Paralimnadia bishopi, 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: 474-476

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Paralimnadia bishopi

n. sp.

Paralimnadia bishopi   n. sp.

( Figs. 4 View FIGURE 4 , 11 View FIGURE 11 , 13 View FIGURE 13 )

Etymology. This species is named to honour the late Dr Jim Bishop   who not only collected the species from remote Cape York, but who made extensive studies into the ecology of the Paralimnadia stanleyana   , so that it is the most understood Australian limnadiid shrimp.

Type material. Holotype: AM P98358 View Materials , male, length 5.0 mm, height 3.8 mm, Cape York Peninsula, sand dune lake near Cape Bedford, 15°14’S, 145°20’E, February–March , 1966, J. Bishop   GoogleMaps   . Allotype: AM P98359, female, length 5.9 mm, height 3.8 mm, collected with holotype.

Other material examined. Queensland: 4 males, 4 females, 2 juveniles, Cape York Peninsula, sand dune lake near Cape Bedford, 15°14’S, 145°20’E, J. Bishop   , February–March 1966, AM P55637 View Materials GoogleMaps   ; 1 male, 3 females, Cape York Peninsula, sand dune lake near Cape Bedford, 15°14’S, 145° 20’E, I.A.E. Bayly , January 1965, AM P55638 View Materials GoogleMaps   .

Diagnosis. Egg irregularly shaped with about 8 broad and rounded protuberances subtended by many grooves and ridges at right angles. Male rostrum triangular and protruding subequally to ocular tubercle. Telson with about 16–20 spines, shortest centrally. Cercopod with 2 shorter and about 7–11 extraordinarily long setae.

Description. Male: Head ( Fig. 13 View FIGURE 13 B) with ocular tubercle prominent, compound eye occupying about 50%. Rostrum protruding little more than ocular tubercle and at right angles from its base, triangular, apex blunt. Ocellus somewhat smaller than compound eye and lying at base of rostrum. Dorsal organ posterior to eye by about half its height, pedunculate and asymmetrical and not quite as high as ocular tubercle.

First antennae ( Fig. 13 View FIGURE 13 B) almost twice length of peduncle of second antennae, with seven lobes, each with numerous short sensory setae. Second antennae with spinose peduncle; dorsal flagellum with 13 antennomeres; ventral flagellum with 14 antennomeres; dorsally with 1–3 short spines and ventrally with 1–5 longer setae. Distal antennomeres with minimal spines and maximal setae.

Carapace ( Fig. 13 View FIGURE 13 A) elongated, oval, pellucid, carapace fold line dark brown. About 5 growth lines. Adductor muscle scar at about 45° to carapace long axis, only visible when animal removed from carapace.

Thoracopods. Eighteen pairs of thoracopods. Claspers with palm trapezoidal, with small rounded expansion distomedially. Apical club spherical with many stout spines pointing medially.Small palp with many short thin spines apically. Finger arcuate with a blunt apex bearing many rounded pits ventrally. Both long palps of clasper ( Fig. 13 View FIGURE 13 D) inserted on apical edge of palm, each with 3 palpomeres, first about 1.5 × palm length, second about 2 × palm length. First joint of first palp with five geniculate setae of increasing length laterally and with lateral pecten on the distal section of seta. Second palp with similar setal arrangement but longer; most lateral setae almost reaching palp apex. Both palp flattened palaform apices with numerous short soft setae. Other thoracopods of typical structure for Paralimnadia   , decreasing in size and complexity posteriorly. Last 10 segments dorsally with 1–3 spines medially, more anteriorly than posteriorly.

Telson ( Fig. 13 View FIGURE 13 C) with about 18 pairs of posterior row spines; anteriormost and posteriormost spines longest; central spines shortest. Spines with spinules. Telsonic filaments originating from mound little higher than dorsal floor of telson, positioned between third and fourth spine. Dorsal floor of telson posterior to mound sloping steeply posterior to mound then with slightly convex surface to base of cercopod. Cercopods subequal in length to telson dorsum, basal 50% hardly thinning to small spine then rapidly thinning to acute apex. About 8 2-segmented setae of various lengths (1.5–4.0 × cercopod basal diameter) with shortest anteriorly and longest posteriorly. All setae plumose along entire length. Ventroposterior corner of telson rounded and hardly protruding.

Female. Head ( Fig. 13 View FIGURE 13 F) with ocular tubercle prominent, with compound eye occupying about 60% of it. Rostrum a rounded prominent bulge protruding subequally to ocular tubercle and with middle basal part occupied by large ocellus, about 60% size of compound eye. Dorsal organ posterior to eye by about its height, pedunculate and asymmetrical and about half as high as ocular tubercle.

First antennae ( Fig. 13 View FIGURE 13 F) little shorter than peduncle of second antennae, with 3 small lobes each with many short sensory setae. Second antennae largely as in male, though antennomeres one less on each flagellum.

Carapace ( Fig. 13 View FIGURE 13 E) as in male, though more vaulted dorsally.

Thoracopods. Seventeen thoracopods of typical Paralimnadia   structure. Trunk dorsum with segments 1–8 naked, segments 9–13 with 3–9 spines medioterminally and segments 14–17 with spine distomedially. Thoracopods 6 and 7 with long flabellum dorsally.

Telson ( Fig. 13 View FIGURE 13 G) as in male, though with 17 pairs of posterior row spines, a little less ordered than in male. Cercopod with about 13 geniculate setae, first 2 short (length about diameter of base of cercopod) and remainder long (about 4 × diameter of base of cercopod). Setation as in male.

Egg ( Fig. 11 View FIGURE 11 C) multidimensionally stellate, maximum diameter 237 µm (range 233–241 µm, n = 5). About 8 rounded, broad protuberances each projecting by about 70 µm from a core diameter of about160 µm and subtended by up to 10 paired ridges and groves largely right angles to the protuberances.

Variability. The number of trunk segments are variable in this species, with 18 or 19 noted in males and 17–20 in females. The male rostrum was not noted to vary in size, though the female rostrum is sometimes less protruding than in the allotye. As usual first and second antennae vary by ±1 lobe/ antennomere respectively. Telsonic spines are even more variable both in number (16–20) and size, though almost always the centre group are shorter than anterior and posterior spines. While cercopod setae vary a little (±1) in number and size, the shortness of the first couple (subequal to cercopod basal diameter) and the extraordinary length (4 × cercopod basal diameter) of the remainder of the cercopods is noteworthy. Ovigerous filaments (flabella) can also be located on thoracomeres 9 and 10 instead of 6 and 7.

Differential diagnosis. This species and P. ammolophos   n. sp. live in very similar habitats (humic waters in coastal dunes), but 1800 km apart. Both have similarly structured eggs, male rostra, and telsonic denticles, but the cercopods and also clasper palps are distinctly different. Both species have the same number of cercopod setae, but in P. ammolophos   n. sp. all are of similar length at about 2.0–2.5 × cercopod basal diameter, whereas in P. bishopi   n. sp. the first two are short and the remainder very long at about 4 × cercopod basal diameter. The basal palpomere of the clasper large palps has about 3 short spines in P. ammolophos   n. sp. and five large spines of variable length in P. bishopi   n. sp. There is also some similarlity to P. s o rd i d a, another east coast sand dune species. It also has a clasper with 3 palpomeres in each long palp, spines at the junction of their first and second segments and 9–12 long cercopod setae, though the distinctive characters of P. bishopi   n. sp. are noted above.

Similarities also exist in their morphology. In all three species the long palp of the clasper has three palpomeres, with stout setae on the basal palpomere junction particularly robust in P. bishop   n. sp. Interestingly all three species also have about 9–12 cercopod setae, though their lengths are longer in P. ammolophos   n. sp. and P. bishopi   n. sp. than in P. s o rd i d a. Furthermore in P. bishopi   n. sp., the cercopod setae are particularly long. The three species are easily distinguished apart by their eggs, lengths of cercopod setae and numbers and lengths of setae on their long palps.

Distribution and ecology. This species is only known from its type locality on Cape York Peninsula, from which it has been collected twice. If this site is like other waterbodies in the area it is probably acid (circa 4.8), humic and of low total salts (circa 52 mg l -1) ( Timms 1986). These northern dune waterbodies share many hydrological, physicochemical and biological similarities with those of southeast Queensland and northern New South Wales ( Bayly 1964; Timms 1982). Of immediate interest is the presence of a species of Paralimnadia   in each.