Midterm II (Echinodermata) Flashcards
Deuterostome Embryogenesis
- Radial Cleavage (opposed to spiral)
- Regulative (indeterminate) embryo (if you were to remove one one cell, still develop into animal)
- Fate of blastopore -> anus (i.e., mouth second)
- Enterocoelous (outpocketing) coelom formation (coelom is formed from outpocketing of developing gut, not base)
Deuterostomia common traits
- Gill slits in pharynx
(true synapomorphy)
Deuterostomes groups
- Ambulacraria -> Echinodermata, Hemichordata
- Chordata
Echinodermata Stem Groups
- Stem Group A
- Motile, bilateral, gills slits - Stem Group B
- Asymmetric, stalked, gill slits - Stem Group C
- Stalked, beginnings or radial symmetry (suspension feeders)
- Probably loss of gill slits - Stem Group D
- Still attached with suspension feeding
- Ambulacral grooves
- Closest to crown group ancestor
Phylum Echinodermata
- “spiny + skin”
Exclusively marine; mostly benthic - 7000+ spp; 5 classes
Lack of cephalization
Loss of gill slits
5 Unique features (autapomorphies):
1. Pentaradial symmetry in adults
2. Calcareous endoskeleton
3. Water vascular system
4. Pedicellariae
5. Dermal branchiae (papulae)
Pentaradial symmetry
- 5 lines of symmetry
- 5 arms: starfish
- evolved from bilateral ancestor
- Larvae Bilateral, so part of bilateral clade, not radial
- Mouth side = oral
- Opposite of mouth = aboral
- Madreporite of aboral side, lets water in
Calcareous Endoskeleton
Mesodermal porous endoskeleton
- meshwork of ossicles (e.g., plates) form the stereom (unique)
- w. spines and tubercle projections
- unique fine meshwork (porous) of CaCO3 (Calcareous)
Connected by mutable “catch collagen”
- Can change from liquid to solid (i.e., change positions without muscular effort)
Water Vascular System
Hydraulic (fluid) system
- canal and tube feet
- only open on one end
- specialized coelomic system
Functions:
- respiration
- excretion
- locomotion
- feeding (evolve for)
Order that water goes in (parts):
Ambulacra
- The bands from which tube feet project
Pedicellariae
On aboral surface
Functions:
- Cleaning
- Food capture
- Defense
Dermal Branchiae (Papulae)
- Also called skin gills
- Projections of thin-walled coelom
(bubbles on surface of aboral, coming from dermal branchiae (breathing))
Basic Internal Characteristics
Nervous system
- No brain ganglia
- Nerve ring, radial nerves, and epidermal nerve net
- Sensory cells, eyespots (tip of arms)
Digestive system
- Feeding mode varies (carnivores (stick stomach out), scavengers, herbivores, deposit feeders, suspension feeders)
Reproduction
- Often separate sexes with external fertilization
Larval Development
- Deuterostome embryology
- Bilateral free-swimming larvae
- left side becomes the oral surface
- right side comes aboral surface
- With tube feet - Metamorphosis to adult form
Regeneration
- Only need is 1/5 of the central disk and 1 arm!
- Also able to deliberately shed body parts or appendages = autotomy
- Used as an escape response to predators
- Or as a means of replacing infected or damaged appendages
Fragmentation, not regeneration
- e.g., Link “comets”
- can cast off an arm without any part of the central body attached, and that arm will slowly grow into a complete starfish
Phylum Echinodermata -> class Asteroidea
“Star-form”; sea stars, starfish
1500+ spp.
The “poster” echinoderm
- Central disc + 5 arms
- Or 7 arms, or almost 50!
Two-part stomach
- can even evert cardiac stomach
Scavenger and carnivores
- can also suspension feed
Keystone Species of class Asteroidea (sea stars)
- Keystone: incredibly important to environment/ecosystem
1. Pisaster ochraceus: purple intertidal seastar - Controls B.C. mussel pops
2. Stichaster australis: reef sea star
Deadly Asteroids
- Ancanthaster planci: Crown-of-thorns (Indonesian) (eat polyps off corals)
- Pycnopodia helianthoides: Pacific sunflower sea star
Dead Asteroids
Good sense of the ecosystem based on whether or not sea stars are healthy
Sea star wasting disease
- white lesions, water vascular system stops working (“limp”); fragmentation; death
Associated with warmer temps and densovirus
Phylum Echinodermata -> Class Ophiuroidea
- “like a serpent”
- Brittle stars and basket stars
- 2000+ species
- Abundant (form huge carpets)
- Move with flexible articulated arms
- closed ambulacral grooves
- Tube feet for feeding, no
suckers
- No pedicellariae, no papulae
- Madreporite on oral side
- No anus (indigestibles out the mouth)
- Organs inside central disc
- Fragile, w. remarkable regeneration
Phylum Echinodermata -> Class Echinoidea
“hedgehog” form
Sea urchins, sand dollars, and heart urchins
Around 950 spp; Green Sea Urchin (Strongylocentrotus droebachiensis)
Compact body within a test
- Ossicles as plates
- Some secondarily bilateral
- e.g., sand dollars and heart urchins
5 ambulacra extents up and around towards anus (aboral)
- i.e. No arms
Tube feet for locomotion w. assist from spines in socket joint (unique)
- Short spines on sand dollars
Many with venomous pedicellariae (3 jaws)
Mostly herbivorous
- Aristotle’s lantern with 5 teeth (circular row of teeth)
- Sand dollars deposit feeders (find them in mud)
Ecological Impacts of Urchins
Kelp forest destruction
- “urchin barren”
Keystone species: sea otter, eat urchins and restore kelp pop
Phylum Echinodermata -> Class Holothuroidea
“obscure form”
Sea cucumbers
Around 1150 species
Elongated on oral-aboral axis
Secondarily bilateral
Reduced ossicles
“Ventral” tube feet specialized for locomotion on “sole”
- No arms
- Benthic crawlers
- Burrowers (circular and longitudinal muscles, no podia)
Class Holothuroidea (II)
Spacious coelomic cavity
- Hydrostatic skeleton
Oral tentacles are modified tube feet for suspension or deposit feeding
- Important nutrient cyclers
Cloaca
- “all-purpose orifice” via anus
- Respiration (respiratory tree) and excretion (unique)
Amazing self defense!
- Evisceration of Cuvierian tubules, resp, tree, or guts
Some are pelagic spp.!
- Benthopelagic
- True pelagic (1 spp.)
Phylum Echinodermata -> Class Crinoidea
“lily” form
Around 625 spp.
Stalk with cirri attached to aboral side of calyx with many arms
Sea lilies:
- flower-shaped on top of stalk attached to substrate
Feather stars:
- Short stalk w. many branched arms
Can move/crawl/sweep/swim via cirri or feathery arms
No pedicellariae, no madreporite, no spines
Mouth and anus on oral side
Many deep water
- But high diversity of feather stars in shallow Indo-Pacific and West Indies
