Bioacoustics of Porirualia

Wells et al. (1982) placed Parastenhelia megarostrum in close proximity to Pa. anglica , Pa. ornatissima , Pa. reducta and Pa. hornelli , all of which share a 3-segmented P1 exopod with segments of subequal proportions. Based on the 9-segmented antennule in the female, the position and length of the inner seta on P1 enp-1, the shape of the female P5 and armature of the male P5 exopod, they placed it closest to Pa. hornelli . Although the hornelli - complex was far from resolved at the time, Wells et al. (1982) considered distinct species status for Pa. megarostrum warranted because it displayed characters reflecting considerable conservatism in the genus, such as the massive size of the rostrum, the length/width ratio of P1 enp-2, the relative position of the setae on the female P5 exopod, abdominal ornamentation, and relative proportions of the exopodal setae on the male P5 exopod. They also attached considerable significance to the distinctive bulbous genital field in the female, which was regarded as an effective isolating factor in the mate recognition of this species. Song et al. (2003) considered Pa. pyriformis most closely related to Pa. hornelli and Pa. megarostrum based on the shared presence of subequal segments in the P1 exopod, the position and length of the inner seta on P1 enp- 1 and the 9-segmented antennule in the female. They also recognized a certain resemblance with Pa. oligochaeta , based on the length and location of the inner seta of P1 enp-1, but the latter species differs in the ornamentation of the anal operculum, armature of ♀ P2–P4, segmentation and armature of ♂ P2–P3 endopods and the presence of six elements on the male P5 exopod. Both Mielke (1990) and Gee (2006) have suggested removing Pa. megarostrum and/or Pa. pyriformis from Parastenhelia because they lack the characteristic sexual dimorphism on the male P3 endopod that defines this genus. Neither species can be accommodated in Thalestrella because they do not exhibit the sexual dimorphism on the antenna that is typical for this genus nor can they be assigned to Foweya since the males lack the modified inner basal spine of P1. Both genera are also characterized by an area of reduced cuticle thickness on the P1 endopod which is not expressed in Pa. megarostrum or Pa. pyriformis . In accordance with earlier views ( Mielke 1990 ; Gee 2006 ), both species are here transferred to a new genus, Porirualia gen. nov. , based on the following suite of apomorphic character states: (a) rostrum very large, reaching to at least halfway the fourth antennulary segment in the female; (b) P1 enp-1 inner seta very long, extending beyond distal margin of segment; and (c) P 5 ♀ with series of transverse striae along inner margin of endopodal lobe; these striae are internal chitinous reinforcements and are more strongly developed in Po. megarostrum ( Wells, Hicks & Coull, 1982 ) comb. nov. than in Po. pyriformis ( Song, Kim & Chang, 2003 ) comb. nov. The new genus shares a sistergroup relationship with Johnwellsia gen. nov. based on the following synapomorphies: (a) distal seta on the mandibular basis modified into short spine; (b) P3 endopod ♂ with only one inner seta on distal segment (homologue of proximal inner seta of ♀ enp-3 not expressed in ♂ ; Fig. 7G–I); and (c) outermost element of P5 endopodal lobe reduced, represented by minute seta in both sexes. There is controversy over the segmentation of the male antennule. Both Wells et al. (1982) and Song et al. (2003) describe it as 9-segmented although the latter authors figure ten segments. The antennule is here reinterpreted as 10-segmented with the geniculation positioned between segments 6 and 7. The small bisetose segment 4 (= ancestral segment XIII; figured but not counted by Song et al. 2003 ) was overlooked by Wells et al. (1982) . The apical segment in Po. megarostrum comb. nov. was described as unarmed, displaying a row of fine marginal hairs; it is unlikely that this observation is correct.