New insights into the colonization of the deep sea: Systematics and zoogeography of the Munnidae and the Pleurogoniidaecomb. nov.(Isopoda; Janiroidea)

Abstract

The Munnidae (sensu Wolff 1962) are a heterogeneous group of tiny marine isopods (Asellota; Janiroidea) generally characterized by stalked eyes and an ambulatory epibenthic existence. They are found in shallow water in many parts of the world, especially in colder regions, and are a small component of the deep-sea fauna. This paper deals with the systematics and zoogeography of these isopods in two sections. The first section redefines the Munnidae and erects a new family with an old name, the Pleurogoniidae. The relationships of the genera in these two new taxa are discussed and the systematics of two related families, the Antiasidae and the Abyssianiridae, is clarified. The second section examines the zoogeographic data on the basis of this new systematic information. The Munnidae are found to be an essentially cosmopolitan, shallow-water family with a few species in the deep sea with very broad depth ranges, perhaps related to the apparent eurytopy of many munnid species. The evidence suggests the Munnidae have entered the deep sea at least twice. The Pleurogoniidae, in contrast, are a southern hemisphere, cold, stenotopic family with a few northern representatives. Pleurogoniids have entered the deep sea on many different occasions and have engendered a morphological subradiation there. Pleurogonium, the main component of the northern pleurogoniid fauna, is rare in the south and is likely to be the emergent representative of the pleurogoniid diversification in the deep sea. The present distributions of the Munnidae and the Pleurogoniidae may illustrate the manner in which the initial isopod invasion and diversification in the deep sea took place far in the past.