Rhynchonellida
Encyclopedia
The taxonomic order
Rhynchonellida is one of the two main groups of living articulate
brachiopod
s, 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.
The hinges come to a point, a superficial resemblance to most (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).
Rhynchonellids lack any brachidium, and are therefore able to extrude their lophophore
out from the shell into the water for more efficient food-gathering. It has been suggested this is why they survived the Devonian
, Permian
-Triassic
, and Jurassic
extinctions, while many other lampshells with a brachidium failed to do so.
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.
is based on Kazlev and Emig.
Extant subgroups
Extinct Subgroups
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Rhynchonellida is one of the two main groups of living articulate
Articulata (Brachiopoda)
The Articulata is a class of brachiopods which comprises those with hinged, calcareous shells that generally bear well developed teeth and sockets and a simple muscle system...
brachiopod
Brachiopod
Brachiopods are a phylum of marine animals that have hard "valves" 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...
s, the other being the order Terebratulida
Terebratulida
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"...
. They are recognized by their strongly ribbed wedge-shaped or nut-like shells, and the very short hinge
Hinge
A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...
line.
The hinges come to a point, a superficial resemblance to most (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).
Rhynchonellids lack any brachidium, and are therefore able to extrude their lophophore
Lophophore
The lophophore is a characteristic feeding organ possessed by four major groups of animals: the Brachiopoda, Bryozoa, Entoprocta, and Phoronida. All lophophores are found in aquatic organisms.-Characteristics:...
out from the shell into the water for more efficient food-gathering. It has been suggested this is why they survived the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
, Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
-Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, and Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
extinctions, while many other lampshells with a brachidium failed to do so.
Strong radiating ribs are common in this group; and there are generally very strong plications or accordion-like folds on the sulcus
Sulcus (anatomy)
A sulcus is a depression or fissure in the surface of an organ, especially the brain.-Elsewhere:* anterior interventricular sulcus* calcaneal sulcus* coronal sulcus* gingival sulcus* gluteal sulcus* interlabial sulci...
(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
Commissure
A commissure is the place where two things are joined. The term is used especially in the fields of anatomy and biology.In anatomy, commissure refers to a bundle of nerve fibers that cross the midline at their level of origin or entry .* The most common usage of the term refers to the brain's...
, 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
Pedicle (zoology)
In zoology, the pedicle refers to a fleshy line brachiopods and some bivalve mollusks use to attach and anchor to a substrate. In brachiopods, the pedicle emerges from a pedicle opening. Some brachiopods do not have a functional pedicle, and thus do not have this pedicle opening....
although the delthyrium may be partially closed.
Morphologically, the rhynchonellid has changed little since its appearance during the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
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
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Era.
Classification
This classification down to the level of generaGenera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
is based on Kazlev and Emig.
Extant subgroups
- Superfamily Pugnacoidea
- Family Basiliolidae
- Subfamily Acanthobasiliolinae
- Acanthobasiliola
- Subfamily Basiliolinae
- Basiliola
- Basiliolella
- Eohemithiris
- Rhytirhynchia
- Subfamily UncertainUncertainUncertain may refer to:* Uncertain, Texas, a town in the United States* Uncertain, an album of The Cranberries- See also :* Uncertaintyuncertain as to be, not sure of.Not to be sure of something of the happening....
- Striarina
- Subfamily Acanthobasiliolinae
- Family Basiliolidae
- Superfamily Dimerelloidea
- Family Cryptoporidae
-
- Aulites
- Cryptopora
-
- Family Cryptoporidae
- Superfamily Norelloidea
- Family Frieleiidae
- Subfamily Freileiinae
- Frieleia
- Compsothyris
- Grammetaria
- Sphenarina
- Subfamily Hispanirhynchiinae
- Abyssorhynchia
- Hispanirhynchia
- Manithyris
- Parasphenarina
- Subfamily Neorhynchiinae
- Neorhynchia
- Subfamily Freileiinae
- Family Tethyrhynchiidae
-
- Tethyrhynchia
-
- Family Frieleiidae
- Superfamily Hemithiridoidea
- Family Hemithyrididae
-
- Hemithiris
- Pemphixina
-
- Family Notosariidae
-
- Notosaria
-
- Family Hemithyrididae
Extinct Subgroups
- Superfamily Ancistrorhynchoidea
- Superfamily Rhynchotrematoidea
- Superfamily Uncinuloidea
- Superfamily Camarotoechioidea
- Superfamily Rhynchotetradoidea
- Superfamily Lambdarinoidea
- Superfamily Wellerelloidea
- Superfamily Rhynchoporoidea
- Superfamily Stenoscismatoidea