L20 - Jawless fishes (cont.) & Gnathostome Jaws

What is a fish?

• A non-monophyletic groups

• All verts that are not tetrapods

What does the lateral line system in fish do?

Sense water currents and vibrations

What are the 5 types of fishes?

1. Hagfishes

2. Lampreys

3. Cartilaginous fishes

4. Ray-fins

5. Lobe-fins

What does Agnatha mean?

without a jaw → jawless fishes

What does the monophyletic group Cyclostomata (clade) of the jawless fishes include?

1. Hagfishes

2. Lampreys

What kind of teeth and kind of nostril do Cyclostomata (lampreys, hagfishes) have?

Keratin and have single median nostril

What class are the hagfishes?

Myxini

The class Myxini (hagfishes) are a part of what superclass?

Cyclostomata

What defines hagfishes?

They are able to produce copious amounts of slime, to defend themselves

Why can hagfishes maintain their internal salts the same level as the external environment?

They are iso-osmotic

How do hagfishes eat?

They are bottom scavengers

• Eat dead things at the bottom

What class are the lampreys?

Class Petromyzontida

How do lampreys feed?

They use suction to feed, the have an oral food.

What does anadromous mean?

Leave sea to spawn upstream

What is the larva lampreys have?

Ammocoete larva

Do lampreys have a long or short lifespan?

short

Why are they considered a nuisance?

They are ectoparasites to fish

What classes are in the Agnatha (jawless fishes)

• Ostracoderms (extinct)

• Cyclostomata (hagfishes and lampreys)

What are Gnathostomes?

Jawed animals, a monophyletic group

Where did the jaws come from? How did they evolve?

From 2 pairs of endochondral cartilaginous articulated arches

What two pairs of endochondral cartilaginous articulated arches did jaws originate from?

Mandibular and hyoid

What did the mandibular and hyoid arches evolve from during the creation of the jaw?

Gill arches

What is another synapomorphy of the Gnathostomes group (jawed fish)?

Paired fins

Which are the paired fins?

Pectoral and Pelvic pairs

What is the origin of these paired fins thought to be?

Lateral plate mesoderm

What are the Gnathostomes?

They are the Placoderms, an extinct group

Do the Placoderms have an endo or exoskeleton?

Both

What are the two part hypothesis origins of paired fins in Gnathostomes?

1. Finfolds

2. Outgrowths of lateral plate mesoderm