Workgroup Biosystematic Documentation, University of Ulm, Helmholtzstrasse 20, Ulm, Germany.
Arthropod Struct Dev. 2010 Mar-May;39(2-3):154-73. doi: 10.1016/j.asd.2010.01.005.
The ontogenetic sequence of +Martinssonia elongata, a derivative of the stem lineage of Eucrustacea, has been re-investigated. Morphological and morphometric data provide a revision of the original description of this species. Specimens originally assigned to second and third developmental stages have been removed from the +M. elongata sequence and assigned, together with several larger specimens, to an entirely new species, +rMusacaris gerdgeyeri gen et. sp. nov having a completely unsegmented body, giving the appearance of a giant euarthropod head larva. This is interpreted either as a hypertrophied larva or a late developmental stage of a neotenic species. Only the earliest unsegmented larvae and segmented instars of the original sequence are ascribed to +M. elongata. The two species are apparently closely related and are closer to Labrophora (+Phosphatocopina + Eucrustacea) than to other Cambrian " 'Orsten' crustacean stem derivatives". The ontogenetic sequences of the two taxa and those of the other derivatives of the recently investigated labrophoran stem lineage indicate several heterochronic peramorphic ('adultising') events during early crustacean evolution. This is most evident in the development of the proximal parts of the appendages.
对 +Martinssonia elongata 的个体发生序列进行了重新研究，它是 Eucrustacea 主干谱系的衍生物。形态学和形态计量学数据对该物种的原始描述进行了修订。最初被分配到第二和第三发育阶段的标本已从 +M. elongata 序列中移除，并与几个较大的标本一起被分配到一个全新的物种 +rMusacaris gerdgeyeri gen et. sp. nov，该物种具有完全不分节的身体，外观类似于巨型节肢动物头部幼虫。这被解释为是一种过度生长的幼虫或幼态持续物种的晚期发育阶段。只有最早的未分节幼虫和原始序列中的分节龄期被归为 +M. elongata。这两个物种显然密切相关，与 Labrophora（+Phosphatocopina + Eucrustacea）比其他寒武纪“'Orsten' 甲壳动物主干衍生物”更接近。这两个分类群的个体发生序列以及最近研究的 labrophoran 主干谱系的其他衍生物的个体发生序列表明，在早期甲壳动物进化过程中发生了几个异时性变态（“成年化”）事件。这在附肢近端部分的发育中最为明显。
