Multiple choice: Which type of cells in Porifera create water currents? Pinacocytes Mesenchyme Choanocytes Current ceils True/False: Porifera are triploblastic and bilaterally symmetric. True False True/False: Protozoans exhibit some tissue level organization. True False Solution Ans. 1. Choanocytes in Porifera create water currents. Ans. 2. False. Have single germ layer. Triploblastic organisms have three germ layers. Ans. 3. False Protozoans are unicellular eukaryotes and lack any tissue level organization. Phylum Porifera: The members lack tissue level organization, thus are NOT triploblastic. Multicellular body, most of them with cellular level of organization, some may form incipient tissue. Generally asymmetric, but some may present superficial radial symmetry. Body Organization: The outer surface of sponges, called pinacoderm, is composed one cell-thick layer of pinacocytes. A rigid skeletal framework (siliceous or calcareous) covering the pinacoderm may also be present in many sponges and is called spicules. The pinacoderm bears perforation through which the water enters the body. The perforation is called ostium (pore is lined by one cell) or dermal pore (pore is lined by several cells). Some pinacocytes are modified as contractile myocytes and generally arranged around oscula/ dermal pores to regulate water flow. The inner one-cell thick surface, called choanoderm, is composed of choanocytes (collar cells). The uniflagellated choanocytes bear a collar of microvilli surrounding the flagella. The oval end of choanocytes is embedded in mesohyl and the flagellated end exposed in the water canal. The large central cavity of sponges is called spongocoel. The coordinated beating of flagella of the choanocytes lining the ostium/ dermal pores draws water in through the water canal system and the food particles are trapped at the collar of choanocytes. The matrix in between pinacoderm and choanoderm is called mesohyl/ mesenchyme and consists of spicules, collagen fibers and many other type of cells (collencytes, archaeocytes, etc.) embedded in a noncellular colloidal mesoglea. It plays crucial roles in digestion, gamete production, secretion of skeletal components, and transport of nutrients and waste removal by amoebocytes. The archaeocytes are amoeboid cells and can different into many other types of cells with specialized functions- sclerocytes (secretes spicules), spongocytes (secretes spongin collagen), collencytes (secrete collagen fibers) and lophocytes (secrete relatively large quantity of fibrillar collagen)..

1. Multiple choice: Which type of cells in Porifera create water currents? Pinacocytes
Mesenchyme Choanocytes Current ceils True/False: Porifera are triploblastic and bilaterally
symmetric. True False True/False: Protozoans exhibit some tissue level organization. True False
Solution
Ans. 1. Choanocytes in Porifera create water currents.
Ans. 2. False. Have single germ layer.
Triploblastic organisms have three germ layers.
Ans. 3. False
Protozoans are unicellular eukaryotes and lack any tissue level organization.
Phylum Porifera:
The members lack tissue level organization, thus are NOT triploblastic. Multicellular body, most
of them with cellular level of organization, some may form incipient tissue. Generally
asymmetric, but some may present superficial radial symmetry.
Body Organization: The outer surface of sponges, called pinacoderm, is composed one cell-thick
layer of pinacocytes. A rigid skeletal framework (siliceous or calcareous) covering the
pinacoderm may also be present in many sponges and is called spicules. The pinacoderm bears
perforation through which the water enters the body. The perforation is called ostium (pore is
lined by one cell) or dermal pore (pore is lined by several cells). Some pinacocytes are modified
as contractile myocytes and generally arranged around oscula/ dermal pores to regulate water
flow.
The inner one-cell thick surface, called choanoderm, is composed of choanocytes (collar cells).
The uniflagellated choanocytes bear a collar of microvilli surrounding the flagella. The oval end
of choanocytes is embedded in mesohyl and the flagellated end exposed in the water canal. The
large central cavity of sponges is called spongocoel. The coordinated beating of flagella of the
choanocytes lining the ostium/ dermal pores draws water in through the water canal system and
the food particles are trapped at the collar of choanocytes.
The matrix in between pinacoderm and choanoderm is called mesohyl/ mesenchyme and consists
of spicules, collagen fibers and many other type of cells (collencytes, archaeocytes, etc.)
embedded in a noncellular colloidal mesoglea. It plays crucial roles in digestion, gamete
production, secretion of skeletal components, and transport of nutrients and waste removal by
amoebocytes. The archaeocytes are amoeboid cells and can different into many other types of
cells with specialized functions- sclerocytes (secretes spicules), spongocytes (secretes spongin
collagen), collencytes (secrete collagen fibers) and lophocytes (secrete relatively large quantity
of fibrillar collagen).