Lecture 16 Flashcards
Phylum Chaetognatha
- “Arrow worms”
- Pelagic marine predators
- Has been placed in Protostomia and Deuterostomia
- DEVELOPMENTAL characters suggest that they are deuterostomes
- Anus arises from blastopore
- Coleom formation is enterocoelous
- MOLECULAR data suggests that they are protostomes
- Additionally, cleavage is similar to crustaceans and nematodes
Phylum Hemichordata
do not have a true notochord
Wormlike bottom-dwellers
Phylum Echinodermata Key Characteristics (3)
- Endoskeleton
- Pentaradial symmetry
- Water vascular system
Spiny Endoskeleton of echinoderms
Endoskeleton
• skeleton or supporting frame work within the
living tissues of an organism
• Made of small calcareous plates (“ossicles”) bound together with connective tissue
• This endoskeleton is beneath the epidermis, but calcareous spines poke through
• Echinoderms are unappealing prey
Calcareous = composed of calcium carbonate
Predators of echinoderms
a few fish with strong teeth,other echinoderms, sea otters eat sea urchins
Pentaradial symmetry of echinoderms
Radial symmetry in five parts (‘penta’)
• Some sea stars have more than five arms
• Start development with five .: still pentaradial
HOWEVER
Larvae of echinoderms are bilaterally symmetrical
Earliest echinoderms were likely bilaterally symmetrical
Some groups (e.g. sea cucumbers, some sea urchins) have
secondarily evolved a superficial bilateral organization
They still have a pentaradial organization of skeletal and most organ systems
Water vascular system of echinoderms
- Unique to echinoderms
- Comprised of canals and specialized tube feet
- Functions: locomotion, food gathering, respiration, and excretion
Classes of phylum echinodermata
- Class Asteroidea: Sea stars
- Class Ophiuroidea: brittle stars and basket stars
- Class Echinoidea: Sea urchins, sand dollars, heart urchins
- Class Holothuroidea: Sea cucumbers
- Class Crinoidea: Sea lilies and feather stars
Class Asteroidea characteristics
Sea Stars
• Central disc that merges with tapering arms
• Pentaradial symmetry:
• Typically five arms, may have more (e.g.
sun stars)
• Oral surface (near mouth) On underside of body
• Aboral surface (opposite mouth)
• Ambulacral groove runs along the oral surface of each arm
• Tube feet are found along the ambulacral grooves
• Madreporite is the structure where water enters the water- vascular system
Asteroidea: Water vascular system
- System opens to the outside through the madreporite (on aboral surface)
- Madreporite leads to a series of canals
- Canals are connected to the podia (tube feet)
- Podia stick through the ossicles in the ambulacral groove
- Muscles and valves control the amount of fluid flowing into the podia – creates movement
Asteroidea: Feeding and digestive system
- Many sea stars are carnivorous;
- The lower part of stomach can be everted through the mouth during feeding
- Steps to eating a clam (if you are a sea star)
- Wrap yourself around prey
- Attach podia to valves and pull apart
- Insert soft, everted stomach into the gap between valves • Begin digestion
- Pull stomach back in
Asteroidea: Regeneration
- Some species can regenerate a whole new sea star from a severed arm (Fragmentation)
- For most asteroids, the arm must contain a portion (about 1/5th) of the central disc
- In other species a whole individual can regenerate from an arm
Asteroidea: Reproduction & Development
- Sexual reproduction
- Dioecious
- external fertilization
- Most sea stars produce free-swimming planktonic larvae • The larvae are bilaterally symmetrical
- Metamorphosis involves a dramatic reorganization
- Bilateral larva becomes a radial juvenile
(Asexual reproduction in some species
By fragmentation and regeneration)
Class Echinoidea characteristics
• Sea urchins, sand dollars, heart urchins
• Dermal ossicles have become closely
fitting plates which form a shell
• Spines protrude in living specimens (long in sea urchins, shorter and softer in sand dollars and heart urchins)
• Lack arms, but have the typical pentamerous plan of echinoderms
Class Echinoidea – body symmetry
- Most living species are ‘regular’
- Radial symmetry
- Sand dollars and heart urchins are irregular
- Radial symmetry + Secondary bilateral symmetry
Class Holothuroidea
- Sea cucumbers
- Odd animals in an odd phylum!
- Elongated oral-aboral axis
- Ossicles are reduced (soft-bodied)
- Pentaradial symmetry
- Secondarily evolved a degree of bilateral symmetry (as adults)
- all echinoderm larvae are bilaterally symmetrical
Class Holothuroidea defense
- Some species cast out a part of their viscera (guts) as a defense mechanism
- Strong muscular contraction either ruptures the body wall or evert its contents through the anus
- Lost parts are regenerated (takes time and energy)
Characters of Chordates (7)
- Bilateral symmetry
- Anterior-posterior axis
- Complete gut
- Coelom “tube-within-a-tube” arrangement
- Metamerism
- Cephalization
- Anus derived from blastopore
(Chordates are deuterostomes, so also… Radial cleavage!!)
Protochordata
- Not a monophyletic group
- Includes two subphyla:
- Urochordata (tunicates)
- Cephalochordata (lancelets, ‘amphioxous’)
- These subphyla are the only invertebrate chordates
- i.e. they are chordates, but not part of Craniata (aka Vertebrata)
Subphylum Urochordata
protochordata (chordata)
• Commonly called tunicates
• Most sessile as adults, some free-living
• The name ‘tunicate’ describes the tough, nonliving tunic (or test) that surrounds the animal
• Only the larval form bears all the chordate hallmarks
• Solitary or colonial
Subphylum Cephalochordata
protochordata (chordata)
• Lancelets
• Modern survivors of an ancient chordate lineage
• Slender, laterally compressed, translucent animals
• Inhabit sandy sediments of coastal waters
• 5 distinct characteristics of chordates but in simple form
• Lack features found in true vertebrates
• No brain
• No true vertebrae
5 Hallmarks of the Phylum Chordata
- Notochord
- Dorsal hollow nerve cord
- Pharyngeal pouches or slits
- Endostyle for filter feeding
- Postanal tail for propulsion
Notochord
• Notochord = Flexible, rod-like body of fluid-filled cells enclosed by a fibrous sheath
• All members of phylum Chordata posess a notochord
• Can be restricted to early development (e.g. vertebrates)
• Organizational role in nervous system development
• Persists throughout life in jawless vertebrates and
protochordates
• Becomes the vertebral column in all jawed vertebrates (i.e. Gnathostomata)
Dorsal Hollow Nerve Cord
In all Chordates…
• Nerve cord is dorsal to the digestive tract and notochord • Nerve cord is hollow
In craniates (=vertebrates)…
• anterior end of nerve cord becomes enlarged to form the brain (the rest is the spinal cord)
• nerve cord passes through vertebrae and the brain is surrounded by a bony or cartilaginous cranium
Note: Invertebrates can also have a nerve cord, but it is ventral to the digestive tract and solid
