochordThe 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 system
More notochord stuffIn 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)
Ancestral and Derived CharactersAside 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 tail
The EndostyleThe endostyle is a specialized organ
associated with the pharynxIn 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 metabolism
Chordate DiversityThe 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)
Protochordates: Tunicates
Tunicate AnatomyTunicates are
filter feedersWater enters the
mouth, filters through the gill slits in the pharynx, and passes out through the atrial siphon
Food passes through a complete digestive tract
Protochordates: Lancelets
Lancelet AnatomyLancelets are
filter feeders like the tunicates, but they have more fully developed musculature, notochord and dorsal nerve cord
Vertebrates with JawsThe 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 survival
Vertebrate Diversity - FishAgnatha – 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 liverOsteichthyes – 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 cavity
Class Agnatha – Jawless Fish
Chondrichthyes – Cartilage Fish
Osteichthyes – Bony Fish
Poikilothermy vs. HomeothermyPoikilothermic
◦ 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 mammals
Vertebrate Diversity – Poikilothermic TetrapodsClass 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 moistClass 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 eggs
Amphibians
Reptiles
Vertebrate Diversity – Homeothermic TetrapodsClass 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
attachment
Mammals
Birds (Class Aves)
Mammalian DiversityClass 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 humans
MonotremesMonotremes have reproductive systems
and behaviors almost identical to reptiles. They are oviparous (egg layers) and their eggs have leathery shells
MarsupialsMarsupials are
viviparous. Their young are born live, but immature and poorly developed
Marsupial young continue their development through prolonged lactation within a protective pouch
Placental MammalsPlacental
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 waste
Marc Kirschner, Harvard: How the chordate got its cordhttps://www.youtube.com/watch?
v=232wtCuLsoIhttps://www.youtube.com/watch?
v=Y0xfpGdh1_Yhttps://www.youtube.com/watch?
v=I1yqkSuTwrU