The
taxonomic
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Rhynchonellida is one of the two main groups of living
articulate brachiopod
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, w ...
s, the other being the order
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 f ...
. They are recognized by their strongly ribbed wedge-shaped or nut-like
shell
Shell may refer to:
Architecture and design
* Shell (structure), a thin structure
** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses
** Thin-shell structure
Science Biology
* Seashell, a hard ou ...
s, and the very short
hinge
A hinge is a mechanical 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: all other ...
line.
The hinges come to a point, a superficial resemblance to many (
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
ally unrelated)
bivalve
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
mollusk
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...
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
A commissure () is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology.
* The most common usage of the term refers to the brain's commissures, of which there are five. Such a commi ...
, the line between the two valves or shells, is zigzagged, a distinguishing characteristic of this group. The prominent beak of the
pedicle valve
Pedicle or pedicel may refer to:
Human anatomy
*Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures
...
usually overlaps that of the brachial valve, in order to allow the shell to open and close. There is usually a functional
pedicle
Pedicle or pedicel may refer to:
Human anatomy
*Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures
...
although the
delthyrium may be partially closed.
Morphologically, the rhynchonellid has changed little since its appearance during the
Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
period. It seems to have evolved from
pentamerids, and in turn gave rise to the first
atrypid
''Atrypa'' is a genus of brachiopod with shells round to short egg-shaped, covered with many fine radial ridges (or costae), that split further out and growth lines perpendicular to the costae and 2-3 times wider spaced. The pedunculate valve is ...
s 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
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
Era.
Classification
This classification down to the level of
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
is based on Kazlev
and Emig.
Extant subgroups
* Superfamily
Pugnacoidea
** Family
Basiliolidae
Basiliolidae is a family of brachiopods belonging to the order Rhynchonellida.
Genera
Genera:
* ''Acanthobasiliola
''Acanthobasiliola'' is a monotypic genus of brachiopods belonging to the family Basiliolidae. The only species is ''Acanthob ...
*** Subfamily
Acanthobasiliolinae
**** ''
Acanthobasiliola
''Acanthobasiliola'' is a monotypic genus of brachiopods belonging to the family Basiliolidae. The only species is ''Acanthobasiliola doederleini''.
The species is found in Malesia
Malesia is a biogeographical region straddling the Equator ...
''
*** Subfamily
Basiliolinae
**** ''
Basiliola''
**** ''
Basiliolella''
**** ''
Eohemithiris''
**** ''
Rhytirhynchia''
*** Subfamily Uncertain
**** ''
Striarina''
* Superfamily
Dimerelloidea
** Family
Cryptoporidae
**** ''
Aulites''
**** ''
Cryptopora''
* Superfamily
Norelloidea
** Family
Frieleiidae
*** Subfamily
Freileiinae
**** ''
Frieleia''
**** ''
Compsothyris''
**** ''
Grammetaria''
**** ''
Sphenarina''
*** Subfamily
Hispanirhynchiinae
**** ''
Abyssorhynchia''
**** ''
Hispanirhynchia''
**** ''
Manithyris''
**** ''
Parasphenarina''
*** Subfamily
Neorhynchiinae
**** ''
Neorhynchia''
** Family
Tethyrhynchiidae
**** ''
Tethyrhynchia''
* Superfamily
Hemithiridoidea
** Family
Hemithyrididae
**** ''
Hemithiris''
**** ''
Pemphixina''
** Family
Notosariidae
**** ''
Notosaria''
Extinct Subgroups
* Superfamily
Ancistrorhynchoidea
* Superfamily
Rhynchotrematoidea
* Superfamily
Uncinuloidea
* Superfamily
Camarotoechioidea
* Superfamily
Rhynchotetradoidea
* Superfamily
Lambdarinoidea
* Superfamily
Wellerelloidea
* Superfamily
Rhynchoporoidea
* Superfamily
Stenoscismatoidea
References
External links
Phylum Brachiopoda
{{Brachiopod orders
Brachiopod orders
Extant Ordovician first appearances