Neopilina
| Neopilina | |
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| The holotype of N. galatheae at the Zoological Museum, Copenhagen | |
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Neopilina
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Neopilina is a highly derived genus of modern monoplacophoran.[1] Some molecular results show that they fall within the polyplacophoran clade,[2] although these results have been called into question.[3] Fossil and morphological data show that they are rather derived and bear very little resemblance to an 'ancestral mollusc'.[1]
Anatomy
Its anatomy[4] led researchers to believe that the cephalopods evolved from the Monoplacophora.[4]
Its pair of preoral tentacles are considered homologous to those of gastropods; like prosobranch gastropod tentacles, their nerves connect to the cerebral ganglia.[4] The post-oral tentacles are equated with bivalves' labial flaps, cephalopods' arms, and scaphopods' captacula.[4]
Cuticular hardenings around the mouth of the organism are considered to be jaw-like and very not far removed from the beaks of cephalopods or the jaws of many gastropods.[4]
The presence of a single shell prompts comparisons to the cephalopod Nautilus, but besides its bilateral symmetry and direction of coiling, there is not a clear equivalence; Nautilus' shell is notably different in the possession of septa (and thus a siphuncle).[4]:64 It bears a similar degree of similarity to most other mollusc groups, leading to speculation that it may reflect a relatively unchanged ancestral mollusc.[4] The shell itself is aragonitic, consisting mainly of a prismatic layer,[5] lined with nacre.[4]
The organism bears five pairs of ctenidia (gills), unusually for molluscs; the rear two are homologous to the two pairs in Nautilus. This is unlike the polyplacophora, who have a number of pairs of ctenidia, but this number varies and is not related to the number of their body 'segments'.[4]
The foot and pallial groove are very difficult indeed to discriminate from the polyplacophora,[4] supporting its placement in this group by molecular methods[2]
Its radula is not unlike that of the polyplacophora; notably, its fifth tooth is modified to be comb-like.[6]
Ecology
Neopilina is a bottom feeder, probably a deposit feeder; whilst alive, its shell is covered by a layer of mucus that might be involved in feeding or locomotion.[7] Neopilina is the connecting link between Annelida and Mollusca.
References
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<references />, or <references group="..." />- ↑ 1.0 1.1 Organisms, Genes and Evolution: Evolutionary Theory at the Crossroads ; Proceedings of the 7th International Senckenberg Conference By Dieter Stefan Peters, Michael Weingarten Contributor Dieter Stefan Peters Published by Franz Steiner Verlag, 2000 ISBN 3-515-07659-X, 9783515076593 243 pages
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- ↑ Lua error in package.lua at line 80: module 'strict' not found. - contains spectacular SEM of prismatic nature of aragonite shell.
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