Porifera: The Sponges
Classes
Class Demospongia: The most diverse, spicules are made of spongin and/or siliceous, these are your "bath sponges"
Class Calcarea: Spicules are made of calcium carbonate
Class Hexactinellida: Spicules are siliceous
Class Demospongia: The most diverse, spicules are made of spongin and/or siliceous, these are your "bath sponges"
Class Calcarea: Spicules are made of calcium carbonate
Class Hexactinellida: Spicules are siliceous
Anatomy
Sponges have diverse body forms ranging from sheets to mounds to tubes. They can range in size from one millimeter to larger than one meter. No matter the body type, all sponges have a canal system, through which they pump water.
Asconoid Syconoid Leuconoid
Sponges have diverse body forms ranging from sheets to mounds to tubes. They can range in size from one millimeter to larger than one meter. No matter the body type, all sponges have a canal system, through which they pump water.
Asconoid Syconoid Leuconoid
Before we get into the canal system, we need to look at the cellular structure.
Sponges do not have any structures that are considered organs (so no organ systems); instead, cells are specialized to perform different functions.
The walls of the sponge are lined with pores called "ostia" which allow water to enter into the spongocoel (the inner cavity of the sponge). The collar cells (choanocytes) move the water along with their flagella. Water exits the spongocoel through a larger opening called the osculum. The osculum acts as the excretory system of the sponge. Eating
Sponges are primarily filter feeders. Food (detritus, plankton, bacteria) that is captured by the choanocytes will be digested by the amoebocytes. There are a few carnivorous sponges that will eat small crustaceans.
Reproduction
Sponges can reproduce asexually or sexually.
Asexual reproduction is completed through a process called "budding" which is an external growth that will separate once "mature". Sponges can also form "gemmules" which are in response to a very harsh environment. Gemmules will remain dormant until the environment is more favorable and then will grow into a mature sponge.
Sexual reproduction occurs by male gametes being released into the water and are taken in via the collar cells. These collar cells will lose their collars and take the sperm to the eggs. The offspring may settle directly and form into an adult or they may remain planktonic for a period of time.
Sponges do not have any structures that are considered organs (so no organ systems); instead, cells are specialized to perform different functions.
- Choanocytes: the "collar" cells--these line the interior body walls, they have a flagellum (tail-like structure) that beat to move water through the canals. The collars absorb nutrients
- Mesenchyme: Sometimes called the mesohyle, the "middle layer" found between the exterior and interior of the sponge
- Amoebocytes: Very important! These cells can change into any of the other types of sponge cells. These can act as digestive cells, secrete spicules which act as the skeleton, or secrete spongin which makes up the "sponge" part of the organism.
- Myocytes & Porocytes: the "muscle" cells, while sponges do not have muscles, these surround the pores and contract to regulate water flow through the sponge.
The walls of the sponge are lined with pores called "ostia" which allow water to enter into the spongocoel (the inner cavity of the sponge). The collar cells (choanocytes) move the water along with their flagella. Water exits the spongocoel through a larger opening called the osculum. The osculum acts as the excretory system of the sponge. Eating
Sponges are primarily filter feeders. Food (detritus, plankton, bacteria) that is captured by the choanocytes will be digested by the amoebocytes. There are a few carnivorous sponges that will eat small crustaceans.
Reproduction
Sponges can reproduce asexually or sexually.
Asexual reproduction is completed through a process called "budding" which is an external growth that will separate once "mature". Sponges can also form "gemmules" which are in response to a very harsh environment. Gemmules will remain dormant until the environment is more favorable and then will grow into a mature sponge.
Sexual reproduction occurs by male gametes being released into the water and are taken in via the collar cells. These collar cells will lose their collars and take the sperm to the eggs. The offspring may settle directly and form into an adult or they may remain planktonic for a period of time.