Rhynchonellida

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Rhynchonellida
Temporal range: Upper Ordovician–Recent
Rhynchotremadentatum.jpg
Rhynchotrema dentatum, a rhynchonellid brachiopod from the Cincinnatian (Upper Ordovician) of SE Indiana.
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Brachiopoda
Class: Rhynchonellata
Order: Rhynchonellida
Kuhn, 1949
Subgroups

See text.

Hemithiris psittacea, a living rhynchonellide Hemithiris psittacea 132279100.jpg
Hemithiris psittacea , a living rhynchonellide
Ladogia sp., a rhynchonellid brachiopod from the Devonian of western Russia (side view). Ladogia Nalivkin, 1941 Devonian Western Russia.JPG
Ladogia sp., a rhynchonellid brachiopod from the Devonian of western Russia (side view).

The taxonomic order Rhynchonellida is one of the two main groups of living articulate brachiopods, the other being the order Terebratulida. They are recognized by their strongly ribbed wedge-shaped or nut-like shells, and the very short hinge line.

Contents

The hinges come to a point, a superficial resemblance to many (phylogenetically unrelated) bivalve mollusk shells. The loss of the hinge line was an important evolutionary innovation, rhynchonellids being the first truly non-strophic shells with a purely internal articulation (teeth-sockets).

Strong radiating ribs are common in this group; and there are generally very strong plications or accordion-like folds on the sulcus (the long middle section) of the shell. This probably helps regulate the flow of water in and out of the shell. All rhynchonellids are biconvex (have a bulbous shell), and have a fold located in the brachial valve. This means that the commissure, the line between the two valves or shells, is zigzagged, a distinguishing characteristic of this group. The prominent beak of the pedicle valve usually overlaps that of the brachial valve, in order to allow the shell to open and close. There is usually a functional pedicle although the delthyrium may be partially closed.

Morphologically, the rhynchonellid has changed little since its appearance during the Ordovician period. It seems to have evolved from pentamerids, and in turn gave rise to the first atrypids and athyrids, both of which are characterized by the development of a complex spiral brachidium. Although much diminished by the terminal Paleozoic extinction, it experienced a revival during the Early Jurassic period, and became the most abundant of all brachiopods during the Mesozoic Era.

Classification

This classification down to the level of genera is based on Kazlev [1] and Emig. [2]

Extant subgroups

Extinct subgroups

Related Research Articles

<span class="mw-page-title-main">Lingulata</span> Class of marine lamp shells

Lingulata is a class of brachiopods, among the oldest of all brachiopods having existed since the Cambrian period. They are also among the most morphologically conservative of the brachiopods, having lasted from their earliest appearance to the present with very little change in shape. Shells of living specimens found today in the waters around Japan are almost identical to ancient Cambrian fossils.

<span class="mw-page-title-main">Craniata (brachiopod)</span> Class of marine lamp shells

Craniata is a class of brachiopods originating in the Cambrian period and still extant today. It is the only class within the subphylum Craniiformea, one of three major subphyla of brachiopods alongside linguliforms and rhynchonelliforms. Craniata is divided into three orders: the extinct Craniopsida and Trimerellida, and the living Craniida, which provides most information on their biology. Living members of the class have shells which are composed of calcite, though some extinct forms my have aragonite shells. The shells are inarticulate and are usually rounded in outline. There is no pedicle; the rear edge of the body cavity is a smooth and flat wall perforated by the anus. This class of brachiopods has an unsupported lophophore with only a single row of tentacles. In the absence of a pedicle, the shell is usually attached directly to a hard substrate. Many craniiforms are encrusting animals which attach directly to the shell of another animal, usually another brachiopod. The plicae from the host brachiopod will then appear within the shell of the craniiform.

<span class="mw-page-title-main">Terebratulida</span> Order of brachiopods

Terebratulids are one of only three living orders of articulate brachiopods, the others being the Rhynchonellida and the Thecideida. Craniida and Lingulida include living brachiopods, but are inarticulates. The name, Terebratula, may be derived from the Latin "terebra", meaning "hole-borer". The perceived resemblance of terebratulid shells to ancient Roman oil lamps gave the brachiopods their common name "lamp shell".

<span class="mw-page-title-main">Orthida</span> Extinct order of brachiopods

Orthida is an extinct order of brachiopods which appeared during the Early Cambrian period and became very diverse by the Ordovician, living in shallow-shelf seas. Orthids are the oldest member of the subphylum Rhynchonelliformea, and is the order from which all other brachiopods of this group stem. Physically they are usually strophic, with well-developed interareas. They also commonly have radiating ribs, sulcus, and fold structures. Typically one valve, often the brachial valve, is flatter than the other. The interior structure of the brachial valves are usually simple. In shape they are sub-circular to elliptical, with typically biconvex valves.

A valve is each articulating part of the shell of a mollusc or another multi-shelled animal such as brachiopods and some crustaceans. Each part is known as a valve or in the case of chitons, a "plate". Members of two classes of molluscs, the Bivalvia (clams) and the Polyplacophora (chitons), have valves.

<span class="mw-page-title-main">Strophomenida</span> Extinct order of brachiopods

Strophomenida is an extinct order of articulate brachiopods which lived from the lower Ordovician period to the mid Carboniferous period. Strophomenida is part of the extinct class Strophomenata, and was the largest known order of brachiopods, encompassing over 400 genera. Some of the largest and heaviest known brachiopod species belong to this class. Strophomenids were among the most diverse and abundant brachiopods during the Ordovician, but their diversity was strongly impacted at the Late Ordovician mass extinction. Survivors rediversified into new morphologies in the Silurian, only to be impacted once again at the Late Devonian mass extinction. However, they still survived till the end of the Permian.

<span class="mw-page-title-main">Brachiopod</span> Phylum of marine animals also known as lamp shells

Brachiopods, phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major categories are traditionally recognized, articulate and inarticulate brachiopods. The word "articulate" is used to describe the tooth-and-groove structures of the valve-hinge which is present in the articulate group, and absent from the inarticulate group. This is the leading diagnostic skeletal feature, by which the two main groups can be readily distinguished as fossils. Articulate brachiopods have toothed hinges and simple, vertically oriented opening and closing muscles. Conversely, inarticulate brachiopods have weak, untoothed hinges and a more complex system of vertical and oblique (diagonal) muscles used to keep the two valves aligned. In many brachiopods, a stalk-like pedicle projects from an opening near the hinge of one of the valves, known as the pedicle or ventral valve. The pedicle, when present, keeps the animal anchored to the seabed but clear of sediment which would obstruct the opening.

<span class="mw-page-title-main">Evolution of brachiopods</span> The origin and diversification of brachiopods through geologic time

The origin of the brachiopods is uncertain; they either arose from reduction of a multi-plated tubular organism, or from the folding of a slug-like organism with a protective shell on either end. Since their Cambrian origin, the phylum rose to a Palaeozoic dominance, but dwindled during the Mesozoic.

<span class="mw-page-title-main">Rhynchonelliformea</span> Subphylum of brachiopods

Rhynchonelliformea is a major subphylum and clade of brachiopods. It is roughly equivalent to the former class Articulata, which was used previously in brachiopod taxonomy up until the 1990s. These so-called articulated brachiopods have many anatomical differences relative to "inarticulate" brachiopods of the subphyla Linguliformea and Craniformea. Articulates have hard calcium carbonate shells with tongue-and-groove hinge articulations and separate sets of simple opening and closing muscles.

<span class="mw-page-title-main">Rhynchonellata</span> Class of marine lamp shells

The Rhynchonellata is a class of Lower Cambrian to Recent articulate brachiopods that combines orders from within the Rhynchonelliformea with well developed pedicle attachment. Shell forms vary from those with wide hinge lines to beaked forms with virtually no hinge line and from generally smooth to strongly plicate. Most all are biconvex. Lophophores vary and include both looped and spiraled forms. Although morphologically distinct, included orders follow a consistent phylogenetic sequence.

<span class="mw-page-title-main">Pentamerida</span> Extinct order of shelled animals

Pentamerida is an order of biconvex, impunctate shelled, articulate brachiopods that are found in marine sedimentary rocks that range from the Middle Cambrian through the Devonian.

<i>Sharpirhynchia</i> Extinct genus of brachiopods

Sharpirhynchia sharpi is a species of extinct, small-sized lampshell, named after Samuel Sharp (1814–1882), an early fossil collector, who discovered the limited time span of some fossils, now known as index fossils. S. sharpi is a marine rhynchonellate brachiopod in the family Rhynchonellidae. It is roughly ½ inch (1.25 cm) measured along the axis, with a slender beak, the brachial valve more convex than the pedunculate valve, and it has 21–31 ribs fanning out from the hinge.

<span class="mw-page-title-main">Rhynchonelloidella alemanica</span> Species of marine lamp shell

Rhynchonelloidella alemanica is a species of extinct, small-sized brachiopod, a marine rhynchonellate lampshell in the family Rhynchonellidae. It is roughly 1.4 cm (0.55 in), and has about 15 ribs fanning out from the hinge.

<span class="mw-page-title-main">Paterinata</span> Extinct class of marine lamp shells

Paterinata is an extinct class of linguliform brachiopods which lived from the lower Cambrian ("Tommotian") to the Upper Ordovician (Hirnantian). It contains the single order Paterinida and the subfamily Paterinoidea. Despite being some of the earliest brachiopods to appear in the fossil record, paterinides stayed as a relatively subdued and low-diversity group even as other brachiopods diversified later in the Cambrian and Ordovician. Paterinides are notable for their high degree of convergent evolution with rhynchonelliform (articulate) brachiopods, which have a similar set of muscles and hinge-adjacent structures.

<i>Cyrtospirifer</i> Extinct genus of brachiopods

Cyrtospirifer is an extinct genus of brachiopods. The fossils are present in the Middle and Upper Devonian.

<i>Argyrotheca</i> Genus of brachiopods

Argyrotheca is a genus of very small to minute lampshells. All species share a large pedicel opening, one ridge on the inside of the pedunculate valve, pits in a diamond pattern on the inside of both valves, and without radial ridges that end in tubercles. It occurs in depths between 6 and 1300 m. It is known since the latest Cretaceous.

<span class="mw-page-title-main">Kutorginata</span> Extinct genus of shelled animals

Kutorginates (Kutorginata) are an extinct class of early rhynchonelliform ("articulate") brachiopods. The class contains only a single order, Kutorginida (kutorginides). Kutorginides were among the earliest rhynchonelliforms, restricted to the lower-middle part of the Cambrian Period.

<span class="mw-page-title-main">Orthotetida</span> Extinct order of marine lamp shells

The orthotetides (Orthotetida) are an extinct order of brachiopods in the class Strophomenata. Though not particularly diverse or abundant relative to strophomenides (Strophomenida) or productides (Productida), orthotetides were nevertheless the longest-lasting order of strophomenates, surviving from the Middle Ordovician (“Llanvirn”) up until the Late Permian. Externally, many orthotetides are difficult to distinguish from strophomenides. Most fundamental differences between the two orders are internal: orthotetides have more elaborate cardinal processes and a greater diversity of shell microstructure.

Askerina is an extinct genus of atrypid brachiopods from subfamily Atrypinae that lived in end-Ordovician (Hirnantian) and Silurian (Aeronian). The type and only known species is Askerina cymbula. Its fossils are known only from the lower parts of the Solvik Formation in central Oslo region, Norway.

Jaffaia is a monotypic genus of brachiopods belonging to the family Dallinidae. The only species is Jaffaia jaffaensis from southern Australia. The species was described by Blochmann in 1910 and recently re-described in the Australian Journal of Taxonomy.

References

  1. M. Alan Kazlev. "Order Rhynchonellida". Archived from the original on March 13, 2006. Retrieved March 10, 2006.
  2. Christian C. Emig. "Systematics of extant brachiopod taxa" (PDF). Archived from the original (PDF) on May 13, 2006. Retrieved March 10, 2006.