Differentiation of three common deep-water hermit crabs (Crustacea, Decapoda, Anomura, Parapaguridae) from the South African demersal abundance surveys, including the description of a new species of Paragiopagurus Lemaitre, 1996.

Jannes Landschoff,Rafael Lemaitre

doi:10.3897/zookeys.676.12987

Abstract

Deep-water hermit crabs of the family Parapaguridae can be abundant (up to 20 kg or 1000 hermit crab individuals per haul) in the trawl bycatch collected during South African demersal abundance research surveys. Until recently, only two parapagurid species had been recognized in the bycatch; Parapagurus bouvieri Stebbing, 1910, and Sympagurus dimorphus (Studer, 1883). Detailed examination of numerous samples of parapagurid specimens from research surveys revealed the existence of a third, undescribed species previously confounded with S. dimorphus, but in fact belonging to a different genus. This new species, Paragiopagurus atkinsonae sp. n. is the 25th in the genus Paragiopagurus Lemaitre, 1996, and has been found only in a small region on the West Coast shelf of South Africa, at depths of 199–277 m. The species is herein fully described and illustrated, including colour images, µCT scans of selected body parts, and CO1 barcode data. The new species is morphologically most similar to P. ventilatus Lemaitre, 2004, a species associated with hydrothermal vents, but differs in armature of the fourth antennal segment (armed with a spine on the dorsolateral distal angle vs. unarmed in P. ventilatus); setation of the antennal flagella (nearly naked vs. with dense setae in P. ventilatus); plumose setation on the third maxillipeds and basal segments of chelipeds (absent vs. present in P. ventilatus); number of rows of scales on the propodal rasp of pereopod 4 (two or three rows vs. one row in P. ventilatus); and degree of telson asymmetry (weakly asymmetrical vs. strongly asymmetrical in P. ventilatus). Paragiopagurus atkinsonae sp. n. is superficially similar to S. dimorphus, with males of the two species showing the same extreme degree of sexual dimorphism on the right cheliped, general light orange colouration, and frequent use of colonial zoanthid carcinoecia for pleonal protection. To aid in future identifications and to facilitate data gathering during surveys, a comparison of P. atkinsonae sp. n. with S. dimorphus is provided, along with descriptions of colouration and photographs of live specimens of all three parapagurid species. Information on taxonomy of the species is summarized, as well as knowledge of their distribution in the demersal research survey regions of South Africa.

Highlights

The South African Department of Agriculture, Forestry and Fisheries (DAFF, formerly Department of Environmental Affairs and Tourism) has conducted biannual demersal fishery surveys since 1986
Three characters present in Paragiopagurus atkinsonae sp. n. exemplify the morphological evolutionary tendencies that in general are observed (Lemaitre 2013) in species of Paragiopagurus. These three characters are: biserial gills that are, at most, weakly divided distally; the drastic sexual dimorphism exhibited on the right cheliped; and in males, the complete loss of paired first and second pleopods modified as gonopods
The two species co-exist and are trawled in large numbers from the same benthic environments, and both species utilize a similar housing strategy for protection, i.e., a carcinoecia formed by potentially the same species of zoanthid polyps

Summary

Introduction

The South African Department of Agriculture, Forestry and Fisheries (DAFF, formerly Department of Environmental Affairs and Tourism) has conducted biannual demersal fishery surveys since 1986. Each survey conducts between 100–120 trawls, the majority of these take place between the 100–500 m isobaths, but some trawls extend to depths >1000 m (Yemane et al 2009). Among the invertebrate bycatch retained in research trawls, deep-water hermit crabs of the family Parapaguridae are common and occasionally, remarkably abundant, they have not always been adequately monitored. On the West Coast, a trawl can contain up to 20 kg (about 1000 individuals) of parapagurids per haul, and these can make up the vast majority of all invertebrates retained in the research trawls Such parapagurid abundance is an indication of their ecological importance on the South African continental shelf. The exact role, that these anomuran crustaceans might play in the benthic community remains to be studied

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