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By the end of this section, you will be able to:
  • Discuss the different types of skeletal systems
  • Explain the role of the human skeletal system
  • Compare and contrast different skeletal systems

A skeletal system is necessary to support the body, protect internal organs, and allow for the movement of an organism. There are three different skeleton designs that fulfill these functions: hydrostatic skeleton, exoskeleton, and endoskeleton.

Hydrostatic skeleton

A hydrostatic skeleton    is a skeleton formed by a fluid-filled compartment within the body, called the coelom. The organs of the coelom are supported by the aqueous fluid, which also resists external compression. This compartment is under hydrostatic pressure because of the fluid and supports the other organs of the organism. This type of skeletal system is found in soft-bodied animals such as sea anemones, earthworms, Cnidaria, and other invertebrates ( [link] ).

Photo shows a white sea star with red bumps along the tops and tips of its arms.
The skeleton of the red-knobbed sea star ( Protoreaster linckii ) is an example of a hydrostatic skeleton. (credit: “Amada44”/Wikimedia Commons)

Movement in a hydrostatic skeleton is provided by muscles that surround the coelom. The muscles in a hydrostatic skeleton contract to change the shape of the coelom; the pressure of the fluid in the coelom produces movement. For example, earthworms move by waves of muscular contractions of the skeletal muscle of the body wall hydrostatic skeleton, called peristalsis, which alternately shorten and lengthen the body. Lengthening the body extends the anterior end of the organism. Most organisms have a mechanism to fix themselves in the substrate. Shortening the muscles then draws the posterior portion of the body forward. Although a hydrostatic skeleton is well-suited to invertebrate organisms such as earthworms and some aquatic organisms, it is not an efficient skeleton for terrestrial animals.

Exoskeleton

An exoskeleton    is an external skeleton that consists of a hard encasement on the surface of an organism. For example, the shells of crabs and insects are exoskeletons ( [link] ). This skeleton type provides defence against predators, supports the body, and allows for movement through the contraction of attached muscles. As with vertebrates, muscles must cross a joint inside the exoskeleton. Shortening of the muscle changes the relationship of the two segments of the exoskeleton. Arthropods such as crabs and lobsters have exoskeletons that consist of 30–50 percent chitin, a polysaccharide derivative of glucose that is a strong but flexible material. Chitin is secreted by the epidermal cells. The exoskeleton is further strengthened by the addition of calcium carbonate in organisms such as the lobster. Because the exoskeleton is acellular, arthropods must periodically shed their exoskeletons because the exoskeleton does not grow as the organism grows.

Photo shows a crab with orange legs and a black body crawling on a tree.
Muscles attached to the exoskeleton of the Halloween crab ( Gecarcinus quadratus ) allow it to move.

Endoskeleton

An endoskeleton    is a skeleton that consists of hard, mineralized structures located within the soft tissue of organisms. An example of a primitive endoskeletal structure is the spicules of sponges. The bones of vertebrates are composed of tissues, whereas sponges have no true tissues ( [link] ). Endoskeletons provide support for the body, protect internal organs, and allow for movement through contraction of muscles attached to the skeleton.

Questions & Answers

what is oxidation?
Rose Reply
 the state or result of being oxidized
Emmanuel
hahahaha thanks, but my teachers requires a thorough meaning about that
Rose
Is the process of oxidizing ,the addition of oxygen to a compound with a loss of electrons, always accompanied by reduction
Korletey
loss of electron....
Anwar
thank you. 😊
Rose
thank you. 😊
Rose
thank you. 😊
Rose
what is oxidized
Oyebanji
the process or result of oxidizing or being oxidized.
Jersey
my pleasure
Anwar
Google itttt.....if need explanation
Anwar
to rose...
Anwar
oxidation is the removal of oxygen addition of hydrogen
SIRAJO
what is genetic
Chibawa Reply
name the enzymes that i found in the saliva
Valuables Reply
draw a bacterium cell and label
Kadijah Reply
What are the osmoregulatory functions of the kidney?
bisi Reply
filter
Meenu
What is ecology
Hebert Reply
what is cell
Etama Reply
cell is the basic unit of life
Asiatou
cell is the basic structural and functional unit of an living organism
Darshan
a cell is the smallest and most basic unit of a living thing
John
cell is the basic unit of life. we are made up of 60,000 billions of cells.Each cell carry out a specific function in the body.
Pallavi
A cell is the smallest basic functioning unit of life.
Ali
where is the pectoral gridle located?
Tiania Reply
What is hypotonic
Bright Reply
what is hypotonic
Dangaya
Hypotonic means weak solution
Ali
the difference between the two cells
Obeng Reply
explain the courses and the correction of lon term sightedness and short term sightedness
Isaac Reply
long sightedness is said to be like someone that can see far object clearly why short sightedness is someone that only can see near obect
SHEDRACK
why drinking excess alcohol causes thirst and dehydration
uwikuzo Reply
Can we chat about nutrition please?
Elia
yes
Uzair
sure
Uzair
Uhm why is it so important to follow the nutritional process?
Elia
BC it contribute to the source of life
SHEDRACK
what is reproduction
smart Reply
it is d act of bringing young ones to life
Oyebanji
to ensure survival of a species🚴‍♀️
Michelle
what is a genotype
Collins
what is hazardous
smart
a cell is the smallest unit of a living thing. so we all have cell
smart
It is the formation of a zygote resulting from the fusion of the sperm cell with the ovum.Thus,this results in the production of new species which are genetically dissimilar from their parent cells.
Pallavi
yes we all have cell round our body without the existances of cell them they will be no life in us as human
SHEDRACK
what is size of cell
Mohd Reply
what is size of Hart
Mohd
nanometers=um sign thingie
Michelle
microns=nanometers
Michelle
monomers and polymers of nucleic acids?
Jyrl Reply
dna and rna involvement
Michelle

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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