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The Solenogastres or Neomeniomorpha are mostly small (less than 5 cm long] worm-like that live symbiotically with (or feed upon) . As with the , many of the typical molluscan characters are absent. They have no shell, eyes, or tentacles. The is rudimentary, and instead of the standard molluscan flattened foot there is a , which the animal uses to creep along the bottom. They are and lack (gills) in the mantle cavity. As with the Caudofoveata, the contains layers of embedded calcareous , possibly a link to early coelomates. The worm-shaped body is derived from the inrolling of the margins.
There are about 250 described species, probably with many more awaiting discovery. They are found primarily below 200 meters and are sometimes quite abundant in deep-sea or . Many reside and feed upon cnidarians ( and ).
Despite being an important part of the deep-sea benthos, neomeniomorphs are poorly known, mainly because the difficulty of studying creatures that live in very deep water.
The Solenogastres have in the past been combined with the Caudofoveata to form the class . In some classifications the terms Aplacophora and Solenogastres seem to be synonymous. However the tendency now is to see them as distinct classes of mollusks.
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Whilst adult physiology may differ greatly between different groups of organisms, embryonic ontogeny may show evolutionary relationships, a fact discovered by the Darwinian philosopher in the 19th century. Here larval ontology indicates the relation between Solengastres and on the one hand, and sclerite-bearing "molluscomorphs" on the other. Salvini-Plawen (1980) provides an illustration (below) showing the similarity between larval forms of each class.
Differentiation of the mantle cover in just metamorphosed Nematomenia banyulensis (Solengastres - A and B) and Middendorffia caprearum (Polyplacophora - C and D). Pl shell plates in formation through the coalescence of the scaly bodies Sp arranged in seven transverse rows. Caption and figure from Salvini-Plawen 1980 p.252
Similarly, a recent discovery of a neomenioid postlarva (Scheltema & Ivanov, 2002) shows it has six iterated, transverse groups of spicules and seven regions devoid of spicules. These resemble the shell fields in developing polyplacophorans, and spicule arrangement is compared to sclerite arrangement on the Cambrian fossils corrugata and evangelista and to the spines and shell plates of the hayae. Such iterative morphogenesis was probably a common theme in late and Cambrian /molluscomorph animals and shows how these groups are related.
It is still unclear to what extent the Solenogastres and Caudofoveata are specialized and to what extent they are primitive, even "living fossils". Both these groups have been hypothesized to be ancient, pre- deep-sea forms, perhaps relics of the original Cambrian procoelomate radiation. Dzik (1993), in contrast, suggests they developed from aberrant chitons like the Silurian gazdzickii (id. at p.368, fig.12), but there is no evidence a shell was ever present. Barnes (1980). Salvini-Plawen (1980) sees Solenogastres as the sister group to all shelled mollusks (Testaria), while a cladistic study by Haszprunar (2000) indicates that Solenogastres are even more underived than Caudofoveata.
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Solenogastres | i. s.: Teuglaherpia tasmanica VN05 |--Neomeniidae [Neomeniamorpha] S-P04 |--Sterrofustia S-P04 |--Pholidoskepia S-P04 | |--Lepidomenia Kowalevsky 1883 [Lepidomeniidae] S-P86 | | `--L. hystrix Marion & Kowalevsky 1886 S-P86 | `--Meiomeniidae S-P86 | |--Meiomenia Morse 1979 S-P86 | | |--M. arenicola Salvini-Plawen & Sterrer 1985 S-P86 | | `--M. swedmarki Morse 1979 S-P86 | `--Meioherpia Salvini-Plawen 1985 S-P86 | |--M. atlantica Salvini-Plawen, Rieger & Sterrer 1985 S-P86 | `--M. stygalis Salvini-Plawen & Sterrer 1985 S-P86 `--Cavibelonia S-P04 |-- S-P04 |--Acanthomeniidae S-P04 |--Rhopalomeniidae S-P04 |--Amphimeniidae S-P04 |--Strophomeniidae S-P04 |--Notomenia Thiele 1897 [Notomeniidae] S-P04 | `--*N. clavigera Thiele 1897 S-P04 |--Epimenia [Epimeniidae] S-P04 | `--E. babai S-P04 |--Syngenoherpia [Syngenoherpiidae] S-P04 | `--S. intermedia S-P04 |--Unciherpiidae [Pararrhopaliidae] S-P04 | |--Uncimenia S-P04 | `--Sialoherpia S-P04 |--Rhipidoherpiidae S-P04 | |--Rhipidoherpia S-P04 | `--Thieleherpia von Salvini-Plawen 2004 S-P04 | `--*T. thulensis (Thiele 1900) [=Proneomenia thulensis] S-P04 |--Drepanomenia Heath 1911 [Drepanomeniidae] S-P04 | |--*D. vampyrella (Heath 1905) [=Neomenia vampyrella] S-P04 | |--D. incrustata (Koren & Danlielssen 1877) S-P04 | |--D. perticata Salvini-Plawen 1978 S-P04 | |--D. pontisquamata von Salvini-Plawen 2004 S-P04 | `--D. tenuitecta von Salvini-Plawen 2004 S-P04 `--Proneomeniidae S-P04 |--Proneomenia Hubrecht 1880 S-P04 | `--P. australis Thiele 1897 H09 `--Dorymenia Heath 1911 S-P04 |--*D. acuta Heath 1911 S-P04 |--D. harpagata S-P04 |--D. quincarinata (Ponder 1970) [=Proneomenia quincarinata] S-P04 `--D. tricarinata S-P04
Nomina nuda: Psammomenia Swedmark 1957 S-P86 `--P. krikophora Swedmark 1957 S-P86 Lepidomenia swedmarki Salvini-Plawen 1986 [=L. hystrix Swedmark 1956 non Marion & Kowalevsky 1886] S-P86
* Type species of generic name indicated
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[H09] Hedley, C. 1909. The Marine Fauna of Queensland: Address by the President of Section D. Australasian Association for the Advancement of Science: Brisbane.
[S-P86] Salvini-Plawen, L. v. 1986. Lower Mollusca. In Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) (L. Botosaneanu, ed.) pp. 148-152. E. J. Brill / Dr. W. Backhuys: Leiden.
[S-P04] Salvini-Plawen, L. von. 2004. Contributions to the morphological diversity and classification of the order Cavibelonia (Mollusca: Solenogastres). Journal of Molluscan Studies 70: 73-93.
[VN05] Vinther, J., & C. Nielsen. 2005. The Early Cambrian Halkieria is a mollusc. Zoologica Scripta 34: 81-89.
Taxonomy 23:36, 24 January 2010 (UTC)