Neoischyrocerus, Conlan, 2021

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 : 58-59

Genus Neoischyrocerus n. comb.

Supplementary Table S3

Type species. N. claustris J.L. Barnard, 1969

Diagnosis. (with differences from Ischyrocerus in bold). Body length at maturity 1–2 mm (usually), rarely 4–6 mm. Tropical and warm temperate distribution, collected from algae, sponges, corals or from a spiny lobster, 0–16 m, 9– 40°N and 5– 34°S.

Pereon: dorsally smooth (most species), ridged or carinate (some species).

Antenna 1: accessory flagellum 2 articles (second minute), projecting forward or flush with the flagellum; antennae 1 and 2 peduncles subequal in width or antenna 2, 10% wider (based on comparison of antenna 1 peduncle article 2 with antenna 2 peduncle article 4), peduncular setae and setal pattern similar to antenna 1, or slightly shorter, not plumose.

Gnathopod 2, adult male: 190–350% the length of gnathopod 1, basis and propodus especially elongate; coxa 1, 60–110% the depth of coxa 2; basis concave or sinuous; ischium anteriorly rounded; propodus often slender (posterior length 180–400% of central width), palm nearly the full length of the propodus, often with a bulge or tooth defining it proximally at the junction of the carpus (sometimes palm continuous with the carpus), sometimes centrally toothed instead and with shallow bulge or teeth at the junction of the dactyl; dactyl half or nearly the full length of the propodus.

Gnathopod 2, juvenile male: shorter than the adult male gnathopod 2, palm bearing 1–2 strong spines about midway along the length of the propodus, dactyl ending at the spines.

Gnathopod 2, female: only slightly larger than gnathopod 1, palm of the propodus convex (usually) or shallowly concave (rarely).

Pereopods 3 and 4: propodus, posterior margin bearing spines or setae; coxa 4, posterior margin straight, not shallowly concave.

Pereopod 5, male: similar to but shorter than pereopods 6 and 7 or variously modified with posteriorly concave basis or posteriorly expanded and spinose merus.

Uropod 1: peduncle with short ventrodistal spinous process underlying the rami, length ~15–35% of the outer ramus length.

Uropod 3: peduncle bearing 1–2 rows of spines dorsally, ending in a single spine at the distal margin, but without a corona of spines around the margin or setae; rami without spines mid-dorsally, outer ramus subequal to or shorter than the inner and bearing 3–8 minute dorsal cusps apically, without (rarely with) a small apical straight spine.

Component species (with transferred species in bold). Ischyrocerus longimanus ( Haswell, 1879) ( Australia) ; I. parvus Stout, 1913 (California) ; I. carinatus K.H. Barnard, 1916 ( South Africa); I. gorgoniae K.H. Barnard, 1940 ( South Africa); I. ctenophorus Schellenberg, 1953 ( South Africa); Coxischyrocerus inexpectatus ( Ruffo, 1959) (Mediterranean, Red Sea?); N. claustris J.L. Barnard, 1969 (California) ; N. lilipuna J.L. Barnard, 1970 (Hawaii) ; I. oahu J.L. Barnard, 1970 (Hawaii) ; I. oahu oahu J.L. Barnard, 1970 (Hawaii) ; N. chinipa J.L. Barnard, 1979 (Galapagos Islands and Panama); I. oahu armatus Ledoyer, 1979 ( Madagascar) ; Tropischyrocerus socia ( Myers, 1989) (Bora Bora) ; I. mediodens Myers, 1995 ( Papua New Guinea); I. parma Myers, 1995 ( Papua New Guinea); I. apiensis Myers, 1997 ( Samoa) ; N. vidali Ortiz & Lalana, 2002 ( Cuba) ; C. rhombocoxus Just, 2009 ( Australia) ; T. pugilus Just, 2009 ( Australia) .

Remarks. Species of Ischyrocerus were transferred to Neoischyrocerus if they demonstrated at least one key character (grossly enlarged and pendulous male gnathopod 2 similar in shape to that of others in the genus; dactyls with comb-like striae as noted in J.L. Barnard (1970), Conlan (1995) and Ortiz & Lalana (2002); similar spination on uropod 3). Presence or absence of these striae were not mentioned by other authors, therefore questioning as to whether this character had been looked for. Mouthpart characteristics were not widely described, but may be useful for generic definition, especially the clavate vs slenderer shape of the mandibular palp and the presence/absence of a long apical seta on the maxilla 1 inner plate.

Excluded but uncertain generic status. Ischyrocerus kapu J.L. Barnard, 1970 from Hawaii. The author based the generic assignment on a single male specimen. He noted its resemblance to N. lilipuna but also considered that it should be in a new genus. On balance, though, he assigned it to Ischyrocerus but noted that this was based on limited information because the specimen lacked antennae and pereopods and the female was also unknown. The male’s gnathopod 2 is unusual in having a long conical extension of the merus underneath the propodus, a feature that is not known for either Ischyrocerus or Neoischyrocerus . Myers (1995) stated that I. kapu is congeneric with other species being transferred to Neoischyrocerus . The male’s propodus is wider than in other members of Neoischyrocerus , but its uropod 3 resembles other species of Neoischyrocerus rather than Ischyrocerus . Further material demonstrating the species’ complete morphology is required before it can be confidently transferred to Neoischyrocerus or to a new genus.