Limnadopsis centralensis, Schwentner, Martin, Timms, Brian V. & Richter, Stefan, 2012

Schwentner, Martin, Timms, Brian V. & Richter, Stefan, 2012, Description of four new species of Limnadopsis from Australia (Crustacea: Branchiopoda: Spinicaudata), Zootaxa 3315, pp. 42-64 : 60-63

Limnadopsis centralensis sp. nov.

( Fig. 10 , 11 )

Etymology. The name refers to central Australia, the region around Alice Springs in the southern Northern Territory.

Type locality. Northern Territory, 31 km ENE of Curtin Springs roadhouse, an unnamed claypan on south side of highway, 25o13’20”S, 132o02’33”E, 8.v.2004, collected by M. Zofkova.

Type material. Holotype 3 AM P.87582; allotype Ƥ AM P.87583; paratypes 5 3 and 5Ƥ AM P.87584.

Other Material. Northern Territory, Idracowra Station (AM P.87585), 5 km NW of Central Australian Railway marker 1144 km and 28.5 km ESE of Erldunda Roadhouse, Middle Dam on a claypan, 25o17’23”S, 133o28’06”E, 27. iv.2004, collected by M. Zofkova.

Description.

Male (Holotype, AM P.87582) ( Fig. 10 a, b, c, d, e)

Carapace. Length 17.8 mm, height 10.9 mm, length/height ratio 1.63 ( Fig. 10 a). Twelve growth lines more or less equidistant from each other, each raised as a narrow band, carapace opaque, brown in colour and with rough surface. Distinct umbo, dorsal margin depressed in umbo region and humped asymmetrically posterior to this, greatest elevation at about two-fifths of the length; dorsal margin largely smooth without dorsal serration, but minor depressed steps at each of last two to three growth lines. Dorso-anterior and dorso-posterior angles distinct, about 110° each; both anterior and posterior carapace margins markedly convex and protruding from the dorsal angles, ventral margin broadly convex.

Head. Eye oval, mound containing the eye protruding with small ocular tubercle anteriorly, frontal organ pyriform, in length about three times the distance between it and mound ( Fig. 10 b). Rostrum extended as blunt blade subequal in length to peduncle of second antenna, angle to frons about 120°, basal third of rostrum occupied by triangular ocellus. First antenna with eight lobes ( Fig. 10 b) and being a little longer than peduncle of second antenna. Peduncle of second antenna with eleven discernable segments, each covered in a row of setae and spines. Left second antennae with only one ramus (possibly due to development error or predation) of 14 antennomeres, right second antenna with normal two rami each with about twelve antennomeres (individual antennomeres hard to count as many partly divided); central antennomeres with six to nine short spines ventrally, length of spines less than half width of antennomere, and eight to ten long setae dorsally ( Fig. 10 c).

Trunk composed of 29 segments decreasing in size posteriorly, fifteen anterior segments without dorsal armature followed by two segments bearing one to three short setae, then seven segments bearing short spines, last five segments lacking dorsal armature. First two thoracopods modified into claspers and typically spinicaudatan in structure ( Olesen et al. 1996), distal medial margin of hand projecting into a rounded tumidity and apical club on hand much longer than its diameter, tip of moveable finger with a spine-bearing outgrowth ( Fig. 10 d). Exopod of thoracopods 1–15 with long thin dorsal ramus, thoracopod V similar in general structure to that of other species of Limnadopsis (Timms 2009) with five endites and endopod (or endite 6) on medial margin and elongated exopod and oval epipod on lateral margin ( Fig. 11 b); fifth endite remarkably enlarged, terminating in palp without setae.

Telson. The two rows of telsonic spines joined anteriorly but separate posteriorly ( Fig. 10 e); 14 telsonic spines of varying size and spacing on each dorsal ridgeline, most thick and blunt. Last spine enlarged with the two preceding spines originating at its base, enlarged spine directed dorso-posteriorly on left side but at right angles to the telsonic dorsal surface on right side. Filaments not seen, so either minute or missing accidently or developmentally. Floor of telson decreasing evenly from about sixth telsonic spine.

Furca. Each ramus evenly concavely curved with basal four-fifths lined dorsally with about 18 setae, each narrowly plumed, decreasing in length posteriorly until a little shorter than width of furcal ramus ( Fig. 10 e); setal row terminates in three short spines, two of which occur at a marked thinning in the diameter of the ramus. Distal fifth narrowing to acute apex and with a line of small denticles dorsally. Ventro-posterior area of telson ramus relatively large, about two-thirds diameter of basal ramus.

Female (Allotype, AM P.87583) ( Fig. 10 g, h, j, k)

Carapace. Length 16.0 mm, height 9.9 mm, length/height ratio 1.62 ( Fig. 10 g). Eleven growth lines largely equidistant from each other, but first two and last one closer to each other; shape and colour as in male.

Head. Eye round, mound containing the eye protruding, frontal organ pyriform, in length about four times the distance between it and mound ( Fig. 10 h). Rostrum equilateral triangle about two-thirds the length of peduncle of second antenna, rostrum apex acute with naupliar eye near its base. First antenna with eight lobes, a little shorter than peduncle ( Fig. 10 h). Peduncle of second antenna with twelve discernable segments each covered dorsally in many short setae, right second antenna with 16 and 12 antennomeres and left second antenna with 17–18 antennomeres in each ramus. Spination and setation of antennomeres as in males.

Trunk: Composed of 27 segments decreasing in size posteriorly, twelve anteriormost segments without dorsal armature, next seven segments with few to many setae of varying length, then seven segments with single short spine, and last segment lacking dorsal armature ( Fig. 10 j).

Telson. Same basic structure as in male, but with 17 telsonic spines on each dorsal ridgeline sharper than in male ( Fig. 10 k); two smaller spines originating at base of last enlarged spine, latter poised at a similar angle on both sides. No apparent telsonic filaments.

Furca: As in male but each ramus with fewer setae (about twelve) on basal two-thirds ( Fig. 10 k). Two spines dorsally at about two-thirds the length of ramus, one of these at distinct thinning of ramus; distal fifth of furcal ramus as in male. Ventro-posterior area of ramus as in male.

Egg. Round, mean = 197.6 µm (n=5) ( Fig. 11 c). Surface with sets of parallel and radiating grooves and rounded ridges; up to eight grooves per set and some pores on ridges.

Variability. Carapace shape seems to be almost invariant, though the minor serration formed by dorsal extensions of the last few growth lines in males is not always present. The number of growth lines ranges from 10–14 in adult males and 10–13 in mature females. The male rostrum is always relatively long (at least as long as the peduncle of the second antenna), but the shape of it is variable: it is sometimes more acute than in the holotype, and asymmetrical ( Fig. 11 a). The first antenna is always longer than the peduncle in males and shorter in females ( Fig. 11 d), and the number of lobes range from eight to twelve, with eight or nine the most common number. The number of antennomeres in each ramus of the second antenna varies from zero to 18; the first condition was observed in a few specimens, possibly due to accidental loss through predation, but the most common number is around 16–17 antennomeres. The number of spines and setae on the antennomeres varies, largely according to position of the along the flagella, but also somewhat randomly in that those at mid length may have four to nine spines and six to twelve setae instead of the standard six and around ten respectively.

Trunk segment numbers hardly vary from 29 in males and 27 in females. The number of segments bearing dorsal setae or spines, respectively, may differ a little from the type specimens, but there are always many more spinebearing than seta-bearing segments in males and about the same number of each in females.

Telson is the most variable of all structures in L. centralensis sp. nov. The number of telsonic spines ranges from 11–15 on each side in males and 12–18 in females ( Fig. 11 e); moreover, they vary in shape from blunt to sharp and from triangular to almost flat and nipple-like. In all males examined, the last spine on the right side sits at an angle of 70–90o to the rest of the row, while that on the left side forms an angle of about 45o; in females, the last spine on both sides sits at about 45° ( Fig. 11 e). Curiously, not one specimen with caudal filaments was encountered; it is not known whether this is a natural state or one resulting from injury. All specimens, male and female, have similar furca, except those from Idrocowra Station, which are different ( Fig. 10 f). The furcal ramus is longer and evenly concave, evenly diminishing in diameter distally. It bears numerous (<20) basal setae but they diminish distally in size more markedly than described above, while the spines at mid length number one or two more than usual and are more widely spaced. The dorsal denticles on the distal fifth of the furcal ramus are more numerous and smaller than in individuals from the type locality.

Distribution: In the Erldunda-Curtin Springs area south of Alice Springs.

Remarks. Of all the species of Limnadopsis , L. centralensis sp. nov. most closely resembles L. paradoxa in the size and shape of the carapace, the number of growth lines and the general structure of the head and telson. What distinguishes the two species, however, is that dorsal serration is virtually absent in L. centralensis sp. nov. but well expressed in L. paradoxa , the first antenna has around 3 more lobes in L. paradoxa , the last spine of the telson usually bears one to three subsidiary spines in L. centralensis sp. nov. and none in L. paradoxa , and the setae on the furcal rami diminish distally in length in L. centralensis sp. nov. but remain around the same length in L. paradoxa . Furthermore, L. centraliensis sp. nov. has at least two more trunk segments than any other species of Limnadopsis except L. birchii ( Baird 1860) . Finally, its resting eggs are very distinct; those of L. paradoxa are the shape of a top with just a few grooves per surface, while those of L. centralensis sp. nov. are round with a large number of adjacent, extended parallel and radiating grooves. L. centralensis sp. nov. eggs are most like those of L. tatei , but the latter have much shorter grooves and ridges and fewer groove/ridge pairs per set.

L. centralensis sp. nov. is unusual among its congeners in that sexual differentiation is minimal. The carapaces of males and females are indistinguishable in shape and size, but there are differences in the length of the first antenna and in the length and shape of the rostrum. Furthermore, the last spine of the telson in males is almost always angled differently on either side.

Many of the specimens examined were damaged, usually missing distal parts of the second antenna and furcal claws, or with damaged telsonic spines and pieces taken out of the carapace, all possibly due to predation. The lack of caudal filaments is hard to blame on predators though, since caudal filaments are generally well protected within the carapace.

No genetic data are available on L. centralensis to date, but such data may reveal further differentiation among the populations studied.

Figures

FIGURE 10. Limnadopsis centralensis sp. nov. a – e, male holotype (AM P. 87582): a, carapace; b, head (left second antenna removed); c, antennomere; d, first clasper; e, telson and furca. f, male paratype (P. 87585) furcal ramus, Idrocowra population. g – k, female allotype (AM P. 87583): g, carapace; h, head; j, trunk dorsum; k, telson and furca. Scale bars: 1 mm. a 1, first antenna; ap, apical club; cf, caudal filament; da, dorsal armature; fu, furcal ramus; ls, last segment; me, mound containing the eye; po, pyriform organ; pd, peduncle of second antenna; ro, rostrum; tm, tumidity below main hand of clasper; ts, telsonic spine.

FIGURE 11. Limnadopsis centralensis sp. nov. a – b, male paratype (AM MI 826): a, head (second antenna removed); b, third thoracopod. c – e, female paratype (AM MI 827): c, resting egg; d, head (second antenna removed): e, telson and furca. Scale bars a, b, d, e, 500 µm; c, 20 µm. 1 – 5, endite 1 – 5; a 1, first antenna; an, first antennomere of second antenna; as, anterior setae; cf, caudal filament; da, dorsal armature; ot, ocular tubercle; en, endopod (= endite 6); ep, epipod; ex, exopod; fu, furcal ramus; md, mandible; me, mound containing the eye; pa, palp; po, pyriform organ; pd, peduncle of second antenna; ps, posterior setae; ro, rostrum; ts, telsonic spine.