Megastygonitocrella ecowisei, 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 : 55-62

Megastygonitocrella ecowisei sp. nov.

( Figs 12–14 )

Type material. Holotype, adult female dissected on one slide ( WAM C37352); allotype, adult male dissected on one slide ( WAM C37353); paratypes: one female dissected on one slide together with Megastygonitocrella trispinosa ( Karanovic, 2006) ( WAM C37354) and two copepodids preserved in 70% ethanol ( WAM C37355); Australia, Western Australia, Pilbara region, Atlas Iron Mine , bore PDPIEZ11B, sample #4110, 10 December 2007, leg. C. Foord & G. Benisson, 20°14’25”S 119°08’40”E.

Description. FEMALE (HOLOTYPE). Body length, excluding appendages and caudal setae, 0.527 mm. Preserved specimen colourless. Nauplius eye absent. Prosome ( Fig. 13I ) comprising cephalothorax and three free pedigerous somites, while urosome comprising fifth pedigerous somite, genital double-somite and three abdominal somites ( Fig. 12A ). Habitus cylindrical, slender, without distinct demarcation between prosome and urosome; greatest width at first free pedigerous somite. Body length/width ratio about 4.9; cephalothorax only slightly wider than genital double-somite. Free pedigerous somites without pronounced lateral or dorsal expansions. Integument not strongly chitinized and without cuticular windows. Rostrum very small and membranous, linguiform, about as long as wide, ornamented with two dorsal sensilla near anterior margin.

Cephalothorax ( Fig. 13I ) with completely incorporated first pedigerous somite, quadriform in dorsal view, slightly longer than wide. Surface of cephalic shield and tergites of three free pedigerous somites ornamented only with several large sensilla. Hyaline fringe of all prosomites narrow and smooth. Fifth pedigerous (first urosomal) somite ornamented with two large dorsal sensilla and two smaller lateral sensilla on each side; hyaline fringe smooth both dorsally and laterally. Large sclerotized joint ( Fig. 12A ) present between fifth pedigerous and genital double somites and visible both ventrally and dorsally.

Genital double-somite ( Fig. 12A ) somewhat wider than long (ventral view), without visible suture or constriction showing original segmentation; ornamented just with six large dorsal sensilla (two at middle, four near posterior margin) and two posterior ventral sensilla. Hyaline fringe completely smooth both ventrally and dorsally. Genital field with single minute copulatory pore at about first quarter of double-somite length, strongly sclerotized but very short copulatory duct and two ovoid seminal receptacles. Single small genital aperture covered by fused reduced sixth legs, represents 38% of somite width; copulatory pore situated very close to gonopore. Third urosomite ornamented with four large sensilla near posterior margin (two dorsal and two ventral) and two parallel ventral rows of minute spinules at midlength; hyaline fringe smooth. Preanal somite without surface ornamentation and with smooth hyaline fringe dorsally and ventrally. Anal somite ( Figs 12A , 13A ) ornamented with pair of large dorsal sensilla and posterior row of small spinules interrupted ventrally between caudal rami. Anal operculum ( Fig. 13A ) convex, not reaching to posterior end of anal somite, represents 47% of somite's width; ornamented near its posterior margin with 10 small spinules of about same size as spinules on posterior dorsal margin of anal somite. Anal sinus smooth and widely opened.

Caudal rami ( Figs 12A , 13A ) short and conical, slightly shorter than their greatest width (ventral view), somewhat divergent, with space between them about one ramus width, with small diagonal chitinous ridge dorsally; armed with seven setae (three lateral, three apical and one dorsal). Ornamentation consists of three minute spinules at base of distal lateral seta and single larger spinule on posterior ventral margin. Dorsal seta inserted almost at posterior end and close to inner margin, slender, smooth, 1.8 times as long as caudal ramus, triarticulate at its base. Proximal lateral seta arising somewhat dorsolaterally at midlength, about as long as dorsal one and only slightly longer than distal lateral seta, which arises at 3/4 of ramus length. Inner apical seta very slender and smooth, about twice as long as ramus. Both principal setae sparsely pinnate at distal end and with breaking plane.

Antennula ( Fig. 12B ) eight-segmented, unornamented, slender, approximately twice as long as cephalothorax. Very long and slender aesthetasc on fourth segment reaches beyond tip of appendage for more than length of last three segments combined and fused basally with large subapical seta; much smaller and even more slender apical aesthetasc on eighth segment fused basally to two apical setae. Setal formula: 1.8.6.3.2.2.4.7. All setae smooth, except seta on first segment unipinnate; only three setae on eighth segment biarticulating on basal part; no setae with breaking plane. Length ratio of antennular segments, from proximal to distal end and along caudal margin, 1: 1.4: 1: 0.9: 0.6: 0.8: 0.4: 0.7.

Antenna ( Fig. 12C ) composed of coxa, basis, two-segmented endopod and one-segmented exopod. Coxa very short, unornamented. Basis about twice as long as wide, unarmed but ornamented with large spinules along inner (anterior) margin. First endopodal segment 1.3 times as long as basis, 2.8 times as long as wide, unornamented and unarmed. Second endopodal segment longest, 1.4 times as long as first and 4.3 times as long as wide, armed laterally with two 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 large spinules along anterior proximal surface and two fringes on posterior surface. Exopod one-segmented, half as long as basis and twice as long as wide, unornamented but armed with three setae; innermost (apical) seta 2.8 times as long as exopod, nearly twice as long as middle seta and 1.2 times as long as outermost one; apical seta bipinnate, while other two unipinnate.

Labrum ( Fig. 12D ) large, trapezoidal, rigidly sclerotized, with relatively wide and slightly convex cutting edge; ornamented with one apical row of small spinules in between two subapical rows of strong spinules, as well as two diagonal rows of hair-like spinules on dorsal (posterior) surface. Two ellipsoid fields of gustatory papillae visible on dorsal surface.

Paragnaths ( Fig. 13B ) ovoid, fused basally into bilobate labium; each ornamented with apical row of spinules, one spinule on outer margin and longitudinal row of four large curved spinules at middle, close to inner margin, which continues into row of small, hair-like spinules that almost reaches to apical margin.

Mandibula ( Fig. 12E ) with narrow cutting edge on elongated coxa, armed with numerous small teeth in between one coarse ventral tooth and one dorsal unipinnate seta; ornamentation consists of long row of spinules at base of palp. Palp uniramous, comprising basis and one-segmented endopod. Basis unarmed and unornamented, 1.8 times as long as wide and 1.3 times as long as endopod. Endopod small and unornamented, about 2.3 times as long as wide; armed apically with four slender smooth setae.

Maxillula ( Fig. 13C ) with large praecoxa; arthrite rectangular, not movable, unornamented but armed with two smooth setae on anterior surface, two setae on dorsal margin and four apical elements. Coxal endite much shrter than praecoxal arthrite, armed apically with one unipinnate and distally curved seta and two slender smooth setae of subequal length. Basis somewhat shorter than coxal endite, armed with five smooth setae. Endopod very small and fused basally to basis, armed with single smooth apical seta.

Maxilla ( Fig. 12F ) small, with proximal endite absent; distal endite well developed, highly mobile, armed with one unipinnate spine and two smooth subequal setae. Basis drawn out into long claw, with shorter spiniform seta at its base, ornamented with single pore at base of dorsal seta and row of spinules along concave margin. Endopod represented by minute segment, armed with two smooth, subequal apical setae.

Maxilliped ( Fig. 13D ) with short syncoxa, twice as long as wide, with few small spinules and single smooth seta near inner distal corner. Basis almost three times as long as wide and 1.3 times as long as syncoxa, unarmed but ornamented with minute spinules along inner margin. Endopod represented by long prehensile 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. 12G ), endopod of other swimming legs one-segmented ( Figs 13E–G ). Armature formula of swimming legs as follows (inner/outer element; inner/terminal/outer element):

Exopod Endopod

Segments 1 2 3 1 2 3

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

Second leg 0/1 1/1 0/2/2 0/1/0 - -

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

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

Intercoxal sclerite of all swimming legs small, with concave distal margin and without surface ornamentation. Praecoxae of all legs unarmed and unornamented. Coxae unarmed but those of first and second legs ornamented with row of spinules on anterior surface; others unornamented. Basis of each leg unornamented, except for few minute spinules at base of inner spine and insertion of endopod on first leg; armed with small outer spine on first and second swimming legs and smooth outer seta on third and fourth legs; first leg with stout spine on inner margin at about 3/5 of its length. All exopodal and endopodal segments ornamented with spinules along outer margin and on outer distal corner; endopod and some exopodal segments with spinules along inner margin as well; inner distal corner of first and second exopodal segments with frilled membrane. All exopodal segments of about same length. First swimming leg ( Fig. 12G ) with first endopodal segment about three times as long as wide and reaching to 2/3 of second exopodal segment; endopod longer than exopod, reaching beyond distal margin of exopod for length of last endopoal segment. Endopod of second and third swimming legs about as long as first exopodal segment; that of fourth leg somewhat shorter. Apical armature element(s) on first leg geniculate, pinnate on outer (concave) side and either smooth (on endopod) or plumose (on exopod) on inner side. Third exopodal segment of other legs with plumose inner apical seta and heterogeneously ornamented outer apical seta (plumose on inner margin, pinnate on outer; transitional stage between seta and spine). Apical endopodal element of second and fourth legs long, but strong and pinnate, much longer than segment, while that on third leg also spiniform but only slightly longer than segment; inner seta on endopod of third leg slender, plumose and about twice as long as apical element. Inner element on second exopodal segment of second to fourth legs short and spiniform, while all outer exopodal spines strong and bipinnate.

Fifth legs ( Fig. 13H ) biramous, with each baseoendopod not fused medially together. Baseoendopod with outer basal seta long and smooth, arising from long setophore. Endopodal lobe very broad, only slightly convex, unornamented and armed with two bipinnate elements; outer armature element more robust and 2.1 times as long as inner one. Exopod quadriform, small, about as long as maximum width, unornamented but armed with four slender smooth setae; length ratio of exopodal setae, from inner to outer side, 1: 0.6: 0.3: 0.7. Longest seta on exopod 0.66 times as long as outer endopodal armature element.

Sixth legs ( Fig. 12A ) completely fused together, forming simple operculum covering single gonopore, each armed with minute smooth seta.

MALE (ALLOTYPE). Body length 0.472 mm. Habitus ( Fig. 14A ), ornamentation of prosomites, rostrum, colour and nauplius eye similar to female. Hyaline fringe of all somites smooth. Genital somite twice as wide as long. Single spermatophore ( Fig. 14J ) longitudinally placed inside fifth pedigerous and genital somites. Anal somite with spinules and sensilla pattern same as in female; anal operculum ( Fig. 14B ) with posterior row of 11 small spinules.

Caudal rami ( Figs 14B–C ) slightly shorter and not divergent, with additional dorsal cuticular pore and posterior ventral row of seven spinules; other ornamentation and armature similar to female.

Antennula ( Fig. 14D ) strongly geniculate, but also long and slender, ten-segmented, with geniculation between seventh and eighth segments, unornamented except for a small dorsal sensillum on first segment. Long aesthetasc on apical acrothek of fifth segment homologous to aesthetasc on fourth segment in female. Smaller aesthetasc on tenth segment fused basally to two apical setae. Armature of first, ninth and tenth segments similar to female. Setal formula: 1.10.6.1.8.1.2.1.4.7. Majority of setae smooth and slender; two setae on fifth segment, one on sixth and one on seventh very short, spiniform and unipinnate; only seta on first segment plumose. Outer (caudal) setae on ninth and tenth segments biarticulating on basal part; no setae with breaking plane.

Antenna, labrum, paragnaths, mandibula, maxillula, maxilla, maxilliped, second swimming leg ( Fig. 14F ), and fourth swimming leg ( Fig. 14H ) similar to female.

First swimming leg ( Fig. 14E ) with inner spine on basis modified, smooth and inflated distally.

Endopod of third swimming leg ( Fig. 14G ) with inner apical seta significantly shorter than in female, i.e. about as long as apical spine.

Fifth legs ( Figs 14I–J ) with narrowly fused baseoendopods, each also armed with two elements; inner element similar to female, while outer element smooth, slender and much smaller than in female. Exopod additionally armed with innermost bipinnate seta; second innermost seta (homologous to innermost seta on female exopod) also proportionally longer.

Sixth legs ( Fig. 14J ) fused basally together and indistinct from somite, each armed with two slender smooth setae; outer seta 1.5 times as long as inner one.

Variability. Only two adult females and one male were collected and studied. Paratype female is slightly smaller (0.531 mm), but no other form of variability was observed. All three specimens were slightly damaged during the collecting and sorting process, with free pedigerous somites deformed and impossible to use for habitus drawings. Some asymmetry observed in the length of the innermost armature element on the fifth leg exopod of the allotype male ( Figs 14I–J ).

Etymology. The specific name is dedicated to the private environmental consulting agency Ecowise Australia Pty Ltd, who collected the material of this species and partly funded the preparation of this paper. The name is a noun in the genitive singular.

Remarks. With its one-segmented endopod of the second, third and fourth legs, the presence of armature elements on the endopodal lobe of the fifth leg and the armature formula of the swimming legs, Megastygonitocrella ecowisei sp. nov. is morphologically most similar to the Caucasian M. ljovuschkini ( Borutzky, 1967) comb. nov. and to the three Australian species described previously from the Pilbara region: M. trispinosa ( Karanovic, 2006) comb. nov., M. bispinosa ( Karanovic, 2006) comb. nov. and M. unispinosa ( Karanovic, 2006) comb. nov. It differs from M. ljovuschkini in the plesiomorphic armature of the third exopodal segment of the fourth leg, as well as by having only two armature elements on the endopodal lobe of the female fifth leg (three in M. ljovuschkini ), but this species is unfortunately incompletely described and many characters in the mouth appendages could not be compared ( Borutzky 1967).

The differences between M. ecowisei and the three previousy described Australian species are also very small and mostly can be found in the fine details of the ornamentation of the body somites and the armature of the fifth leg ( Karanovic 2006). Additionally, M. ecowisei differs from M. bispinosa by having only one inner seta on the third expodal segment of the fourth leg (two in the latter species) and a relatively much longer apical spine on the endopod of the second and fourth legs. Although both species have two armature elements on the endopodal lobe of the female fifth leg, they are of a different nature. In M. ecowisei they represent the ancestral second and third elements from the outer margin ( Table 2, characters 51 & 52), while those in M. bispinosa represent the second and fourth elements (characters 51 & 53). The ornamentation of the anal somite is also much more pronounced in M. bispinosa . Other small differences can be observed in the proportion of the antennular and antennal segments, structure of the hyaline fringe on the abdominal somites and proportions and ornamentation of the caudal rami.

The ventral ornamentation of the abdominal somites, relative length of the apical endopodal armature element on the second and fourth legs and armature of the endopodal lobe of the fifth leg are some of the most important differences between M. ecowisei and M. unispinosa . The two species additionally differ by the armature of the maxilliped syncoxa, which in the latter species carries three elements and is probably an atavistic character.

Finally, M. ecowisei can be distinguished from M. trispinosa by the absence of cuticular windows on the prosomites, reduced ornamentation of the urosomites, proportion of the antennular and antennal segments and endopodal armature elements on the swimming legs, a much shorter copulatory duct of the female genital field and some other small details in the proportion and ornamentation of the mouth appendages. The two species have even been found to live simpatrically in a single bore (i.e. bore PDPIEZ11B above and new material for M. trispinosa below), so there is no question about their separate specific status.

Figures

FIGURE 12. Megastygonitocrella ecowisei gen. et sp. nov., holotype female: A—compressed abdomen, ventral view; B—antennula; C—antenna; D—labrum; E—mandibula; F—maxilla; G—first swimming leg. Scale = 0.1 mm.

FIGURE 13. Megastygonitocrella ecowisei gen. et sp. nov., A–H, holotype female; I, allotype male: A—anal somite and caudal rami, dorsal view and somewhat compressed; B—paragnaths; C—maxillula; D—maxilliped; E—second swimming leg; F—third swimming leg; G—fourth swimming leg; H—fifth leg; I—cephalothorax and two free prosomites, lateral view. Scale = 0.1 mm.

FIGURE 14. Megastygonitocrella ecowisei gen. et sp. nov., allotype male: A—cephalothorax and two free prosomites, dorsal view; B—anal somite and right caudal ramus, lateral view; C—right caudal ramus, dorsal view; D—antennula; E—basis of first swimming leg; F—endopod of second swimming leg; G—endopod of third swimming leg; H— endopod of fourth swimming leg; I—left fifth leg; J—right fifth and sixth legs, with spermatophore inside. Scales = 0.1 mm.