对笔石

对笔石属（学名：Didymograptus）是正笔石目下的一属笔石，生存于奥陶纪的海洋中，是一种群居性浮游生物。^[2]其化石分布于美洲、欧洲、亚洲、澳大利亚和纽西兰等地。

对笔石属 化石时期：478–443 Ma PreЄ Є O S D C P T J K Pg N 奥陶纪
Didymograptus murchisoni
科学分类
界：	动物界 Animalia
门：	半索动物门 Hemichordata
纲：	羽鳃纲 Pterobranchia
目：	†正笔石目 Graptoloidea
科：	†均分笔石科 Dichograptidae
属：	†对笔石属 Didymograptus McCoy（英语：Frederick McCoy）, 1851[1]
种
见内文
异名
Cladograpsus Geinitz, 1852

特征

对笔石群体的形状与音叉相似，大小从1至10公分不等，两条枝在接近末梢处逐渐变宽。胞管构造简单。^[2]

物种

本属包括以下物种：^[1]

• Didymograptus (Expansograptus) abnormis Hsu, 1934
• Didymograptus (Expansograptus) acriculus Keble & Harris, 1934
• Didymograptus (Expansograptus) adamantinus T.S.Hall, 1914
• Didymograptus (Didymograptus) artus Elles & Wood, 1901
• Didymograptus (Expansograptus) asperus Harris & Thomas, 1938
• Didymograptus (Expansograptus) aureus T.S.Hall, 1914
• Didymograptus (Expansograptus) balticus Tullberg, 1938
• Didymograptus bartrumi Benson & Keble, 1935
• Didymograptus (Didymograptellus) bidens Keble, 1927
• Didymograptus (Expansograptus) constrictus J.Hall, 1865
• Didymograptus (Expansograptus) cuspidatus Ruedemann, 1904
• Didymograptus demissus (Törnquist, 1901)
• Didymograptus (Expansograptus) dilatans T.S.Hall, 1914
• Didymograptus distinctus Harris & Thomas, 1935
• Didymograptus (Expansograptus) ellesae Ruedemann, 1908
• Didymograptus (Expansograptus) elongatus Harris & Thomas, 1914
• Didymograptus ensjoensis Monsen, 1937
• Didymograptus eocaduceus Harris, 1933
• Didymograptus euodus Lapworth, 1875
• Didymograptus (Expansograptus) extensus J.Hall, 1858
• Didymograptus filiformis (Tullberg, 1880)
• Didymograptus hemicyclus Harris, 1933
• Didymograptus holmi (Törnquist, 1901)
• Didymograptus (Expansograptus) latus T.S.Hall, 1907
• Didymograptus (Corymbograptus) mundus T.S.Hall, 1914
• Didymograptus (Expansograptus) nicholsoni Lapworth, 1875
• Didymograptus (Expansograptus) nitidus J.Hall, 1858
• Didymograptus pacificus Ruedemann, 1947
• Didymograptus paraindentus Berry, 1960
• Didymograptus (Expansograptus) perditus T.S.Hall, 1914
• Didymograptus (Expansograptus) procumbens T.S.Hall, 1914
• Didymograptus protobalticus (Monsen, 1937)
• Didymograptus (Didymograptellus) protobifidus Elles, 1933
• Didymograptus pusillus (Tullberg, 1880)
• Didymograptus (Expansograptus) similis J.Hall, 1865
• Didymograptus spinulosus Perner, 1895
• Didymograptus (Didymograptus) stabilis Elles & Wood, 1901
• Didymograptus (Didymograptus) stavus Legg, 1976
• 瑞典对笔石 Didymograptus (Expansograptus) suecicus Tullberg, 1880
• Didymograptus (Expansograptus) superstes Lapworth, 1876
• Didymograptus taylori T.S.Hall, 1899
• Didymograptus turgidus (Lee, 1974)
• Didymograptus undulatus (Törnquist, 1901)
• Didymograptus uniformis Elles & Wood, 1901
• Didymograptus (Corymbograptus) v-deflexus Harris, 1924
• Didymograptus (Expansograptus) validus Toernquist, 1901
• Didymograptus (Expansograptus) vicinus Harris & Thomas, 1938