Lucionitocrella yalleenensis, 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 : 30-35

Lucionitocrella yalleenensis sp. nov.

( Figs 8–9 )

Type material. Holotype, adult female dissected on one slide ( WAM C37356); allotype, adult male dissected on one slide ( WAM C37357); Australia, Western Australia, Pilbara region, Yalleen Station , bore MILLYARRA64A, 20 November 2003, leg. M. Scanlon and J. Cocking (DEC), 21°49’03”S 116°42’39”E.

Description. FEMALE (HOLOTYPE). Total body length, measured from tip of rostrum to posterior margin of caudal rami (excluding appendages and caudal setae), 0.421 mm. Preserved specimen colourless. Nauplius eye absent. Prosome comprising cephalothorax and three free pedigerous somites, while urosome comprising fifth pedigerous somite, genital double-somite and three abdominal somites. Habitus ( Fig. 8A ) cylindrical but not very slender, without distinct demarcation between prosome and urosome; prosome/ urosome ratio 0.95; greatest width at third (second free) pedigerous somite. Body length/width ratio about 4.7; cephalothorax about 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 ( Figs 8A–B ) incorporating first prosomite, nearly cylindrical in dorsal view, about 1.2 times as long as wide; represents about 24% of total body length. Surface of cephalic shield and tergites of first three free pedigerous somites ornamented with few large sensilla; third pedigerous somite additionally with pair of dorsal cuticular pores. Hyaline fringe of all prosomites narrow and smooth. Fifth pedigerous (first urosomal) somite ornamented with four dorsal and two lateral sensilla (one on each side); hyaline fringe smooth both dorsally and laterally. Sclerotized joint ( Figs 8A & C , 9A ) present between fifth pedigerous and genital double somites and clearly visible both ventrally and dorsally.

Genital double-somite ( Figs 8C , 9A ) 0.8 times as long as wide (ventral view), without visible suture but slightly constricted ventrally at 2/5; ornamented with eight large sensilla dorsally (four at middle, four near posterior margin), two posterior ventral sensilla, two ventral cuticular pores at midlength and transverse row of small spinules between ventral sensilla; hyaline fringe completely smooth both ventrally and dorsally. Genital field with single small copulatory pore (at about proximal third of double-somite length), narrow but well sclerotized copulatory duct and two small triangular seminal receptacles. Single small genital aperture covered by fused reduced sixth legs, represents 37% of somite width. Third urosomite ornamented with six large sensilla near posterior margin (four dorsal and two ventral) and posterior ventral row of spinules; hyaline fringe smooth. Preanal somite with smooth hyaline fringe dorsally and ventrally, ornamented only with short posterior row of small spinules ventrally between two cuticular pores. Anal somite ( Figs 8C , 9A–B ) ornamented with pair of large dorsal sensilla, four lateral cuticular pores (two on each side) and transverse interrupted row of spinules (medial ones longest) along posterior ventral margin. Anal operculum ( Fig. 9B ) slightly convex, not reaching to posterior end of anal somite, represents 57% of somite's width; ornamented near its posterior margin with 26 minute spinules of significantly smaller size than spinules on posterior ventral margin of anal somite. Anal sinus smooth and widely opened.

Caudal rami ( Figs 8C , 9A–B ) short, slightly longer than their greatest width (ventral view), conical, slightly divergent, with space between them about one ramus width; armed with seven armature elements (three lateral, one dorsal and three apical). Ornamentation consists of two spinules at base of distal lateral seta, one dorsal cuticular pore and posterior row of four or five spinules ventrally. Dorsal seta smooth, inserted near posterior margin and close to inner margin, about twice as long as caudal ramus, triarticulate at base. Proximal lateral seta about 0.7 times as long as dorsal one, arising somewhat dorsolaterally at about 2/5 of ramus length. Distal lateral seta smooth, arising at 3/4 of ramus length, 0.8 times as long as dorsal one. Inner apical seta smooth, about as long as ramus. Middle apical seta strongest, broken along breaking plane on both rami. Outer apical seta with breaking plane, ornamented with spinules on both margins.

Antennula ( Fig. 9C ) eight-segmented, unornamented, slender, slightly longer than cephalothorax. Strong aesthetasc on fourth segment reaches beyond tip of appendage for length of last segment; much more slender apical aesthetasc on eighth segment fused basally with two apical setae. Setal formula: 1.8.6.3.2.2.4.7. All setae smooth, except for unipinnate seta on first segment, without breaking plane and uniarticulate at base. Length ratio of antennular segments, from proximal end and along caudal margin, 1: 1.8: 1: 1.2: 0.6: 0.8: 0.6: 0.9.

Antenna ( Fig. 9D ) composed of coxa, basis, two-segmented endopod and one-segmented exopod. Coxa very short, unarmed and unornamented. Basis three times as long as coxa, about 1.3 times as long as wide, unornamented and unarmed. First endopodal segment about 1.8 times as long as wide and 1.3 times as long as basis, unornamented and unarmed. Second endopodal segment longest, 1.5 times as long as first and 2.8 times as long as wide, armed medially at 2/3 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. Exopod one-segmented, very small, 0.3 times as long as basis and 2.2 times as long as wide, unornamented but armed with single unipinnate seta, which 4.3 times as long as exopod.

Labrum ( Fig. 9E ) not very large compared with cephalothorax, trapezoidal, rigidly sclerotized, with relatively narrow and convex cutting edge; ornamented with one apical row of small spinules in between two subapical rows of strong spinules (seven on each side). Two small ellipsoid fields of gustatory papillae visible on dorsal (posterior) surface.

Paragnaths ( Fig. 9F ) ovoid, fused basally into bilobate labium; each ornamented with apical row of large 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 spinules that almost reaches to apical margin, as well as some minute apical spinules on interlobal plate.

Mandibula ( Figs 9G–H ) with narrow cutting edge on elongated coxa, armed with coarser teeth at ventral half, finer teeth at dorsal half and one unipinnate seta dorsally. Palp very small, uniramous, comprising basis and one-segmented endopod. Basis unarmed and unornamented, 2.3 times as long as wide. Endopod also slender and unornamented, about as long as basis but somewhat wider at distal part; armed apically with five slender smooth setae.

Maxillula ( Fig. 9I ) with large praecoxa; arthrite rectangular, not movable, unornamented but armed with two smooth setae on anterior surface, three short setae on dorsal margin and four apical elements (probably three spines and one seta). 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 smooth setae apically and one smooth seta subapically. Endopod a minute but distinct segment, armed apically with single smooth seta.

Maxilla ( Fig. 9J ) with proximal syncoxal endite absent; distal endite well developed, highly mobile, armed with one curved 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. 9K ) with well developed syncoxa ornamented with several minute spinules near inner distal corner and armed with single smooth seta subapically, 1.5 times as long as wide. Basis twice as long as wide and almost 1.4 times as long as syncoxa, unarmed and unornamented. 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. 8D ), endopod of other legs one-segmented ( Figs 8E–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 0/2/2 1/0 0/0 1/1/1

Second leg 0/1 1/1 0/2/3 1/1/0 - -

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

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

Intercoxal sclerite of all swimming legs with concave distal margin and without surface ornamentation. Praecoxae of all legs very short and unornamented. Coxa of third swimming leg ornamented with several minute spinules on anterior surface, that of other legs unornamented; all coxae unarmed. Basis of each leg ornamented with row of spinules near outer margin, that of first leg also with posterior row between rami and several small spinules near inner margin; first and second legs armed with short smooth spine, third and fourth legs with slender 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 distal margin. All exopodal segments of about same length. First swimming leg ( Fig. 8D ) with first endopodal segment about three times as long as wide and almost reaching to distal margin of second exopodal segment; endopod longer than exopod, reaching beyond distal margin of exopod for length of last endopodal segment. Endopod of second and third swimming legs ( Figs 8E–F ) as long as first exopodal segment; endopod of fourth swimming leg ( Fig. 8G ) half as long as first exopodal segment. Apical armature element(s) on first leg geniculate, pinnate on outer (concave) side and either plumose (innermost one on exopod) or smooth (all others) 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). Inner element on second exopodal segment short and spiniform, while all outer exopodal spines strong and bipinnate. Apical endopodal element(s) of second to fourth legs slender and plumose, more than three times as long as segment, while inner seta short, bipinnate and spiniform.

Fifth legs ( Figs 8C & H , 9A ) fused completely together into single distinct plate, with each leg represented by two unornamented but armed lateral knobs. Inner knob, representing exopod, armed with three smooth slender setae, innermost one longest, outermost shortest. Outer knob represents outer basal part and armed with single long smooth seta; this seta much longer than any seta on inner knob. Endopodal lobe reduced to simple hyaline fringe, unarmed and unornamented.

Sixth legs ( Fig. 8C ) completely fused together, indistinct, forming simple operculum covering single gonopore, without ornamentation but each armed with single minute seta.

MALE (ALLOTYPE). Body length 0.418 mm. Habitus, ornamentation of prosomites, rostrum, colour and nauplius eye similar to female. Hyaline fringe of all prosomites smooth and no cuticular windows observed .

Genital somite more than twice as wide as long. Single small, longitudinally placed spermatophore visible inside fifth pedigerous and genital somite ( Fig. 9L ). Urosomite ornamentation similar to female, although genital somite with one additional lateral sensillum and preanal somite with longer ventral row of smaller spinules.

Anal somite and caudal rami ( Fig. 9L ) proportions, armature and ornamentation very similar to female.

Antennula ( Fig. 9M ) long and slender, ten-segmented, not strongly geniculate, with geniculation between seventh and eighth segments, unornamented. Very long and broad aesthetasc present on apical acrothek of fifth segment (homologous to aesthetasc on fourth segment in female); one smaller aesthetasc on tenth segment fused basally to two apical setae. First two and last two segments similar to female. Setal formula: 1.10.6.1.6.1.2.1.4.7. Most setae smooth and slender; all setae without breaking plane; two setae on fifth segment and one each on sixth and seventh very short and unipinnate. Just four lateral setae on tenth segment and one seta on ninth segment biarticulating on basal part; all other setae uniarticulate.

Antenna, labrum, paragnaths, mandibula, maxillula, maxilla, maxilliped, second swimming leg ( Fig. 9O ) and fourth swimming leg very similar to female.

First swimming leg ( Fig. 9N ) with inner spine on basis significantly modified, smooth and inflated distally.

Third swimming leg ( Fig. 9P ) with outer apical element on endopod spiniform and bipinnate (not plumose) and much shorter than in female.

Fifth leg ( Figs 9L & Q ) remarkably similar to female, except middle seta somewhat longer and exopodal lobe less pronounced.

Sixth legs ( Fig. 9L ) not fused medially together, distinct from somite, represented by slightly asymmetrical ellipsoid cuticular plates without armature or ornamentation.

Variability. No important asymmetries or variablities were observed between the one male and one female collected and studied (other than sexually dimorphic characters).

Etymology. The species is named after the type locality, Yalleen Station, with the addition of the Latin suffix for place “- ensis ”. The specific name consequently is an adjective for place.

Remarks. As mentioned in the Remarks section for the previous species, Lucionitocrella yalleenensis gen. et sp. nov. differs from all other Stygonitocrella s. l. members by the plesiomorphic three outer armature elements of the third exopodal segment of the second leg. Other plesiomorphic features include the presence of an inner apical seta on the ultimate endopodal segment of the third leg ( Table 2, character 37), as well as distal inner seta on the endopod of the fourth leg (character 46), which it shares only with the Mexican Eduardonitocrella mexicana ( Suárez-Morales & Iliffe, 2005) comb. nov. (see S. mexicana in Table 2). However, the two species are not closely related and we have previously explained the nonhomologous nature of their endopodal armature elements of the third leg in the Remarks section for Gordanitocrella trajani gen. et sp. nov. (see above). The two species also differ in many other characters, including their armature pattern on the endopodal segment of the second and fourth legs (characters 26, 27, 28, 43, 44 & 46 in Tables 1 & 2), anal operculum (plesiomorphic in E. mexicana ), as well as reductions in the antennula, mandibula, maxilla and maxilliped in E. mexicana and in the antenna in L. yalleenensis .

In the species included in this study, an antennal exopod with only 1 seta was observed only in L. yalleenensis and Inermipes humphreysi Lee & Huys, 2002 , but it also occurs in the completely unrelated Abnitocrella halsei Karanovic, 2006 (see Karanovic, 2006), and some other taxa. It is interesting to note that while the armature of the fifth leg in L. yalleenensis is quite reduced, the leg itself is not fused to the somite. Thus, superficially similar fifth legs that are highly reduced in the genera Abnitocrella Karanovic, 2006 , Kimberleynitocrella gen. nov. and Lucionitocrella gen. nov. are in fact very different when examined more closely and especially when considering homologous armature elements and the nature and extent of reductions in their segmentation. However, closely related species in this branch of freshwater ameirids with differently reduced fifth legs indicated to us that this character (or this group of characters) is less relevant for reconstructing their phylogenetic relationships. That is why those characters were weighted less in our cladistic analysis. It seems that Lucionitocrella has no obvious autapomorphic features (or they are masked with homoplastic characters in other members), and it is placed on the cladogram as a sister group to all other Stygonitocrella s. l. species, except Kimberleynitocrella and Gordanitocrella gen. nov. The genus is well defined by a combination of plesiomorphic and apomorphic features.

Figures

FIGURE 8. Lucionitocrella yalleenensis gen. et sp. nov., holotype female: A—habitus, dorsal view; B—cephalothorax, lateral view; C—urosome, ventral view; D—first swimming leg; E—second swimming leg; F—third swimming leg; G—fourth swimming leg; H—right fifth leg. Scales = 0.1 mm.

FIGURE 9. Lucionitocrella yalleenensis gen. et sp. nov., A–K, holotype female; L–Q, allotype male: A—urosome, lateral view; B—anal somite and caudal rami, dorsal view; C—antennula; D—antenna; E—labrum; F—paragnaths; G— cutting edge of mandibula; H—mandibular palp; I—maxillula; J—maxilla; K—maxilliped; L—urosome, lateral view; M—antennula; N—basis of first swimming leg; O—endopod of second swimming leg; P—endopod of third swimming leg; Q—left fifth leg. Scales = 0.1 mm.