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Chapter 25: Problem 4

Discuss the important features of cartilaginous fishes, rayfinned fishes, coelacanths, and lungfishes.

Short Answer

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Cartilaginous fishes (sharks, rays, chimaeras) have a skeleton made of cartilage, placoid scales, and internal fertilization. Ray-finned fishes (Actinopterygii) are the largest fish group with a bony skeleton, dermal bone scales, and external fertilization. Coelacanths (Sarcopterygii) are rare lobe-finned fishes with lobe-shaped fins, a diphycercal tail, rostral organ, and live birth. Lungfishes (Dipnoi) possess gills and a primitive lung, paired fins, aestivation capability, and external fertilization with male nest-guarding.

Step by step solution

01

Introduction to Fish Groups

Fish are a diverse group of animals that can be classified into various groups, including cartilaginous fishes, ray-finned fishes, coelacanths, and lungfishes. Each group has distinguishing characteristics that set them apart from one another. In this lesson, we will discuss their key features.
02

Cartilaginous Fishes

Cartilaginous fishes (Chondrichthyes) include sharks, rays, and chimaeras. The primary feature that differentiates them from other fishes is their skeleton, comprised entirely of cartilage rather than bone. Some of their key characteristics include: - Placoid scales, which are made of enamel-like material and give their skin a rough texture - Fins supported by skeletal rods - No swim bladder, meaning they must actively swim to remain buoyant - Razor-sharp teeth that can be replaced when lost - Internal fertilization and a varied mode of reproduction, ranging from laying eggs to live birth
03

Ray-Finned Fishes

Ray-finned fishes (Actinopterygii) are the largest group of fishes, with over 30,000 species, accounting for nearly 99% of all fish species. These fishes have a bony skeleton and fin rays made of bone spines that support fin membranes. Some key characteristics include: - Large swim bladder that helps with buoyancy - Scales made of dermal bone, called ganoid, cycloid, or ctenoid scales - Most have external fertilization, where females lay eggs and males fertilize them in the water - An operculum, a bony gill cover, protects the gills
04

Coelacanths

Coelacanths (Sarcopterygii) are a rare group of lobe-finned fishes, with only two known species. They are considered living fossils, with their closest relatives dating back to over 300 million years ago. Some key features of coelacanths include: - Lobe-shaped fins supported by a strong central core of bone, which gives them more range of movement than ray-finned fishes - A diphycercal tail (a symmetrically forked tail) with the upper and lower lobes being of equal size - A secondary "rostral organ" in their snout, used for electroreception - Internal fertilization with the female giving birth to live offspring
05

Lungfishes

Lungfishes (Dipnoi) are another group of lobe-finned fishes, with only six known species. They have both gills and a primitive lung, allowing them to survive in oxygen-poor waters or during periods of drought. Some important features of lungfishes include: - Paired fins and a long, eel-like body - The ability to aestivate, a form of dormancy in which they survive in a cocoon made of mucus and earth during drought - Some species are obligate air breathers, meaning they rely exclusively on their lungs for gas exchange - External fertilization, with males guarding the nests and fanning the water to provide oxygen for the developing eggs and larvae

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