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|regnum = Animalia |phylum = Mollusca |classis = Cephalopoda |subclassis = Ammonoidea |ordo = Ammonitida |subordo = Ancyloceratina |superfamilia = Turrilitoidea |familia = Diplomoceratidae |subfamilia = Polyptychoceratinae |genus = ''Astreptoceras'' |genus_authority = Henderson, 1970 }} ''Astreptoceras'' is an extinct upper Cretaceous ammonoid cephalopod named by Hendeson in 1970. Fossils belonging to this genera have been found in Antarctica and New Zealand. The only described species is ''Astreptoceras zelandicum'' (Marshall, 1926). It is a small heteromorph ammonite with almost circular cross-section of the shell. Shell has probably only one straight shaft that is initially without ribs and constrictions. At diameter of about 2 mm there appears first constrictions and at late growth stages, these can be preceded by a collar and shallow secondary constriction. Weak ribs occurs at late growth stages.〔Henderson, R.A. 1970 Ammonoidea from the Mata Series (Santonian-Maastrichtian) of New Zealand. Special papers in palaeontology, 6: 81 p.〕 ==References== *Nomenclator Zoologicus () *Sepkoski's list of cephalopod genera () 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Astreptoceras」の詳細全文を読む スポンサード リンク
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