Calcareous sponge

Some sponges live in the sea.

They use tiny hard bits to stay strong. These bits look like little stars. They are made of stone-like parts.

These sponges stay in one place. They eat by filtering the water. Most live in warm, shallow water.

These sponges are usually small. They are often dull in color. Some can be very bright.

They can look like vases. They can also look like tubes. They are amazing sea animals!

Calcareous sponges are a special kind of sea animal. They belong to a group called Calcarea. These sponges make tiny hard parts called spicules. These spicules are made of calcium carbonate. This is a stone-like material. Most of these spicules have three points. Some have two or four points.

These sponges live only in the ocean. Most live in warm, shallow water. They stay in one place. They eat by filtering water. Most are small and have dull colors. A few are very bright. They can look like vases. Some look like a mesh of thin tubes.

These sponges have been around for a long time. They likely first appeared during the Cambrian Period. The oldest known kind is called Gravestockia. It was found in Australia. These sponges reached their greatest variety during the Cretaceous period. There are about 800 kinds of these sponges living today. They are split into two groups. One group is called Calcinea. The other group is called Calcaronea. These groups are different in how they grow.

Calcareous sponges are a special group of sea animals. They belong to a class called Calcarea. These sponges are different from most other sponges. They build their bodies using tiny hard parts called spicules. These spicules are made of calcium carbonate. This is the same material found in shells. Most of these spicules have three points. Some have only two points or four points.

These sponges have a unique way they work. Their spicules grow from the outside-in. They form inside a hollow organic sheath. Unlike other sponges, they do not have microscleres. These are tiny bits that usually make flesh stronger. The skeleton can look like a mesh or a honeycomb. Some sponges have a body like a vase. Others look like a mesh of thin tubes. Some even form large, irregular shapes.

These animals have a very long history. They likely first appeared during the Cambrian Period. The oldest known kind is named Gravestockia. Scientists found it in Australia. These sponges reached their greatest variety during the Cretaceous period. Some old studies used a different name for them. They used to call the class Calcispongiae. Now, the name Calcarea is much more common.

There are many facts about how they live. All Calcarea are strictly marine animals. This means they live only in the ocean. Most live in shallow, tropical waters. They are sedentary filter feeders. This means they stay in one place to eat. They are usually small and have dull colors. However, a few species are brightly colored. Today, there are about 800 living species. This is a small part of the 11,000 total sponge species.

Scientists study how these sponges are related. The class is split into two groups. One group is called Calcinea. The other group is called Calcaronea. These groups grow in different ways. Calcinea develop from a larva called a parenchymella. This larva has a solid center. Calcaronea develop from an amphiblastula larva. This larva has a hollow center. Some scientists think these sponges are very special. They might even belong in their own phylum.

Calcareous sponges are unique marine animals belonging to the class Calcarea. These organisms are defined by their skeletal structures called spicules. These spicules are composed of calcium carbonate. Specifically, they consist of high-magnesium calcite or aragonite. Most species possess triradiate spicules, which means they have three points in a single plane. However, some species may also have two-pointed or four-pointed spicules.

The way these sponges build their skeletons is quite distinct from other groups. Most common sponges are siliceous, meaning they use silica for their structures. Calcareans lack microscleres, which are tiny spicules used to reinforce the flesh in other sponges. Instead, their spicules develop through an outside-in process. They mineralize within a hollow organic sheath. This process results in a skeleton that can take many forms. It might look like a mesh, a honeycomb, or even a solid structure. Some extinct species were hypercalcified, meaning solid calcite cemented their spicules together.

These sponges exhibit a variety of body plans and shapes. They can be radially symmetrical and vase-shaped. Other species form colonies that look like a meshwork of thin tubes. Some even grow into irregular, massive forms. All three major sponge body plans are present in this class: asconoid, syconoid, and leuconoid. While most are small and drab in color, a few species are known to be brightly colored.

The history of Calcarea stretches back to the early history of life. They likely first appeared during the Cambrian Period. The oldest known genus is Gravestockia, found in the Atdabanian stage of Australia. Scientists believe calcareans may have descended from heteractinid sponges. These heteractinid sponges also appeared during the early Cambrian. The class reached its peak of diversity during the Cretaceous period.

In terms of numbers, calcareous sponges are a small group within the sponge world. There are approximately 11,000 living species of Porifera. Out of that total, only about 800 are calcareans. All members of this class are strictly marine. This means they live only in saltwater environments. Most are found in shallow, tropical waters. They are sedentary filter feeders, meaning they stay in one place to feed. Like the Homoscleromorpha, they are also exclusively viviparous.

Scientists divide the class Calcarea into two main subclasses. These are Calcinea and Calcaronea. They are distinguished by their soft tissue and how they develop. For example, calcineans develop from a larva called a parenchymella. This larva has a solid center and radial symmetry. In contrast, calcaroneans develop from an amphiblastula. This larva has a hollow center and semi-bilateral symmetry. These developmental differences help researchers classify the various orders within the class.

There is ongoing debate regarding where these sponges fit in the tree of life. Some molecular analyses suggest Calcarea might not be exclusively related to other sponges. This would mean they should be designated as their own phylum. If this were true, the sponge phylum Porifera would be paraphyletic. Some researchers, such as Borchiellini et al. in 2001, argued they are closer to Eumetazoa. Eumetazoa are non-sponge animals. Other studies suggest a sister group relationship with Ctenophora, which are known as comb jellies. However, many authors doubt these ideas. They argue that genetic studies may have incomplete sampling. They believe anatomical traits prove calcareans are true sponges.