Protatlanta rotundata
Encyclopedia
Protatlanta rotundata is an extinct species
of sea snail
, a holoplankton
ic marine
gastropod mollusk in the family
Atlantidae
.
, with the result that the larval shell seems to be embedded rather obliquely within the younger whorls. The diameter of the teleoconch increases rapidly, the result being a shell that strongly resembles Planorbarius
(but, of course, dextral). The surface of these younger whorls bears flexuous growth lines, and a dense and very fine, somewhat irregular spiral striation, only visible where light reflects on the shell. On the body whorl
a distinct peripheral belt is present on which the growth lines are strongly bent backward, indicating a deep sinus in the apertural margin.
The larval shell is globular, about as wide as high and has approximately five whorls
which attach very high onto the preceding whorl. In apical view, therefore, the second and third whorls are very narrow, even much narrower than the nucleus and first whorl of the protoconch
. The fifth whorl gradually attaches somewhat lower on the penultimate whorl. All protoconch whorls have a number of very narrow, distant and thread-like spiral lirae with a zigzag structure, just one of which remains visible between the upper and lower sutures. One spiral at the place of the suture and a further one on the base of the protoconch are somewhat stronger developed, but do not or only faintly show the zigzag structure. The boundary with the teleoconch is indicated by a rather sudden disappearance of the ornament.
Protatlanta rotundata differs considerably from the type of the genus, Protatlanta souleyeti
. Not only does the adult shell in Protatlanta rotundata reach a diameter that is roughly five times that of Protatlanta souleyeti, but the morphology of its protoconch and the shape of the fully grown shell are utterly different. Also, as both species occur together in the Pangasinan
samples, Protatlanta rotundata can certainly not be considered to be the ancestor species. The presence of a subperipheral belt much the same as in Protatlanta souleyeti, on the other hand, demonstrates that a conchiolin
keel has been present in this species.
of the Dominican Republic
and has a wide horizontal and vertical distribution; Langhian
-Serravallian
(Italy, Malta, Cyprus; RGM collections), Tortonian
(Sicily), Piacenzian
(Spain, Jamaica, Philippines), Pliocene
of Anda, Pangasinan
, Luzon, Philippines and ‘Middle Pliocene-Early Pleistocene
’ (Japan).
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 :...
.
Description
The width of the shell can reach up to 10 mm. In the largest specimen there are almost two teleoconch whorls that initially attach very high onto the protoconchProtoconch
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...
, with the result that the larval shell seems to be embedded rather obliquely within the younger whorls. The diameter of the teleoconch increases rapidly, the result being a shell that strongly resembles Planorbarius
Planorbarius
Planorbarius is a genus of freshwater air-breathing snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails, or planorbids, which all have sinistral or left-coiling shells.-Species:...
(but, of course, dextral). The surface of these younger whorls bears flexuous growth lines, and a dense and very fine, somewhat irregular spiral striation, only visible where light reflects on the shell. On the body whorl
Body whorl
Body whorl is part of the morphology of a coiled gastropod mollusk.- In gastropods :In gastropods, the body whorl, or last whorl, is the most recently-formed and largest whorl of a spiral or helical shell, terminating in the aperture...
a distinct peripheral belt is present on which the growth lines are strongly bent backward, indicating a deep sinus in the apertural margin.
The larval shell is globular, about as wide as high and has approximately five whorls
Whorl (mollusc)
A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...
which attach very high onto the preceding whorl. In apical view, therefore, the second and third whorls are very narrow, even much narrower than the nucleus and first whorl of 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...
. The fifth whorl gradually attaches somewhat lower on the penultimate whorl. All protoconch whorls have a number of very narrow, distant and thread-like spiral lirae with a zigzag structure, just one of which remains visible between the upper and lower sutures. One spiral at the place of the suture and a further one on the base of the protoconch are somewhat stronger developed, but do not or only faintly show the zigzag structure. The boundary with the teleoconch is indicated by a rather sudden disappearance of the ornament.
Protatlanta rotundata differs considerably from the type of the genus, Protatlanta souleyeti
Protatlanta souleyeti
Protatlanta souleyeti is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.Protatlanta souleyeti is the type species on the genus Protatlanta...
. Not only does the adult shell in Protatlanta rotundata reach a diameter that is roughly five times that of Protatlanta souleyeti, but the morphology of its protoconch and the shape of the fully grown shell are utterly different. Also, as both species occur together in the Pangasinan
Pangasinan
Pangasinan is a province of the Republic of the Philippines. The provincial capital is Lingayen. Pangasinan is located on the west central and peripheral area of the island of Luzon along the Lingayen Gulf, with the total land area being 5,368.82 square kilometers . According to the latest census,...
samples, Protatlanta rotundata can certainly not be considered to be the ancestor species. The presence of a subperipheral belt much the same as in Protatlanta souleyeti, on the other hand, demonstrates that a conchiolin
Conchiolin
Conchiolin and perlucin are complex proteins which are secreted by a mollusc's outer epithelium ....
keel has been present in this species.
Distribution
Protatlanta rotundata was originally described from the (Late?) MioceneMiocene
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...
of the Dominican Republic
Dominican Republic
The Dominican Republic is a nation on the island of La Hispaniola, part of the Greater Antilles archipelago in the Caribbean region. The western third of the island is occupied by the nation of Haiti, making Hispaniola one of two Caribbean islands that are shared by two countries...
and has a wide horizontal and vertical distribution; Langhian
Langhian
The Langhian is, in the ICS geologic timescale, an age or stage in the middle Miocene epoch/series. It spans the time between 15.97 ± 0.05 Ma and 13.65 ± 0.05 Ma . The Langhian was a continuing warming period defined by Lorenzo Pareto in 1864, it was originally established in the Langhe area north...
-Serravallian
Serravallian
The Serravallian is in the geologic timescale an age or a stage in the middle Miocene epoch/series, that spans the time between 13.65 ± 0.05 Ma and 11.608 ± 0.005 Ma...
(Italy, Malta, Cyprus; RGM collections), Tortonian
Tortonian
The Tortonian is in the geologic timescale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma . It follows the Serravallian and is followed by the Messinian....
(Sicily), Piacenzian
Piacenzian
The Piacenzian is in the international geologic timescale the upper stage or latest age of the Pliocene. It spans the time between 3.6 ± 0.005 Ma and 2.588 ± 0.005 Ma...
(Spain, Jamaica, Philippines), 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...
of 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 and ‘Middle Pliocene-Early Pleistocene
Early Pleistocene
Calabrian is a subdivision of the Pleistocene Epoch of the Geologic time scale. ~1.8 Ma.—781,000 years ago ± 5,000 years, a period of ~.The end of the stage is defined by the last magnetic pole reversal and plunge in to an ice age and global drying possibly colder and drier than the late Miocene ...
’ (Japan).