Editing Tusk shell (section)

{{short description|Class of elephant tusk shell molluscs}}
{{Automatic taxobox
| taxon = Scaphopoda
| name = Scaphopods
| fossil_range = [[Carboniferous]]–[[Neogene]] ({{geological range|Mississippian|earliest=Middle Ordovician|Recent|ref=<ref name=Steiner1992/><!-- Steiner says earliest are Mid Ord--><ref>{{Cite book
| chapter = The Scaphopoda
| volume = 42
| pages = 137–236
| doi = 10.1016/S0065-2881(02)42014-7
| series = Advances in Marine Biology
| last1 = Reynolds
| first1 = Patrick D.
| title = Molluscan Radiation - Lesser-known Branches
| pmid = 12094723
| isbn = 9780120261420
| year = 2002
}}</ref><!-- Earliest concrete fossils accepted here are Mississippian-->) }}
| image = Scaphopoda (10.3897-zookeys.707.13042) Figure 23.jpg
| image_caption = Various Scaphopoda, from left to right: ''[[Fissidentalium]]'', [[Gadilida]], ''[[Gadila (mollusc)|Gadila]]'', and [[Gadilida]].
| authority = [[Heinrich Georg Bronn|Bronn]], 1862
| subdivision_ranks = Orders
| subdivision = * [[Dentaliida]] 
* [[Gadilida]]
}}
{{Sea shell topics}}

'''Scaphopoda''' {{IPAc-en|s|k|æ|ˈ|f|ɒ|p|ə|d|ə}} (plural '''scaphopods''' {{IPAc-en|ˈ|s|k|æ|f|ə|p|ɒ|d|z}}, from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as '''tusk shells''' or '''tooth shells''', are a [[class (biology)|class]] of shelled [[Marine life|marine]] [[invertebrate]]s belonging to the [[phylum]] [[Mollusca]] with worldwide distribution and are the only class of exclusively [[infaunal]] marine molluscs. Shells of species within this class range in length {{convert|0.5-18|cm|abbr=on}} (with  ''Fissidentalium metivieri'' as the longest).<ref>{{cite journal | pmc=4714876 | year=2016 | last1=Vermeij | first1=G. J. | title=Gigantism and Its Implications for the History of Life | journal=PLOS ONE | volume=11 | issue=1 | pages=e0146092 | doi=10.1371/journal.pone.0146092 | pmid=26771527 | bibcode=2016PLoSO..1146092V | doi-access=free }}</ref> Members of the order [[Dentaliida]] tend to be larger than those of the order [[Gadilida]].

These molluscs live in soft [[substrate (biology)|substrates]] offshore (usually not [[intertidal]]ly). Because of this subtidal habitat and the small size of most species, many [[beachcombing|beachcombers]] are unfamiliar with them; their shells are not as common or as easily visible in the beach drift as the shells of [[sea snail]]s and [[clam]]s.

Molecular data suggest that the scaphopods are a sister group to the [[cephalopod]]s, although higher-level molluscan phylogeny remains unresolved.<ref>{{Cite journal| last3=Lindgren, A.R.| last1=Giribet | first3=A. R. | first1=G.| last4=Huff, S.W. | first4=S. W. | first2=A.| last5 = Schrödl, M | first5=M.| last6 = Nishiguchi, M.K. | first6=M. K.| title = Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons| last2= Okusu, A| journal = Proceedings of the National Academy of Sciences of the United States of America| volume = 103| issue = 20| pages = 7723–7728| date=May 2006 | pmid = 16675549| pmc = 1472512| doi = 10.1073/pnas.0602578103|bibcode = 2006PNAS..103.7723G | doi-access=free }}</ref>