Directional Terms You Must Know

Caudal – towards the tail Ventral – towards the belly Dorsal – towards the back Anterior – towards the head Posterior – towards the rear Lateral – to the sides Medial – towards the middle

Distal – farther from the core of the body

Proximal – closer to the core of the body

Buccal – mouth region Pharyngeal – muscular swallowing

region of throat Integumentary – the skin system Respiratory – dealing with gas

exchange Cardiovascular – dealing with

circulation of blood

Chordate Evolution

Four defining characteristics of the phylum Chordata Notochord Post-anal tail Pharyngeal gill slits

or pouches Dorsal hollow nerve

cord

Advantages of Chordate Characteristics Notochord – provides stabilizing

structure and muscle attachment = mobility in water

Gill slits/pouches – efficient oxygen delivery system in large bodied organisms

Post-anal tail – propulsion DHNC – No clear hypothesis why

dorsal would be any better than ventral

Subphyla of the Chordates

Urochordata – tunicates (sea squirts) Cephalochordata – Lancelets

(amphioxus) Vertebrata – more accurately called

“Craniata”, including anything with a cranium

Hypotheses on Vertebrate Evolution Urochordate Ancestor: (1928) proposes larval

tunicates are ancestor; larval forms retained form into adulthood and gained gonads to reproduce (“paedomorphosis”)

Cephalochordate Ancestor: (1991) proposes a lancelet ancestor due to many fossil forms that show notochord, myomeres, gill structure, and caudal projections.

Vertebrata Groups Agnathans – lampreys and hagfish Gnathostomes – “jaw opening”

cartilaginous fish, bony fish, amphibians, reptiles, birds, & mammals

Hagfish vs Lampreys No jaws Cartilaginous

skeleton No paired or dorsal

fins No eyes Many mucus glands

No jaws Cartilaginous

skeleton No paired fins, but

dorsal fin present Eyes well developed No mucus glands

AGNATHA

Hagfish

Lampreys

Gnathostomes – Animals with Jaws Hinged jaws were the most important

evolutionary development Jaw structure is thought to be derived from the

first gill arch Jaw was probably at first a hinged mechanism

that prevented reflux of water during breathing Jaws allowed new sources of food and new

nichesMORE FOOD = BETTER SURVIVAL = MORE

BABIES = MORE REPRESENTATIVES WITH THOSE GENES FOR THE “GOOD” TRAIT

Jaw Development

Development of Paired Fins

Paired fins include the pectoral and pelvic fins.

Pectoral fins are used for balancing and turning

Pelvic fins are for stabilizing motion Both kinds help control pitch, yaw, and

roll

Pitch, Yaw, and Roll?!?

Origin of Paired Fins

Paired fins might have evolved from the most posterior gill arch, folds of the body wall, or from spiny appendages along the body.

The fossil record provides no clear answer to which hypothesis is accurate or if more than one may be accurate.

Acanthoidians (“spiny sharks”) that support the idea of fins from spines

Paired Fins – continued

Once paired fins arose, wide radiation of fish groups occurred.

Many fish groups are now extinct, but fish are still the most abundant and widespread vertebrate

OsteichthyesChondrichthyes

Placoderms – Mean and Extinct

Class Chondrichthyes – cartilaginous fishSharks

Rays Skates

Chimaeras (Ratfish)

Chondrichthyan characteristics

Cartilaginous skeleton No bony structures except in the teeth

and scales Placoid scales (hooked from the side

view) Approximately 850 living species,

mostly marine

Subclasses of the Chondrichthyes

Elasmobranchii – sharks, skates, rays Holocephali – chimaeras (also called

ratfish)

Skates vs Rays

Skates vs Rays

Dorsoventrally flattened

Hugely enlarged pectoral fins

More muscular tail Usually 2 dorsal fins Lay eggs in cases Pelvic fin is one lobe

Dorsoventrally flattened

Hugely enlarged pectoral fins

Whip-like tail Sometimes

poisonous Dorsal fins usually

absent Pelvic fin is 2 lobed

Chimaera Facts Males have a single

clasper on the head used for clenching the female during mating.

The gills are covered with a fleshy flap.

They have grinding plates rather than separate teeth.

Deep-sea dwellers

Shark Facts Have 5 to 7 gill slits. Range in size from 7 inches long (dwarf

lanternshark) to 39 feet long (whale shark)

Birth Patterns

Oviparous – laying eggs outside of the body, most often with external fertilization (salmon, gray nurse shark)

Ovoviviparous – eggs are retained in the female body but are not connected to her during development, internal fertilization (dogfish, hammerheads, coelacanths)

Viviparous – egg is fertilized internally and retains a connection to the mother for nutrients until birth (bull sharks, surf perch, guppies, mollies)

Structures Unique to Fish that Chondrichthyes and Osteichthyes Share Lateral line system to detect pressure

waves. Two chambered heart with single atrium

and ventricle. Have a range of birth patterns from

oviparous, ovoviviparous, to viviparous birth.

Osteichthyes – The Bony Fish

“Bony Fish” have skeletons made of bone.

The two subclasses exist: the-ray finned fish (Actinopterygii) and the lobe-finned fish (Sarcopterygii)

The ray-finned fish comprise 97% of all living species of fish.

Sarcoptyergii Lobe-finned fish

have fleshy fins with internal bones.

Lungfish and coelacanths belong to this group.

Lungfish

“Lung” is a highly vascularized swim bladder.

They do also have gills. Gulp air at surface

when oxygen levels drop.

Can survive droughts by burying themselves into mucus-lined burrows.

The Ray-Finned Fish

“Ray finned” means the fins are webs of membrane supported by internal bony spines called fin rays.

Have a bony plate covering the gills, called the operculum.

Have a symmetrical homocercal tail. Have a swim bladder used for buoyancy

and gas exchange.