Lecture 13 Flashcards
What evidence is there that deuterostomes all share a common ancestor that is different to protostomes?
Early developmental patterns and phylogenetic analysis of gene sequences
What three early developmental patterns characterize deuterostomes?
- Radial cleavage (ancestral)
- Formation of mouth at opposite end of the embryo from the blastopore (ancestral)
- Development of a coelom
How is deuterostome coelom development different to that of protostomes?
Coelom develops from mesodermal pockets that bud off from the cavity of the gastrula rather than by splitting of the mesoderm
What are the three major clades of deuterostomes?
Echinoderms
Hemichordates
Chordates
What are all deuterostomes?
Troploblastic, coelomate with internal skeletons
How are segmented body plans of deuterostomes different to those of annelids and arthropods?
Segments are less obvious
What fossil has taught scientists about the ancestors of modern deuterostomes?
520 million year old fossil beds in china
What ancient fossils had a skeleton similar to modern echinoderm?
homalozoans
What ancient fossils had pharyngeal slits?
Vetulicosystids
What ancient fossil had a large mouth, six pairs of external gills and a segmented posterior body with light cuticle?
Yunnanozoans
What do the ancient deuterostome fossils show?
Support phylogenetic analyses of living species showing deuterostomes were bilaterally symmetrical, segmented with pharynx with slits for water flow
What evolved later in some deuterostome evolution?
Pentaradial symmetry
How many groups of echinoderms are there?
23, 6 remaining
What are hemichordates and echinoderms known as together?
ambulacrarians
What are some features of ambulacrarians?
Bilateral symmetry
Ciliated larvae
What happens to adult echinoderms?
They undergo radical change as they develop into adults to have pentaradial symmetry
What sides do echinoderms have?
Oral side (containing mouth) and aboral side (containing anus)
What two unique structural features do echinoderms have?
Water vascular systems
Internal skeleton
What does an echinoderm internal skeleton consist of?
Calcified internal plates covered by thin layers of skin and sometimes mucus, fused inside body.
What does the water vascular system of echinoderms consist of?
A net work of water-filled canals leading to extensions called tube feet.
What is the function of the water vascular system?
Gas exchange, locomotion, feeding
How does water enter the water vascular system of echinoderms?
A perforated structure called a madreporite
What structure leads from the madreporite and where does it go?
Calcified canal lead to another canal that rings the esophagus (ring canal)
What radiates from the ring canal (canal that surrounds the esophagus) in echinoderms?
Other canals that extend through the arms connecting with tube feet.
What do echinoderms use tube feet for?
Moving and capturing prey
What is a major echinoderm clade that includes sea lilies and feather stars?
Crinoids
How do sea lilies attach to a substratum?
A flexible stalk consisting of a stack of calcareous discs
Describe the body of a sea lily.
Cup shaped consisting of a tubular digestive system, five to several hundred arms (in multiples of 5) extend outwards from the cup.
How are feather stars different from sea lilies?
They grasp the substratum with their flexible appendages
What are some other echinoderms, other than crinoids?
sea urchins
sea cucumbers
brittle stars
sea stars
Describe the body of a sea urchin.
Hemispherical shape, covered with spines attached to underlying skeleton via ball and socket joints.
How are sea cucumbers orientated in an atypical way?
Mouth is anterior and anus posterior, rather than oral and aboral
What do sea cucumbers primarily use their tube feet for?
Attaching to substratum rather than moving
Where are the gonads and digestive organs located in sea stars?
In their arms
What do the tube feet of sea stars function for?
Locomotion, gas exchange, attachment
What does each tube foot of a sea star consist of?
An internal ampulla connected by a muscular tube to an external suction cup that sticks to the substratum
How are brittle stars different to sea stars?
Their flexible arms are composed of jointed hard plates.
Describe sea daisies.
Tiny disc shaped body with a ring of marginal spines, two ring canals, no arms.
How do sea lilies feed?
By orientating their arms to water currents, food particles stick to tube feet covered in mucus secreting glands, transferred to grooves in arms, ciliary action carries to mouth
How do sea cucumbers catch food?
Anterior tube feet modified into feathery sticky tentacles which is periodically withdrawn and wiped in mouth
What do sea stars eat?
Polycheates, gastropods, bivalve mollusks, small crustaceans such as crabs and fish
How do sea stars each a bivalve?
Sea star pushes its stomach out through its mouth through the space of the shell gap, enzymes digest prey
How do sea urchins eat?
They scrape algae from rocks using a rasping structure
What animals make up hemichordates?
Acorn worms and pterobranchs
What are the three parts of the hemichordate body plan?
Poboscis
Collar
Trunk
Where do acorn worms live?
Muddy and sandy marine sediments
What does the digestive tract of acorn worms consist of?
Pharynx
intestine
What surrounds the pharyngeal slits of acorn worms?
Highly vascularised tissue
What are pterobranchs?
Sedentary marine animals living in tubes secretes by the proboscis
What are the three clades of chordates?
Urochordates, cephalochordates, vertebrates
What 3 derived structures do all chordates display at some stage during their development?
- Dorsal, hollow nerve cord
- Tail that extends past anus
- Dorsal supporting rod called notochord
What is the notochord composed of?
A core of large cells with turgid fluid filled vacuoles (rigid but flexible)
What happens to the notochord in urochordates?
It is lost in metamorphosis to adult stage
What happens to the notochord in most vertebrates?
It is replaced by skeletal structures to provide support
What feature is present at some point during the developmental stages of chordates?
Pharyngeal slits (not a derived trait)
What did the pharynx function as in chordate ancestors/
Site of O2 uptake and CO2 removal and water(as in acorn worms)
What is the enlarged pharynx in lancelet’s called?
The pharyngeal basket
What are the three major groups of urochordates?
Ascidians
Thaliaceans
Larvaceans
(All marine animals)
What are most species of urochordates?
Ascidians (sea squirts)
What do some ascidians form and how?
Colonies
By asexual budding
What is the body of an adult ascidian like?
Bag like
Enclosed by a tough tunic composed of proteins and polysaccharides secreted by epidermal cells
What is the ascidian pharynx enlarged into?
The pharyngeal basket- used in filter feeding
What do bands of muscle surrounding the notochord of ascidians do?
Provide support for body
What happens to the larvae of most species of ascidians?
They settle on the floor to form sessile adults
Where to thaliaceans live? (salps)
Singly or in chain like colonies
What are larvaceans?
Solitary planktonic animals that retain their notochord who snare sinking organic particles in their slimy houses
What are lacelets?
Small animals who use their notochord for burrowing
What do vertebrates have?
A jointed, dorsal vertebral column that replaces notochord during early development as their primary supporting structure
Where did the lineage that led to vertebrates evolve?
In estuarine environment (where freshwater meets salt water)
What is believed to be the sister group of vertebrates?
hagfishes
What does the weak circulatory system of hagfishes consist of?
Three small accessory hearts
What type of skull do hagfish have?
A partial cranium containing no cerebrum or cerebellum (two major brain regions)
What else to hagfish lack?
No jaw or stomach, vertebrae
What type of skeleton do hagfish have?
One composed of cartilage
What group are hagfish sometimes considered to be?
Craniates- if not closely related
Cyclostomes when placed with lampreys
What do hagfish eat?
Polychaete worms
What type of development do hagfish undergo?
Direct development
Where do lampreys live?
Freshwater or coastal salt water (breed in freshwater)
What do lampreys have?
Complete braincase,
Cartilaginous skeletons
Complete vertebrae
What is lamprey larvae called?
Ammocoetes
What type of metamorphosis do ammocoetes undergo?
Complete
What type of feeding do lampreys have?
Parasitic
Some don’t feed- survive only a few weeks to breed
What 4 features characterize vertebrates?
- Rigid internal skeleton
- Anterior skull with large brain
- Internal organs suspended in coelom
- Well developed circulatory system with contracting ventral heart
What names is given to fish who evolved jaws via modification of the skeletal arches that supported the gills?
Gnathostomes
What are the advantages of jaws?
Improve feeding efficiency- particularly when teeth evolved
What do fins do for fish?
Stabilize their position in water
Propel them through water
What fins do most fish have?
Pair of pectoral fins behind gill slits
Pair of pelvic fins anterior to pelvic region
Median dorsal and anal fins stabilize the fish as it moves and provide propulsion
What fins help fish propel and turn rapidly?
Caudal fins
What group of finned fish became abundant during the Devonian period and includes sharks, skates and rays?
Chondrichthyans
What do chondrichthyans and chimeras have there skeletons composed from?
Catillage
How do sharks move forwards?
Lateral undulations of their bodies and caudal fins
How do skates and rays move forwards?
Vertical undulations of enlarged pectoral fins
Give an example of cartilagenous fishes migrating into freshwater.
Stingrays were found in a rive system of South America.
Where do chimeras live?
Deep-sea or cold waters
In some early fish, what supplemented gas exchange function of the gills?
Gas-filled sacs
What did gas-filled sacs in early fish enable?
Fish to live where oxygen was periodically in short supply (such as freshwater environments)
What did lung-like sacs evolve into?
Swim bladders-organs of buoyancy
What skeletons do ray-finned fish have?
Internal skeletons of calcified, rigid bone
What do the gills of ray-finned fish open into?
A single chamber called an operculum
What does movement of the operculum do?
Improves flow of water over the gills
What do ray-finned fish eat?
Exploit nearly all types of aquatic food
Many ray-finned fish are solitary, however, in open water they form aggregations called…
schools
What did the evolution of lung-like sacs set stage for?
Evolution of land animals
What enabled some fish to support themselves in shallow water and later move to land?
Changes in structure of fins
