Test (biology)
Channel: all the knowledge of the universe PRINCIPIA
Date: 2022-01-17

Test (biology), by Wikipedia https://en.wikipedia.org/wiki?curid=10086055 / CC BY SA 3.0

#Mollusc_shells
#Echinoidea
#Marine_biology
Test of a shingle urchin （Colobocentrotus atratus） In biology, a test is the hard shell of some spherical marine animals, notably sea urchins and microorganisms such as testate foraminiferans, radiolarians, and testate amoebae.
The term is also applied to the covering of scale insects.
The related Latin term testa is used for the hard seed coat of plant seeds.
The anatomical term "test" derives from the Latin testa （which means a rounded bowl, amphora or bottle）.
The test is a skeletal structure, made of hard material such as calcium carbonate, silica, chitin or composite materials.
As such, it allows the protection of the internal organs and the attachment of soft flesh.
Test of a sea urchin.
The test of sea urchins is made of calcium carbonate, strengthened by a framework of calcite monocrystals, in a characteristic "stereomic" structure.
These two ingredients provide sea urchins with a great solidity and a moderate weight, as well as the capacity to regenerate the mesh from the cuticle.
According to a 2012 study, the skeletal structures of sea urchins consist of 92% of "bricks" of calcite monocrystals （conferring solidity and hardness） and 8% of a "mortar" of amorphous lime （allowing flexibility and lightness）.
This lime is constituted itself of 99.
9% of calcium carbonate, with 0.
1% structural proteins, which make sea urchins animals with an extremely mineralized skeleton （which also explains their excellent conservation as fossils）.
Foraminiferan tests.
The test of foraminifera, a group of single-celled organisms, is extremely evolutionarily diverse.
Many different methods of constructing the test are present, from lacking a test in Reticulomyxa, proteinaceous tests in the "allogromiids", agglomerated tests made from foreign particles in many groups including textulariids,
silica tests in silicoloculinids, and aragonite or calci...