Oxygyrus keraudrenii
Encyclopedia
Oxygyrus keraudrenii is a species
of sea snail
, a holoplankton
ic marine
gastropod mollusk in the family
Atlantidae
.
Oxygyrus keraudrenii is the only species in the genus Oxygyrus.
) attains the largest size (shell diameter to 10 mm) among the Atlantidae. Body coloration is light bluish-purple, with the color darkening with age. The larval shell is calcareous
and displays a distinctive pattern of zigzag-shaped spiral ridges that are evenly spaced and cover the shell surface. The teleoconch is composed of conchiolin
, a transparent cartilaginous material, and its surface lacks sculpture
. With growth the teleoconch overgrows the protoconch
and eventually surrounds it. A shell spire
, as seen in all other atlantids, is lacking and the spire region is termed involute. The conchiolin keel is glass-like and has a truncate anterior edge that ends at the shell aperture
.
The shell of this easily recognisable species is completely involute, with a similar ‘umbilicus‘ at both the top and the base of the shell. This feature makes it impossible to count the number of protoconch whorls, as only one is visible in each of them. The juvenile shell initially is slightly wider than high, but gets relatively wider during growth. Its surface is slightly irregularly covered with approximately 20-24 spiral lirae in a zigzag-shape that usually leave a narrow zone free just below the periphery. In between these lirae the shell’s surface is granulated. The apertural margin of the shell is deeply sinuated, as can be seen from the shape of the growth lines and also at the place where the ornamented protoconch changes quite suddenly to the much less clearly ornamented teleoconch (this transition is well-illustrated by Thiriot-Quiévreux, 1973, fig. 1A, and Batten & Dumont, 1976, fig. 24).
In the largest available specimen from Pliocene of Philippines, the teleoconch has one complete whorl, widening rapidly, which makes the shell about twice as wide as high. In this specimen the apertural margin is irregularly broken, indicating that the teleoconch might even have more than one calcified teleoconch whorl in complete specimens. In another specimen from Philippines (H = 1.60, W = 2.52 mm), the teleoconch has three quarters of a whorl. On the post-larval shell a vague spiral ornament is present and the peripheral belt remains visible as a slightly produced zone reaching the apertural margin.
The type c eye morphology is only seen in one other species of atlantid (Atlanta helicinoides) and one carinariid (Cardiapoda richardi
). The shape of the operculum
is unique among atlantids, broadly triangular, approaching trapezoidal in shape, and lacking the apical spiral part present in all other atlantids. Also unique to the operculum is that when the animal retracts into its shell, only about one-half of the operculum covers the shell aperture. The radula
is very large and is triangular in shape.
Recent specimens of Oxygyrus keraudreni have an uncalcified shell
of conchiolin
in the adult stage. Janssen (2007) have found an indication that, during the Pliocene, individuals of this species were yet further calcified than are extant specimens. This could point to a developmental trend
involving a reduction of calcareous matter in the course of time, as a gradual weight reduction beneficial for holoplankton
ic life. The distinct peripheral belt demonstrates that a conchiolin keel was present.
in tropical to subtropical waters.
in Tiep, Roxas
(map) and Anda, Pangasinan
, Luzon, Philippines in 2001 (published in 2007). Oxygyrus keraudrenii is known, in very few specimens only, from Jamaica (Janssen, 1998) and the Mediterranean Pliocene (Italy, Spain, France; Janssen, 2004). The French occurrence was dated as Zanclean
and thus it may be assumed that Oxygyrus occurred approximately since the Miocene
-Pliocene
transition. Miocene representatives or related forms are unknown.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of sea snail
Sea snail
Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs....
, a holoplankton
Holoplankton
Holoplankton are organisms that are planktonic for their entire life cycle. Examples of holoplankton include some diatoms, radiolarians, some dinoflagellates, foraminifera, amphipods, krill, copepods, and salps.-Sources:Asexual Holoplankton:...
ic marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
gastropod mollusk in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Atlantidae
Atlantidae
Atlantidae is a family of sea snails, holoplanktonic gastropod molluscs in the clade Littorinimorpha.According to taxonomy of the Gastropoda by Bouchet & Rocroi the family Atlantidae has no subfamilies.- Description :...
.
Oxygyrus keraudrenii is the only species in the genus Oxygyrus.
Description
Oxygyrus keraudreni (along with Atlanta peroniiAtlanta peronii
Atlanta peronii is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae....
) attains the largest size (shell diameter to 10 mm) among the Atlantidae. Body coloration is light bluish-purple, with the color darkening with age. The larval shell is calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
and displays a distinctive pattern of zigzag-shaped spiral ridges that are evenly spaced and cover the shell surface. The teleoconch is composed of conchiolin
Conchiolin
Conchiolin and perlucin are complex proteins which are secreted by a mollusc's outer epithelium ....
, a transparent cartilaginous material, and its surface lacks sculpture
Sculpture (mollusc)
The sculpture of a mollusc shell is the three-dimensional ornamentation on the outer surface, as distinct from the basic shape of the shell itself or colouration. Sculpture may be concave as well as convex. Sometimes it has microscopic detail. Sculpture refers to the calcareous outer layer, not the...
. With growth the teleoconch overgrows the protoconch
Protoconch
A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...
and eventually surrounds it. A shell spire
Spire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
, as seen in all other atlantids, is lacking and the spire region is termed involute. The conchiolin keel is glass-like and has a truncate anterior edge that ends at the shell aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
.
The shell of this easily recognisable species is completely involute, with a similar ‘umbilicus‘ at both the top and the base of the shell. This feature makes it impossible to count the number of protoconch whorls, as only one is visible in each of them. The juvenile shell initially is slightly wider than high, but gets relatively wider during growth. Its surface is slightly irregularly covered with approximately 20-24 spiral lirae in a zigzag-shape that usually leave a narrow zone free just below the periphery. In between these lirae the shell’s surface is granulated. The apertural margin of the shell is deeply sinuated, as can be seen from the shape of the growth lines and also at the place where the ornamented protoconch changes quite suddenly to the much less clearly ornamented teleoconch (this transition is well-illustrated by Thiriot-Quiévreux, 1973, fig. 1A, and Batten & Dumont, 1976, fig. 24).
In the largest available specimen from Pliocene of Philippines, the teleoconch has one complete whorl, widening rapidly, which makes the shell about twice as wide as high. In this specimen the apertural margin is irregularly broken, indicating that the teleoconch might even have more than one calcified teleoconch whorl in complete specimens. In another specimen from Philippines (H = 1.60, W = 2.52 mm), the teleoconch has three quarters of a whorl. On the post-larval shell a vague spiral ornament is present and the peripheral belt remains visible as a slightly produced zone reaching the apertural margin.
The type c eye morphology is only seen in one other species of atlantid (Atlanta helicinoides) and one carinariid (Cardiapoda richardi
Cardiapoda richardi
Cardiapoda richardi is a species of sea gastropod, a holoplanktonic marine gastropod mollusk in the family Carinariidae....
). The shape of the operculum
Operculum (gastropod)
The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...
is unique among atlantids, broadly triangular, approaching trapezoidal in shape, and lacking the apical spiral part present in all other atlantids. Also unique to the operculum is that when the animal retracts into its shell, only about one-half of the operculum covers the shell aperture. The radula
Radula
The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...
is very large and is triangular in shape.
Recent specimens of Oxygyrus keraudreni have an uncalcified shell
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
of conchiolin
Conchiolin
Conchiolin and perlucin are complex proteins which are secreted by a mollusc's outer epithelium ....
in the adult stage. Janssen (2007) have found an indication that, during the Pliocene, individuals of this species were yet further calcified than are extant specimens. This could point to a developmental trend
Evolutionary developmental biology
Evolutionary developmental biology is a field of biology that compares the developmental processes of different organisms to determine the ancestral relationship between them, and to discover how developmental processes evolved...
involving a reduction of calcareous matter in the course of time, as a gradual weight reduction beneficial for holoplankton
Holoplankton
Holoplankton are organisms that are planktonic for their entire life cycle. Examples of holoplankton include some diatoms, radiolarians, some dinoflagellates, foraminifera, amphipods, krill, copepods, and salps.-Sources:Asexual Holoplankton:...
ic life. The distinct peripheral belt demonstrates that a conchiolin keel was present.
Distribution
The geographical distribution is cosmopolitanCosmopolitan distribution
In biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
in tropical to subtropical waters.
Fossil distribution
From the fossil record Oxygyrus keraudrenii has been found from PliocenePliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
in Tiep, Roxas
Roxas
Roxas various by language: Roahaas , Roahous , Rohan , Rohanna , Rojo , Roja Red , Rocksas , Rocksberry, Roxbury, Roxberry, Rowhous , Rosas , Roxburg , Roxburghe , Roxborough , Rocshire , Roxshire , Rochas and Rocha , Roach , Roashan Places in the Philippines:* Pres. Manuel A...
(map) and Anda, Pangasinan
Anda, Pangasinan
Anda is a 4th class island-municipality in the province of Pangasinan, Philippines. The people of Anda generally speak Bolinao. The island is near the Hundred Islands, a popular tourist destination for its caves and beaches....
, Luzon, Philippines in 2001 (published in 2007). Oxygyrus keraudrenii is known, in very few specimens only, from Jamaica (Janssen, 1998) and the Mediterranean Pliocene (Italy, Spain, France; Janssen, 2004). The French occurrence was dated as Zanclean
Zanclean
The Zanclean is the lowest stage or earliest age on the geologic time scale of the Pliocene. It spans the time between 5.332 and 3.6 Ma ± 0.005 Ma . It is preceded by the Messinian age of the Miocene epoch, and followed by the Piacenzian age....
and thus it may be assumed that Oxygyrus occurred approximately since the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
-Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
transition. Miocene representatives or related forms are unknown.