Information about Plectronocerida
The primitive and ancestral Plectronoceratidae are included in the suborder, Plectronoceratina (Flower, R.H. 1964) of the Ellesmerocerida, but sometimes included in a separate order known as the Plectronocerida.
The Plectronoceratina are known from the Upper Cambrian of China and Manchuria and of North America (Texas, New Mexico?). Two families are recognized (Flower, 1964), the generally straight to endogastric Plectronoceratidae and the slightly exogastric Balkoceratidae.
Endogastric refers to a condition in which the lower or ventral side is concave and the back or dorsum is convex, in other words -belly in. Exogastric refers to the opposite condition in which the ventral side is instead convex and the back, concave, that is – belly out.
The Plectronoceratidae gave rise to the rest of the ellesmerocerid families and to the unique Discosorida. The Balkoceratidae which are unrelated to later exogastric forms died out by the end of the Cambrian and left no progeny.
The Plectronoceratidae, which typify the suborder, represented by Plectronoceras are characterized as follows. Plectronoceratidae are minute, generally compressed orthocones and endogastric cyrtocones with close spaced septa separating short chambers and a ventrally marginal siphuncle. Septal necks vary from very short to extending back almost to the previous septum in mature portions of conchs -that is may be subholochoanitic. Connecting rings are thick and typically expanded into the adjacent chambers as siphuncular bulbs where not confined by septal necks. The connecting rings are poorly calcified and fragile, being of chitiniferous organic material. Genera are defined on the basis of overall form and internal details.
Plectronocerids were probably benthic animals that crawled along the bottom in search of food or safety , facing down with the shell carried above. Nothing is known of their specific soft part anatomy or to what extent tentacles, if any, had developed, or whether the gastropod-type foot had evolved into a siphon by that time.
Small beginners, for what has turned out to be a large and diverse class of animals, the molluscan cephalopods.
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The Plectronoceratina are known from the Upper Cambrian of China and Manchuria and of North America (Texas, New Mexico?). Two families are recognized (Flower, 1964), the generally straight to endogastric Plectronoceratidae and the slightly exogastric Balkoceratidae.
Endogastric refers to a condition in which the lower or ventral side is concave and the back or dorsum is convex, in other words -belly in. Exogastric refers to the opposite condition in which the ventral side is instead convex and the back, concave, that is – belly out.
The Plectronoceratidae gave rise to the rest of the ellesmerocerid families and to the unique Discosorida. The Balkoceratidae which are unrelated to later exogastric forms died out by the end of the Cambrian and left no progeny.
The Plectronoceratidae, which typify the suborder, represented by Plectronoceras are characterized as follows. Plectronoceratidae are minute, generally compressed orthocones and endogastric cyrtocones with close spaced septa separating short chambers and a ventrally marginal siphuncle. Septal necks vary from very short to extending back almost to the previous septum in mature portions of conchs -that is may be subholochoanitic. Connecting rings are thick and typically expanded into the adjacent chambers as siphuncular bulbs where not confined by septal necks. The connecting rings are poorly calcified and fragile, being of chitiniferous organic material. Genera are defined on the basis of overall form and internal details.
Plectronocerids were probably benthic animals that crawled along the bottom in search of food or safety , facing down with the shell carried above. Nothing is known of their specific soft part anatomy or to what extent tentacles, if any, had developed, or whether the gastropod-type foot had evolved into a siphon by that time.
Small beginners, for what has turned out to be a large and diverse class of animals, the molluscan cephalopods.
References
- Rousseau H Flower, 1964, The Nautiloid Order, Ellesmeroceratida (Cephalopoda), Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico
- W.M. Furnish and Brian F Glenister, 1964, Nautiloidea - Ellesmerocerida; Treatise on Invertebrate Paleontology, Vol K, p K129 –
See also
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The Cambrian is a major division of the geologic timescale that begins about 542 ± 1.0 Ma (million years ago) at the end of the Proterozoic eon and ended about 488.3 ± 1.7 Ma with the beginning of the Ordovician period (ICS, 2004).
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Discosorida
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Discosorida
Discosorida are a unique order of cephalopods that lived from the beginning of the Middle Ordovician, thru the Silurian, and into the Devonian...... Click the link for more information.
Progeny can refer to:
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- progeny, A genetic descendant or offspring,
- An academic progeny (see student)
- Other uses
- Progeny Linux Systems
- Progeny (Stargate Atlantis) - an episode of the television series Stargate Atlantis
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orthocone is a usually long straight shell of a nautiloid cephalopod. During the 18th and 19th centuries, all shells of this type were named Orthoceras, but it is now known that many groups of nautiloids developed or retained this type of shell.
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septum (Latin: something that encloses; plural Septa) is a partition separating two cavities or spaces. Examples include:
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- Nasal septum: the cartilage wall separating the nostrils of the human nose.
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The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula.
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Strombus
Species
Strombus gigas
Strombus luhuanus
Strombus pugilis
Strombus tricornis
Strombus canarium
Strombus dolomena
Strombus gibberulus
Strombus conomurex
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Species
Strombus gigas
Strombus luhuanus
Strombus pugilis
Strombus tricornis
Strombus canarium
Strombus dolomena
Strombus gibberulus
Strombus conomurex
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benthic zone is the lowest level of a body of water, such as an ocean or a lake. It is inhabited by organisms that live in close relationship with (if not physically attached to) the ground, called benthos or benthic organisms.
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Belemnoidea
Extinct Orders
Aulacocerida
Phragmoteuthida
Belemnitida
Diplobelida
Belemnoteuthina
Belemnites (or belemnoids) are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the
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Extinct Orders
Aulacocerida
Phragmoteuthida
Belemnitida
Diplobelida
Belemnoteuthina
Belemnites (or belemnoids) are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the
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Lituites
Species
all extinct
Lituites is an extinct genus of the nautiloids, and is one of the most primitive known cephalopods. It originated in the Ordovician period, around 460 million years ago.
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Species
all extinct
Lituites is an extinct genus of the nautiloids, and is one of the most primitive known cephalopods. It originated in the Ordovician period, around 460 million years ago.
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