The vast majority of animals don't have a defined cranium or pedis.
We will start our investigation with the simplest of the animals.
The split between the Parazoa and the Eumetazoa is believed to have taken place over a billion years ago.
The Porifera do not have "true" tissues that are embryologically related to the insects and mammals.
They don't create a true gastrula during embryogenesis and as a result don't produce a true ectoderm.
Even though they aren't considered to have true tissues, they do have specialized cells that perform certain functions, like the internal "pinacoderm" of a sponge.
The poriferans can be said to have tissues, but they are likely not embryologically related to our own.
Adults are non-motile and spend their life attached to a substratum.
The sponge's body structure allows the movement of water through the sponge.
Water can move through various canals and chambers to allow the exchange of food and waste as well as the exchange of gases to nearly all body cells.
The simplest invertebrates are the sponges.
There are thousands of sponges yet to be classified.
The water enters through numerous openings in the body wall.
In some sponges, multiple feeding chambers open off of a central spongocoel and in others, several feeding chambers connect to one another.
sponges do not have true tissue-layer organization, but they do have a number of functional "tissues" composed of different cell types.
The protective function of pinacocytes is similar to that of our epidermis.
The ostia allow water to enter the body of the sponge.
The sponges have a name for these pores.
Ostrum are formed by porocytes, single tube-shaped cells that act as valves to regulate the flow of water into the sponge.
The folds in the body wall of the sponge form ostia.
The gel-like consistency of mesohyl keeps the tubular appearance of sponges.
The feeding chambers are lined with choanocytes.
The structure of a choanocyte is critical to its function, which is to generate a directed water current through the sponge and to trap and eat food particles.
The feeding cells are similar to unicellular choanoflagellates.
This similarity shows that sponges and choanoflagellates are related.
The choanocyte's body is made of mesohyl and contains all the necessary cells for normal cell function.
A mesh-like collar with a single flagellum in the center of the column istruding into the "open space" inside the feeding chamber.
If the sponge consists of a colony of attached sponges, the beating of the flagella from all choanocytes draws water into the sponge through the numerous ostia, into the spaces lined by choanocytes, and eventually out through the osculum.
The food particles are trapped by the choanocytes and slide down toward the body of the cell.
Choanocytes can differentiate into sperm for sexual reproduction when they leave the mesohyl and leave the sponge with expelled water through the osculum.
The video shows the water moving through the sponge body.
They give rise to eggs for sexual reproduction and deliver vitamins from choanocytes to other cells within the sponge.
The amoebocytes can differentiate into other cell types of the sponge, such as collenocytes and lophocytes.
Spongocytes and sclerocytes can give rise to spicules, which are spikes of calcium carbonate, in some sponges.
The basic body plan and some of the specialized cell types found in sponges are shown.
You can take a tour through the sponge and its cells.
Most sponges are supported by small bone-like spicules in the mesohyl.
The body of the sponge is supported byicules.
The presence and composition of spicules are the basis for differentiating three of the four classes of sponges.
Sponges in class Calcarea produce calcium carbonate spicules and no spongin, while those in class Hexactinellida produce six-rayed siliceous spicules and no spongin.
The last class used sponges as bath sponges.
There areicules in the glass sponges.
Some of the spicules may be large.
Most of the sponges' body cells are fused together to form a multinucleate syncytium.
The sponges have no mesohyl because their cells are connected in this way.
The Sclerospongiae is a fourth class of sponges.
These sponges are called coralline sponges after their calcium carbonate skeletons.
Some of the sponges are hundreds of years old, based on the rate of deposition.
Sponges regulate their different processes through a variety of mechanisms.
Their metabolism, reproduction, and locomotion are regulated by these processes.
Sponges lack a lot of systems.
The food is trapped in the osculum as water passes through it.
choanocytes are the main cells that are engaged in feeding and are eaten by the smaller organisms.
Pinacocytes can be phagocytized at the sponge's surface by particles larger than the ostia.
In sponges, amoebocytes transport food from cells that have eaten food to those that have not.
In sponges, all digestion is inside.
The limit of this type of digestion is that the food particles are small.
Gas exchange, circulation, excretion are performed by the cells that line the openings within the sponge and the water that is passing through those openings.
The sponge has cell types that get oxygen from water.
Carbon dioxide is released into the water.
The nitrogenous waste produced as a result of the metabolism is washed through the sponge with the help of individual cells.
There are sponges that host green algae or cyanobacteria.
Intercellular communication in sponges can regulate events like contraction of the sponge's body or activity of the choanocytes.
Sexual as well as asexual methods are used to reproduce sponges.
During the process of asexual reproduction, a piece of the sponge breaks off, settles on a new site, and develops into a new individual, either budding or genetically identical.
An atypical type of asexual reproduction can only be found in freshwater sponges.
A pneumatic cellular layer that may be reinforced with spicules surrounds an inner layer of archeocytes.
In freshwater sponges, gemmules can survive hostile environmental conditions and then serve to recolonize the habitat once environmental conditions improve.
A new sponge can be created by attaching gems to a substratum.