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Published byAbigayle Pearson Modified over 9 years ago
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Deuterostomes Hemichordates Echinoderms Protostomes
Cephalochordates Urochordates (Ascidians) Vertebrates (us) Deuterostomes Hemichordates Echinoderms Protostomes Spiralia (Platyzoa, Polyzoa, Trochozoa..) Ecdysozoa (Arthropoda, Nematoda..)
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Embryonic Development: Early Cleavage
Zygote Protostomes Deuterostomes Radial, Indeterminate Cleavage each cell can potentially develop into a complete embryo Spiral, Determinate Cleavage fate of cells is set early in development 2 cells 4 cells 8 cells 8 cells, top view
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Spiral Cleavage in Protostomes
32 cell stage - labeled with Wilson’s coding system Annelid cross Rosette cross Molluscan cross
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From Blastula to Gastrula
ectoderm blasto- coel Invagination endoderm archenteron blastopore Gastrulation = formation of embryonic germ layers - separates cells fated to interact with the environment (movement, sensory, protection) from those that will process food (= the gut)
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Protostome Deuterostome Fate of Blastopore Coelom Formation
GASTRULA STAGE Fate of Blastopore Coelom Formation
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Coelom formation Schizocoely (protostomes) Enterocoely (deuterostomes)
Ectoderm Blastocoel future mesoderm Archenteron (larval gut) Endoderm Mesoderm forms out of ball of cells descended from 4d micromere cell Mesoderm forms from cells that pinch off from blastopore
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Coelom formation via schizocoely
Solid mass of mesoderm, derived from 4d micromere cell; gives rise to paired coelomic spaces - associated with segmentation in annelids, arthropods
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Coelom formation via enterocoely
Pouching of archenteron production of mesoderm-lined coelomic spaces - may results in a 3-part coelom in deuterostome embryos (and some lophophorates) 3-part coelom
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Evolution of the Bilateria
Ancestor probably had deuterostome features as an embryo Protostomes Deuterostomes - spiral cleavage - blastopore becomes mouth - mesoderm derived from 4d cell - ventral nerve chord - coelom formed by schizocoely, hollowing out of mesodermal mass from 4d micromere cell - radial cleavage - blastopore becomes anus - mesoderm from archenteron - dorsal nerve chord - coelom forms by enterocoely, pinching out of gut (with a 3-part arrangement in body)
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Phylum Echinodermata ~7,000 spp. Deuterostomes with penta-radial symmetry as adults, bodies organized along oral-aboral axis (mouth anus) - Calcified endoskeleton derived from mesoderm; bony ossicles or plates filled with living tissue (stroma) Water vascular system, derived from coelom, powers the podia (= tube feet) and serves as circulatory system - Decentralized nerve ring + radial nerves - Mutable connective tissue that can harden, soften - Mostly dioecious (separate sexes) Bilaterally symmetric larvae, such as bipinnaria (starfish) and pluteus larvae (urchins, brittlestars)
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Aboral surface Oral surface
Madreporite: opening to water vascular system ambulacral (open on grooves asteroids) mouth central disc body rays = ambulacra podia (tube feet) line open grooves
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Body Orientation in Echinoderms
Ophiuroids Crinoids Asteroids (stars) Echinoids (urchins) Holothurians (cucumbers) mouth ambulacral surface, w/ podia
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Endoskeleton Echinoderms have an epidermis covering a mesoderm-derived dermis layer containing the calcified endoskeleton - skeleton is composed of ossicles, porous plates of CaCO3 filled with living dermal cells called stroma stroma tissue fills these spaces Under the dermis layer (i.e., beneath the skeleton): - layer of muscle - coelom (i.e., components of the water vascular system)
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Endoskeleton Pisaster ossicles
ossicles may be spread throughout the body, embedded in connective tissue as in sea stars & sea cucumbers Pisaster ossicles ossicles may fuse together to form the solid test (inner shell) & spines of sea urchins, or the arm vertebrae of brittle stars
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Pedicellariae Pincer-like structures on aboral surface, formed from ossicles - have their own muscles, nerves + reflex arcs - may be hollow & inject toxins Function in both physical and chemical defense by pinching and poisoning predators - also anti-fouling: keep surface clean by pinching any larvae or algal spores that try to settle on body surface
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Phylum Echinodermata Class Asteroidea - sea stars
Class Ophiuroidea - brittle stars & basket stars Class Crinoidea - crinoids Class Echinoidea - sea urchins & sand dollars Class Holothuroidea - sea cucumbers
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Phylum Echinodermata Class Asteroidea - sea stars
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Class Asteroidea – sea stars
1,500 species in 5 orders - 5 or more arms, not distinct from central disc - open ambulacral grooves lined with podia that have internal ampullae (fluid-filled bulbs) gills found in grooves & across body surface
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surface of Astrometis spines gills pedicellariae podia
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Water Vascular System each lateral canal ends in a tube foot
- extends around central disc regulate internal pressure
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Water Vascular System Seawater enters through madreporite, mixes with coelomic fluid and is is pumped through the system by cilia When an ampulla contracts, it pushes fluid into the tube foot (1) sucker is pushed against substrate; adheres via secretions (2) muscles in tube foot contract, pushing fluid back out (3) muscles pull up sucker of foot, creating vacuum– this creates the tremendous suction that holds foot to substrate (4) suction is released when ampulla again contracts, sending fluid into foot sucker and relieving vacuum
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Cross-Section of an Asteroid Arm
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paired digestive glands
run down each arm everted for feeding
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Sea stars use their tube feet to pull open shells of bivalves
such as mussels, clams - then turn their stomach inside-out, into the shell - digest the soft bivalve tissue inside its own shell sea star hunched over a mussel, ready to start pulling its shell open Stomach of the bat star Asterina pushed out against glass
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Asteroids as keystone predators
Pisaster ochraceous and P. giganteus function as keystone predators in rocky intertidal habitats, preserving biodiversity - mussels are competitive dominants for space, so they crush everything else off the rocks if their populations grow unchecked loss of biodiversity - by consuming mussels, sea stars create free space for other organisms promotes biodiversity in rocky intertidal zone
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Asteroids as keystone predators
maximum foraging distance - sea stars consume any mussel they can crawl to, open, and eat during a single high tide vertical zonation, with mussels restricted to the tops of rocks above foraging reach of sea stars, which hang out near the base where it’s wet and cool
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Crown-of-Thorns starfish, Acanthaster plancki
eats live coral polyps in last few decades, major outbreaks have resulted in massive coral mortality in Australia; human influences suspected
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Sea stars are famous for regenerating lost arms
- some (Linkia) re-grow whole body from a dropped arm ! Asteroid larvae can also bud off asexually, the only known larvae capable of reproduction Which is healing? which is asexual reproduction?...
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Phylum Echinodermata Class Asteroidea - sea stars
Class Ophiuroidea - brittle stars & basket stars Class Crinoidea - crinoids Class Echinoidea - sea urchins & sand dollars Class Holothuroidea - sea cucumbers
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Class Ophiuroidea – brittle stars
2,000 species in 3 orders Body with 5 or more arms, distinct from central disc Tube feet have no suckers; no anus is present Coelom in arms is reduced, due to large vertebral ossicles Ambulacral grooves closed - Madreporite on oral surface (underneath)
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Ophiuroid Cross-section
Central disc Arm Digestive system confined to central disc
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Ophiuroid External Anatomy
oral surface aboral surface
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Ophiuroid Oral Surface
bursal slits, openings that draw in water for gas exchange with coelomic fluid-filled sinuses mouth ventral arm shield arm spines
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Ophiuroid Arm Cross-section
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Ophiuroids are predominantly deposit
or suspension feeders - food particles are trapped in mucous or passed podia-to-podia to the mouth Basket stars use multi-branched arms to suspension feed or catch larger prey; incomplete gut
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