Paralimnadia westraliensis, Timms, Brian V., 2016

Timms, Brian V., 2016, A review of the Australian endemic clam shrimp, Paralimnadia Sars 1896 (Crustacea: Branchiopoda: Spinicaudata), Zootaxa 4161 (4), pp. 451-508 : 495-498

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Paralimnadia westraliensis

n. sp.

Paralimnadia westraliensis n. sp.

( Figs. 3 View FIGURE 3 , 20 View FIGURE 20 , 23 View FIGURE 23 )

Etymology. The specific epithet is derived from ‘Westralia’ a contraction of ‘ Western Australia,’ the state in which this species has a wide distribution.

Type material. Holotype: WAM C61757 View Materials , male, length 9.8 mm, height 7.0 mm, Western Australia, Grass Patch , Sieda farm 6.6 km E, pool in uneven ancient dune system in eastern paddock, 33°13’ 45.6”S, 121°47’14.3”E ,, coll GoogleMaps . 2 February 2007, BVT. Allotype: WAM C61758, female, length 8.1 mm, height 5.4 mm, from type locality, coll. 2 February 2007, BVT. Paratypes: WAM C61759, 2 males, 9.4 × 6.0 mm, 9.9 × 7.2 mm, 2 females 9.8 × 7.0 mm, 7.8 × 5.3 mm, from type locality, coll. 2 February 2007, BVT; AM P99024, 2 males 9.7 × 6.0 mm, 8.1 × 5.0 mm, 2 females 8.0 × 5.3 mm, 7.6 × 5.0 mm, from type locality, coll. 2 February 2007, BVT.

Other material examined. Western Australia: Grass Patch 8.2 km SW, Swan Lagoon, 33°16’ 11.4”S, 121°38’38.5”E, 24 January 2007, BVT, 28 specimens, WAM C61760 View Materials GoogleMaps ; Grass Patch , 6.6 km ESE, Ridley Rd, pool in ancient dune system, 33°14’28.2”S, 121°47’8.3”E, 25 Januray 2007, BVT, 7 specimens, WAM C61761 View Materials GoogleMaps ; Grass Patch , 13.4 km NE, Guest Rd, unnamed lake, 33° 07’56.1”S, 121°48’10.4”E, 25 Januray 2007, 82 specimens, WAM C61762 View Materials GoogleMaps ; Esperance , 22 km E, pool, 10 December 1959, D.H.D. Edward, AM P55632 View Materials ; Perenjori , 48 km ESE at Wanarra Station, scrape 2 km W of homestead, 29°30’35.4”S, 116o 46’ 21.1”E, 20 August 2011, 20 specimens, WAM C61763 View Materials GoogleMaps ; Cue 15.7 km WNW, Austin Downs Station, depression near homestead, 27°22’59.9”S, 117°44’44.8”E, 31 August 2004, BVT, 42 specimens, WAM C61764 View Materials GoogleMaps .

Diagnosis. Egg spherical with many narrow superficial grooves but no paired pits. Male rostrum often broad with apex rounded, sometimes triangular. Clasper with long palp of 3 palpomeres and prominent projection mediodistally. Telsonic spines number ca. 25 and cercopods setae about 12, sometimes fewer; these setae slightly longer than basal cercopod diameter. Cercopod with inermic middle section.

Description. Male. Head ( Fig. 23 View FIGURE 23 A) with ocular tubercle prominent, compound eye occupying about 80%. Rostrum protruding about 1.2 × ocular tubercle, at right angles from base, broad, apex rounded. Triangular ocellus about half size of compound eye and lying at base of rostrum. Distal half of rostum with growth lines arranged chevron-like. Dorsal organ posterior to eye by about half its length, pedunculate and asymmetrical, three-quarters as high as ocular tubercle.

First antennae ( Fig. 23 View FIGURE 23 A) about 1.5 × length of peduncle of second antennae, with 9 lobes, each with numerous short sensory setae. Second antennae with spinose peduncle a little longer than rostrum; dorsal flagellum with 12 antennomeres; ventral flagellum with 13 antennomeres, dorsally with 1–4 short spines and ventrally with 0–5 longer setae. Most central antennomeres with about 3 spines and 3 or 4 setae; distal antennomeres with minimal spines and maximal setae.

Carapace elongated oval, opaque light brown, hardly any indication of growth lines. Adductor muscle scar at about 40° to carapace long axis, only visible when animal removed from carapace.

Thoracopods. Eighteen pairs of thoracopods. Claspers ( Fig. 23 View FIGURE 23 C) with palm trapezoidal with endite III distomedially projecting about one-fifth of distal palm width. Apical club spherical with many stout spines pointing medially. Small palp with many short aciculate spines apically. Finger arcuate with blunt apex bearing many rounded pits ventrally. Both long palps inserted on apical edge of palm, with 3 palpomeres and inerm at palpomere junctions; many limp filiform setae on flattened palaform apical area. First long palp 1.25 × palm length, second palp 2 × palm length. Other thoracopods of typical structure for Paralimnadia , decreasing is size and complexity posteriorly. Last 10 segments dorsally with short spine medially.

Telson ( Fig. 23 View FIGURE 23 B) posterior spine rows with about 28 pairs of spines, with anteriormost spine about 1.5 × length of next few, and penultimate spines slightly longer than most spines, the remainder short. Spines with spinules. Telsonic filaments originating from mound slightly higher than dorsal floor of telson positioned at 7–8th spine. Floor of telson posterior to mound with steep declivity, then a slightly convex surface to base of cercopod. Cercopods almost as long as telson spine row, basal 65% hardly narrowing to small spine then a tapering to acute apex. Basal 40% with about 12 setae of medium length (a little longer than basal cercopod diameter) then cercopod inermic (20–25% of cercopod length) followed by small spine, then cercopod narrowing to sharp apex with many tiny denticles. Cercopod setae geniculate and plumose. Ventroposterior corner of telson broadly triangular with wide apex posteriorly.

Female. Head ( Fig. 23 View FIGURE 23 F) with ocular tubercle prominent, compound eye occupying about 80%. Rostrum an asymmetrical prominent bulge subequal to ocular tubercle; middle basal part occupied by triangular ocellus, about half size of compound eye. Dorsal organ posterior to eye by about three-quarters of its height, pedunculate and asymmetrical and about three quarters as high as ocular tubercle.

First antennae ( Fig. 23 View FIGURE 23 F) subequal in length to peduncle of second antennae, with 5 small lobes each with many short sensory setae. Second antennae largely as in male, though flagella perhaps with one fewer antennomere.

Carapace ( Fig. 23 View FIGURE 23 E) as in male, though more vaulted dorsally.

Thoracopods. Seventeen to 18 thoracopods of typical Paralimnadia structure. Trunk dorsum with segments 1– 9 inermic, segments 10–14 with 3–7 spines/setae distomedially and 15–17 segments with 1 spine distomedially. Thoracopods 9 and 10 with pair of long flabella dorsally.

Telson ( Fig. 23 View FIGURE 23 G) as in male.

Egg ( Fig. 20 View FIGURE 20 I–L) spherical with 34–42 straight grooves, each about 40–50 µm long and surrounded by ridges, either rounded in cross section or sharp and often terminating in slightly raised area. Groove-ridge systems interdigitated so that adjacent units uncoordinated and often at angle. No paired pits on either side of one groove.

Variability. The abundant material from the Grass Patch area shows many variations from that of the types. The relative size of the compound eye varies between specimens from about 40–80%; the ocellus size is also variable. The male rostrum may be narrowly triangular and only slightly larger than the ocular tubercle. First antennal lobes vary from 6 to 9 and the antennomeres 9–14, with the ventral flagellum usually with about one more than the dorsal flagellum. Telsonic spines vary from 19 to 28, with some variation in relative length. The cercopod is the least variable component, with almost always 8–12 setae and a 60:40 (or 65: 35) division between the setae carrying base and narrowing denticulated distal portion. The isolated Wanarra population had only 6 cercopod setae, but still an inerm portion of the cercopod ( Fig. 23 View FIGURE 23 D)

The remote Cue population varied more the others. The egg has fewer groove/ridge systems with some parallel aligned and the tumidities at the ridge ends are greater than normal ( Fig. 20 View FIGURE 20 L). The inermic part of the cercopod is shorter than usual and there are only 9 or 10 cercopod setae. In most specimens the first long palp has two palpomeres and the second palp three palpomeres, the reverse of the usual situation.

Differential diagnosis. Only four species of Paralimnadia ( P. multispinosa n. sp., P. queenslandicus n. sp., P. saxitalis n. sp. and P. westraliensis n. sp.) have spherical eggs without any protrusions. Just two of these are grooved, P. queenslandicus n. sp. always having two pores on either side of one groove, which P. westraliensis lacks. Paralimnadia westraliensis has a large number (>24) of telsonic spines, a character shared only with P. multispinosa —the two are separated by P. multispinosa n. sp. having just two palpomeres on the first long palp, while P. westraliensis n. sp. has three. The other feature of note in P. westraliensis n. sp. is the inermic central part of the cercopod, shared with P. stanleyana , P. badia and P. multispinosa n. sp. These three species differ, however, in P. stanleyana having a mixture of short setae and spines on the cercopod, P. badia having a completely inermic cercopod and P. multispinosa n. sp. by having only 6 cercopod setae as against 8-10 in most P. westraliensis n. sp. plus the difference in claspers mentioned above. Overall P. westraliensis n. sp. is most similar to P. multispinosa n. sp. but besides the small differences noted above, their eggs are very different (cf. Fig. 23 View FIGURE 23 I–L with Fig. 23 View FIGURE 23 A).

Distribution and ecology. Paralimnadia westraliensis is common in the Esperance hinterland, but there are also outliers in the northern Wheatbelt and northern Goldfields. It was probably distributed throughout the Wheatbelt and maybe beyond, but the salinization of the wheatbelt has reduced its distribution to the largely unaffected Esperance hinterland. Here, it occurs largely in pools in the old dunefields, though in one case (a lake on Guest Road), it was found in a normally saline lake that was much enlarged and significantly diluted by major unseasonal summer rainfall ( Timms 2009).


Western Australian Museum