Gordanitocrella trajani, 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 : 21-29

Gordanitocrella trajani sp. nov.

( Figs 5–7 )

Type material. Holotype, adult female dissected on one slide ( WAM C37336); allotype, adult male dissected on one slide ( WAM C37337); paratypes: one adult female and one male dissected together on one slide ( WAM C37338), one adult female and one male together on one slide in toto ( WAM C37339), five males, three females and one copepodid preserved in 70% ethanol ( WAM C37340); Australia, Western Australia, Pilbara region, N of Newman, bore Corktree , depth 31 m, 29 October 2006, leg. P. Hancock (Jar no. FMG36 ), 22°47’32”S 119°18’34”E.

Other material examined. One adult male dissected on one slide ( WAM C37341); one adult female and three copepodids preserved in 70% alcohol ( WAM C37342); Australia, Western Australia, Pilbara region, near Weeli Wolli spring, bore HD11D, 17 November 2003, leg. J. Cocking & M. Scanlon, 20°57’06”S 119°09’23”E .

One adult female dissected on one slide ( WAM C37343); one adult female and one copepodid preserved in 70% alcohol ( WAM C37344); Australia, Western Australia, Pilbara region, Pebble Mouse Creek , bore WB3 , 17 November 2003, leg. J. Cocking & M. Scanlon, 23°00’09”S 119°07’56”E .

Description. FEMALE (HOLOTYPE). Total body length, measured from tip of rostrum to posterior margin of caudal rami (excluding appendages and caudal setae), 0.563 mm. Preserved specimen colourless. Nauplius eye absent. Habitus ( Figs 5A–B ) cylindrical, slender, without distinct demarcation between prosome and urosome; prosome/urosome ratio 0.85; greatest width at first free pedigerous somite. Body length/width ratio about 5.3; cephalothorax only 1.1 times as wide as genital double-somite. Free pedigerous somites without pronounced lateral or dorsal expansions. Integument not strongly chitinized and without cuticular windows. Rostrum ( Fig. 5A ) small and membranous, linguiform, reaching to just beyond proximal third of first antennular segment, about twice as long as wide and not demarcated at base; ornamented with two dorsal sensilla near anterior margin.

Cephalothorax ( Fig. 5A ) with completely incorporated first pedigerous somite, almost cylindrical in dorsal view, somewhat longer than wide; represents 21% of total body length. Surface of cephalic shield and tergites of three free pedigerous somites ornamented only with large sensilla. Hyaline fringe of all prosomites narrow and smooth. Fifth pedigerous (first urosomal) somite ornamented posteriorly with two large dorsal sensilla and two smaller lateral sensilla (one on each side); hyaline fringe finely serrated dorsally and laterally, smooth ventrally ( Figs 5B–C ). Large sclerotized joint ( Figs 5A–C ) present between fifth pedigerous and genital double somites and visible both ventrally and dorsally.

Genital double-somite ( Fig. 5C ) 0.8 times as long as wide (ventral view), without visible suture and only slightly wider at anterior part; ornamented with two large sensilla dorsally, two sensilla ventrally, two small cuticular pores laterally (one on each side), one short transverse row of minute spinules at dorsal midline and uninterrupted posterior row of spinules, those on ventral side larger. Hyaline fringe finely serrated both ventrally and dorsally. Genital field with single small copulatory pore, narrow sclerotized copulatory duct and two semicircular seminal receptacles, posterior part of which reaches beyond copulatory pore. Copulatory pore situated slightly posterior from proximal fourth of double-somite length. Single small genital aperture covered by fused reduced sixth legs, represents 40% of somite width. Third urosomite ornamented also with four large sensilla near posterior margin (two dorsal and two ventral), uninterrupted posterior row of spinules and two lateral pores, but additionally ornamented ventrally with four cuticular pores (two at anterior and two at posterior part) and short and slightly interrupted transverse row of minute spinules between posterior pores, very close and parallel to posterior row; hyaline fringe finely serrated. Preanal somite with finely serrated hyaline fringe dorsally and ventrally, ornamented with continuous posterior row of spinules and one additional row of spinules and two pores ventrally. Anal somite ( Figs 5B–C , 6A ) ornamented with pair of large dorsal sensilla, two lateral and four ventral cuticular pores, short transverse row of minute spinules at lateral 2/3, interrupted and arched row of minute spinules ventrally at 1/3 and posterior row of somewhat larger spinules, interrupted ventrally between caudal rami. Anal operculum convex, not reaching to posterior end of anal somite, represents 57% of somite's width; ornamented near its posterior margin with 29 spinules of about same size as spinules on posterior dorsal margin. Anal sinus widely opened, ornamented with two diagonal rows of minute spinules.

Caudal rami ( Figs 5B–C , 6A , 7A ) slender, about twice as long as greatest width (ventral view), nearly cylindical, clearly convergent, with space between them more than 1.5 times as wide as one ramus, with small diagonal chitinous ridge dorsally and ventral posterior margin produced somewhat inwards; armed with seven armature elements (three lateral, one dorsal and three apical). Ornamentation consists of several small spinules at base of dorsal and distal lateral seta, one ventral and two lateral pores and posterior ventral row of five larger spinules. Dorsal seta smooth, inserted close to inner margin, at about 2/3 of ramus length, 1.7 times as long as caudal ramus, biarticulate at its base. Proximal and distal lateral setae smooth and of about same length, 0.6 times as long as dorsal one; proximal seta arising somewhat dorsolaterally and slightly more anteriorly than dorsal seta; distal lateral seta arising at 4/5 of ramus length. Inner apical seta very slender and small, smooth, about 0.6 times as long as ramus. Both principal setae broken at breaking plane and inserted more dorsally than apically.

Antennula ( Fig. 6B ) eight-segmented, slender, approximately 1.3 times as long as cephalothorax. Long and relatively slender aesthetasc on fourth segment reaches beyond tip of appendage for 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. Only seta on first segment unipinnate, all other setae smooth. Only four setae on eighth segment articulating on basal part; all setae without breaking plane. First segment ornamented with short row of long spinules at middle of anterior surface; other segments without ornamentation. Length ratio of antennular segments, from proximal to distal end and along caudal margin, 1: 1.7: 1: 1: 0.5: 0.6: 0.4: 0.8.

Antenna ( Fig. 5D ) composed of coxa, basis, two-segmented endopod and one-segmented exopod. Coxa very short, unornamented. Basis about 1.7 times as long as wide, unarmed but ornamented with two short rows of long spinules along anterior margin. First endopodal segment slightly longer and more slender than basis, unornamented and unarmed. Second endopodal segment longest, 1.5 times as long as first and 3.6 times as long as wide, armed medially with two smooth 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 and two fringes on posterior surface. Exopod one-segmented, small, 0.4 times as long as basis and 2.7 times as long as wide, unornamented but armed with two setae; inner seta bipinnate, slender, arising apically, 1.7 times as long as outer one and almost 2.5 times as long as exopod; outer seta curved, unipinnate and much stronger than inner seta.

Labrum ( Fig. 5E ) large compared to cephalothorax, trapezoidal, rigidly sclerotized, with relatively broad and convex cutting edge, ornamented with one apical row of small spinules in between two subapical rows of strong spinules. Two ellipsoid fields of gustatory papillae visible on dorsal (posterior) surface.

Paragnaths ( Fig. 5F ) ovoid, fused basally into trapezoidal labium; each ornamented with apical row of spinules (which becomes smaller towards inner margin), one spinule on outer margin and longitudinal row of four large curved spinules at middle, close to inner margin.

Mandibula ( Figs 5G–H ) with narrow cutting edge on elongated coxa, armed with numerous small teeth in between three ventral coarse teeth and one dorsal unipinnate seta. Palp uniramous, comprising basis and onesegmented endopod. Basis slender, unarmed and unornamented, 2.5 times as long as wide and 1.7 times as long as endopod. Endopod also slender and unornamented, about twice as long as wide; armed apically with five slender smooth setae.

Maxillula ( Fig. 5I ) with large praecoxa; arthrite rectangular, not movable, unornamented, armed with two smooth setae on anterior surface, three setae on dorsal margin and four apical elements (probably three spines and one seta). Coxal endite shorter than praecoxal arthrite, armed apically with one curved pinnate and two slender smooth setae, all of about same length. Basis about as long as coxal endite, armed with four smooth setae apically and one smooth seta subapically. Endopod a minute but distinct segment, armed with minute smooth apical seta.

Maxilla ( Fig. 5J ) with proximal syncoxal endite absent; distal endite well developed, highly mobile, armed with one pinnate spine and two smooth setae (middle seta nearly twice as long as other two elements). Basis drawn out into long claw, with much shorter spiniform curved seta at its base. Endopod represented by minute segment, armed with two smooth subequal, long apical setae.

Maxilliped ( Fig. 5K ) with well developed syncoxa, ornamented with several minute spinules at inner distal corner and armed with single smooth seta near outer distal corner, 1.8 times as long as wide. Basis 2.8 times as long as wide and almost 1.3 times as long as syncoxa, unarmed but ornamented with interrupted row of small spinules along inner margin. Endopod represented by long 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. 6C ), endopod of other swimming legs one-segmented ( Figs 6D–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 1/1 0/2/3 1/0 0/0 1/1/1

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

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

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

Intercoxal sclerite of all swimming legs with concave distal margin and without surface ornamentation. Praecoxae short and smooth. Coxa of first leg with diagonal row of spinules at inner distal corner, that of other legs smooth; all coxae unarmed. Basis of each leg ornamented with spinules near outer margin, that of first leg additionally with several slender spinules on inner margin; armed with outer pinnate spine on first and second swimming legs and outer smooth seta on third and fourth legs; first leg with stout spine and produced pseudospine structure on inner distal corner. All exopodal and endopodal segments ornamented with slender spinules along inner margin and strong spinules along outer margin and on outer distal corner; inner distal corner of first and second exopodal segments with frilled membrane. All exopodal segments of about same length. First endopodal segment of first swimming leg ( Fig. 6C ) large, about 2.4 times as long as wide and reaching to 2/3 of second exopodal segment; endopod significantly longer than exopod. Endopod of second and third swimming legs about as long as first exopodal segment; that of fourth leg half as long. All setae on each ramus (except minute inner seta on third endopodal segment of first leg) strong and some also spiniform. Apical armature element(s) on first leg geniculate.

Fifth leg ( Figs 5C , 6H ) biramous, but baseoendopod fused medially together and to somite. Endopodal lobe not recognizable, forming straight smooth hyaline fringe and without armature or ornamentation. Basal outer seta slender and smooth, on long setophore, which also is fused basally to somite. Exopod a distinct segment, ovoid, small, slightly longer than its maximum width, unornamented and armed with three slender smooth setae; length ratio of exopodal setae slightly different on left and right leg, although innermost seta longest and outermost seta shortest. Longest exopodal seta 0.44 times as long as outer basal seta.

Sixth legs ( Fig. 5C ) completely fused together, indistinct, forming simple operculum covering single gonopore, without any ornamentation but each armed with single minute seta.

MALE (ALLOTYPE). Body length 0.484 mm. Habitus, ornamentation of prosomites, rostrum, colour and nauplius eye similar to female. Hyaline fringe of all prosomites smooth, those of urosomites finely serrated.

Genital somite twice as wide as long, with small and slender spermatophore longitudinally placed inside fifth pedigerous and genital somites ( Fig. 7D ). Anal somite with slightly longer lateral row of spinules ( Fig. 7C ), but otherwise same as in female. Anal operculum with 32 spinules.

Caudal rami ( Fig. 7C ) slightly more elongated and almost parallel, but armature and ornamentation very similar to female.

Antennula ( Fig. 7E ) long and slender, ten-segmented, but with last two segments partly fused, unornamented and strongly geniculate, with geniculation between seventh and eighth segments. 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. Armature of first, ninth and tenth segments similar to female. Setal formula: 1.10.6.1.6.1.2.1.4.7. Majority of setae smooth and slender; seta on first segment unipinnate and slender; two setae on fifth, one on sixth and one on seventh segment very short, unipinnate and spiniform. Just two lateral setae on ninth and three on tenth segment biarticulate at their base. Setae without breaking plane.

Antenna, labrum, mandibula, maxillula, maxilla, maxilliped and second, third ( Fig. 7G ) and fourth swimming legs similar to female.

First swimming leg ( Fig. 7F ) with inner spine on basis modified as smooth, apically curved outwards and slightly inflated element; cuticular protrusion at base of inner spine similar to female; basis without ornamentation on inner margin.

Third swimming leg ( Fig. 7G ) with inner seta on endopod somewhat shorter and with fewer and smaller pinnules; other details similar to female.

Fifth legs ( Fig. 7D ) more fused to somite than in female, with smaller exopod completely fused basally to somite; otherwise similar to female. Left exopod armed with three slender setae like in female, while right exopod additionally armed with long and strong spine as innermost element; this spine 1.8 times as long as longest seta on segment.

Sixth legs ( Fig. 7D ) fused medially together, indistinct from somite, each armed with two smooth short setae; outer seta about 1.7 times as long as inner one.

Variability. Body length of females ranges from 0.560 mm to 0.571 mm (0.565 mm average; n = 9), while in males it ranges from 0.473 mm to 0.493 mm (0.484 mm average; n = 7). The insertion of endopodal elements on the third swimming leg is slightly asymmetrical in the holotype female ( Figs 6E–F ). One paratype female has the exopod of the left fifth leg with the innermost seta shorter than the middle one and also the outermost seta is inserted further away from the other two than in the holotype female ( Fig. 6I ). Another paratype female has a somewhat smaller and more rounded exopod of the fifth leg ( Fig. 6L ), as well as a somewhat more ornamented endopod of the second and third legs ( Figs 6J–K ). The male from Weeli Wolli has the innermost seta on the third leg endopod inserted more basally than in the allotype ( Fig. 7I ), but also somewhat longer setae on the sixth legs and a slightly larger spermatophore ( Fig. 7H ); the fifth legs are also somewhat different from the allotype, especially in the relative length of the setae. Remarkably, all examined males had the additional spine always on the right fifth leg.

Etymology. The species name is dedicated to Dr Trajan K. Petkovski (Natural History Museum of Macedonia), who first recognized and established the genus Stygonitocrella in 1976, although he did not designate a type species and thus the name became unavailable under the current Zological Code. The name is a noun in the genitive singular.

Remarks. If we consider only the segmentation of the swimming legs (as was done in the past) this species would fit perfectly into the diagnosis of the genus Stygonitocrella Reid, Hunt & Stanley, 2003 , with its one-segmented endopod of the second, third and fourth legs. However, a closer examination reveals that Gordanitocrella trajani gen. et sp. nov. has no close relatives among recent representatives of this group of freshwater ameirids.

For example, while three armature elements on the ultimate endopodal segment of the third leg can be found in three other species of Stygonitocrella s. l., they are not homologous with each other: in Kimberleynitocrella billhumphreysi gen. et sp. nov. they represent the ancestral outer subapical spine, outer apical seta and distal inner seta (note: middle inner seta also sometimes present in this species), i.e. characters 35, 36 & 38 in Table 2; in Gordanitocrella trajani gen. et sp. nov. the outer apical seta and middle and distal inner setae are present, i.e. characters 36, 38 & 39; in Lucionitocrella yalleenensis gen. et sp. nov. the two apical setae and middle inner seta are expressed, i.e. characters 36, 37 & 39; while in Eduardonitocrella mexicana ( Suárez-Morales & Iliffe, 2005) comb. nov. we find two apical setae and a distal inner seta, i.e. characters 36, 37 & 38. A similar comparison can be made for many other leg segments (see Tables 1 & 2), which shows that these four freshwater ameirids all had an independent evolutionary path, instead of a common origin, from some more primitive forms of this family.

Plesiomorphic features of G.trajani place it relatively basal on the phylogenetic tree and relatively close to K.billhumpheysi ( Fig. 18 ); they include: an inner seta on the second exopodal segment and three outer spines on the third exopodal segment of the first leg; an inner seta on the third exopodal segment of the second, third and fourth legs; and more than two setae on the ultimate endopodal segment of the third leg. However, unlike K. billhumphreysi , G. trajani has a relatively well developed endopod of the fourth leg, which is armed with the ancestral outer apical seta ( Table 2, character 44), as well as a distinct exopod of the female fifth leg and the presence of a maxillular endopod. These two species also differ in many other apomorphic characters.

A one-segmented endopod of the second leg armed with an ancestral outer apical seta and distal inner seta ( Table 2, characters 26 & 28), would position G. trajani close to L. yalleenensis , but the latter ameirid has no plesiomorphic features on the third exopodal segment of the first leg, nor inner setae on the third exopodal segment of the second and third legs. Further, L. yalleenensis has, unlike any other Stygonitocrella s. l., a plesiomorphic armature on the outer side of the third exopodal segment of the second leg (with three outer spines) and differs from G. trajani also in having two armature elements on the endopod of the fourth leg, as well as by many other less important characters in the antenna, fifth leg, caudal rami, etc. The new genus differs from E. mexicana even more than from the two Australian genera mentioned here (see below). The only obvious autapomorphic feature of the genus Gordanitocrella gen. nov. is its inner distal spiniform process on the basis of the first leg in both sexes ( Figs 6C , 7F ). Caudal rami of this genus are also different from those observed in other members of Stygonitocrella s. l., but it is very hard to formulate these differences into commentable characters.

Figures

FIGURE 5. Gordanitocrella trajani gen. et sp. nov., holotype female: A—habitus, dorsal view; B—habitus, lateral view; C—urosome, ventral view; D—antenna; E—labrum; F—paragnaths; G—cutting edge of mandibula; H— mandibular palp; I—maxillula; J—maxilla; K—maxilliped. Scales = 0.1 mm.

FIGURE 6. Gordanitocrella trajani gen. et sp. nov., A–H, holotype female; I, paratype female (0.571 mm); J–L, paratype female (0.562 mm): A—anal somite and caudal rami, dorsal view; B—antennula; C—first swimming leg; D— second swimming leg; E—right endopod of third swimming leg; F—left endopod of third swimming leg, without armature; G—fourth swimming leg; H—left fifth leg; I—left fifth leg; J—endopod of second swimming leg; K— endopod of third swimming leg; L—left fifth leg. Scale = 0.1 mm.

FIGURE 7. Gordanitocrella trajani gen. et sp. nov., A & B, holotype female; C–G, allotype male; H & I, male from Weeli Wolli (0.473 mm): A—anal somite and caudal rami, ventral view; B—genital field; C—anal somite and right caudal ramus, lateral view; D—fifth and sixth legs, with spermatophore visible inside; E—antennula; F—basis of first swimming leg; G—endopod of third swimming leg; H—fifth and sixth legs, with spermatophore visible inside; I— endopod of third swimming leg. Scale = 0.1 mm.

FIGURE 18. Cladogram of the freshwater ameirids with a one-segmented endopod of the fourth leg (Stygonitocrella s. l.).