Brachyscelus Spence Bate, 1861

Zeidler, Wolfgang, 2021, A review of the hyperiidean amphipod family Brachyscelidae Stephensen, 1923 (Crustacea: Amphipoda: Hyperiidea), Zootaxa 5026 (3), pp. 405-439 : 409

Key to the species of the genus Brachyscelus Spence Bate, 1861

1. Pereopod 6; basis with relatively broad antero-distal lobe, overlapping ischium, with rounded or straight distal margin..... 2

- Pereopod 6; basis with relatively narrow, almost pointed, antero-distal lobe, only reaching to middle or limit of ischium.... 3

2. Pereopod 6; antero-distal lobe of basis with straight distal margin. Pereopod 5; basis with small, rounded antero-distal lobe, overlapping about half of ischium. Telson longer than broad. Head of mature males pointed.................................................................................................... B. crusculum Spence Bate, 1861

- Pereopod 6; antero-distal lobe of basis with rounded distal margin. Pereopod 5; basis without antero-distal lobe, or lobe only marginally overlapping ischium. Telson as long as broad or slightly shorter. Head of mature males rounded............. 4

3. Gnathopod 1; carpal process with single row of large teeth, with few minor serrations; postero-distal corner of propodus with two large teeth followed by 2–3 slightly shorter teeth on posterior margin. Male A2; terminal article very short, much less than half-length preceding article............................................................ B. rapax ( Claus, 1871)

- Gnathopod 1; carpal process with large teeth interspersed with smaller ones; postero-distal corner of propodus with two large teeth followed by several much shorter teeth on posterior margin. Male A2; terminal article about half-length preceding article..................................................................... B. rapacoides Stephensen, 1925

4. Head depth equal in length to first five pereonites combined, or slightly less. Gnathopoda carpal process with relatively long teeth with few serrations. Carpus of gnathopod 1 of males without antero-distal lobe........... B. globiceps ( Claus, 1879)

- Head depth longer than pereon. Gnathopoda carpal process with relatively stubby teeth, with slightly serrated margins. Carpus of gnathopod 1 of males with small, rounded antero-distal lobe partly overlapping propodus.................................................................................................. B. macrocephalus Stephensen, 1925