Genus Allorchestes Dana, 1849
Dana, 1849: 136.
Stebbing, 1906: 581.
“Distinguished from Hyale by gnathopod 2 in male which has the 5th segment produced behind between the 4th and 6th segments, and from Hyalella by having the telson more or less divided; sometimes the palp of maxilla 1 agrees with that of Hyale, sometimes with that of Hyalella,”
The main diagnostic character of this genus is the process of the 5th segment in the male 2nd gnathopod. The females of the two genera, Hyale and Allorchestes, to quote Barnard (1940), appear to be “indistinguishable”. Although this diagnostic characteristic is unmistakeable in the adult males of Allorchestes the generic distinction is slurred over by the development of a similar process in the juveniles of Hyale, a process which does not always entirely disappear in the adult males of Hyale. The feature is sufficiently troublesome for Reid (1951) to raise the question of “what difference, if any, exists between Hyale and Allorchestes… careful examination of specimens of the latter genus (Hyale) often reveals such a lobe of greater or smaller size.… In the present specimens (Hyale perieri) it is quite large, though it may still be masked by segment 4 as it lies in the cup-like depression of that segment.” Earlier, in drawing attention to this fact, Reid (1947) quoted Mr. Clarence R. Shoemaker of the United States National Museum as suggesting “that the size of this extension in Hyale may be associated with the age of the individual—being large in young males but becoming progressively reduced as maturity is approached,” and Reid adds that breeding experiments are necessary to settle this point.
This view, that extension is associated with age, is substantially that put forward by Chilton (1926) and is one with which I agree, it being well exemplified in Hyale grandicornis. Yet this does not settle the question of whether the genera should remain separate. This is a case in which the status quo is not unworkable, and the adults of each species seem easily ascribed to one genus or the other, unlike the state in Orchestia and Parorchestia where separation was not dependent on maturity. Until further evidence to the contrary is available, I believe that there is more to be gained by retaining the smaller genera, and I must admit to a conviction that both are valid genera. Admittedly, they may sometimes raise difficulties, but it is soon obvious from a few adult males which genus is concerned.
Two species of Allorchestes are recorded from New Zealand and the Subantarctic Islands.
Allorchestes compressus Dana, 1852.
A. compressa & A. australis Dana, 1852: 205–206.
A. australis & A gaimardii? Dana, 1853–55; 892, Pl. 60, Fig. a–o.
Allorchestes compressus Stebbing, 1906: 581–582.
Stephenson, 1927: 351.
Allorchestes (compressus Dana?) Stephensen, 1938: 261.
Stephensen records this species from Perseverance Harbour, Campbell Island (1938); and from Port Ross, Auckland Islands (1927), the latter with the information that the species is “new to the subantarctic islands of New Zealand.”
I have no specimens and there are none in the Chilton Collection from either New Zealand or the Subantarctic. The species may be distinguished from A. novizealandiae in that the finger of the male first gnathopod matches the palm and does not overlap it.
Allorchestes novizealandiae Dana, 1852. (Figs. 147–169).
Allorchestes novizealandiae Dana, 1852: 207 (female).
Allorchestes intrepida Dana, 1852: 207 (male).
Allorchestes novizealandiae Dana, 1853–55: 894, Pl. 61, Fig. la-v.
Bate, 1862: 37, Pl. 6, Fig. 3.
Stebbing, 1906: 581.
Chilton, 1926: 517–518.
Stephensen, 1938: 261.
Allorchestes neozelanica Thomson & Chilton, 1886: 144.
Hyale prevostii (partim) Della Vale, 1893: 519.
Hyale chiltoni Thomson, 1899: 206.
Differs from Hyale grandicornis f. novaezealandiae by the generic characteristics and as below.
Text-fig. 9.—Allorchestes novizealandiae Dana. 147—Antenna 1, ♂. 148—Antenna 2, ♂. 149—Maxilla 1. 150—Maxilliped. 151—Gnathopod 1, ♂. 152—Gnathopod 1, ♂, palm and dactylos. 153—Gnathopod 1, ♀. 154—Gnathopod 1, ♀, palm and dactylos 155—Gnathopod 1, ♀, sideplate ventral margin 156—Gnathopod 2, ♂. 157—Gnathopod 2, ♀. 158—Peraeopod 1. 159—Peraeopod 2. 160—Peraeopod 3.161—Peraeopod 3, basos posterior margin 162—Peraeopod 4. 163—Peraeopod 5. 164—Coupling setae from broodplate margins. 165—Epimeral plates 1—3. 166—Uropod 1. 167—Uropod 2. 168—Uropod 3. 169—Telson.
Male: Length, 14 mm; depth, 4 mm; width, 4 mm. Female: Length, 12 mm; depth, 3 ½ mm; width, 3 ½ mm.
Antennae. First: Reaches ⅓ along flagellum of antenna 2; flagellum of more than 14 segments, groups of small setae on distal angles; segments subtriangular in cross-section. Peduncle segments have a few small setae on end margins, 1st as long as 2nd plus 3rd. Second: Flagellum of 16–18 or more segments, 4 equidistant groups of small setae on end margins. Peduncle, 3rd segment ½ length 4th, 4th about ¾ length of 5th, all distally setose, 2 or so small stout spines on superior margin, of 3rd and 4th; 4th has tuft of small setae medially on inferior margin, 5th has 3 tufts on inferior margin, a few on surface, about 5 small spines on superior margin.
Mouthparts. First Maxillae: Inner plate reaches base of palp on outer, end seta reaches past base of innermost tooth; palm minute, dome-shaped, has small end seta. Mandibles: Spine row of 3 spines, lacks tuft of setae above molar process and scabrous spine below. Maxilliped: Inner plate subrectangular, reaches merus extremity, has about 4 small scabrous spines on curved outer angle, a few on surface between and below distal teeth, about 5 long plumose setae down cleft to ischium. Outer plate subovate, has small spines on end and inner margins, down almost to ischium level; about 3 long fine spines on outer margin and ischium level. Basos, ischium and merus have single or paired spines on outer distal angle; basos angle sharp, even produced distally a little. Merus cup-shaped, distal margin concave, inner margin ⅓ length of outer, single long spine on inner distal angle. Carpus large, outer margin ½ length inner, ⅔ merus outer margin, pair of spines medially and on end; inner margin produced as broad flange, rounded distal angle extends nearly ½ along propod, margin mostly fringed with numerous fine spines, row of 4 or more long spines near propod inner base. Propod outer margin as long as merus, inner slightly shorter, wider distally than at base, distal angles fringed with long fine spines, fringe at most extends ½ down inner margin, 6 or so long fine-combed spines across dactylos base. Dactylos nearly propod length, has fine combs of minute setae on surface; end nail nearly ½ dactylos length, has minutely-combed inner margin, 1 to 3 spines at nail base.
Gnathopods. First: Sideplate subrectangular, anterior margin a little concave, chain of cell-like cavities along ventral. These are also present in other sideplates; nerves are visible running inwards from the minute spines; posterior margin not noticeably excavate, triangular process absent. Basos has 4 or so very long setae on convex posterior margin; group of setae on posterodistal angle, length more than twice width. Ischium subrectangular, width ½ length, length ½ basos, long setae on posterodistal angle. Merus as large, has long setae on broadly rounded posterodistal angle. Carpus width ⅔ length, length ¾ basos, has 1 or 2 long setae on anterior margin, group on anterodistal angle; posterior free margin produced between propod and merus as inverted cup-like process with marginal fringe of setae. Propod subrectangular, width ½ length, as long as carpus, has about 4 pairs of fine setae on straight posterior margin, posterodistal angle produced distally in blunt lobe so small palm is proximally excavate; angle has stout spine which is one of semicircular row of 4 across lobe; lobe has several short and long setae. Long dactylos projects greatly beyond posterior margin; surface is minutely scaled; propod anterodistal angle has tuft of setae. Female: Sideplate subrectangular width ½ depth. Numerous very long fine setae above basos insertion and proximally on basos posterior margin; basos anterior margin minutely spined, width ⅓ length. Ischium, merus and carpus as in male but more slender. Propod similar, but palm simple, slightly convex and transverse, defined by single spine on posterodistal angle; palm has marginal setae, is slightly shorter than dactylos. Second: Sideplate subrectangular, deeper than wide, barely excavate posteriorly. Basos constricted proximally, width ⅓ length, posterior margin has several very long setae, setae on distal angle. Merus ½ basos length, ischium slightly smaller, both subrectangular, posterodistal
angles setose, anterior ischium margin has noticeable medial spur, merus postero distal angle rounded, distal margin concave. Carpus subequal, spoon-like process fringed with setae extending from posterodistal angle between merus and propod and overlying ½ of propod posterior margin. Propod subovate, as long as basos, greatest width ⅔ length, palm barely convex, as long as posterior free margin which has about 3 marginal pairs of small setae; palm has small spines each side, is defined by small pocket for dactylos tip and 2 stout seta-tipped spines. Dactylos inner margin has fine setae, surface has minute spines. Female: Carpus posterior margin produced in great pouch-like process fringed with marginal setae and extending ⅔ along propod. Propod as in Gn. 1, female, but proportionately shorter and broader. Otherwise as in Gn. 2, male.
Peraeopods. First: Sideplate subrectangular, wider than deep, barely excavate posteriorly. Basos proximally constricted, width not ⅓ length, posterior margin and distal angle have several very long setae. Ischium ¼ basos length, posterodistal angle setose. Merus posterior margin has single seta ⅔ along, small setae on distal angles; length more than twice width, nearly ⅔ basos; anterodistal angle produced downwards a little. Carpus narrower, ¾ merus length, several small setae on straight posterior margin. Propod ⅔ basos length, posterior margin has 5 single spines each with 1 or 2 setae. Dactylos has fine seta on inner margin near tip, margin is faintly pectinate. Second: Sideplate strongly excavate posteriorly so L-shaped, as wide as deep; otherwise like Pr. 1 Third: Sideplate anterior lobe subtriangular, posterior subovate. Gills simple. Basos greatly expanded, a few stout single spines on more or less straight anterior margin, greatly convex posterior margin is minutely spined and crenulate; chain of cell-like cavities along border as in sideplates of previous appendages, chains continuous distally, are proximally fragmented into groups of cells around spines. From the base of each spine a nerve runs in towards the centre of basos which is nearly as wide as long, expands posteriorly past ischium. Ischium not ⅓ basos length, has 2 pairs of stout spines anteriorly. Merus piriform, nearly ½ basos length, distally as wide as anterior margin is long, posterior margin widens distally, anterior margin has 3 groups of stout spines, serrate posterior margin has 4 single stout spines, stout spines on distal angles. Carpus ⅔ merus length, similar in shape, has 2 groups of spines anteriorly, posterior margin lacks spines. Propod ⅔ basos length, width ⅓ length, posterodistal angle setose, anterior margin has about 4 pairs of short stout spines. Dactylos ½ propod length, otherwise as in Pr. 1. Fourth: Basos slightly longer than wide, anterior margin has short stout spines, posterior margin is minutely spined and crenulate, as in Pr. 3. Segments proportionately longer and narrower than in Pr. 3, otherwise similar. Fifth: Basos widest about ⅔ along posterior margin, as wide as anterior margin is long, anterior margin has short stout spines, posterior extends ½ down merus, minutely serrate, proximal ⅔ spined, remaining portion crenulate and minutely spined, has cell-chain, otherwise as in Pr. 3.
Epimeral Plates. First: Subovate. Second: Subrectangular but concave anterior margin rounding to convex ventral margin, posterodistal angle sharp. Third: Posterodistal angle sharp, 1 or 2 minute setae on posterior margin.
Pleopods. One ramus is usually longer than the other, but there appears to be no consistency as to which one. Coupling spines anchor-shaped; peduncle has numerous long fine setae proximally.
Broodplates. Have marginal setae modified into hooks like those described by Reid for A. furcata (1951). These hooks also occur in Hyale grandicornis, but in the latter they are much closer to those figured by Reid, shorter than in A. novizealandiae, and much more definitely narrowed before the end hook.
Uropods. First: Inner ramus has 2 or 3 dorsal spines, outer lacks dorsal spines, each has 4 or 5 end spines; peduncle has 4 spines dorsally on outer margin, one on inner distal angle. Second: Inner ramus as long as peduncle, longer than outer, has 2 dorsal spines, 4 end ones; outer lacks dorsal spines, has 4 end spines. Third:
Peduncle longer than lanceolate ramus, has 2 spines distally; short spine and 2 setae on end of ramus. Telson: Subsquare, cleft, medially ½ length, distal margin forms slightly upturned rim.
Localities. Brighton, Otago, coll. Jan. 1890; Timaru, coll. E. W. Bennett, 1922; Lyall Bay, Wellington; Akaroa; West Coast, North Island; Waipapa Point; Dunedin; Lyttelton; Cape Maria van Diemen; Chatham Islands.
Hypotypes. Slides A.1-A.5, Tray 62, male, Chilton Collection (Brighton); Slides C.31, male, and C.32, female (Timaru).
Discussion. Allorchestes novizealandiae is easily recognised by the shape of the first and second gnathopods of the male, particularly the first in which the dactylos is greatly longer than the palm. This is possibly the characteristic to which Chilton (1926) refers when he says there is a reliable characteristic by which the adult males can be distinguished from the young males of Hyale grandicornis which have a similar carpal process. Other marks of this species are the hook-like setae on the borders of the broodplates, like those figured by Reid (1951) for A. furcata; and the chain of cell-like cavities like those which he figures for A. ornata. In A. novizealandiae these cavities also occur on the posterior margins of the basos of Pr. 3–5.
There has been some difficulty in the past in separating A. novizealandiae from Hyale grandicornis, but there are numerous differences between the two species, and it should be possible to distinguish young or adult A. novizealandiae from young H. grandicornis males using the following differences.
|Hyale grandicornis juvenile||Allorchestes novizealandiae|
|Gnathopod 1||Fringe of several spines midway along posterior margin of propod||A few very fine setae along propod posterior margin|
|Palm straight, horizontal||Palm in form of large tooth|
|Dactylos as long as palm||Dactylos overlaps palm by nearly ½ its length|
|Sideplate subovate, posteriorly excavate, with spur-like triangular process||Sideplate distinctly subrectangular, without posterior excavation, no traingular process|
|Peraeopods 1, 2||Sideplate subovate, not markedly deeper than wide||Sideplate rectangular, second L-shaped, and deeply excavate, 1st much deeper than wide.|
|Peraeopods 3, 4, 5||No sign of cell-like cavities.||Cell-like cavities very noticeable.|
|Uropod 3||Ramus cylindrical, with 2 or more end spines||Ramus lanceolate, 1 spine and 2 setae on end.|
|Telson||Cleft to base, lobes subtriangular||Only ½ cleft to base, lobes subsquare.|
The telson shape is perhaps the most spectacular of these differences, but all of them, as well as the carpal process of the male second gnathopod, appear to be of very real value in distinguishing the two species, and they are easily picked up in examination.