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Phylum Brachiopoda Lingulata and Lamp shells Lyrics: Shin Kubota, Music and Vocal: Juri Goto |
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The Brachiopoda is a small benthic animal about several cm long and has two shells. On the surface, every species of the Brachiopoda looks like a bivalve. The first time this group of animals was taxonomically classified in the 18th century, they were mistakenly identified as a group that belongs to the Bivalvia in the phylum Mollusca. Unlike the left and right arrangement of shells in true bivalves, the shells of the Brachiopoda are very different that they are dorso-ventrally arranged. The Brachiopoda is divided into two major groups, and they are known as living fossils: one is the Lingulata, and the other is lamp shells. Among the colored shells of the Brachiopoda, red and black are common, but the majority of them are grayish yellow. The profiles of the shells vary greatly, from round to pentagonal. Some of the extinct species had long spines. The maximum size of the Braciopoda reaches 30 cm in length. Lingulates extend their long leg called pedicle to burrow into sandy or muddy sediments. They use the lophophore, which looks like the gill of mollusks, to filter seawater and capture small particles as foods. Thus, they are gentle animals. The lophophore contains the feeding apparatus along with the respiratory system. Through large surface area of the lophophore, gas is exchanged (respiration). Lingula anatine is a well-known lingulate who is common in the Sea of Ariake, Kyushu, Japan and its pedicles were eaten in the past. In Korea, the pedicles are sold in supermarket as food. Lingulates do not have a hinge to connect two shells. In addition, the lophophore may or may not have a hard bone. At the end of the U-shaped digestive tract is the anus. The anal opening is on the outside of the lophophore. This configuration is the same as that of the Ectoprocta. In contrast, the lamp shell (Calciata) has a short leg, i.e. pedicle, which is used to attach to the rocks on the sea floor. They look like a bivalve, Anomia chinensis, and filter seawater to collect small particles for food. The ventral (pedicle) valve has a large bulge and is always larger than the dorsal (brachial) valve. These valves have a hinge and because of this feature, the lamp shells may also be called the Articulata. In addition, a stiff bone (brachium or carpal bone) supports the lophophore. Another characteristic is that there is no anus at the end of the digestive system. Each individual of the Brachiopoda is either male or female (gonochoric). After external fertilization in the sea, the trochophora larvae grow, and the Lingulata and Calciata larvae develop into uniquely shaped larvae of their respective types. Some larvae live as plankton as short as only one day while others live as plankton as long as several weeks. They eventually settle on the sea floor and develop into adults. Their life span is believed to be several years. Only about 350 species of brachiopods are known to exist on the planet today. The majority of them live in the sea less than 200 m deep. Some of them live in the sea deeper than 5000 m. Brachiopods can be found in every ocean from the Polar Regions to the equatorial waters. The diversity of the extinct brachiopod species is far greater than that of the extant species. It is known that the Brachiopda is differentiated into at least 10,000 species since the Cambrian period in the Paleozoic era. Based on the combination of the morphological and molecular information, the Brachiopoda is considered to be closely related to the Phoronida. |
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The Lingulata has two shells |
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