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Discussion
Only one specimen of this species has so far been found, a female from “a small pool near the top of Mount Auglem, 2800 feet above sea-level, Stewart Island, N.Z. (J. Crosby Smith)”. This specimen, with one or two of the appendages dissected off, is mounted in Chilton's slide collection. I had hoped to expand his description further and to make further comparisons with the other two species of Phreatogammarus, but short of remounting the specimen, a course I am loath to take, this does not seem possible I have been able to make one or two additions to the description, but there are other features which Chilton figured and I am unable to—e.g, the third uropods. The only one visible on the slide is rather hopelessly mixed up with the peraeopods.
It is not possible to make out with any certainty the absence or presence of eyes. One of the broodplates is quite obvious, making it fairly certain this is a female.
Phreatogammarus helmsii Chilton, 1918 (Figs 42–65.)
Phreatogammarus propinquus Chilton. 1909a 56 (in part).
Phreatogammarus helmsii Chilton. 1918: 85–86, fig. 5–10.
Length (Q. Charlotte specimen) 4 ½ mm; depth, 1 mm.; width, 1 mm. Eyes black, small, reniform.
Antennae. First Length, 2 mm. Like P. fragilis but proportions slightly different, shorter; flagellum of about 24 segments; accessory of 2. Peduncle, 3rd segment slender, ½ length 2nd; ⅓ length 1st; width of 1st about ⅖ length. Second: Length 1 ¼ mm. Flagellum of 13 segments, like P. fragilis but peduncle less strongly bristled; 2nd segment has prominent gland-cone; 3rd slightly wider than long, less than ⅓ length 4th; 4th barely shorter than 5th.
Mouthparts Not greatly differing from P. fragilis. Mandibles: Spine row of about 5 (left) and 3 (right) scabrous spines Palp, 1st segment short; 2nd, length 3 times width, long setae on distal ½ of inner margin and on end; 3rd, convex margins taper bluntly, width less than ½ length, length ¾ 2nd segment, short setae on distal ⅔ of inner margin, 2 or 3 very long setae on end, 2 or 3 on surface, inner surface strongly bristled. Maxilliped (Female specimen, Kenepuru): Basos, 2 or 3 long setae on inner surface proximally, 2 on outer distal
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angle; series of long setae on inner portion of distal margin. Ischium has single seta just below merus inner proximal angle, outer margin very short. Inner plate subrectangular, outer distal angle rounded, distal margin wide; outer margin slightly convex, reaching ⅓ along carpus; 3 stout teeth on inner ½ of end margin, fine plumose setae on margin, beside and below teeth also; about 6 longer plumose setae on cleft margin; outer very finely bristled. Outer plate reaching end of carpus, convex outer margin has 4 or 5 long plumose setae distally; inner margin nearly straight, about 10 stout blunt teeth in row down margin to just below end of inner plate; a double row of short setae inside teeth and extending slightly further down plate Merus inner margin ½ length outer, width ¾ greatest length. Carpus greatest length twice merus, width ⅖ length, margins parallel, outer has pair of setae medially, 3 or 4 long setae on distal angle; inner and end margins fringed with usually-paired setae most of length, 2 or 3 ranks of setae on inner margin. Propod ⅔ carpus length; slightly narrower, margins slightly convex; distal ⅔ of inner setose, end margin on one surface and distal ⅓ of outer margin have long setae. Stout curved dactylos has a strong nail, 1 or 2 setae on outer margin, length ½ propod.
Gnathopods. First: Sideplate subrectangular, angles rounded, width ½ length, setae on ventral and anterodistal margins, 2 long spines on posterior near distal angle (margin in these specimens inversely crenulate). Basos widening slightly distally, width ⅓ length; anterior margin has short single setae, posterior has long setae medially, short strong setae distally, tuft of long setae on distal angle. Ischium ⅓ basos length, posterodistal angle setose. Merus ⅓ basos length, ovate, 2 or 3 setae on anterior margin, long setae on distal ½ of posterior, greatest width ⅗ length. Carpus subtriangular, anterior margin ½ basos length, distal width 2/3 length, a few ranks of 2 or 3 setae on surface, anterior margin has 3 groups of setae, posterior strongly indented twice for tufts of long setae; distal angle strongly setose; end margin has median rank of about 6 plumose setae, rank of smaller plumose setae posteriorly Propod somewhat ovate, widening slightly distally, greatest width more than ½ length; length ½ basos; anterior margin has 5 tufts of long setae, posterior has 2, several setae on surface; palm oblique (partly due to mounting) and slightly convex, has strong fringe of long setae, about 6 short spines on each surface of palm. Stout curved dactylos not reaching end of palm; inner margin has very oblique teeth; outer has single seta proximally, about 3 small setae across end surface. Second: Sideplate sub-rectangular, deeper than wide, angles broadly rounded, ventral margin and distal portions of lateral margins setose as in Gn. 1 (inversely crenulate in these specimens). Gills large, ovate; broodplates very large with long marginal setac. Basos, merus and ischium very like Gn. 1; basos width ⅓ length, ischium ⅓ basos length; merus width ½ length, length ⅓ basos Carpus width ⅔ length, length ½ basos, setae on distal margin not obviously plumose. Propod ovate, greatest width ½ length, length ¾ basos, setose as in Gn. 1, but palm much more oblique, defined only by single large spine at outer margin, as long as free posterior margin; stout dactylos almost reaching end of palm, inner margin very obliquely toothed.
Peraeopods First: Sideplate subrectangular, ventral margin convex, lateral margins parallel, deeper than wide, margin setose as above and (in these) inversely crenulate. Basos and ischium as in Gn. 2, basos has slender spines distally on margins. Merus ¾ basos length, width ⅓ length; 3 long spines and 1 or 2 short
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Text-fig. 4.—Phreatogammarus helmsii Chilton. 53—Maxilliped (lacking right palp). 54—Gnathopod 1, female 55—Gnathopod 2, female. 56—Peraeopod 3, female. 57—Peraeopod 4 basos. 58—Epimeral plate 1. 59—Epimeral plate 2. 60—Epimeral plate 3 61—Uropod 1. 62—Uropod 2. 63—Uropod 3. 64—Dorsum of urosome. 65—Telson.
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ones on anterior margin, 5 groups of 2 or 3 short spines on posterior. Carpus slender, width ⅓ length, length ⅖ basos; about 4 groups of 2 or 3 spines posteriorly, 2 or 3 fine setae on anterodistal angle. Propod as wide, ½ basos length, anterior margin has single seta medially, several on angle; posterior has about 6 short single spines. Stout dactylos ½ propod length, a short strong seta on inner margin, finer one on surface. Second: Sideplate basically subrectangular, angles rounded, posterior margin shallowly excavate, distal ½ of margin oblique, with setae; ventral margin and distal ½ of anterior also setose. Third, Fourth and Fifth: Sideplates difficult to discern but basically similar to P. fragilis. Basos ovate, narrowing distally, posterior margin proximally tending to expand in convex lobe; width between ½ and ⅓ length; anterior margin has 6 or 7 groups of 1 or 2 short spines, several fine setae proximally, about 10 or 12 small spines posteriorly. Third: (Kenepuru). Ischium ⅕ basos length, spined anterodistally Merus ⅔ basos, linear, width ⅓ length; margins spined. Carpus narrower, as long as merus, each margin has 3 or 4 groups of spines. Propod a little longer, very slender, margins spined. Stout dactylos more than ¼ propod length, seta on inner margin.
Epimeral Plates. First: Somewhat ovate, single spine anterodistally, ventrally rounded, deeper than wide, convex posterior margin has about 4 finer spines. Second: Subrectangular, almost as wide as deep, anterodistal angle rounded, 2 or 3 strong spines ventrally, 6 or 7 spines on more or less straight posterior margin. Third: Subrectangular, wider than deep, anterior margin slightly concave, anterodistal angle rounded, convex ventral margin has 4 or 5 strong spines anteriorly, posterior margin has 6 or 7 spines, more or less straight.
Pleopods. As in P. fragilis.
Uropods. First: Rami shorter than peduncle, 3 single spines on outer dorsal margin, 3 on inner, 2 at outer angle; rami with 5 or 6 end spines, 2 on each dorsal margin except outer margin of inner ramus which has 1. Second: Peduncle as long as rami; inner dorsal margin has 2 single short spines; outer distal angle has 2 spines together; inner ramus has 4 stout end spines, 1 on each dorsal margin, 6 on end. Third: Rami much longer than peduncle, dorsal and distal peduncle margins strongly spined. Rami each with end circlet of about 6 strong spines; margins have 2 to 5 groups of 1 to 3 strong spines, usually with a long seta, not obviously plumose; fewer spines on median than other margins. Telson: Ovate, tending to subsquare, cleft to base, about 4 spines on end margin of each lobe, a pair on surface.