Neopilina

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]

Neopilina
The holotype of N. galatheae at the Zoological Museum, Copenhagen
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Class:
Monoplacophora
Order:
Tryblidiida
Superfamily:
Tryblidioidea
Family:
Neopilinidae
Genus:
Neopilina
Species
  • N. bruuni Menzies, 1968
  • N. galatheae Lemche, 1957
  • N. rebainsi Moskalev, Starobogatov & Filatova, 1983

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 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]

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References
  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
  2. Giribet, G.; Okusu, A, A.; Lindgren, A.R., A. R.; Huff, S.W., S. W.; Schrödl, M, M.; Nishiguchi, M.K., M. K. (May 2006). "Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons". Proceedings of the National Academy of Sciences of the United States of America. 103 (20): 7723–7728. Bibcode:2006PNAS..103.7723G. doi:10.1073/pnas.0602578103. PMC 1472512. PMID 16675549.
  3. Wägele, J Wolfgang; et al. (2009). "Phylogenetic support values are not necessarily informative: the case of the Serialia hypothesis (a mollusk phylogeny)". Frontiers in Zoology. 6 (12): 12. doi:10.1186/1742-9994-6-12. PMC 2710323. PMID 19555513.
  4. Lemche, H; Wingstrand, K.G. (1959). "The anatomy of Neopilina galatheae Lemche, 1957 (Mollusca, Tryblidiacea)". Galathea Rep. 3: 9–73. Archived from the original (Link to archived index page with links to free full text + plates) on 2019-07-22.
  5. Stephen Weiner and Lia Addadi (2007). "Design strategies in mineralized biological materials" (PDF). - contains spectacular SEM of prismatic nature of aragonite shell.
  6. Wingstrand, Karl Georg. "On the anatomy and relationships of recent Monoplacophora" (PDF). Galathea. 16: 007–094.
  7. Menzies, R. J.; Ewing, M.; Lamar Worzel, J.; Clarke, A. H. (1959). "Ecology of the Recent Monoplacophora". Oikos. 10 (2): 168–182. doi:10.2307/3565144. JSTOR 3565144.
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