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