Pterobranchia

Pterobranchia, often called pterobranchs, are a special group of small, worm-shaped animals. They belong to the Hemichordata and live in tiny tubes on the ocean floor. These creatures feed by catching tiny plants and animals called plankton from the water, using hair-like structures called cilia on their tentacles.

There are about 25 known living species of pterobranchs, found in three groups called Rhabdopleura, Cephalodiscus, and Atubaria. Scientists also know of many more extinct types, some from as far back as the Cambrian Period.

The group Pterobranchia was first described by a scientist named Ray Lankester in 1877. At first, it only included one group, Rhabdopleura. Later, when scientists studied another group called Cephalodiscus, they realized it was also part of this family.

Using special tools like the electron microscope, scientists have discovered that pterobranchs may be closely related to an ancient group of creatures called graptolites. This helps us understand how life in the ocean has changed over millions of years.

Biology

Pterobranchs are small, worm-like animals that live on the ocean floor, often in deep water. They eat by filtering tiny bits of food from the water using special hair-like structures called cilia on their tentacles.

These creatures have bodies divided into three parts: a wide, flat front part, a collar, and a trunk. Most pterobranchs live inside tubes they make themselves, and many live together in groups called colonies. One special type, called Atubaria, does not live in tubes and is found on coral.

Their collar has arms with tentacles that help them catch food. The trunk has a simple digestive system. Some pterobranchs have small openings called gill slits, while others do not. They can reproduce by laying eggs that develop into free-swimming babies, or by creating new colonies through a process called budding.

Evolution

Paleontology

The earliest pterobranchs, including Yuknessia and Galeaplumosus, were found from the mid-Cambrian Lagerstätten. Even earlier small carbonaceous fossils come from the Buen Formation.

Taxonomy

By comparing 18S ribosomal RNA sequences, scientists found that pterobranchs are closely related to enteropneust hemichordates.

Class Pterobranchia Lankester 1877

• Subclass Cephalodiscida Fowler 1892 stat. nov.
  • Order Cephalodiscida Fowler 1892
• Subclass Graptolithina Bronn 1849
  • Order ?†Camaroidea Kozlowski 1928 sensu Kozlowski 1949
  • Order ?†Crustoidea Bulman 1970
  • Order ?†Dithecoidea Obut, 1960
  • Order ?†Tuboidea Kozlowski 1938 sensu Kozlowsk 1949
  • Order Rhabdopleurida Fowler 1892 sensu Beklemishev 1951
  • Clade †Eugraptolithina Mitchell et al., 2013
    • Order †Dendroidea Nicholson 1872
    • Order †Graptoloidea Maletz, Carlucci and Mitchell 2009

Genomics

Genetic code

The two types of pterobranch animals, Rhabdopleura compacta and Cephalodiscus, use different genetic codes in their tiny energy-making parts of cells, called mitochondria.