Brachiopod classification facts for kids

Brachiopods are amazing sea creatures that look a bit like clams, but they are actually very different! Scientists are always learning new things about how living things are related. This means they often discuss the best ways to group and name different animals, like brachiopods.

For a long time, there was one main way to classify brachiopods, set up in 1869. But in the 1990s, new ideas came along. Here are the main ways scientists have tried to group these cool animals:

• Traditional Way: This method divided brachiopods into two main groups.

* The Articulata group had shells that were connected by special "teeth" and "sockets," like a hinge. * The Inarticulata group had shells that were held together only by muscles, without these teeth.

• Shell Material Way: Another idea from the 1990s looked at what the shells were made of.

* The Calciata group included brachiopods with shells made of a material called calcite. This group included the Craniida and most of the "articulate" brachiopods. * The Lingulata group had shells made of a tough material called chitin and a mineral called calcium phosphate. This group included the Lingulida and Discinida.

• Three-Part Way: Also from the 1990s, this idea split brachiopods into three distinct groups:

* The Craniida were placed in their own group called the Craniformea. * The Lingulida and Discinida were grouped together as Linguliformea. * The Rhynchonellida and Terebratulida were put into the Rhynchonelliformea group.

How Scientists Classify Animals

When scientists classify animals, they use certain rules and ideas. Here's how they think about it:

Old Ways of Grouping Animals

For a long time, scientists classified animals based on:

• Body Plan: They looked at the overall shape and structure of an animal's body. They thought animals with similar body plans were closely related.
• Simple to Complex: There was an idea that living things evolved from simpler forms to more complex ones.
• Early Development: They also looked at how animals developed from an embryo, focusing on very basic features.

Scientists create groups like "phyla" (a big group of animals) to help them understand the natural world. However, we now know that how an animal looks (its "morphology" or "traits") can change more easily over time than scientists first thought.

New Ways Using DNA

Today, scientists use modern tools to classify animals.

• Molecular Data: They often use information from an animal's DNA (its genetic code). This "molecular data" is considered more accurate and reliable.
• Evolutionary Clues: We now know a lot more about the specific sequences in DNA than about how body shapes changed over millions of years. Because of this, DNA evidence helps scientists create classifications that show how animals truly evolved and are related.

Different Brachiopod Groups: Key Differences

Let's look at some of the main differences between these brachiopod groups:

Hinge and Anus

• The Lingulida, Discinida, and Craniida (which are part of the "Inarticulata" in the traditional view) do not have teeth in their shell hinges. Their shells are held together by muscles.
• The Terebratulida and Rhynchonellida (the "Articulata") have special teeth and sockets that connect their shells, like a strong hinge.
• Most brachiopods have a U-shaped gut, and their anus (where waste leaves the body) is at the front. But the Terebratulida and Rhynchonellida do not have an anus at all!

Pedicle and Shell Layers

• The pedicle is a stalk that helps some brachiopods attach to surfaces.

* Lingulida have a long pedicle that helps them burrow into sand. This pedicle contains a body cavity with muscles. * Discinida have a shorter pedicle that attaches them to hard surfaces. It also contains a body cavity with muscles. * Craniida do not have a pedicle. Instead, they cement themselves directly to hard surfaces. * Terebratulida and Rhynchonellida have a short pedicle that attaches them to hard surfaces, but it doesn't contain a body cavity.

• The outer layer of their shell, called the periostracum, is different:

* Lingulida and Discinida have a periostracum made of glycoprotein and chitin. * Craniida have chitin. * Terebratulida and Rhynchonellida have proteins.

• The main mineral layer of the shell also varies:

* Lingulida and Discinida use apatite (a form of calcium phosphate). * Craniida, Terebratulida, and Rhynchonellida use calcite (a form of calcium carbonate).

Other Features

• Some brachiopods have stiff hairs called chaetae around the opening of their shells.

* Lingulida, Discinida, Terebratulida, and Rhynchonellida have them. * Craniida do not.

• The coelom is an internal body cavity.

* Lingulida, Discinida, Terebratulida, and Rhynchonellida have a fully divided coelom. * Craniida do not.

Modern Brachiopods

Today, there are about 330 different kinds of living brachiopods. These are grouped into over 100 genera (plural of genus, a smaller group of related species). Most of the brachiopods alive today belong to the Rhynchonelliformea group.