Pseudostegias setoensis Shiino, 1933
An, Jianmei, Williams, Jason D. & Yu, Haiyan, 2011, Three abdominal parasitic isopods (Isopoda: Epicaridea: Bopyridae: Athelginae) on hermit crabs from China and Hong Kong, Journal of Natural History 45 (47 - 48), pp. 2901-2913: 2906-2911
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|Pseudostegias setoensis Shiino, 1933|
Abbreviated synonymy (see Markham 2010, for complete synonymy before 2010.) Pseudostegias setoensis Shiino, 1933: 290–293 , fig. 16 [type locality Seto, Japan; infesting Clibanarius bimaculatus (De Haan, 1849) ]. McDermott et al. 2010: 11 (table). Markham 2010: 183–185, 153 (table); figs. 34, 35.
?Non Pseudostegias setoensis Markham 1994: 247–249 , fig. 17.
Infesting Clibanarius virescens Hess. Hong Kong, Siu Kau Yi Chai (Island near Peng Chau), 22 ◦ 17 ′ 16.70 ′′ N, 114 ◦ 3 ′ 28.65 ′′ E, 3 June 2004, J. Williams coll., 3 ♀, 3 ♂, USNM1155302 View Materials GoogleMaps .
Description of female
Length of reference female (CIEA920301) (not including pleopods and uropods) 9.33 mm, body roughly rectangular, dextral. No pigmentation ( Figure 3A, B View Figure 3 ).
Head pentagonal, longer than wide, eyes absent ( Figure 3A View Figure 3 ). Antennule and antennae of three and four articles, respectively; antennae with a tuft of terminal setae ( Figure 3C View Figure 3 ). Maxilliped without palp, with plectron short and blunt ( Figure 3D View Figure 3 ). Barbula with three short and blunt projections on each side, flat middle region ( Figure 3E View Figure 3 ).
Pereon with mid-dorsal ridge, broadest across pereomere 6. Pereomeres 1 and 2 surrounding head, pereomers 3, 4 fused medially, and pereomeres 2–7 produced into pair of posterolateral points. Oostegites completely enclosing highly vaulted brood pouch ( Figure 3B View Figure 3 ). Oostegite 1 ( Figure 3F, G View Figure 3 ) more than twice as long as wide, extending beyond head, bearing round anterior edge and sharp posterolateral point, internal ridge with two blunt tuberculate structures. Fifth oostegites largest, covering half of pereon ventrally ( Figure 3B View Figure 3 ). First five pereopods ( Figure 3H, I View Figure 3 ) of nearly same size, pereopods 6 and 7 much longer.
Pleon of six pleomeres, first four pleomeres bearing biramous pleopods and lanceolate lateral plates ( Figure 3A, B View Figure 3 ). Lateral plates progressively longer in posterior pleomeres and extending laterally. Pleomere 5 with pair of globose lateral plates ( Figure 3A View Figure 3 ) and biramous pleopods. Pleomere 6 with pair of uniramous uropods. Lateral plates, exopodites of pleopods and uropods lanceolate, endopodites of first three pleopods much larger, covering pleonal surface and creating posterior extension of the brood chamber, within which male often resides ( Figure 3A, B View Figure 3 ).
Description of male
Length of reference male (CIEA920302) 3.30 mm, maximal width across pereomere 5, 0.92 mm, head length 0.31 mm, head width 0.68 mm, pleonal length 1.32 mm.
Male attached inside brood chamber. Body elongate, sides nearly parallel except for anteriorly rounded head and posterior end with tapering pleon ( Figure 3J View Figure 3 ).
Head roughly oval, wider than long, and distinctly separated from pereomere 1. Small dark eyes near posterolateral regions ( Figure 3J View Figure 3 ). Antennule of three articles, with tuft setae on terminal article; antennae of five articles, with tuft of setae on distal end of last two articles ( Figure 3L View Figure 3 ).
Pereomeres nearly subequal, with truncate margins. Large gap between adjacent pereomeres. All pereopods of similar structure and proportions ( Figure 3M View Figure 3 ).
Pleon fused into single piece, pleomere 1 indicated by anterior enlargement, pleomeres indicated by low, rounded structures on ventral sides of pleon (reduced pleopods). uropods lacking.
The genus Pseudostegias contains seven described species. The new specimens from China ( Figure 3 View Figure 3 ) and Hong Kong ( Figures 4 View Figure 4 , 5 View Figure 5 ) are similar to recent descriptions of Pseudostegias setoensis (e.g. Markham 2010). However, they are also very similar to Pseudostegias dulcilacuum Markham, 1982 . The two species are reportedly distinguished by barbula digitation, posterolateral projection of oostegite 1, and morphology of the pleonal appendages ( Markham 2010). Unfortunately, these features are quite variable in the reports of both species. We believe it is likely that Pseudostegias dulcilacuum is a junior synonym of Pseudostegias setoensis but further research, ideally incorporating morphological and molecular data, is required to determine the extent of variation in the species. The crenulate or digitate posterior margins of the pereomeres found in the present specimens are similar to those reported in the original description of Pseudostegias dulcilacuum ( Markham, 1982) , although the digitation appears more pronounced in some of the new specimens. The two larger digitiform lateral projections under the fifth oostegites in Pseudostegias setoensis from Hong Kong ( Figure 4B View Figure 4 ) have not been recorded before and their function is unknown. These could be of taxonomic importance in Pseudostegias and should be considered in future studies.
The record of Pseudostegias setoensis from the Chesterfield Islands and New Caledonia by Markham (1994) probably respresents a distinct species (as suggested by Williams and Boyko 1999). Unlike all other reports of Pseudostegias setoensis that come from shallow-water hermit crabs (members of the genera Calcinus , Clibanarius , Diogenes ), the specimens from the Chesterfield Islands were found on hosts from deeper waters (400 m) ( Strigopagurus boreonotus Forest ). In addition, the specimens from this locality are distinguished by a broader body shape of the females, more foliose female pleonal appendages, and different head morphology of males ( Markham 1994).
The specimens from China ( Figure 3 View Figure 3 ) and Hong Kong ( Figures 4 View Figure 4 , 5 View Figure 5 ) are similar in most characters. However, female specimens from Hong Kong had digitate projections on the barbula ( Figure 4C View Figure 4 ), posterior margins of pleomeres with crenulate margin or highly digitate in ventral respect ( Figure 4A, B View Figure 4 ), with two distinct lateral digitiform projections under the fifth oostegites ( Figure 4B View Figure 4 ), the fifth lateral plates kidney shaped ( Figure 4F View Figure 4 ). Male specimens almost similar.
Prevalence and impact on host
In total, 7.5% (three of 40) of Clibanarius virescens Hess collected from Hong Kong were parasitized by Pseudostegias setoensis in 2004. None of the 1000+ Pagurus minutus from this region examined were found with Pseudostegias setoensis , indicating that the parasite has some degree of host specificity. To date, the species has only been documented from diogenid hermit crabs.
One host specimen of Clibanarius virescens collected in Hong Kong showed evidence of the damage caused by Pseudostegias setoensis ( Figure 5E, F View Figure 5 ). A hole in the host exoskeleton left by the mouthparts of the female isopod was oval in shape (approximately 100 µm in length and 50 µm in width) and positioned on the abdomen near the pleopods of the host. The exoskeleton of the hosts also displayed points where the dactyl and propodus of the pereopods were used to attach ( Figure 5E, G View Figure 5 ).
Range and hosts
Japan on Clibanarius bimaculatus (De Haan) ( Shiino 1933) ; Hainan, China on Calcinus laevimanus (Randall) (herein); Hong Kong on Clibanarius bimaculatus , Clibanarius ransoni Forest ( Markham 1982) and Clibanarius virescens (herein); Thailand on Clibanarius padavensis de Man ( Markham 1985); Taiwan on Clibanarius striolatus Dana ( Shiino 1958); Australia on Diogenes pallescens Whitelegge ( Markham 2010);?Chesterfield Islands and New Caledonia on Strigopagurus boreonotus Forest ( Markham 1994; see discussion above).
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