Paguristione uniuropodus, a new genus and a new species of Pseudioninae infesting hermit crabs from China (Crustacea, Isopoda, Bopyridae)

Abstract Paguristione uniuropodus gen. n., sp. n. infests Paguristes sp. in the East China Sea. Paguristione gen. n. differs from the closely related genera Pseudione and Pagurion by its females having indistinct lateral plates on the last two pleomeres and its male with a long tapering pleon of six pleomeres, lacking both pleopoda and uropoda.


Introduction
Bopyrid isopods infesting hermit crabs belong to the subfamilies Pseudioninae (branchial parasites) and Athelginae (dorsoabdominal parasites). An, Markham and Yu (2010), An, Williams and Yu (2011) and An, Li and Markham (2013) have reported a total of eight bopyrid species infesting hermit crabs in the South China Sea. Markham (1992) recorded six species of bopyrids infesting hermit crabs in Hong Kong. Boyko (2004) reported one such species from Taiwan. In Chinese waters as a whole, An (2006) reported ten species of bopyrids infesting hermit crabs. Currently, throughout Asia, 36 species are recorded infesting 48 hermit crabs from Asia (Table 1). Worldwide, Mc-Dermott,  catalog 83 species of bopyrids infesting hermit crabs, of which 41 species in ten genera are branchial parasites. As hosts worldwide, 11 species of Paguristes are known to bear bopyrids (Table 2); their parasites, all branchially infesting members of the subfamily Pseudioninae, are in the genera Asymmetrione, Pseudione, Parapagurion and now the new genus Paguristione.
Specimens used in this study were collected from the East China Sea in 1958, and one of the authors (An 2006) examined the parasites and reported Parapagurion glabra sp. n. infesting Paguristes sp. in her doctoral dissertation (not a published work in the sense of the ICZN). Further examination shows that they represent a new species in a new genus. The name Parapagurion glabra is here entered into its synonymy.

Material and methods
Materials for this study originated from Chinese Comprehensive Oceanographic Survey. All materials examined have been deposited in the Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China (IOCAS). Specimens were viewed and drawn using a Zeiss Stemi SV Apo microscope.
Etymology. Combination of the genus name of its host, Paguristes and bopyrid genus name Ione. Gender feminine.
Pleon of 6 distinct pleomeres, first three produced into small lateral plates and bearing biramous pleopods; fourth and fifth pleomeres lacking lateral plates. Terminal pleomere greatly reduced and deeply embedded in fifth, bearing uniramous uropoda. All pleopodal rami produced into tapering points and progressively smaller posteriorly, extending to sides of pleon and leaving ventral surface of pleon uncovered.
Head semicircular, broader than long, much narrower than first pereomere, distinctly separated from first pereomere and not at all embedded into it (Fig. 1J). Eyes absent. Antennae visible only ventrally, not extending to margins of head, of 3 and 4 articles respectively; second antenna with sparse short setae on terminal article (Fig. 1L).
Etymology. Latin noun uniuropodus, referring to the uniramous uropoda of the female, used in apposition.
Remarks. The new genus differs from other closely similar hermit-crab-infesting genera Pseudione, Pagurion and Parapagurion thus: female with only rudimentary pleonal lateral plates (only first three pleomeres with small lateral plates) and uniramous uropoda, male with head and pleon abruptly narrower than contiguous pereomeres, first pereopod smaller than pereopods 2-4 and pleopodal appendages completely lacking. Females of Pseudione have distinct pleonal lateral plates on pleomeres 1-5; its males have pleopods, and their heads and pleons are smoothly narrower than the pereon. Females of Pagurion have distinct lamellar pleopodal appendages on all pleomeres 1-6 and biramous uropoda; its males have equally width pereopods and uniramous pleopods. Females of Parapagurion are nearly symmetrical and bear well-developed lateral plates on pleomeres 1-5 and uniramous uropods; the first pereopods of the males are never smaller than the second ones.