Marine creatures like crabs have 12 legs

  • Thread starter Craps
  • Start date
  • Tags
    Marine
In summary, crabs have 12 legs, with 10 being small and 2 being large, for manipulation and walking purposes. They have complex mouth parts that allow them to eat a variety of foods. Fish that can breathe air and oxygen in water have a specialized organ called the labyrinth organ. Lungs are not efficient at extracting oxygen from water due to their design. As humans have evolved on land for a long time, it would be a significant change for us to return to underwater life.
  • #1
Craps
13
0
I know marine creatures like crabs have 12 legs, 10 are small and 2 are very big. Do you know why they have small mouths ? do you know what food is for crabs ?
As a side note, I really wonder why human refuse under-water life and choose land life ? I guess perhaps because in water we hold our breath long, right ?

Thanks
 
Last edited by a moderator:
Biology news on Phys.org
  • #2
The reason we couldn't live underwater is because our lungs perform resperation wiht the oxygen in the air around us. Underwater creatures like fish, have other organs like gills that can get the oxygen from the water.
 
  • #3
yomamma said:
The reason we couldn't live underwater is because our lungs perform resperation wiht the oxygen in the air around us. Underwater creatures like fish, have other organs like gills that can get the oxygen from the water.

Then how do you explain fish that *do* breath air *and* oxygen in water, i.e. some specialized fishes in the mangroves?
 
  • #4
Craps said:
I know marine creatures like crabs have 12 legs, 10 are small and 2 are very big. Do you know why they have small mouths ? do you know what food is for crabs ?
As a side note, I really wonder why human refuse under-water life and choose land life ? I guess perhaps because in water we hold our breath long, right ?

Thanks

To begin, crabs are members of the phylum arthropoda, which includes spiders, insects and other crustaceans like shrimp, lobster, isopods (subphylum crustacea). Also they have only ten appendages in total, one pair for manipulation of objects (chelipeds) and the other four pair for walking. They have rather complicated mouth parts with small pincers and mandible types. Variations in the set-up of the mouth parts across all the crab species allow them to eat many different food types like biofilms on sand grain, vegetation like algae, or animals like molluscs, fish, etc.
 
  • #5
Bladibla said:
Then how do you explain fish that *do* breath air *and* oxygen in water, i.e. some specialized fishes in the mangroves?

Are you talking about anabantoids? They have a specialised organ (the labrynth organ) for breathing air, that is separate from the gills.

As far as I'm aware, lungs are capable of removing oxygen from water, but the problem is they can't do it anywhere near fast enough to sustain a person. The oxygen content of water is quite variable, but at best, still a small fraction of that in air. The lungs also aren't designed to move water in and out the same as they can with air, as water is a lot more dense. This means that once water has entered the lungs, most of it will not leave by normal breathing, and so it cannot be replenished with oxygenated water.
Gills work by a different principle to lungs. Unlike lungs, gills have an inlet and an outlet for water, instead of it having to enter and leave through the same route. This allows water to pass through the lamellae (efficient gas absorbing parts. I'm not going to go into detail about how they work) almost constantly, increasing the amount of time that oxygen is being absorbed. Even if humans had gills, they probably would not be able to survive underwater, as they are warm blooded and require more oxygen than cold blooded creatures such as fish.
 
  • #6
To speak to the "humans returning to water" question, I would think that it really goes back to how long we have, as an evolutionary line, been "out of the water". If you believe in evolution then we humans evolved from much simpler creatures a long time ago and this established our path to land-based life. It's not like an even remotely human creature crawled out of the oceans and decided to give dry land a try. Our line has been firmly entrenched ( no pun intended) on land for quite sometime and while it may not necessarily be an evolutionary step backwards for us to go return to the water, it sure would be one heck of a step sideways.
 

Related to Marine creatures like crabs have 12 legs

What is the purpose of crabs having 12 legs?

The 12 legs of crabs serve multiple purposes. Firstly, they are used for walking and navigating through their aquatic environment. Additionally, the back pair of legs are modified into paddles for swimming and the front pair are used for grasping prey. The remaining legs are used for grooming and defense.

Do all marine creatures have 12 legs?

No, not all marine creatures have 12 legs. The number of legs varies among different species. For example, some species of crabs have 10 legs, while others may have up to 14 legs. Other marine creatures, such as octopuses, do not have legs at all but instead have tentacles.

Are all 12 legs of a crab the same size?

No, the 12 legs of a crab are not all the same size. The front pair of legs, also known as chelipeds, are typically larger and stronger than the other legs. This is because they are used for grasping and crushing prey. The remaining legs are generally smaller and are used for walking and other tasks.

Can crabs regrow lost legs?

Yes, crabs have the ability to regrow lost legs. If a crab loses a leg due to injury or predation, it can regenerate a new leg through a process called autotomy. This process involves the crab purposely breaking off its own leg at a specific joint and then regenerating a new leg over time.

Why do some crabs have asymmetrical legs?

Some crabs have asymmetrical legs, meaning one leg is larger than the other. This is typically seen in male fiddler crabs, where the larger claw is used for attracting mates and defending territory. In other species, such as hermit crabs, the asymmetrical legs are used for protection by fitting into and blocking the entrance of their borrowed shells.

Similar threads

Replies
1
Views
606
  • Biology and Medical
Replies
8
Views
2K
Replies
5
Views
1K
  • Biology and Medical
Replies
23
Views
7K
  • Biology and Medical
Replies
18
Views
5K
  • STEM Academic Advising
Replies
18
Views
2K
  • Biology and Medical
Replies
26
Views
6K
  • Biology and Medical
Replies
1
Views
1K
  • Biology and Medical
Replies
2
Views
1K
  • Biology and Medical
Replies
7
Views
2K
Back
Top