The Global Diversity of Parasitic Isopods Associated with Crustacean Hosts (Isopoda: Bopyroidea and Cryptoniscoidea)

Jason D Williams,Christopher B Boyko,Ethan P White

doi:10.1371/journal.pone.0035350

Jason D Williams, Christopher B Boyko + Show 1 more

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https://doi.org/10.1371/journal.pone.0035350

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Abstract

Parasitic isopods of Bopyroidea and Cryptoniscoidea (commonly referred to as epicarideans) are unique in using crustaceans as both intermediate and definitive hosts. In total, 795 epicarideans are known, representing ∼7.7% of described isopods. The rate of description of parasitic species has not matched that of free-living isopods and this disparity will likely continue due to the more cryptic nature of these parasites. Distribution patterns of epicarideans are influenced by a combination of their definitive (both benthic and pelagic species) and intermediate (pelagic copepod) host distributions, although host specificity is poorly known for most species. Among epicarideans, nearly all species in Bopyroidea are ectoparasitic on decapod hosts. Bopyrids are the most diverse taxon (605 species), with their highest diversity in the North West Pacific (139 species), East Asian Sea (120 species), and Central Indian Ocean (44 species). The diversity patterns of Cryptoniscoidea (99 species, endoparasites of a diverse assemblage of crustacean hosts) are distinct from bopyrids, with the greatest diversity of cryptoniscoids in the North East Atlantic (18 species) followed by the Antarctic, Mediterranean, and Arctic regions (13, 12, and 8 species, respectively). Dajidae (54 species, ectoparasites of shrimp, mysids, and euphausids) exhibits highest diversity in the Antarctic (7 species) with 14 species in the Arctic and North East Atlantic regions combined. Entoniscidae (37 species, endoparasites within anomuran, brachyuran and shrimp hosts) show highest diversity in the North West Pacific (10 species) and North East Atlantic (8 species). Most epicarideans are known from relatively shallow waters, although some bopyrids are known from depths below 4000 m. Lack of parasitic groups in certain geographic areas is likely a sampling artifact and we predict that the Central Indian Ocean and East Asian Sea (in particular, the Indo-Malay-Philippines Archipelago) hold a wealth of undescribed species, reflecting our knowledge of host diversity patterns.

Highlights

Within crustaceans, a wide range of groups including amphipods, barnacles, copepods, and isopods have formed parasitic relationships with invertebrate and vertebrate hosts
We excluded all nomina nuda, all ‘‘species’’ of Microniscus, any replacement names for homonyms, and Proteolepas bivincta Darwin, 1854
Total number of described species and genera were reported for the biogeographic regions (‘‘Marine Regions’’) of [15], which are similar to the regions defined by the National and Regional Implementation Committees (NRIC) [16]

Summary

Introduction

A wide range of groups including amphipods, barnacles, copepods, and isopods have formed parasitic relationships with invertebrate and vertebrate hosts. Bopyroids and cryptoniscoids (795 species) are unique in that they use crustaceans as both intermediate and definitive hosts (Figure 1A–H). Epicarideans have a long history of taxonomic study dating back to 1724 and the first mention in the literature as a supposed larva of a flatfish parasitizing a shrimp [9] and the subsequent naming of the first bopyrid species in 1798 [10].

Results

Conclusion