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Name the five classes of fish (pisces)

- Agnatha
- Acanthodii* (extinct)
- Placodermi* (extinct)
- Chondrichthyes
- Osteichthyes


Describe the Agnatha subclass, Ostracoderms and give an example

- Oldest known vertebrate at 450 million years old. They probably originated in freshwater, but they might've moved to marine. They came from the Devonian period. They lacked paired appendages or jaws and had a pharyngeal pumping system, different than the ciliary filter-feeding system of protochordates. They had nasal openings and pineal glands. They had dermal armor.
- Example: Pterapsis - Had an armored head shield, paired spines, and a reversed heterocercal tail.


List the characteristics of the Agnathan subclass, Cyclostomata and give examples.

Not extinct. They still lack jaws and paired appendages, and are divided into two nonextinct species: Hagfish, and Lampreys.
- Lampreys: Predators, Filter Feeders, Gills in their mouths/pouches, pineal organ, and a single nostril that doesn't open to the pharynx. They are born in freshwater, move out into marine water, then move back into freshwater to breed. This is calls Anadromous.
- Hagfish: Entirely marine, no suction-type mouth, but rasping tongue with tentacles by their mouth. They were primarily scavengers, had a single nostril that opened into the pharynx, had multiple gill pouches, and were all-around disgusting animals.


What are Gnathostomes?

Gnathostomes: It means Jawed Fish. These were not one of the five classes...for some reason. Unofficially, it refers to the first generation of jawed fishes...Officially, it means pretty much any type of fish except Agnathans.
- They had a stomach, and swallowed food in morsels.
- They developed paired appendages to make swimming and escaping easier. And the evolution of lungs and bladders meant that they could control their depth by altering their buoyancy (except sharks)


Describe Acanthodii

- Dead and gone now. But they had a more streamlined body that agnathans, and they had dense armor on their bodies, but not large scales (but they had something called ganoid scales.)
- They have numerous paired and unpaired spikes
- Most of them were freshwater, but the older ones were probably marine.


Describe the class Placodermi

- These guys are extinct. But they were Large (up to 30 ft long)
- There was a movable joint between their head/shield thing and their trunk. Both of which were heavily armored.
- They had a streamlined body, and paired pectoral and pelvic fins. They were swimmers, and probably pretty predatorial.
- Note: Not all of these guys were large. Some were quite small.


Describe some characteristics of the class chondrichthyes

- (Picture sharks), (Or ratfish/chimera)
- They laid large-yolked eggs, paired nostrils, and gills that open to the exterior. More distinctively they were all-cartilage.
- The two subclasses are extinct, ranged from 3-6 feet, and probably represented the first sharks. Some were freshwater.


Describe the osteichthyes subclass: Sarcopterygii

-These guys had lobed paired fins.
- Their internal bone skeletons were made up of cartilage and bone.
- Examples included: coelacanth, rhipidistian, and Lungfish


Describe the subclass of osteichthyes, actinopterygii

- Ray-finned fish
- Internal fin skeleton was made of spines
Examples include: Sturgeons, Bowfins, Most freshwater and marine bony fish


Who is believed to have been the first fish to become terrestrial?

Some evidence pointed to the coelanth, but nowadays, we believe it was an ancestor of the Lungfish, because they had lungs. And a blood and circulatory system somewhat comparable to that of a frog.