Potamalpheops, Powell, 1979

Yamashita, Ryunosuke, Komai, Tomoyuki & Koreeda, Reo, 2024, Potamalpheops yamakawai n. sp., representing the first record of the genus from Japan (Decapoda: Caridea: Alpheidae), Zootaxa 5555 (1), pp. 91-104 : 100-101

Key to species of Potamalpheops

1. Telson with 1 spiniform seta on each posterolateral angle.................................. 2 ( P. haugi species group)

– Telson with 2 spiniform setae on each posterolateral angle................................ 3 ( P. monodi species group)

2. Cheliped merus unarmed; diaeresis of uropodal exopod with 9–13 teeth....................... P. haugi ( Coutière, 1906) [West Africa; freshwater]

– Cheliped merus armed with tooth on distoventral margin; diaeresis of uropodal exopod with 15–25 teeth.................................................................................................. P. pylorus Powell, 1979 [West Africa; peat swamps, transitional fresh-brackish water]

3. Pereopod 5 merus unarmed............................................................................. 4

– Pereopod 5 merus armed with at least 1 spiniform seta........................................................ 8

4. Carapace lateral surface with distinct longitudinal groove; eyestalk reduced, with unpigmented cornea................................................................................................. P. stygicola ( Hobbs, 1973) [ Mexico; freshwater caves]

– Carapace lateral surface without groove; eyestalk normally developed, with darkly pigmented cornea.................. 5

5. Extra-corneal teeth located lateral to cornea.................................................................6

– Extra-corneal teeth located dorsolateral to cornea............................................................ 7

6. Rostrum armed with subapical spine on ventral margin; antennal carpocerite short, reaching 0.6 length of scaphocerite...................................................................................... P. johnsoni Anker, 2003 [SE Asia ( Singapore); mangroves]

– Rostrum unarmed on ventral margin; antennal carpocerite long, reaching 0.8–0.9 length of scaphocerite... P. yamakawai sp. nov. [ East Asia ( Japan); brackish water, penetrating into freshwater]

7. Rostrum distinctly overreaching distal corneal margins; eyestalk without anteromesial setae.................................................................................................. P. palawanensis Cai & Anker, 2004 [SE Asia ( Philippines); caves, transitional fresh-brackish water]

– Rostrum just reaching distal corneal margins; eyestalk with anteromesial setae................ P. amnicus Yeo & Ng, 1997 [SE Asia ( Malaysia, Singapore, Indonesia); freshwater]

8. Carapace with interrupted longitudinal groove on lateral surface; [rostrum reaching distal corneal margins].................................................................................................. P. galle Anker, 2005 [South Asia ( Sri Lanka); transitional fresh-brackish water]

– Carapace without longitudinal groove on lateral surface....................................................... 9

9. Rostrum reaching or not reaching distal corneal margins..................................................... 10

– Rostrum clearly overreaching distal corneal margins........................................................ 14

10. Uropodal exopod with simple distolateral tooth............................................................ 11

– Uropodal exopod with bifid distolateral tooth.............................................................. 13

11. Rostrum very short, not reaching bases of antennular peduncles; eyes reduced, largely covered by frontal margin of carapace; extra-corneal tooth obsolescent; cheliped with robust chela............................. ... P. darwinensis Bruce, 1993 [Northern Australia; mangroves]

– Rostrum at least reaching mid-point of corneas; eyes normally developed, corneas fully exposed; extra-corneal tooth acuminate; cheliped with moderately slender chela................................................................... 12

12. Carapace with row of setae on pterygostomial margin; cheliped carpus longer than palm......... P. monodi ( Sollaud, 1932) [West Africa; freshwater]

– Carapace without setae on pterygostomial margin; cheliped carpus as long as palm.............................................................................................. P. tyrymembe Soledade, Santos & Almeida, 2014 [ Brazil, mangroves]

13. Carapace ventrolateral margin with row of sparse setae; penultimate article of antennular peduncle 2–3 times longer than broad; cheliped carpus 1.3–1.7 times as long as palm; pereopod 4 ischium armed with 1 spiniform setae... P. miyai Yeo & Ng, 1997 [SE Asia ( Indonesia, Philippines); mangroves]

– Carapace ventrolateral margin without setae; Penultimate article of antennular peduncle nearly as long as broad; cheliped carpus subequal in length to palm; pereopod 4 ischium unarmed.............................. P. hanleyi Bruce, 1991 [Northern Australia; mangrove swamps]

14. Rostrum not reaching distal margin of basal article of antennular peduncle; eyestalk with spiniform anteromesial tubercle; [rostral ventral margin usually with subapical spine].................... P. nazgul Christodoulou, Iliffe & De Grave, 2019 [ Solomon Islands; anchialine caves]

– Rostrum reaching or overreaching distal margin of basal article of antennular peduncle; eyestalk without anteromesial tubercle............................................................................................ 15

15. Antennular stylocerite reaching distal margin of basal peduncular article; pereopod 3 propodus with 10 spiniform setae on flexor margin............................................................. .. P. pininsulae Bruce & Ilife, 1992 [ New Caledonia; anchialine caves]

– Antennular stylocerite distinctly overreaching distal margin of basal peduncular article; pereopod 3 propodus with no more than 9 spiniform setae on flexor margin....................................................................... 16

16. Rostrum reaching 0.3–0.6 length of penultimate article of antennular peduncle; cheliped carpus as long as chela.......................................................................................... P. tigger Yeo & Ng, 1997 [SE Asia ( Malaysia, Singapore); mangroves]

– Rostrum reaching distal margin of basal article of antennular peduncle; cheliped carpus shorter than chela..................................................................................................... P. kisi Marin, 2021 [SE Asia ( Vietnam), mangroves]