Pterobranchia

Description

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

Species

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

History

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

Science and Discovery

Using special tools like the electron microscope, scientists have discovered that pterobranchs may be related to an ancient group of creatures called graptolites. This helps us learn about how ocean life 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 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, while others do not. They can reproduce by laying eggs or by creating new colonies.

Evolution

Paleontology

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

Taxonomy

By studying 18S ribosomal RNA sequences, scientists learned 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 cell parts called mitochondria.