Everything You Need To Know About Phylum Porifera And How To Identify Them

Phylum porifera are today known as sponges. They are multicellular animals that used to be considered plants up to 1765.

More and more phylum porifera animals have been discovered over the years.

As it stands now, there are thought to be over 8,000 species of these animals. Of all of these animals, the vast majority of them are marine.

These animals have bodies that are covered in tiny pores or holes, as their names suggest. As such, this is actually one of the most noticeable characteristics.

While you might not realize it, you are already likely familiar with a number of phylum porifera. If you want to find out all about these unique creatures, just keep reading.

We will go through everything you need to know about them, from their characteristics and a number of examples of them.

Phylum Porifera

As we briefly mentioned, phylum porifera are small marine animals with bodies covered in tiny pores or holes. They used to be considered plants up until 1765 until it was found that they were animals.

The vast majority of these animals are marine – meaning they live in the sea and oceans.

However, there are some that live in freshwater locations such as rivers, lakes, and streams. There are over 8,000 species, though there are likely many more that we do not yet know about.

They are invertebrates, and their channels and pores allow water to circulate directly through them. These animals are considered to be the lowest multicellular animals that belong to the Animalia kingdom.

They have a level of organization that is cellular, and are not mobile. Instead, they attach themselves to other things to stay supported, such as rocks.

Porifera are asymmetrical animals for the most part. Rather than having a skeleton, their bodies are supported by either spongin fibers or spicules, which we will explore a little later.

These animals are hermaphrodites, which means that they are not separated by sexes.

This means that one individual can create both eggs and sperm. However, they also have other means of reproducing, which we will look at later on in this post.

Example Animals In This Phylum

There are many examples of animals that are in the porifera phylum.

These include the following:

• Spongilla (freshwater sponges) – Spongilla chaohuensis, Spongilla alba, Spongilla friabilis, Spongilla aspinosa
• Cliona (boring sponges) – Cliona grant, Cliona griffithsii, Cliona coccinea, Cliona sulphurea
• Sycon (calcareous sponges) – Sycon barbadense, Sycon asperum, Sycon antarcticum, Sycon album
• Hyalonema (glassrope sponges) – Hyalonema agujanum, Hyalonema aculeatum, Hyalonema abyssale, Hyalonema azuerone
• Euplectella (marine / glass sponges) – Euplectella jovis, Euplectella aspera, Euplectella gibbsa, Euplectella crassistellata

Morphology And Anatomy Of Phylum Porifera

As we already mentioned, the animals classified in phylum Porifera are simple organisms known as sponges. They are covered in pores, and have no true organs.

They are asymmetrical, unlike most other animals, though they do sometimes display radial symmetry.

Their lack of symmetry is thought to be because of their continuous morphogenesis – a biological process which causes the tissue to develop the shale via control of spatial distribution of cells while the embryo develops.

The majority of animals in this classification are very small, only reaching a few inches in size. However, there are some that can reach six feet tall or more.

They can also range in shape, with some having branches while others are simply tube-shaped. These variations mean that some of them are very recognizable, whereas others are not.

Most of these animals grow upright, resembling something like a tree, but this may not always be the case.

While many of them can appear to be like trees with many branches, some will look like underwater vases and be relatively smooth.

The channels or canals, as well as their pores, allow water to flow through them. Sponges are diploblasts, much like Cnidarians.

This means that their bodies are only made of two basic germ layers – the endoderm and the ectoderm. The endoderm is the inner layer, whereas the ectoderm is the outer layer of the animal.

As many will be aware, sponges can come in a wide array of colors. They can be yellow, orange, and even red, among other colors.

The darker sponges are typically found deeper in the sea, and can be a dark brown.

It’s important to note that while a number of sponges can take the form of trees or vases, some can also be ball-shaped or flattened.

The shape they have is typically determined by the conditions they live in – the environmental conditions.

An example of this would be that any sponges that live in rougher waters are more likely to have a flattened appearance, for safety and function.

Looking at the morphology of the animals in the Porifera classification, they can easily be split up into three distinct groups.

Let’s take a look at them each below to help gain a better understanding of them.

Phylum Porifera Groups

Asconoid Sponges

Asconoid sponges are known to have the most simple bodies of the sponges. These animals are basic bodies, and are typically very small in size with vase-shaped bodies.

They have radial symmetry, with very thin outer walls and a large spongocoel enclosed inside.

This spongocoel is lined with choanocytes, which are flagellated cells that are involved in the process of filtering particles.

The spongocoel, also called the paragaster, is the large cavity where water enters through the pores.

Much like every other sponge we know of, these animals have pore-covered bodies that extend from the surface to the spongocoel.

These pores are also called “ostia”, and they are made up of porocytes – large tubular cells.

In order to control the flow of water through it, the pores can contract and open on command. While these pores in asconoid sponges are tiny, there are a lot of them.

To expel the water, it is pushed out through an opening on the top of the organism called the osculum. When this happens, the unwanted water is expelled from the spongocoel that sits below.

The majority of asconoid sponges are in the Homocoela (Leucosolenida) order, and some examples of these include:

• Leucosolenia arachnoides
• Leucosolenia albatrossi
• Leucosolenia cervicornis
• Leucosolenia complicata

Syconoid Sponges

Syconoid sponges belong to the Heterocoela order. These sponges are far more complex in their body structures, and are typically larger.

Water enters through much larger pores compared to asconoid sponges, in order to enter the spongocoel.

Instead of the spongocoel directly opening, however, the pores, which are made of pinacocytes, will open into incurrent canals, which are narrow canals.

Unlike sponges in the asconoid group, syconoid sponges do not have flagellated (choanocyte) cells in the spongocoel lining. Because of this, all the digestion actually takes place in the canals themselves.

Instead of flagellated cells in the lining of the spongocoel lining, there are epithelial cells. These came cells are the ones that line the surface of our bodies.

Water enters the radial canal from the incurrent canal via the prosopyle pores. Inside these radial canals are flagellated pores.

Some synconoid sponges have radial canals that open into another chamber – this chamber is known as the excurrent chamber.

The water enters this chamber through pores that are larger, called apopyles, which allow water into the spongocoel.

Syconoid sponges also have the ability to be separated into a further three groups. This will, however, depend on how complex the canal system of the sponge is.

These three groups are as follows:

• Simple Sycon – the radial canal projections have spaces between them that can serve as the dermal ostia (pores), and they never touch.
• Complex Sycon – tubular spaces, incurrent canals, or inhalant canals are formed due to the arrangement of the radial canals. The sponges with this characteristic have many pores, including the dermal ostia and prosopyles.
• Sycon With a Cortex – fused radial canals are the primary characteristic of this group of sponges. The sponge’s incurrent canals, which are formed via the fusion of a number of radial canals, are long and large enough to traverse to reach the outer surface by traversing through the cortex.

Some examples of syconoid sponges include the following:

• Sycon protectum
• Sycon ciliatum
• Grantia coompressa

Leuconoid Sponges

Of all sponges, those in the leuconoid group have the most complex body plans. Unlike other groups of sponges, those in this group do not typically have one central spongocoel.

Instead, they have a cavity with many branches, resulting in a number of smaller chambers clustered in the space.

These chambers are usually oval or round, and lined with choanoflagellates.

What ties these sponges in with other sponges is the fact that they also have a number of dermal pores.

Like other sponges, the water will enter the body and choanocyte chambers via these pores and go through the canals.

When the water reaches the various chambers, it is then transferred to the excurrent canal and is pushed out of the body via the oscula.

Leuconoid sponges actually have more than one oscula, unlike many other sponges. These sponges are typically a lot larger, too, often reaching six feet in height.

They have mesenchyme-filled leucon chambers, and are known to have the most effective system for filtering water.

While the majority of sponges that are in Porifera are leuconoid sponges, there are many varieties. Some of these include:

• Stellata
• Spongilla
• Tetilla

Cell Types And Arrangement

Since these animals are some of the most simple in the world, there are only a handful of different cells they have. As we mentioned earlier, sponges are diploblasic.

This means that they have only two simple germ layers – the endoderm and the ectoderm. In sponges that are asconoids, their outer layers have flattened cells that we call pinacocytes.

These are flat cells that cover both the external surface, as well as the excurrent and incurrent canals of these sponges.

On the surface, these pinacocyte cells fit together like stone slabs, forming a covering. This covering is called the pinacoderm, and resembles many mammals’ epidermis.

These cells’ edges have unique, wavy contours. These patterns enhance the adhesion between cells thanks to the increased amount of surface area to work with.

Choanocytes cells are the cells that cover the inner part of the sponge.

These are specialized cells, and have a single elongated flagellum that is surrounded by cilia, unlike pinococytes.

When the flagellum participates in its beating action, it actually helps with both the expulsion and suction of water into the sponge.

Porocytes are the third type of cell. These cells are cylindrical and travel along the whole wall of the animal.

Water is allowed to be transported into the sponge’s body via the incurrent pores that line these cells.

The beating action that the choanocytes flagellum pumps water away from the cell, expelling it via the atrium.

This happens while also being forced through the pores and into the body. This process makes it possible so that the water is only able to move in one direction.

Amoebocytes are another group of cells that can be found in sponge bodies. These cells can be found in the mesoglea (mesenchyme).

The cells are motile, and play a role in a number of important functions within the sponge. Some of these functions include removing debris and secreting sponge skeleton.

However, there are a few more amboebocyte cells that you may come across. These include the following, listed below:

• Archaeocytes – Involved in nutrition and regeneration
• Sclerocytes – Spicules or secretory cells
• Spongocytes – Spongin or secretory cells
• Collencytes – Collagen or secretory cells
• Lophocytes – Fibrillar collagen or secretory cells

The Skeleton of Phylum Porifera

The skeleton is what determines and defines the shape of the sponge.

The general shape of a sponge can vary depending on the skeleton, and as the animal grows, the mesenchyme produces specialized cells (spongocytes and sclerocytes).

Both of these are materials that are needed in order for the skeleton to develop and grow.

The skeleton is also an important part in keeping the chambers and water canals open. While helping determine the sponge shape is important, it is needed in the overall function of the sponge.

On top of that, the skeleton also aids in the survival of sponges as it creates a rough texture.

Tiny spiny projections are also formed thanks to the skeleton, which discourage many predators from trying to attack or eat the sponges.

Sclerocytes are cells that produce and secrete spicules, while spongocytes are the cells that are responsible for producing spongin fiber.

When it comes to the skeleton of various sponges, they could have both fibers, or simply one. This can vary from one type of sponge to the next.

Calcareous sponges have spicules that usually have calcium carbonate. However, in siliceous sponges, the spicules are primarily made of silica.

The spicules can be divided into two groups, depending on their size.

These two groups are the microscleres and megacleres. As their names suggest, the microscleres are small, and the megacleres are large.

The microscleres have a role in permeating the mesenchyme, whereas the megacleres form the main supporting skeleton framework.

The spongin, which is a protein, in siliceous sponges are thought to serve by forming a network that branches out within the skeleton structure.

Spongin could also bind the spicules together.

However, in some sponges such as keratosan sponges, spongin and a few foreign structures are the only two components that make up the skeleton structure.

In these calcareous sponges, rather than their size, the shape is the important factor that is considered in order to determine the spicule type.

There are a number of spicule shapes to consider, which we will take a quick look at below.

Shape-based spicules include:

• Monaxon Spicules – these spicules come in a variety of shapes, from twisted forms to C-shapes and rods. They all have one axis that can either be curved or straight.

• Tetraxon Spicules – these spicules have four points or rays, as their name suggests. These rays come from one common point, but their sizes can vary depending on the type of sponge. Alternatively, they might be modified to appear disc-like.

• Triaxon Spicules – these spicules, also known as hexactinal spicules, are made up of three axes. These axes all cross at a right angle, which results in the structure having six rays. These rays can vary in size, and can even have spines, knobs, and be curved.

• Polyaxon Spicules – these spiracles have rays coming from a point, resulting in star-shaped or spiny-looking spheres.

Other spicule types include:

• Spheres – these spicules typically have a concentric form.

• Desma – these spicules are larger and get silica deposited on them. They are formed from various other spicule types, such as triradiate, tetraxon, and minute monaxon spicules.

Hexactinellids, also called glass sponges, are very different compared to calcareous and siliceous sponges.

They have a very glass-like appearance, and their skeletons are made from siliceous fiber, which is glass-like.

In some species, projecting spicules have been proven to aid in the transmission of light from a bioluminescent crustacean that is living in the spongocoel of the animal.

In the deep sea, where everything is dark, this has resulted in stunning light displays in the depths.

These glass sponges are also unique as they have a special general structure. Some species have honeycomb-like structures, and have open body plans with a number of large, open spaces.

In these, syncytium makes up the dermal membrane, or the covering. Inside that, there are choanablasts, which are continuous.

Choanocytes are cells that are responsible for giving rise to stolons that are connected to the collar unit. Sometimes, they are even responsible for connecting these units to one another.

Like various other sponges, these kidneys of sponges are known to contain scleroblasts, which are involved in the spicule production. These cells, however, are not connected to the syncytium.

The Habitat and Distribution of Phylum Porifera

Animals that are in the phylum Porifera group are exclusively aquatic creatures. This means that they are unable to survive on dry land.

They are only found in environments with water, such as oceans, seas, rivers, and lakes.

While the vast majority of these animal species are marine, which means they like in the seas and oceans, there are some that live in freshwater.

In fact, around 238 freshwater Porifera species were discovered living in freshwater locations by 2012. By now, no doubt that number will have gone up.

Those Porifera animals found to be living in freshwater conditions are also spread across six major families.

For example, members of the Spongilla group have been found to live in freshwater habitats throughout the world, except the continent of Antarctica.

Some species are more widespread and abundant throughout the world, whereas others are rare and isolated to certain areas.

For example, a sponge that is only found in a select few regions would be E. muelleri. On the other hand, E. lacustris is found in many areas.

Whether they are in marine or freshwater environments, these sponges have been known to thrive at various depths. Some like shallow water, while others prefer intermediate and deep waters.

One example of a sponge that likes the abyssal zone would be glass sponges – as you may think from their light displays.

All types of sponges are sessile – meaning they are unable to move on their own. Instead, they attach themselves to rocks or similar structures, and live there.

Despite this, sponges are actually incredibly good at adapting to their environments.

An example of this would be the species H. lookdanoffi, which have extremely slow metabolisms to ensure their survival at low temperatures.

This ability enables them to become dormant during the winter, allowing them to thrive. When temperature eventually starts to improve, the sponge becomes active again.

Sponges such as Pharetronids have been known to exhibit degenerative behaviors when they are in freshwater, and improve when they are in salt water.

They also have the ability to live in symbiotic relationships with various other organisms, such as some algae and bacteria.

This allows them to live harmoniously, and even benefit from one another’s existence.

An example of this would be to look at the fact that some sponges can accommodate bacteria that are capable of photosynthesis. This allows the sponge to have access to food very easily, making life easier.

Finally, the sponge’s shape is another incredibly important factor to consider with their adaptability and environments.

While the skeleton influences the shape of the sponge, the shape is an important characteristic for all sponges.

For example, sponges that live on rocky coastlines are typically flatter and encrusting.

This shape allows them to attach themselves securely to rocks and not get knocked off, which is what would happen if they were not flat.

It’s important to note that the shape and overall bodies of sponges are also very important when it comes to their feeding habits.

The cells’ flagella, which line the interval cavity, makes it so that water is only able to move in one direction. This makes it easier to get high amounts of food particles.

Reproduction Of Phylum Porifera

Like all animals, reproduction is important. In the phylum Porifera, the sponges are able to reproduce in two different ways – sexual and asexual.

While some species, such as H. mmorei are able to change themselves from male to female, there are generally males and females.

When it comes to changing the sex of a sponge, some sponges even change colors. The sponges that are able to change from one sex to another, they so not have reproductive organs that are permanent (gonads).

As such, when they prepare for reproduction, only certain parts of their bodies change into sites of gamete production.

Sexual Reproduction

The sperm cells then get captured by the females, transported to the egg cell and fertilization occurs.

This happens inside the mesenchyme, and the zygote will develop into a larva form before eventually being released into the water.

This is the main way of reproducing for every sponge. However, the process of fertilization can vary from one species to another. In some species, it will be internal, while for others, it will be external.

External fertilization will happen when eggs and sperm are ejaculated through the osculum into the water. For some species, however, only the sperm is ejaculated.

• Respiration – oxygen is absorbed through diffusion and leaves through the osculum.

• Nutrition – sponges survive by sieving out microorganisms and other debris as the water goes through their pores and into the canal system. It is then ejected through the sculum. All the food particles are kept and transported to the cell cytoplasm in the cavity.

• Nervous and Circulatory System – sponges don’t have circulatory or nervous systems. Ciliated cells are thought to play a role in sensing any disturbances.

Asexual Reproduction

There are three primary methods that can be used to asexually reproduce for sponges. Let’s take a look at them below:

Fragmentation

Fragmentation refers to the type of asexual reproduction that happens when a fragment, or part, of a sponge breaks off it detaches. Breaking might happen because of water currents that are too strong, or from animals or humans.

The broken fragment will use the pinacocytes and choanocytes it has before beginning to reshape itself. It will attach itself to a new spot like a rock, a rebuild itself as time passes to make a new, functioning sponge.

This, of course, is a cloning process rather than that we would consider to be “true” reproduction.

Budding

Budding is not a common way of reproducing, and has only been seen in a select few sponge species. This will happen if a sponge has collencytes and archaeocytes.

When budding happens, a group of cells located near the case of the animal will begin to multiply and create a bulge. That bulge will grow over time, becoming a new animal, until it breaks off and fixes itself to a new location.

In rare cases, it has been observed that the new animal will simply remain attached to the “parent”.

Gemmules

Gemmules are survival pods that are produced by the majority of freshwater sponges. When conditions are not favorable, a sponge may release thousands of these pods as they die.

These pods can survive for months, and even in harsh conditions, Eventually, they will germinate and become new sponges.

To Summarize

Phylum Porifera, or sponges, are simple animals in the animal kingdom. They come in many shapes and sizes, and have fascinating bodies and bodily processes.

These animals used to be considered plants, but science has shown us otherwise.

Sponges are incredibly interesting fields of study, and are bound to only become more interesting as we learn more about them over time.

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