Learning Objectives- Chapter 15 Chondrichtyes

Gnathosomes

Phylum Chordata

Superphylum Vertebrata

Class Chondrichthyes

-Subclass Elasmobranchii

-Subclass Holocephali

Fish that have jaws

Gill Arches

Support structures for gill filaments

Jaw bones

They evovled from the gill arches closet to the mouth/ Modified gill arches

Paired Fins

Pectorals Fins and Pelvic Fins

Evovled as stabilizers for swimming

Placoid Scales

Tough scales found on cartilaginous fishes

Spiral Intestinal Valve

A corkscrew-shaped lower portion of the intestine

Cartilaginous Skeleton

Less dense, more flexible

Ossified

Having turn into bone or bony tissue

Serial Tooth Replacement

Teeth arranged in rows, fall out and are replaced

Ram Ventilation

Mouth is open and water is forced over the gills by forward movement of the whole animal

Spiracles

A pair of round openings behind the eye

Countercurrent Gas Exchange

When the blood and water flow in opposite directions ( derived state)

Concurrent Gas Exchange 

When the blood and water flow in the same direction (ancestral state)

2 Chamber Heart 

A simple type of heart that consists of two main chambers: an atrium and a ventricle

Nictitating Memberanes

Protect eyes during feeding

Lateral Line System

Series of pores and canals lined with cells called neuromasts specialized to detect vibrations

Ampullae of Lorenzini

Sensory organs in the head that detect electrical charges

Large-Oil Rich Livers

Used in Chondrichthyes to achieve neutral buoyancy

Urea

Nitrogenous waste product from breakdown of protein in the blood

Euryhaline

Cartilaginous fish are found primarily in estuarine environments were salinity changes regularly

Claspers

On pelvic fins used to grasp females while swimminng and transfers sperm into the female’s cloaca

Cloaca

Common cavity at the end of the digestive tract for the release of both excretory and genital products

Ovoviviparity

“Yolk sac viviparity”, young mature within the body of the parent, but only feed off the yolk sac (no placenta)

Placental Viviparity

The young are nourished by a placenta ( tapped into the parent blood supply)

Oophagy

Embryos eating eggs while still in the uterus

Intrauterine Cannibalism

When the largest embryo eats other developing embryos

Low Fecundity

Few offspring produced each cycles

Long Gestation

Time embryos spend developing

Fusiform

Spindle-shaped

Heterocercal Tail

An asymmetrical caudal fin where the upper lobe is larger than the lower lobe, and the vertebral column extends into the upper lobe

Stingrays

A whip-like tail that is equipped with a venomous spine at the base of the tail and used in defense.

Skates

Look similar to stingrays but lack the whip-like tail and venomous spine: also have 2 small dorsal fins on caudal fins

Sawfish

Large, benthic rays reaching up

What did jaws evolve from?

From the front gill arches of jawless fish

What do jawed fish belong to?

Gnathostomes (“jaw mouths”).

Why were jaws helpful?

Helped with breathing, biting, and catching food.

What is the skeleton of cartilaginous fish made of?

Cartilage (not bone).

What kind of scales do they have?

Placoid scales (tooth-like and rough).

How many gill slits do they have?

5–7 pairs, no operculum (cover)

What kind of fins do they have?

Paired pectoral and pelvic fins.

What is a spiral valve?

A spiral-shaped intestine that helps absorb food.

What are the two main groups of cartilaginous fish?

Elasmobranchii (sharks, rays, skates) and Holocephali (chimaeras).

How do cartilaginous fish control salt and water?

They keep urea in their blood to match seawater salt levels.

What organs remove extra salt?

Kidneys, intestines, and the rectal gland.

What are euryhaline fish?

Fish that can live in both fresh and salt water (like bull sharks).

Do they use internal or external fertilization?

Internal fertilization.

What are claspers?

Male fins used to transfer sperm.

What does oviparous mean?

Lays eggs (like “mermaid’s purse”).

What does ovoviviparous mean?

Eggs hatch inside the mother; babies feed on yolk.

What does viviparous mean?

Gives birth to live young using a placenta.

What is oophagy?

Embryos eat extra eggs in the uterus.

Why do sharks reproduce slowly?

They have few babies, long pregnancies, and grow slowly.

How do cartilaginous fish stay afloat?

Their big oily liver helps them float

Do they have a swim bladder?

No, only bony fish do.

What is countercurrent exchange?

Water and blood flow opposite ways for better oxygen uptake.

What is co-current exchange?

Water and blood flow the same way; less oxygen absorbed.

Which type do most fish use?

Countercurrent exchange

What do nostrils (nares) do?

Smell chemicals in the water.

What protects shark eyes?

A nictitating membrane (eyelid).

What does the lateral line do?

Detects vibrations and movement in the water.

What are the Ampullae of Lorenzini?

Sense electrical signals from prey.

Do jawless fish have jaws?

No.

What are the scales of cartilaginous fish like?

Placoid and rough

What are the scales of bony fish like?

Smooth (cycloid or ctenoid).

Do cartilaginous fish have an operculum (gill cover)?

No.

How do bony fish stay buoyant?

With a swim bladder.

What body shape do sharks have?

Streamlined (fusiform) with a heterocercal tail.

What shape are rays and skates?

Flat bodies with wide fins

What’s special about stingrays?

They have a venomous tail spine.

What’s special about electric rays?

They make electricity to shock prey

What are chimaeras (ratfish)?

Deep-sea fish with flat teeth and one gill opening

Why are sharks important?

They’re top predators that keep ecosystems balanced.

How many cartilaginous fish are threatened?

About 1 in 4 species.

Why are they endangered?

Overfishing, finning, habitat loss, and slow reproduction.

Why do they recover slowly?

They grow and reproduce very slowly.