Lowryella, Morino & Miyamoto, 2016

Morino, Hiroshi & Miyamoto, Hisashi, 2016, A New Talitrid Genus and Species, Lowryella wadai, from Estuarine Reed Marshes of Western Japan (Crustacea: Amphipoda: Talitridae), Species Diversity 21, pp. 143-149 : 144-145

Lowryella gen. nov. [New Japanese name: Yoshihara-hamatobimushi zoku]

Type species. Lowryella wadai sp. nov. (monotypic)

Diagnosis. Body size medium. Eyes large. Antenna 1 reaching anterior end of peduncular article 4 of antenna 2; peduncle longer than flagellum, with peduncular articles 1–3 subequal in length. Antenna 2 short and slender in both sexes, with flagellum subequal to peduncle in length. Upper lip lacking robust setae. Lacinia mobilis of left mandible 4-dentate, that of right mandible 3-dentate with fine scales. In maxilliped, outer margin of precoxa not stepped; palp articles 2 and 3 broad; article 2 mediodistally lobed; article 4 reduced, masked by apical robust setae on article 3.

Gnathopod 1 deeply subchelate in both sexes (stronger in male); in male, merus, carpus, and propodus each with pellucid lobe, lateral surface of propodus with submarginal row of elongate robust setae; in female, posterodistal margins of basis and ischium each bearing small bulge with scabrous surface, propodus with broad pellucid lobe, lateral surface with submarginal row of elongate robust setae, palm slightly exceeding dactylus. Gnathopod 2 sexually dimorphic; in male, propodus large and powerfully subchelate, palmar margin almost straight, dactylus apically blunt; in female, basis broad and parallel-sided, merus with pellucid lobe, propodus mitten-shaped. Pereopods 3–7 cuspidactylate (bicuspate), locking robust-setae on propodi well-developed, meri and carpi in female stouter than those of male. Dactylus of pereopod 4 not pinched. Coxa of pereopod 4 wider than deep. Posterior lobe of coxa on pereopod 6 smoothly curved anteroventrally. Propodus of pereopod 7 in male with tuft of setae mediodistally. Coxal gill of gnathopod 2 largest and lobed, that of pereopod 3 smallest, those of pereopods 5 and 6 same in size; coxal gills of pereopods 3–6 convoluted. Oostegites subovate, with simple-tipped setae.

Pleonite side plates lacking marginal pits. Pleopods welldeveloped, peduncles marginally bare or with a few robust setae. Peduncle of uropod 1 with distolateral robust seta shorter than subdistal seta; inner ramus with single row of marginal robust setae, outer ramus with bare margin. Rami of uropod 2 subequal in length, bearing 1 or 2 marginal rows of robust setae. Uropod 3 with broad peduncle; ramus short. Telson lobe armed only with groups of apical robust setae.

Etymology. The new genus is named in honor of Dr James K. Lowry, who has contributed much to the taxonomy of the Talitridae and other amphipod groups.

Remarks. This new genus displays the following morphological features: (1) large eyes, (2) a short and slender antenna 2 in both sexes, (3) a 4-dentate lacinia mobilis of the left mandible, (4) a mediodistally lobate article 2 and reduced article 4 of the maxillipedal palp, (5) a deeply subchelate gnathopod 1 in both sexes, (6) a distinct pellucid lobe on the merus of male gnathopod 1, (7) a bulging basis and ischium of female gnathopod 1, (8) cuspidactylate pereopods, (9) a non-pinched dactylus of pereopod 4, (10) a distally setose propodus of male pereopod 7, (11) a small coxal gill of pereopod 6 (as large as that of pereopod 5), (12) a marginally bare outer ramus of uropod 1, and (13) only apical robust setae on the telson lobe. Among these, bulges on the basis and ischium of female gnathopod 1 and the small coxal gill of pereopod 6 are unique to this genus.

Lowryella belongs to the 4-dentate, cuspidactylate talitrids ( Bousfield 1984) and shows morphological similarities to one genus of salt-marsh talitrid, Tropicorchestia , and two land-hopper genera, Mizuhorchestia Morino, 2014 and Nipponorchestia Morino and Miyamoto, 2015 . This new genus, however, can be distinguished by the combination of the character states summarized in Table 1.

The beach-flea genus Traskorchestia Bousfield, 1982 has the cuspidactylate pereopods 3–7 like those of Lowryella , but the former is distinguishable from the latter in having a 5-dentate lacinia mobilis on the left mandible, marginal robust setae on the outer ramus of uropod 1, and lateral and apical robust setae on the telson lobe. Palustral talitrids of the genus Uhlorchestia also show morphological similarities with the new genus, sharing large eyes, a non-sexually dimorphic and slender antenna 2, a 4-dentate lacinia mobilis of the left mandible, a reduced article 4 of the maxillipedal palp, a deeply subchelate gnathopod 1 in both sexes (stronger in males), and well-developed pleopods. But Uhlorchestia differs from Lowryella in having a non-lobate article 2 of the maxillipedal palp, simplidactylate pereopods, marginal robust setae on the outer ramus of uropod 1, and both lateral and apical robust setae on the telson lobe.

Occupying the same type of habitat (salt marshes and estuaries) but quite distantly separated geographically ( Uhlorchestia in the eastern Atlantic and Tropicorchestia in tropical Australia), the similarities between these two talitrids and the new genus are more easily attributable to convergent evolution than to a recent common ancestor. Japanese endemic genera Mizuhorchestia and Nipponorchestia are also similar to Lowryella , but inhabit the environment from coastal land to inland forest ( Morino 2014; Morino and Miyamoto 2015a). Their developed coxal gill of the pereopod 6 and reduced pleopodal rami differ from the state of those appendages of Lowryella ( Table 1), and could be ascribed to adaptation to terrestrial life ( Friend 1986). Wildish (1988) suggested that the land colonization via estuarine habitats could be one of the possible routes for terrestrial talitrids. In the view of the above, it can be assumed that these three Japanese genera are phylogenetically closely related, and Lowryella could be a direct part of the ancestral lineage of the terrestrial talitrid genera in Japan. This hypothesis could be assessed by means of molecular phylogenic analysis.