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Eiler, Stefan M.; Haug, Carolin; Haug, Joachim T. (2016): Detailed description of a giant polychelidan eryoneicus-type larva with modern imaging techniques (Eucrustacea, Decapoda, Polychelida). In: Spixiana, Vol. 39, No. 1: pp. 39-60
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Polychelida occupies an important phylogenetic position within Decapoda. All modern representatives of this monophyletic group inhabit the deep sea and show a mixture of traits known from different other decapod groups. For example, they share some derived characters with Eureptantia and retain ancestral ones, which they share with, e.g. Caridea. In their specific systematic position, somewhere between Caridea and Eureptantia, they can be seen as an evolutionary link between these groups. More precisely, their morphotype combines aspects of the 'shrimp' morphotype and of the 'lobster' morphotype. Just to name some examples, representatives of Polychelida have 1) a triangular telson, which is an ancestral trait they share with the 'shrimp' morphotype, whereas the 'lobster' morphotype has a rectangular telson, and 2) their dorso-ventrally compressed pleon is a typical trait of Eureptantia ('lobster' morphotype), while representatives of Caridea still have a laterally compressed pleon ('shrimp' morphotype). Additionally, modern polychelids show peculiarities of their own evolutionary lineage. Most strikingly, besides the fact that all modern forms are blind, is that the benthic modern adulti develop from highly specialized pelagic larvae, which can reach a size of several centimeters and thus represent giant larvae. We present a detailed documentation of a modern giant eryoneicus larva taking advantage of composite autofluorescence imaging. This includes several outer structures, such as the thoracopods and pleopods, but also inner structures, such as their gizzard and its masticatory organs. Additionally, we provide the first high-resolution 3D photographs of such a larva to show its morphological structures in situ with correct topology.