Global Diversity of Marine Isopods (Except Asellota and Crustacean Symbionts)

Gary C B Poore,Niel L Bruce,Brian R Mackenzie

doi:10.1371/journal.pone.0043529

Abstract

The crustacean order Isopoda (excluding Asellota, crustacean symbionts and freshwater taxa) comprise 3154 described marine species in 379 genera in 37 families according to the WoRMS catalogue. The history of taxonomic discovery over the last two centuries is reviewed. Although a well defined order with the Peracarida, their relationship to other orders is not yet resolved but systematics of the major subordinal taxa is relatively well understood. Isopods range in size from less than 1 mm to Bathynomus giganteus at 365 mm long. They inhabit all marine habitats down to 7280 m depth but with few doubtful exceptions species have restricted biogeographic and bathymetric ranges. Four feeding categories are recognised as much on the basis of anecdotal evidence as hard data: detritus feeders and browsers, carnivores, parasites, and filter feeders. Notable among these are the Cymothooidea that range from predators and scavengers to external blood-sucking micropredators and parasites. Isopods brood 10–1600 eggs depending on individual species. Strong sexual dimorphism is characteristic of several families, notably in Gnathiidae where sessile males live with a harem of females while juvenile praniza stages are ectoparasites of fish. Protandry is known in Cymothoidae and protogyny in Anthuroidea. Some Paranthuridae are neotenous. About half of all coastal, shelf and upper bathyal species have been recorded in the MEOW temperate realms, 40% in tropical regions and the remainder in polar seas. The greatest concentration of temperate species is in Australasia; more have been recorded from temperate North Pacific than the North Atlantic. Of tropical regions, the Central Indo-Pacific is home to more species any other region. Isopods are decidedly asymmetrical latitudinally with 1.35 times as many species in temperate Southern Hemisphere than the temperate North Atlantic and northern Pacific, and almost four times as many Antarctic as Arctic species. More species are known from the bathyal and abyssal Antarctic than Arctic GOODS provinces, and more from the larger Pacific than Atlantic oceans. Two areas with many species known are the New Zealand-Kermadec and the Northern North Pacific provinces. Deep hard substrates such as found on seamounts and the slopes are underrepresented in samples. This, the documented numbers of undescribed species in recent collections and probable cryptic species suggest a large as yet undocumented fauna, potentially an order of magnitude greater than presently known.

Highlights

Isopod crustaceans occupy all habitats, from the desert to the deep sea with the exception of terrestrial Antarctica
History of discovery While the first isopods were named by Linnaeus, the starting point for the history of discovery for marine Isopoda can be thought of as 1840, the date of publication of Milne Edwards’ treatise on Crustacea [7]
In the period 1840–1900 progress was erratic, largely reliant on European or North American expertise and the material basis for isopod taxonomy at that time was limited by available collecting methods and the technical limitations of the equipment used

Summary

Introduction

Isopod crustaceans occupy all habitats, from the desert to the deep sea with the exception of terrestrial Antarctica. Most examples rely on morphological data and have hypothesised relationships between all isopod taxa [37], between families and genera of Anthuroidea [41,42], between families of Valvifera [43], phylogeny and biogeography of Corallanidae [44] and Gnathiidae [45], or between genera of Idoteidae ( including Holognathidae and Chaetiliidae) [46] and Aegidae [47] and within genera of Sphaeromatidae [48] and Cirolanidae [49,50].

Results

Conclusion