Hinge Teeth
   HOME

TheInfoList



OR:

Hinge teeth are part of the anatomical structure of the inner surface of a
bivalve shell A bivalve shell is the enveloping exoskeleton or mollusc shell, shell of a bivalve mollusc, composed of two hinged halves or ''valve (mollusc), valves''. The two half-shells, called the "right valve" and "left valve", are joined by a ligament and ...
, i.e. the shell of a
bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...
mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000  extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...
. Bivalves by definition have two
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...
s, which are joined together by a strong and flexible
ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...
situated on the hinge line at the dorsal edge of the shell. In life, the shell needs to be able to open slightly to allow the foot and siphons to protrude, and then close again, without the valves moving out of alignment with one another. To make this possible, in most cases the two valves are articulated using an arrangement of structures known as hinge teeth (often referred to collectively as the "dentition"). Like the ligament, the hinge teeth are also situated along the hinge line of the shell, in most cases. In most families of bivalves, the two valves of the shell are almost perfectly symmetrical with one another along the hinge line, although the placement and shape of the teeth may differ slightly in the left valve and right valve in order for the two valves to articulate properly. Each related group of bivalves tends to have distinctive hinge teeth, and because of this, examining the arrangement of the hinge teeth in a bivalve shell is often essential for identification and classification. A formal terminology is used to describe the different types of dentition.


In taxonomy

The hinge teeth, or the lack thereof, is an important feature in identifying bivalves because the teeth are generally similar within the major
taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...
groups. Historically the hinge teeth have provided a convenient means by which to construct classification schemes and attempt to indicate the
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
relationships within the class
Bivalvia Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...
.Invertebrate Paleobiology on-line syllabus on Bivalves, by Dr. Burt Carter, Georgia Southwestern State University, at: http://itc.gsw.edu/faculty/bcarter/paleo/labs/moll/biv2.htm There are formal names for the various types of hinge tooth arrangements or ''dentition''.


Kinds of hinge teeth


Taxodont

The ''taxodont'' hinge shows either one or two rows of similar interlocking teeth on either side of the umbones, as is the case in the ark clams ( Arcidae), the bittersweets ( Glycymerididae), and the nut clams ( Nuculidae). File:Arcidae hinge.jpg, Arcidae hinge File:Glycymerididae hinge.jpg, Glycymerididae hinge


Dysodont

The ''dysodont'' hinge shows a strong ligament along the hinge line, with weak teeth near the umbones, as in the marine mussels (
Mytilidae The Mytilidae are a family (biology), family of small to large Marine life, marine and Brackish water, brackish-water bivalve molluscs in the order (biology), order Mytilida. One of the genera, ''Limnoperna fortunei, Limnoperna'', even inhabits f ...
). File:Mytilidae hinge.jpg,
Mytilidae The Mytilidae are a family (biology), family of small to large Marine life, marine and Brackish water, brackish-water bivalve molluscs in the order (biology), order Mytilida. One of the genera, ''Limnoperna fortunei, Limnoperna'', even inhabits f ...
hinge


Isodont

The ''isodont'' hinge has lateral tubercles and sockets on either side of a thick ligament which is referred to as a
resilium In anatomy, a resilium is part of the bivalve shell, shell of certain bivalve mollusks. It is an internal ligament (bivalve), ligament, which holds the two valves together and is located in a pit or depression known as the resilifer. The resilium ...
. This arrangement is typical of the
oysters Oyster is the common name for a number of different families of Seawater, salt-water bivalve molluscs that live in Marine (ocean), marine or Brackish water, brackish habitats. In some species, the valves are highly Calcification, calcified, a ...
(
Ostreidae The Ostreidae, the true oysters, include most species of molluscs commonly consumed as oysters. Pearl oysters are not true oysters, and belong to the order Pteriida. Like scallops, true oysters have a central adductor muscle, which means the s ...
),
scallops Scallop () is a common name that encompasses various species of marine bivalve molluscs in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related famili ...
(
Pectinidae Scallop () is a common name that encompasses various species of Marine (ocean), marine bivalve mollusc, molluscs in the Taxonomy (biology), taxonomic Family (biology), family Pectinidae, the scallops. However, the common name "scallop" is also ...
), thorny oysters (
Spondylidae ''Spondylus'' is a genus of bivalve molluscs, the only genus in the family (biology), family Spondylidae and subfamily Spondylinae. They are known in English as spiny oysters or thorny oysters (although they are not, in fact, true oysters, but ...
), and kittens paws ( Plicatulidae). File:Ostreidae hinge.jpg,
Ostreidae The Ostreidae, the true oysters, include most species of molluscs commonly consumed as oysters. Pearl oysters are not true oysters, and belong to the order Pteriida. Like scallops, true oysters have a central adductor muscle, which means the s ...
hinge File:Pectinidae hinge.jpg,
Pectinidae Scallop () is a common name that encompasses various species of Marine (ocean), marine bivalve mollusc, molluscs in the Taxonomy (biology), taxonomic Family (biology), family Pectinidae, the scallops. However, the common name "scallop" is also ...
hinge File:Spondylidae hinge.jpg,
Spondylidae ''Spondylus'' is a genus of bivalve molluscs, the only genus in the family (biology), family Spondylidae and subfamily Spondylinae. They are known in English as spiny oysters or thorny oysters (although they are not, in fact, true oysters, but ...
hinge File:Plicatulidae hinge.jpg, Plicatulidae hinge


Crurae

The hinge has lamellar ridges on or near the hinge plate, and these function as hinge teeth. This arrangement is characteristic of the Pandoridae, the jingle shells
Anomiidae Anomiidae is a family of saltwater clams, marine bivalve molluscs related to scallops and oysters, and known as anomiids. It contains seven genera. The family is known by several common names, including jingle shells, mermaid's toenails, and ...
, and
Dimyidae Dimyidae is a family of extremely flattened, small (<1 cm), pleurothetic, relatively rare marine
Anomiidae Anomiidae is a family of saltwater clams, marine bivalve molluscs related to scallops and oysters, and known as anomiids. It contains seven genera. The family is known by several common names, including jingle shells, mermaid's toenails, and ...
hinge


Schizodont

The ''schizodont'' hinge has reverse V-shaped scissurate teeth, and often an elongated lateral tooth. This arrangement is found in most
Unionidae The Unionidae are a Family (biology), family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is a ...
freshwater mussels. File:Unionidae hinge.jpg,
Unionidae The Unionidae are a Family (biology), family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is a ...
hinge


Pachyodont

The ''pachyodont'' hinge has large obscure tubercules with corresponding pits on the opposite valve. This arrangement is characteristic of the
Chamidae Chamidae, common name the jewel boxes or jewel box clams, is a family of marine bivalve mollusks in the order Venerida.Abbott, R.T. & Morris, P.A. ''A Field Guide to Shells: Atlantic and Gulf Coasts and the West Indies.'' New York: Houghton Mif ...
, the jewel boxes. File:Chamidae hinge.jpg,
Chamidae Chamidae, common name the jewel boxes or jewel box clams, is a family of marine bivalve mollusks in the order Venerida.Abbott, R.T. & Morris, P.A. ''A Field Guide to Shells: Atlantic and Gulf Coasts and the West Indies.'' New York: Houghton Mif ...
hinge


Heterodont

The ''heterodont'' hinge has two to three wedge-shaped cardinal teeth set in the center near the umbones, and generally also has elongated lateral teeth on the anterior and posterior margins (on one or both sides). This arrangement is characteristic of the venus clams (
Veneridae The Veneridae or venerids, common name: Venus (mythology), Venus clams, are a very large family of minute to large, saltwater clams, marine bivalve molluscs. Over 500 living species of venerid bivalves are known, most of which are edible, and m ...
), the cockles ( Cardiidae) and several other important groups. File:Veneridae close up heterodont hinge.jpg,
Veneridae The Veneridae or venerids, common name: Venus (mythology), Venus clams, are a very large family of minute to large, saltwater clams, marine bivalve molluscs. Over 500 living species of venerid bivalves are known, most of which are edible, and m ...
: '' Pitar'' hinge File:Veneridae hinge.jpg, Veneridae: ''
Tivela Tivela is a genus of saltwater clams, marine (ocean), marine bivalve molluscs in the subfamily Meretricinae of the family Veneridae, the Venus clams. MolluscaBase eds. (2022). MolluscaBase. Trigona Megerle von Mühlfeld, 1811. Accessed through: W ...
'' hinge File:Veneridae hinge 3.jpg, Veneridae: '' Dosina'' hinge File:Cardiidae hinge.jpg, Cardiidae hinge


Desmodont

In the ''desmodont'' hinge, also known as an ''asthenodont'' hinge, the hinge consists of a large ligamentous resilifer (or chondrophore) which replaces the cardinal teeth, as in the soft-shell clams (
Myidae Myidae, common name the softshell clams, is a Taxonomy (biology), taxonomic family (biology), family of marine (ocean), marine bivalve molluscs in the order (biology), order Myida. Genera Genera within the family Myidae include: * ''Cryptomya'' ...
). File:Myidae hinge.jpg, ''
Myidae Myidae, common name the softshell clams, is a Taxonomy (biology), taxonomic family (biology), family of marine (ocean), marine bivalve molluscs in the order (biology), order Myida. Genera Genera within the family Myidae include: * ''Cryptomya'' ...
'' hinge File:Pholadidae hinge.jpg, ''
Pholadidae Pholadidae, known as piddocks or angelwings, are a family (biology), family of bivalve molluscs similar to a clam. Background Piddocks are unique in that each side of their shells is divided into 2 or 3 separate sections. Furthermore, one of the ...
'' hinge


Anodont

The ''anodont'' hinge is characterized by a strong ligament (or a series of transverse ligamental grooves as in the ''Isognomonidae''), however, true teeth are absent in adults as is the case in the pen shells (
Pinnidae The pinnidae are a taxonomic family of large saltwater clams sometimes known as pen shells. They are marine bivalve molluscs in the order Pteriida. Shell description The shells of bivalves in this family are fragile and have a long and triang ...
), tree oysters (
Isognomonidae Isognomonidae is a family of medium-sized to large saltwater clams. They are pearl oysters, marine bivalve molluscs in the superfamily Pterioidea Pterioidea is a superfamily of epifaunal marine bivalves mostly inhabiting continental shelf r ...
), the pearl oysters (
Pteriidae Pteriidae, also called the feather oysters, is a family (biology), family of medium-sized to large saltwater oysters. They are pearl oysters, Marine (ocean), marine bivalve mollusks in the order Pteriida. Some of the species in this family are i ...
), and some freshwater mussels such as the genus ''
Anodonta ''Anodonta'' is a genus of freshwater mussels in the family Unionidae, the river mussels. Species (and previous species) Species in this genus include: * '' Anodonta anatina'' Linné, 1758 – duck mussel * '' Anodonta beringiana'' Middendo ...
''. File:Pinnidae hinge.jpg,
Pinnidae The pinnidae are a taxonomic family of large saltwater clams sometimes known as pen shells. They are marine bivalve molluscs in the order Pteriida. Shell description The shells of bivalves in this family are fragile and have a long and triang ...
hinge File:Pteriidae hinge.jpg,
Pteriidae Pteriidae, also called the feather oysters, is a family (biology), family of medium-sized to large saltwater oysters. They are pearl oysters, Marine (ocean), marine bivalve mollusks in the order Pteriida. Some of the species in this family are i ...
hinge File:Isognomonidae hinge.jpg,
Isognomonidae Isognomonidae is a family of medium-sized to large saltwater clams. They are pearl oysters, marine bivalve molluscs in the superfamily Pterioidea Pterioidea is a superfamily of epifaunal marine bivalves mostly inhabiting continental shelf r ...
hinge


References

{{Bivalve anatomy Mollusc shells