Kimberleynitocrella billhumphreysi, Karanovic & Hancock, 2009

Karanovic, Tomislav & Hancock, Peter, 2009, On the diagnostic characters of the genus Stygonitocrella (Copepoda, Harpacticoida), with descriptions of seven new species from Australian subterranean waters 2324, Zootaxa 2324 (1), pp. 1-85 : 12-20

Kimberleynitocrella billhumphreysi sp. nov.

( Figs 1–4 )

Type material. Holotype, adult female dissected on two slides ( WAM C37326); paratypes: one adult female dissected on one slide ( WAM C37327) and two copepodids preserved in 70% ethanol ( WAM C37328); Australia, Western Australia, Kimberley region, Argyle Diamond Mine , bore MB13 , 10 October 2002, leg. W.F. Humphreys and R. Webb (sample BES: 9698), 16°43’18”S 128°24’02”E.

Other material examined. One adult female in 70% ethanol ( WAM C37329); Australia, Western Australia, Kimberley region, Argyle Diamond Mine , bore MB13 S, 10 October 2002, leg. W.F. Humphreys and R. Webb (sample BES: 9752), 16°43’18”S 128°24’03”E .

One adult male dissected on one slide ( WAM C37330); one adult male and one adult female preserved in 70% ethanol ( WAM C37331); Australia, Western Australia, Kimberley region, Argyle Diamond Mine , bore B13S, 10 October 2002, leg. W.F. Humphreys and R . Webb (sample BES: 10015), 16°43’18”S 128°24’01”E.

One adult female dissected on two slides ( WAM C37332); one adult female preserved in 70% ethanol ( WAM C37333); Australia, Western Australia, Kimberley region, Argyle Diamond Mine , bore MB29 S, 14 October 2002, leg. W.F. Humphreys and R . Webb (sample BES: 9759), 16°41’37”S 128°27’11”E.

One adult male dissected on one slide ( WAM C37334); one adult male preserved in alcohol ( WAM C37335) ; Australia, Western Australia, Ord River , bore WP10, pump 100–200, depth 27.35 m, 26 November 2004, leg. P. Hancock (sample ORIN37 ); 15°27’52”S 128°53’34”E .

Description. FEMALE (HOLOTYPE). Total body length, measured from tip of rostrum to posterior margin of caudal rami (excluding appendages and caudal setae), 0.895 mm. Preserved specimen colourless. Nauplius eye absent. Habitus ( Figs 1A–B ) cylindrical, slender, without distinct demarcation between prosome and urosome; prosome/urosome ratio 0.7; greatest width at posterior end of cephalothorax. Body length/width ratio about 5.3; cephalothorax 1.2 times as wide as genital double-somite. Free pedigerous somites without pronounced lateral or dorsal expansions. Integument weakly chitinized and without cuticular windows. Rostrum very small, membranous, ovoid, about as long as wide and not demarcated at base; ornamented with two dorsal sensilla.

Cephalothorax ( Fig. 1A ) incorporating first prosomite, trapezoidal in dorsal view, about as long as wide; represents about 19% of total body length. Surface of cephalic shield and tergites of first three free pedigerous somites ornamented with few small sensilla. Hyaline fringe of all prosomites narrow and smooth. Fifth pedigerous (first urosomal) somite ornamented posteriorly with two dorsal sensilla and two lateral sensilla (one on each side); hyaline fringe smooth both dorsally and laterally, weakly discernible ventrally. Sclerotized joint present ventrally, but not dorsally, between fifth pedigerous and genital double somites.

Genital double-somite ( Figs 1A–B , 2A ) as long as wide (ventral view), without visible suture but slightly constricted laterally at 2/5; ornamented with eight large dorsal sensilla (four at middle, four near posterior margin), four posterior ventral sensilla and one long and two short transverse rows of small spinules between medial ventral sensilla. Hyaline fringe completely smooth. Genital field with single large copulatory pore (at about 3/7 of double-somite’s length), weakly sclerotized wide copulatory duct and two small semicircular seminal receptacles. Single small genital aperture covered by fused reduced sixth legs, represents 36% of somite width. Third urosomite ornamented with six large sensilla near posterior margin (two dorsal and four ventral) and single posterior ventral row of minute spinules; hyaline fringe smooth. Preanal somite with smooth hyaline fringe; ornamented only with very short posterior ventral row of small spinules. Anal somite ( Figs 1A–B , 2A ) ornamented with pair of large dorsal sensilla and transverse row of small spinules along posterior margin, those on each corner near anal operculum somewhat longer. Anal operculum ( Fig. 3A ) convex, not reaching to posterior end of anal somite, represents 52% of somite's width; ornamented near its posterior margin with 56 minute spinules of significantly smaller size than spinules on posterior dorsal margin of anal somite. Anal sinus smooth and widely opened.

Caudal rami ( Figs 2A–2B , 3B–3C ) short, as long as greatest width (ventral view), conical, slightly divergent, with space between them more than one ramus width; armed with seven armature elements (three lateral, one dorsal and three apical). Ornamentation consists of two minute spinules at base of dorsal seta, two larger spinules at base of distal lateral seta and posterior row of six to eight spinules ventrally. Dorsal seta smooth, inserted near posterior margin and very close to inner margin, about twice as long as caudal ramus, triarticulate at base (i.e. inserted on two pseudojoints). Proximal lateral seta about 0.6 times as long as dorsal one, arising somewhat dorsolaterally at middle of ramus length. Distal lateral seta smooth, arising at 5/6 of ramus length, about as long as dorsal one. Inner apical seta small, smooth, about as long as ramus. Middle apical seta strongest, with breaking plane, ornamented with minute spinules along both margins from about first quarter to midlength, twice as long as outer apical seta and more than half as long as body. Outer apical seta with breaking plane, ornamented with several minute spinules only on outer margin.

Antennula ( Fig. 2C ) eight-segmented, unornamented, slender, approximately 1.4 times as long as cephalothorax. Strong aesthetasc on fourth segment fused basally with adjacent large seta and reaches beyond tip of appendage for less than half length of last segment; slender apical aesthetasc on eighth segment fused basally with two apical setae. Setal formula: 1.9.6.4.2.3.4.7. All setae smooth, without breaking plane and uniarticulate at base. Length ratio of antennular segments, from proximal to distal end and along caudal margin, 1: 1.5: 1.1: 1.3: 0.6: 0.8: 0.5: 1.1.

Antenna ( Fig. 1D ) composed of coxa, basis, two-segmented endopod and one-segmented exopod. Coxa very short, unarmed and unornamented. Basis about 1.7 times as long as wide, unarmed but ornamented with row of small spinules along anterior margin. First endopodal segment about 2.2 times as long as wide and 1.2 times as long as basis, unornamented and unarmed. Second endopodal segment longest, 1.6 times as long as first and 4.3 times as long as wide, armed medially at 3/4 with two unipinnate spines flanking thin seta; apical armature consisting of five geniculate setae, longest one fused basally to additional smaller seta bearing proximal tuft of fine setules; ornamentation consists of few spinules along anterior surface. Exopod onesegmented, half as long as basis and 2.2 times as long as wide, unornamented but armed with three pinnate setae; innermost apical seta bipinnate, nearly three times as long as other two subequal setae and twice as long as exopod; other two setae with apical tuft of closely packed setules.

Labrum ( Fig. 1E ) not very large compared with cephalothorax, trapezoidal, rigidly sclerotized, with relatively narrow and slightly convex cutting edge, ornamented with one apical row of small spinules in between two subapical rows of strong spinules (eight on each side). Two small round fields of gustatory papillae visible on dorsal (posterior) surface.

Paragnaths not observed in satisfactory position.

Mandibula ( Fig. 1F ) with narrow cutting edge on elongated coxa, armed with coarser teeth at ventral half, finer teeth at dorsal half and one dorsal unipinnate seta. One short row of spinules present on outer part of coxa. Palp uniramous, comprising basis and one-segmented endopod. Basis unarmed and unornamented, 1.5 times as long as wide. Endopod slender and unornamented, about 1.3 times as long as basis and 3.2 times as long as wide; armed with five slender smooth apical setae.

Maxillula ( Fig. 1G ) with large praecoxa; arthrite rectangular, not movable, ornamented with arched row of spinules ventrally and armed with two smooth setae on anterior surface, two setae on dorsal margin and four apical elements (probably three spines and one dorsal seta; dorsal seta ornamented with two long setules). Coxal endite armed apically with one pinnate, strong and recurved seta dorsally and two smooth slender setae ventrally, all of about same length. Basis somewhat shorter than coxal endite, armed with four apical smooth setae and one subapical smooth seta. Endopod absent.

Maxilla ( Fig. 1H ) with proximal syncoxal endite absent; distal endite well developed, highly mobile, armed with one curved and basally fused, bipinnate spine and two smooth subequal setae, which 1.4 times as long as spine. Basis drawn out into long and nearly straight claw, with shorter spiniform curved seta at its base; no cuticular pore or other ornamentation observed. Endopod represented by minute segment, armed with two smooth subequal, long apical setae.

Maxilliped ( Fig. 1I ) with well developed syncoxa, 1.8 times as long as wide, unornamented and armed with single smooth seta subapically. Basis 2.5 times as long as wide and almost 1.2 times as long as syncoxa, unarmed but ornamented distolaterally with short transverse row of small spinules. Endopod represented by long and slightly curved claw, ornamented distally with row of spinules along concave side; with thin seta at base.

All swimming legs with three-segmented exopod; endopod of first leg three-segmented ( Fig. 3D ), endopod of second and third swimming legs two-segmented ( Figs 2D , 3E ), while endopod of fourth swimming leg reduced to small knob ( Fig. 3F ). Armature formula of swimming legs as follows (for preultimate segments—inner/outer elements; for ultimate segments—inner/terminal/outer elements): Exopod Endopod

Segments 1 2 3 1 2 3

First leg 0/1 1/1 0/2/3 1/0 0/0 1/1/1

Second leg 0/1 1/1 1/2/2 0/0 (2)/1/1 -

Third leg 0/1 1/1 1/2/2 0/0 1/1/1 -

Fourth leg 0/1 1/1 2/2/2 - - -

Intercoxal sclerite of all swimming legs with concave distal margin and without surface ornamentation. Praecoxae of all legs very short and unornamented. Coxa of first swimming leg ornamented with several long spinules on inner distal margin, that of other legs unornamented; all coxae unarmed. Basis of first leg ornamented posteriorly with arched row of spinules along anterior surface of endopod base; second leg with row of spinules near outer margin; third and fourth legs with spinules only along outer margin; each leg armed with slender smooth seta on outer margin (longest one on third leg); first leg with short stout spine on inner distal corner. All exopodal and endopodal segments ornamented with strong spinules along outer margin; some segments also with spinules along inner and distal margins. All exopodal segments of about same length. First endopodal segment of first swimming leg ( Fig. 3D ) large, about 2.8 times as long as wide and almost reaching to midlength of third exopodal segment; endopod longer than exopod, reaching beyond distal margin of exopod for length of last endopodal segment. Endopod of second swimming leg ( Fig. 2D ) reaching to midlength of second exopodal segment; its second segment twice as long as first. Endopod of third leg ( Fig. 3E ) as long as first exopodal segment; its second segment twice as long as first. Endopod of fourth swimming leg ( Fig. 3F ) reduced to tiny knob, without armature or ornamentation. All setae on each ramus (except minute inner seta on third endopodal segment of first leg) strong and many also spiniform.

Fifth leg ( Figs 1B & J–K ) represented only by two unornamented but armed lateral knobs on surface of somite. Inner knob, representing exopod, armed with four smooth slender setae; outermost seta strongest and longer than other three. Outer knob represents outer part of basis and armed with long unipinnate seta; this seta much longer than any seta on inner knob. Endopodal lobe absent.

Sixth legs ( Fig. 2A ) completely fused together, indistinct, forming simple operculum covering single gonopore, without ornamentation or armature.

MALE (WAM C37330). Body length, excluding caudal setae, 0.738 mm. Habitus, ornamentation of prosomites, rostrum, colour and nauplius eye similar to female. Hyaline fringe of all prosomites smooth; no cuticular windows observed.

Genital somite more than twice as wide as long, with single small, longitudinally placed spermatophore visible inside ( Fig. 4A ). Urosomite ornamentation similar to female, although preanal somite without spinules and second, third and fourth urosomites with additional lateral sensilla.

Anal somite and caudal rami ( Fig. 4A ) proportions, armature and ornamentation very similar to female, just dorsal sensilla significantly longer.

Antennula ( Fig. 4B ) long and slender, ten-segmented, not strongly geniculate, with geniculation between seventh and eighth segments; ornamented with arched row of spinules only on first segment anteroproximally. Aesthetasc on apical acrothek of fifth segment very long and broad (homologous to aesthetasc on fourth segment in female); smaller aesthetasc on tenth segment fused basally to two apical setae. First two and last two segments similar to female. Setal formula: 1.9.7.1.8.1.2.1.4.7. Most setae smooth and slender; two setae on fifth segment and one on sixth very short, strong and unipinnate; proximal seta on seventh segment unipinnate, strong and relatively long. Just two setae on ninth segment and three lateral setae on tenth segment biarticulating on basal part; all other setae uniarticulate; all setae without breaking plane.

Antenna, labrum, mandibula, maxillula, maxilla, maxilliped and second ( Fig. 4D ) and fourth swimming legs ( Fig. 4F ) similar to female.

First swimming leg ( Fig. 4C ) with inner spine on basis significantly modified, smooth and inflated distally.

Third swimming leg ( Fig. 4E ) with inner distal seta on second endopodal segment plumose and slender, not spiniform and bipinnate as in female; other details similar to female.

Fifth leg ( Figs 4G–H ) remarkably similar to female, except outer basal seta smooth and outer exopodal seta somewhat stronger.

Sixth legs ( Fig. 4A ) fused together medially, indistinct from somite and each armed with single small smooth seta, about as long as smaller exopodal setae on fifth leg.

Variability. Body length of females ranges from 0.815 mm to 0.895 mm (0.849 mm average; n = 6), while in males it ranges from 0.738 mm to 0.754 mm (0.742 mm average; n = 4). The holotype female has an asymmetrical endopod of the second swimming leg ( Fig. 2D ), with one or two inner spiniform setae on the second segment. All other specimens have two inner spiniform setae on the second endopodal segment of the second swimming leg ( Figs 3G , 4D ). Second endopodal segment of the third swimming leg in both males and females can be with ( Figs 3H , 4E ) or without ( Fig. 3E ) an inner spiniform seta. Small differences in ornamentation of the swimming legs were also observed, as well as in the proportions of the last endopodal segment especially when they carry different armature elements ( Figs 3E & H ). The fifth legs ( Figs 1J–K ) are also slightly asymmetrical in the holotype, particularly the length of the outermost exopodal seta. Other female and male ( Figs 4G–H ) specimens have their fifth legs less asymmetrical. The number of minute spinules on the anal operculum can also vary, but they are always smaller than those along the posterior margin of the anal somite next to the operculum.

Etymology. The species is named in honour of Dr William F. Humphreys (Western Australian Museum), who collected the type material. The name is a noun in the genitive singular.

Remarks. Reduction of the endopod of the fourth swimming leg to a minute knob is known only in three other ameirid harpacticoids: two species of the genus Psammonitocrella Huys, 2009 , described from Arizona ( USA) by Rouch (1992), and the type and only species of the genus Neonitocrella Lee & Huys, 2002 , described by Miura (1962) from Japan. However, it is more than likely that this reduction may have occurred independently, as a result of convergence or parallelism (homoplasy), between these two genera and Kimberleynitocrella gen. nov. considering that they do not share any other synapomorphies.

The genus Kimberleynitocrella gen. nov. also has very reduced fifth legs (although all four exopodal setae are still present; their slender nature and close position to the outer basal seta reveal their exopodal rather than endopodal origin), as well as some unusual reductions in the mouth appendages (the absence of the endopod of the maxillula, for example), but it stands apart from the other ameirids studied here mostly because of its plesiomorphic characters: three outer spines on the third exopodal segment of the first leg; inner seta present on the second exopodal segment of the first leg; third exopodal segment of the second and third legs with one inner seta and that of the fourth leg with two inner setae; endopod of the second and third leg two-segmented; and most importantly, endopod of the second and third legs with three or four armature elements, which include the outermost subapical spine, ancestral outer apical seta and one or two inner (lateral) elements. These, and some other plesiomorphic characters in the antennula, antenna and genital double-somite in female, clearly define Kimberleynitocrella gen. nov. as a sister group of the remaining Stygonitocrella s. l. species and, in combination with previously mentioned apomorphic features, support its separate generic status.

Clearly, this strange ameirid had to evolve from an ancestor that was even more primitive than most recent freshwater representatives of this family, possibly from a marine or brackish Nitocra Boek, 1865 species. This and some other plesiomorphic features observed in other Stygonitocrella s. l. species presented here, prompted us to choose Biameiropsis barrowensis Karanovic, 2006 as the outgroup for the cladistic analysis presented in this paper, because this anchialine ameirid has most characters in their plesiomorphic state and will also be a suitable outgroup for any future cladistic analyses of other freshwater ameirid genera.

Figures

FIGURE 1. Kimberleynitocrella billhumphreysi gen. et sp. nov., holotype female: A—habitus, dorsal view; B—habitus, lateral view; C—principal apical caudal setae; D—antenna; E—labrum; F—mandibula; G—maxillula; H—maxilla; I— maxilliped; J—right fifth leg; K—left fifth leg. Scales = 0.1 mm.

FIGURE 2. Kimberleynitocrella billhumphreysi gen. et sp. nov., holotype female: A—urosome, ventral view; B—left caudal ramus, lateral view; C—antennula; D—left second swimming leg and endopod of right leg. Scales = 0.1 mm.

FIGURE 3. Kimberleynitocrella billhumphreysi gen. et sp. nov., A–F, holotype female; G & H, paratype female (0.846 mm): A—anal operculum; B—left caudal ramus, dorsal view; C—right caudal ramus, ventral view; D—first swimming leg; E—third swimming leg; F—fourth swimming leg; G—endopod of second swimming leg; H—endopod of third swimming leg. Scale = 0.1 mm.

FIGURE 4. Kimberleynitocrella billhumphreysi gen. et sp. nov., male (WAM C37330; 0.738 mm): A—urosome, lateral view; B—antennula; C—basis of first swimming leg; D—endopod of second swimming leg; E—endopod of third swimming leg; F—basis of fourth swimming leg; G—right fifth leg; H—left fifth leg. Scales = 0.1 mm.