Ringanui, Fenwick, Graham D., 2006

Fenwick, Graham D., 2006, Ringanui, a new genus of stygobitic amphipod from New Zealand (Amphipoda: Gammaridea: Paraleptamphopidae), Zootaxa 1148, pp. 1-25 : 3-5

Ringanui n. gen.

Calliope .— Chilton, 1882b: 177 –179, pl. 9, figs 1–10 (part, male only). Calliopius .— Chilton, 1884: 89; Chilton, 1894: 234 –244, pl. 22 figs 1–16, pl. 23, figs 1–9 (part, male only).

Paraleptamphopus .— Chilton, 1924: 273; Bousfield, 1982: 272–273; Barnard & Barnard, 1983: 50, 52, 164–165, 712–713 (part, male only).

Type species: Ringanui koonuiroa n. sp., here designated.

Species composition: Ringanui koonuiroa n. sp.; Ringanui toonuiiti n. sp.

Diagnosis

Antenna 1 peduncle article 2 or articles 2–3 and primary flagellum calceolate in both sexes; accessory flagellum 1­articulate, less than length of primary flagellum article 1. Antenna 2 flagellum calceolate in both sexes. Lower lip well developed, inner lobes poorly developed. Mandible palp with E2, B3, E3 setae, molar triturative. Maxilla 1 inner plate medial margin with 4–5 plumose SS. Maxilliped inner plate quadrate mediodistally, not exceeding midpoint of palp article 2. Gills present on pereonites 2–6 or 7. Oostegites large, fleshy, with 3–5 few short SS on distal margin. Coxae 1–4 about as deep as wide, coxa 1 widened distally into rounded antero­distal lobe; coxa 4 postero–proximally excavate; coxa 5 anterior and posterior lobes developed subequally; coxa 6 anterior lobe reduced; coxa 7 anterior lobe absent. Gnathopod 1 very large; articles 3–4 short, subequal in length; article 5 short, <0.3 x length of article 6; article 6 very large, palm angle <45°, palm>0.5 x article length, defined by one or more large RS; dactyl large, curved. Gnathopod 2 moderately large, subdominant and different structure to gnathopod 1; article 3 c. 0.3 x length of article 2, subequal in length to article 4; article 5 triangular,>0.5 x as long as article 6, posterior margin forming a broadly rounded, setose lobe; article 6 ovate, palm 45°, defined by RS. Pereopods 5–7 article 2 expanded postero­proximally, tapered distally, with postero­distal lobes variously developed; dactyls with 3–5 setules along posterior margins. Epimera 1–3 ventral margins naked. Pleopods 1–3 well developed, biramous; peduncles stout, lacking setae other than coupling hooks; rami well developed, 7–15 articulate, strongly setose; outer ramus shorter than or equal to inner. Uropods 1–2 peduncles longer than rami, spinose; rami spinose, with apical RS; outer ramus slightly to conspicuously shorter than inner; uropod 2 not extending posteriorly as far as uropods 1 or 3, just exceeding uropod 3 peduncle. Uropod 3 peduncle stout, shorter than or equal to rami in length; rami conical in shape, margins spinose, RS paired or paired with 1 large plumose SS, apices bereft of RS, with 0–2 subterminal setules. Telson thin, laminar (lateral aspect), subrectangular to tapering, distally slightly to conspicuously emarginate, lacking RS.

Etymology

The name Ringanui is derived from the Maori words ringa (hand) and nui (big) in reference to the very large gnathopod 1 characteristic of this genus.

Remarks

The genus Paraleptamphopus has caused severe confusion among taxonomists. This confusion arose because Chilton (1882b) presumed that his female P. subterraneus was conspecific with those he regarded as males, because they co­occurred in some wells and differed in few characters: his presumed male was larger, rarer, possessed calceoli (“sensory capsules”) on both antennae, and both gnathopods were larger and different in morphology to those of his presumed female. By the time he wrote his 1894 re­description of the species, Chilton appeared to be having some difficulties with his understanding of the species, noting that the male appeared to differ very markedly from the female. He admitted (1894: 236) that he had “seen only about half a dozen males altogether, while I must have seen hundreds of specimens of the female”. He was puzzled by the absence of any specimens intermediate in form between the female and presumed male, although he described a few characteristics of one. Chilton concluded from this second set of studies that “there is very great dissimilarity between the two sexes, chiefly in the gnathopoda, both of these in the male differing considerably from those in the female”, whereas this was not the norm in other amphipods. He also noted that the observed differences in mouthpart characters between his sexes were as great as those often used to distinguish genera. A more explicit element of doubt was expressed in his thoughts on coxal gills where he noted (1894: 240) “two plates attached to the coxa, both in the second gnathopod and in the first and second peraeopoda, in the male specimen dissected, I have not found them in the female specimens, and am not sure that the second plate is a gill­plate”, before stating “It differs in appearance from the true gill­plate, and might be considered a broodplate, but it bears no setae on the margin, and I am practically certain that the specimen is a male”.

Comparison of the “males” illustrated in Chilton’s 1882b and 1894 papers show several significant differences in their gnathopods. Gnathopod 1 differs most conspicuously in the size of robust seta defining the palm. The length of the large spine in the 1882 “male” equals the width of article 6, whereas the largest spine in the 1894 “male” was <0.3 x the width of article 6. The shapes of article 6 differ appreciably between specimens. Similar differences are apparent in comparing second gnathopods. Articles 5–6 were stouter in the 1882 “male” compared with the 1894 “male” and these articles also differed considerably in shape.

By 1894, available evidence indicated that up to three taxa may be confused with P.subterraneus , although Chilton continued adhering to his single species thesis. Stebbing (1899) was not convinced that the species was monospecific: in erecting the genus Paraleptamphopus , he stated (p. 210): “In this genus I place Calliope subterranea, Chilton , and Pherusa caerulea, G.M. Thomson ; but the form which Dr. Chilton regards as the adult male of his Calliopius subterraneus I leave at present unclassified”. It is notable that Stebbing (1899) was unequivocal in designating Paraleptamphopus subterraneus (Chilton, 1882) as the type species, but his preceding comment also makes it clear that the type species is Chilton’s (1882b) female, not the male. The genus Ringanui , therefore, is erected to accommodate Chilton’s 1882b and 1894 males.