Ischyrocerini Krøyer, 1838

Conlan, Kathleen E., 2021, New genera for species of Jassa Leach (Crustacea: Amphipoda) and their relationship to a revised Ischyrocerini, Zootaxa 4921 (1), pp. 1-72 : 57-58

Tribe Ischyrocerini Krøyer, 1838

Supplementary Table S2

Type genus. Ischyrocerus Krøyer, 1838

Diagnosis (with changes from Just (2017) in bold).

Antennae: slender, antenna 1 with accessory flagellum (occasionally vestigial).

Mandible: palp with 3 articles, the third expanded distally (occasionally similar in shape to the second).

Coxae 1–4: progressively deepening, subrectangular to oval (occasionally coxa 1 much smaller than and mostly obscured by coxa 2 and differing in shape), margins entire.

Gnathopod 1: carpus shorter than the propodus (occasionally longer), propodus oval to weakly subchelate.

Gnathopod 2: propodus in adult male (and occasionally in the female) moderately to strongly enlarged compared to gnathopod 1, of varying shape (occasionally hardly modified).

Pereopods 3–4: merus moderately to fully overlapping the carpus anteriorly, dactyl shorter than the carpus (occasionally longer).

Pereopods 5–7: of similar form, increasing in length backwards (occasionally 6 larger than 5 and 7).

Urosomites: 1–3 free.

Uropods 1 and 2: peduncle without distoventral corona of spines, with 2 subequal rami with or without an underlying peduncular spinous process (occasionally uropod 2 outer ramus modified).

Uropod 3: peduncle long (occasionally short), broad proximally, narrow distally, biramous (occasionally uniramous), outer ramus terminating in cusps and/or spine(s).

Telson: entire, with one to many dorsally or apically projecting setae or spines.

Component genera. Jassa Leach, 1814 ; Ischyrocerus Krøyer, 1838 ; Paradryope Stebbing, 1888 ; Microjassa Stebbing, 1899 ; Parajassa Stebbing, 1899 ; Hemijassa Walker, 1907 ; Isaeopsis K.H. Barnard, 1916 ; Pseudischyrocerus Schellenberg, 1931 ; Bathyphotis Stephensen, 1944 ; Ventojassa J.L. Barnard, 1970 ; Neoischyrocerus Conlan, 1995 ; Scutischyrocerus Myers, 1995 ; Ruffojassa Vader & Myers, 1996 ; Veronajassa Vader & Myers, 1996 ; Alatajassa Conlan, 2007 ; Myersius Souza-Filho & Serejo, 2014 ; Pleojassa n. gen.; Plumulojassa n. gen.

Changes to Ischyrocerus and Neoischyrocerus

Ischyrocerus is primarily a cold water, Northern Hemisphere genus, captured from deep trawls ( Stephensen 1944; Gurjanova 1951) as far north as the high Arctic, but also found in the intertidal and shallow subtidal zone (J.L. Barnard 1962). It has been extensively found in the Southern Hemisphere as well, though mostly in warmer waters ( Myers 1995, 1997; Just 2009). This large genus requires revision and may prove to be less cosmopolitan than previously thought by J.L. Barnard & Karaman (1991).

Three genera have been created for warm water Ischyrocerus -like species: Neoischyrocerus Conlan, 1995 (4 species), Coxischyrocerus Just, 2009 (2 species) and Tropischyrocerus Just, 2009 (2 species). These genera embrace species in which the male develops an enormously lengthened and pendulous gnathopod 2 (about 200–300% the length of gnathopod 1) with an anteriorly rounded ischium and a very long propodus with the palm nearly the full length of the propodus, and the proximal end of the palm marked by a bulge next to the carpus (the S. Californian N. claustris (J.L. Barnard, 1969) , N. chinipa (J.L. Barnard, 1979) from the Galapagos and Pacific Panama, N. vidali Ortiz & Lalana, 2002 from the Cuban Caribbean, C. inexpectatus ( Ruffo, 1959) from the Mediterranean Sea and T. socia ( Myers, 1989) from Bora Bora), a tooth-like projection (e.g., N. lilipuna (J.L. Barnard, 1970) from Hawaii and T. pugilus Just, 2009 from Australia), or with neither (e.g., C. rhombocoxus Just, 2009 from Australia). The dactyl may be the full length of the propodus or shorter, the length growth related. By comparison, the female’s gnathopods are similarly sized with the second only slightly larger than the first. Other commonalities are antennae with long filtering setae that are not pediform or sexually dimorphic, a 2-articulate accessory flagellum with the second article minute, pereopods 3 and 4 with little overlap of the merus over the carpus, a well developed peduncular spinous process under the rami of uropod 1, a spiny peduncle of uropod 3 with the outer ramus bearing a row of minute cusps and the inner ramus tipped by a small spine, and the telson with a pair of strong, dorsally projecting spines.

The difficulty with these genera is where species cross the generic boundaries. Examples are: enlarged coxa 2 relative to coxa 1 in the adult male ( C. rhombocoxus and N. claustris ), similar gnathopod propodus appearance as noted above, and similar female gnathopod palms (convex in all species in the three genera except for T. pugilus ), pereopod 3 and 4 propodus posteriorly spinose ( N. lilipuna , N. vidali , T. socia and C. inexpectatus ). The generic-level differences among the genera therefore recede into issues of sexual variation (e.g., enlargement of coxa 2 relative to coxa 1 that was used to define Coxischyrocerus but also occurs in Neoischyrocerus , or the modified pereopod 5 basis shape in adult males of C. rhombocoxus and C. inexpectatus ).

Therefore, Coxischyrocerus Just, 2009 and Tropischyrocerus Just, 2009 are herein merged into the senior genus Neoischyrocerus Conlan, 1995 . Myers (1995, 1997) noted the need for diminutive Indo-Pacific species placed at that time in Ischyrocerus or Jassa to be placed in their own genus and these are also included, as noted below.