Difference Between Chondrichthyes and Osteichthyes

The main difference between Chondrichthyes and Osteichthyes is that the Chondrichthyes is the class of bony fish whose endoskeleton is made up of cartilages whereas Osteichthyes is the class of cartilaginous fish whose endoskeleton is made up of bones. Furthermore, Chondrichthyes can only be found in marine water while Osteichthyes can be found in both fresh and marine water.

Chondrichthyes and Osteichthyes are the two main groups of fish classified based on the composition of the endoskeleton.

Key Areas Covered

1. Chondrichthyes
     – Definition, Characteristics, Behavior
2. Osteichthyes
     – Definition, Characteristics, Behavior
3. What are the Similarities Between Chondrichthyes and Osteichthyes
     – Outline of Common Features
4. What is the Difference Between Chondrichthyes and Osteichthyes
     – Comparison of Key Differences

Key Terms

Chondrichthyes, Osteichthyes, Endoskeleton, Lobe-Finned Fish, Ray-Finned Fish

Chondrichthyes – Definition, Characteristics, Behavior

Chondrichthyes is the class of cartilaginous fish whose exoskeleton is made up of cartilages. Most importantly, Chondrichthyes are only found in marine water. Most Chondrichthyes show a massive growth. The largest cartilaginous fish is the whale shark, which weighs 21.5 tonnes. Some other Chondrichthyes include great white shark, basking shark, thresher shark, skates, and rays. Sharks eat whales, seals, and other fish while skates and rays eat crabs, shrimps, oysters, clams, etc.

Figure 1: White Shark

Male Chondrichthyes uses claspers to grasp the female during reproduction. Rays are viviparous while skates are oviparous.       

Osteichthyes – Definition, Characteristics, Behavior

Osteichthyes is the class of bony fish with an endoskeleton made up of bones. It diverged from Chondrichthyes 420 million years ago. It lives in both freshwater and marine habitats. The largest bony fish is the ocean sunfish or common mola, which weighs up to 2.3 tonnes. Ray-finned and lobe-finned fish are the two types of Osteichthyes. Ray-finned fish has a single dorsal fin while lobe-finned fish has two dorsal fins.

Figure 2: Osteichthyes (Epinephelus lanceolatus)

Osteichthyes have a rounded body tapered at the ends. This shape is called a fusiform. Osteichthyes have both pectoral and pelvic fins in pairs while the dorsal, anal, and tail fins are single. The lateral line that runs through the body consists of a series of sensory organs called neuromasts, which help to sense both water pressure and vibrations.

Similarities Between Chondrichthyes and Osteichthyes

• Chondrichthyes and Osteichthyes are the two classes of fish, who are aquatic chordates.
• Both fish belong to the superclass Pisces.
• Both have both endoskeleton and exoskeleton.
• Breathing of both fish occurs through gills.
• They have a mouth with jaws.
• Their fins are paired.

Difference Between Chondrichthyes and Osteichthyes

Definition

Chondrichthyes refers to a class of fishes that includes those with a cartilaginous skeleton while Osteichthyes refers to a class of fishes that includes those with a bony skeleton.

Also known as

Chondrichthyes are cartilaginous fish or elasmobranchii while Osteichthyes are bony fish or teleostomi.

Habitat

Furthermore, Chondrichthyes can be exclusively found in marine water while osteichthyes can be found in both fresh and marine water.

Number of Species

More than 970 Chondrichthyes species have been identified worldwide while more than 27,000 bony fish species have been identified worldwide.

Endoskeleton

The endoskeleton of Chondrichthyes is completely made up of cartilages while the endoskeleton of Osteichthyes is completely made up of bones.

Exoskeleton

The exoskeleton of Chondrichthyes is made up of very small denticles coated with sharp enamel known as placoid while the exoskeleton of Osteichthyes is made up of thin bony plates known as cycloids.

Position of the Mouth

The mouth of Chondrichthyes is ventrally-located while the mouth of Osteichtheys is at the anterior tip of the body.

Oral Jaw Sets

Also, Chondrichthyes has a single set of jaws while Osteichthyes has two sets of jaws.

Gill Pairs

Moreover, Chondrichthyes has 5-7 gill pairs while Osteichthyes has 4 pairs of gills.

Operculum

The gills of Chondrichthyes are not covered by an operculum while the gills of Osteichthyes are covered by an operculum.

Air Bladder

Chondrichthyes do not have air bladders and they use oil-filled liver of buoyancy while Osteichthyes have an air bladder called swim bladder, gas bladder or fish maw.

Tail Fin

The tail fin of Chondrichthyes is heterocercal while the tail fin of Osteichthyes is homocercol.

Mode of Nutrition

Chondrichthyes is generally carnivores while Osteichthyes can be carnivores, omnivores, herbivores, filter-feeders or detritivores.

Fertilization

Some Chondrichthyes undergo internal fertilization while most Osteichthyes undergo external fertilization.

Excretion

The main excretion form of Chondrichthyes is urea while Osteichthyes excretes ammonia.

Examples

Some Chondrichthyes include skates, sharks, and ray fish while some examples of Osteichthyes are salmon fish, trout, rohu, and seahorse.

Conclusion

Chondrichthyes are cartilaginous fish whose endoskeleton is made up of cartilages while endoskeleton of Osteichthyes is made up of bones. Also, Chondrichthyes can only be found in the marine water while Osteichthyes lives in both fresh and marine water. The main difference between Chondrichthyes and Osteichthyes is the composition of their endoskeleton and habitat.

Reference:

1. “Chondrichthyes – Rays, Sharks, Skates, Chimaeras .” Wildlife Journal Junior, Available Here
2. Manisha, M. “Class Osteichthyes (With Diagram) | Bony Fishes.” Biology Discussion, 12 Dec. 2016, Available Here

Image Courtesy:

1. “White shark” By Terry Goss (CC BY 2.5) via Commons Wikimedia 
2. “Epinephelus lanceolatus young” By © Citron (CC BY-SA 3.0) via Commons Wikimedia