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The oldest “intermetamorphic” larva of an achelatan lobster from the Lower Jurassic Posidonia Shale, South Germany

100%

Haug J. T. , Haug C. , Schweigert G.

Acta Palaeontologica Polonica

2019

tom 64

nr 4

Achelatan lobsters, also known as spiny and slipper lobsters, develop via a highly specialised larval form. This special larva, phyllosoma, is flat, translucent, possesses elongate legs and can grow to enormous sizes. Although these larvae may appear very fragile, they are well-known as fossils. Thousands of specimens have been found in the lithographic limestone of Southern Germany (Tithonian, Upper Jurassic, about 150 mya). At least three types of fossil, but modern-appearing phyllosoma larvae are known. Additionally, fossil larvae that possess only some of the characters of modern-day phyllosoma larvae are known from the same Lagerstätte, but also from the younger limestone beds of Lebanon. Here we report a new achelatan fossil from the older Posidonia Shale (Toarcian, Lower Jurassic, 175–183 mya). The specimen shows certain characters of a phyllosoma larva, but other characters appear like those of post-phyllosoma stages of achelatan lobsters. This specimen is therefore the oldest occurrence of an achelatan lobster larva. We compare the new specimen with other fossil larvae with such mixed or “intermetamorphic” morphologies.

Dispersal - limited biodiversity of tropical insular streams

80%

Covich A. P.

Polish Journal of Ecology

2006

tom 54

nr 4

Numerous species are adapted for colonization of insular fresh waters by using different mechanisms of active and passive dispersal, especially among oceanic islands at low latitudes. Over time, similar animal communities have assembled in many tropical streams and rivers on isolated islands. These freshwater communities are characterized by a relatively low number of species of fishes, decapods, gastropods and insects that typically have complex life cycles including passive, long-distance dispersal. These species often disperse during marine phases with drifting larvae or by rafting and aerial transport of resistant, dormant stages. Active dispersal is sometimes effective for relatively short-distance movements from one island’s streams to another island’s nearby drainage basin within an archipelago (a “stepping-stones” dispersal pattern). Identifying distinct differences among aquatic communities on “true oceanic” islands of different ages and geologic histories requires a longterm biogeographic perspective including the degree of spatial isolation of populations and differences in rates of speciation. Consequently, the total biodiversity of insular streams is a complex combination of dispersal from multiple sources of species from continents and other islands, as well as evolution of new endemics. Recolonization of streams following natural disturbances and the impacts of introduced species result in dynamic changes in species accumulation and turnover in these insular freshwater ecosystems. Analysis of dispersal to islands provides general perspectives on managing fragmented habitats, especially the effects of invasive species that also shed light on factors affecting the equilibrium composition of animal communities in island-like ecosystems on continents.