ZOO*2090

What proportion of described animal species are in the phylum chordata?

3.25-6.5

What are the closest relatives to the phylum cordata? What group do they all belong to?

The Hemicordata and the echinodermata. Together with the Chordata they form the Deuterostoma.

What is the sister group to the deuterostomas? What is the defining characteristic that separates the two groups?

The protostomas. Protostomas develop the mouth first, Deuterostomas develop anus first and mouth second.

What are the three subphylums of the Chordata?

Cephalocordata, urochordata, vertebrates. Vertebrata, Urochordata are the most likely sister groups.

What are the Cephalocordata?

Lancelets/ Amphioxus
- filter feeders, use pharyngeal gill system driven by cilia
- no differentiated brain/ special sense organs/ heart
- No metamorphosis over lifetime

What are the Urochordata?

tunicates/ sea squirts
- marine filter feeders
- larvae have chordate characteristics which are reduced in the adult form after metamorphosis
- have rudimentary hearts and cerebral ganglion

What are the 5 characteristics of the Chordata?

notochord, dorsal hollow nerve cord, pharynx with pouches or slits, endostyle/ thyroid gland/ subpharyngeal gland, post- anal tail. All five must be present at some stage in life, but they are transient in many species.

What is a notochord?

A fluid filled elastic rod, dorsal to the gut and ventral to the nerve cord. It is responsible for organizing embryo development, structural integrity, and preventing collapse during contraction. It often disappears during development, becoming highly specialized in adults, ex. often replaced by the vertebral column.

What is a dorsal hollow nerve cord?

A hollow nerve tube formed in embryo by the invagination of surface cells, from dorsal to gut tube. It coordinates body movements/ functions and develops into the spinal cord and brain in vertebrates.

What are pharyngeal slits?

Slits located in the pharyngeal pouches, behind the oral cavity in the digestive tract. in aquatic species, they are important to create currents for feeding/ respiration. in terrestrial species they are simply transient embryonic species.

What is the subpharyngeal gland?

A groove in the floor of the pharynx (endostyle) that secretes mucus, traps food particles and is involved in iodine metabolism. It is found in cephalocordates and lamprey larvae, proposed as an early thyroid.

What is the post- anal tail?

A tail posterior to the anus (SHOCKER), used for swimming and propulsion, present only in embryonic phase in some species (ex. humans)

What caused problems with the early vertebrate fossil record?

Early soft bodied, jawless forms didn’t fossilize well

What is the widely accepted transition from ancestral invertebrates to vertebrates?

Cilia-mucus filter feeders, Muscular pump suspension feeders, jaws for predatory feeding. Jaws had a major evolutionary advantage because they facilitated hunting, gathering (not passive feeding).

What groups does the chordata include?

all vertebrate and invertebrate groups with chordate characteristics

What does the craniata include?

all chordates with a braincase (skull)

What does the vertebrata include?

all chordates with a braincase and vertebral column

What are the 4 major innovations of vertebrates?

vertebral column, anterior enlargement of the nerve cord (brain), skeletal structure protecting the brain (cranium), distinct organs

What are some innovations common in many but not all vertebrates?

Jaws, paired limbs, amniotic eggs

What are the 3 main components of the vertebral column?

the centrum: cylinder enclosing/ replacing the notochord
the dorsal neural arch: encloses the nerve cord
the ventral hemal arch: encloses blood vessels

Why is there debate about hagfish being classified as vertebrates?

they have a very incomplete vertebral column

What is cephalization?

anterior clustering of specialized sensory organs/ receptors derived from neural crest cells and ectodermal placodes seen exclusively in vertebrates.

What is an early feature associated with cephalization?

Sensory organs

How do invertebrates eat?

suspension feeding with cilia

How do jawless fishes eat?

larvae use muscular pump suspension, adults use suction feeding

What are gnathosomes?

jawed vertebrates

How are limbs thought to have evolved?

The fish fin axis curved around with digits on the posterior margin, lobe fin was a precursor for terrestrial life on earth, may have enabled life on land

What was significant about the amniotic egg?

allowed life cycles independent of water, enabling terrestriality by isolating the embryo in a fluid- filled cavity

What are class Agnatha?

hagfishes, lampreys

What are class Chondrichthyes?

sharks and rays

What are class Osteichthyes?

Bony fishes

What are class amphibia?

frogs/ salamanders/ caecilians

What are class Reptilia?

snakes, lizards, crocodilians, turtles

What are class Aves?

Birds

What are class mammalia?

Mammals

What is the most diverse group of vertebrates? Why?

Teleosts (bony fishes)- first to evolve, seem to have more plastic, variable genomes

What are the 3 steps of vertebrate development?

1. Cleavage: make cells

2. Gastrulation and neurulation: formation of multilayer structures, early gut, and neural tube

3. Differentiation/ organogenesis: from cell layers to organs

What is a blastocoel?

the internal chamber in a developing vertebrate, formed during cleavage

What does the ectoderm become?

nervous system, eyes, epidermis

What does the endoderm become?

pharynx, digestive tract, liver, pancreas, urinary bladder

What does the mesoderm become?

dermis, bones, muscles, blood vessels, heart, kidneys, gonads

What is the vertebral column?

A supportive backbone where the vertebrae replace the notochord

What are the 5 vertebrate innovations?

Vertebral column, cranium/ cephalization, Jaws, Limbs, Amniotic Egg

What is the difference between the agnatha and the gnathostoma?

Gnathostoma (jawed vertebrates) are more diverse, evolved later than Agnatha (jawless fishes)

What are the 2 extant Agnatha (cyslostomes)? What is unique about them?

Hagfishes, Lamprey. They have a mouth opening but no biting mechanism derived from their pharyngeal arches and have generally maintained their structure over 300 my, called living fossils- oldest extant vertebrates.

What are conodonts?

extinct agnatha, known for tooth like fossils, other fossils highlighted vertebrate characters. Despite being jawless, their tooth like elements were attached to pharyngeal plates used to actively hunt capture prey. Also had large eyes, locomotor system to facilitate active predation

What are the ostracoderms?

Extinct jawless fishes that had a bony exoskeleton, precursor to bony fishes

What is the circulatory system of the hagfish like?

They have one branchial heart (like us) and multiple venous hearts

What is the great hagfish debate?

Some think not vertebrates, group lampreys closer to vertebrates and classify hagfish as craniates, recent DNA evidence shows Hagfish are vertebrates who lost their vertebrae through evolution

What are the 2 theories surrounding the evolution of jaws?

Serial theory: the jaw arises entirely from one of the anterior branchial arches

Composite theory: the mandibular arch is formed from the elements of several adjacent arches

What are some possible selective pressures for the evolution of jaws?

• active feeding

• increased respiratory demands of active lifestyles required additional respiratory muscles, leading to more robust branchial arches which later modified to feeding jaws

What are the characteristics of placoderms?

Early gnathostomes, extinct. Heavily armored with jointed necks, fearsome bites.

What are the Chondrichthyans?

class of cartilaginous fishes, fertilize internally via claspers, placoid scales, presence of spiracle. Split into the subclasses elasmobranchii and the holocephali

What is unique about shark morphology?

Marine, most are carnivorous predators, some are filter feeders. They have detatched upper jaws (hyostylic jaws), they have vision, chemoreceptors and electroreceptors, and they use an oily liver and motion of their heterocercal tail to stay buoyant.

What are the acanthodii?

distant offshoots of gnathostome evolution, extinct. Had unique fin spines formed by specialized scales

What are the Osteichthyes?

fishes with much more bone in their endoskeleton, swim with strengthened fins (either rays or bone and muscles), split into actinopterygii and sarcopterygii

What are the Actinopterygii?

ray finned fishes, include teleosts

What are teleosts?

Bony fish with ossified vertebrae, swim bladder, true homocercal tail, circular, flexible scales, and a skull that allows jaw mobility.

What are the Sarcopterygii?

Lobe- finned fishes, lobe fins have bone and muscle, with rays only at the tips. Contain Coelecanths and lungfishes.

What is unique about coelecanths?

have a braincase divided by hinge-like joint, swim bladder filled with oil, and retain an oil- filled notochord. Relatively unchanged compared to ancestors 100 mya, thought to be extinct until found off coast of south africa

What is unique about lungfishes?

Have lungs, allowing them to breathe air, no swim bladder, can estivate (sleep on dry land), lack stomach

What are the tiktaalik?

Fish that fall under the Sarcopterygii, show intermediate characteristics between lobe finned fishes and tetrapods (fishopod?), had limb like pectoral fins that could have enabled standing, functional wrist like joints and a mobile neck.

What is the most diverse group of living vertebrates? What percentage of vertebrate biodiversity does it comprise?

Actinoptergians (ray finned fishes)- >50% of the living vertebrate species.

How does suction feeding work in teleosts?

Driven by volume changes caused by the outward expansion of the buccal cavity, forward movement of the jaws

What is Euautostylic jaw suspension? What species is it found in?

When the upper jaw is braced along the braincase, does not involve hyomandibula. Found in placoderms and lungfishes.

What is Amphistylic jaw suspension? Who is it found in?

When the hyomandibula braces the upper jaw along the braincase as a sort of strut, found in early sharks, early bony fishes, and coelecanths.

What is hyostylic jaw suspension?

Contact with the chondrocranium is primarily through the hyomandibula, palatoquadrate can slide forwards in sharks. In bony fishes, new bony elements are present, and the jaw is more manouverable.

What is Metautostylic jaw suspension?

The quadrate attaches the chondrocranium directly to the lower jaw, no support from the hyomandibula.

What are the sections of the skeleton in vertebrates?

Axial: spinal cord, ribcage
Cranial: head skeleton/ skull
Appendicular: limbs/ fins

What are the components of the vertebrae and their purposes?

centrum: body
neural arch: protects spinal cord
Hemal arch: protects blood vessels in tail vertebrae
apophyses: muscle attachment

How does the role of the notochord change during fish evolution?

In early fishes, the notochord provided support for the vertebral elements, in modern fishes it is greatly reduced, surrounded by the vertebral column which is supported by ligaments

What group had amphocoelus vertebrae? What does this mean?

Fish have them, they possess no interlocking elements and are concave at both ends. Allows for movement by lateral undulation of the body

What possess the only caudal vertebrae with a hemnal arch?

fish

What are girdles?

Braces that support pairs of appendages- posterior is pelvic , anterior is pectoral

What is the function of paired fins?

Provide stability, fine control when mobile

What is the function of median fins?

Keep body from rolling

What is the function of the caudal fin?

propulsion during undulation

What is notable about the fish axial skeleton?

First vertebra is fixed to the skull, amphicoelous vetebrae (not interlocking), have only caudal and trunk vertebrae (only caudal region with a hemal arch), notochord remains throughout life in some. Move by lateral undulation of the body

What is the difference between shark and teleost pectoral girdles?

Shark: right/ left halves fused in midline, not joined to skull/ vertebral column. Teleosts: joined to skull via cleithrum bones, increased strength.

What is the structure of the pelvic girdle in fishes?

2 plates, sometimes fused mid- ventrally to form pelvic symphisis, free floating in fishes, attached to body by muscles and ligaments and serves as a pivot and anchor point

What are the layers of vertebrate integuement, from outer to inner?

Epidermis, dermis, hypodermis. Hypodermis is not present in all vertebrates, however the other two are

What parts of the integuement do the ectoderm, mesoderm, and neural crest become in embryonic development?

Ectoderm becomes the epidermis, the mesoderm becomes the dermis, and the neural crest cells become the chromatophores.

What are the 3 layers of the epidermis? Which is present in all vertebrates?

1. stratum germinativum- present in all vertebrates, produces new cells

2. stratum granulosum- recieves cells from germinativum (basement)

3. stratum corneum- keratinized for waterproofing

What are the 2 layers of the dermis? What else is included?

stratum spongosium: pigment cells, like chromatophores

stratum compactum: lots of fibres
full of connective tissues, blood vessels, small nerves

how do feather, hair and other epidermal derivatives get their colour?

They do not produce their own- instead they have pigment trasferred into them via chromatophores

What is the hypodermis?

The layer located under the dermis, connects the skin to underlying muscles, in endotherms it contains fat cells for energy storage and temperature regulation

What are the functions of the integuement?

barrier, defense, osmotic balance, and colouration

How does the integuement vary across vertebrates?

Variation in the type and number of glands, extent of bone development in dermis, fish have very little stratum corneum (exception is lamprey teeth) whereas birds and mammals have feathers, hair, claws

What are cosmoid scales?

Dermal bone and scales of ostracoderms and placoderms, scales of early sarcopterygians

What are gamoid scales?

Scales made of bone covered in a thick layer of enamel, entire surface covered by a thin layer of epidermis.

What are elasmoid scales?

Scales found in teleosts, with a loss of enamel and thin lamellar bone only

What is the general description of evolution of scales?

loss of deep layers such as lamellar/ vascular bone or superficial layers like enamel and dentin compared to the large armour and scales seen in ancient fishes

What is the basic structure of fish gills?

They have gill arches with gill rakers on the pharyngeal edge and gill filaments involved in respiration on the distal edge. Gill filaments are primary lamellae, secondary lamellae further increase surface area

How does the countercurrent exchange system work in fish gills?

Water travels through the gills in the opposite direction of blood flow, oxygen moves via diffusion into the deoxygenated blood.

How do pouched gills work in lamprey?

no gill covering, cannot breathe while feeding, tidal ventilation of gill pouches through muscle compression and relaxation of brancial apparatus

How do internal gills work in Chondrichthyes (septal gills)?

Dual pump ventilation- water travels unidirectionally in mouth, over gills. Gill arches are separated by intebranchial septa. First gill is hemibranch, rest are holobranch.

What is the purpose of spiracles?

used by sharks and other cartilaginous fishes to “ventilate” gills while buried in sand. Some extant, primitive bony fishes use them for air breathing. It is a primitive trait.

How do opercular gills work? Who has them?

Found in Actinoptergii, dual pump ventilation pushes water over gills and out SINGLE hole, gill arches are covered and protected by bony operculum

What powers dual pump gill ventilation?

Buccal and opercular components work together, with one closed and one open, they alternate to create the pump.

What is the difference between swim bladders and lungs?

Lungs are paired, dorsal to gut whereas swim bladder is a single elongated sac dorsal to the gut.