Paralimnadia hyposalina, 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 : 480-482

Paralimnadia hyposalina n. sp.

( Figs. 4 , 11 , 16 )

Etymology. The specific epithet is based on the Greek ‘hupo,’ usually written as ‘hypo’ meaning ‘under, below or slightly’ and the Latin ‘salarium’ meaning salt, the word combination hyposaline used to describe inland waters 3 to 20 g /L ( Hammer 1986). This is only the second clam shrimp to be found living in such waters, the first being Eocyzicus parooensis Richter &Timms, 2005 .

Type material. Holotype: WAM C61750, male, length 8.0 mm, height 4.9 mm, Coomberdale , via Moora , Western Australia, pan dissected by Coomberdale West Road, 30°28’01.7”S, 115°59’04.9”E, 7 September 2011 , BVT. Allotype: WAM C61751, female length 6.8 mm, height 4.8 mm, collected with holotype. Paratypes: AM P99010, 2 males, 7.6 × 4.7 mm, 6.9 × 4.8 mm, 2 females, 8.0 × 5.0 mm, 7.8 × 4.9 mm, collected with holotype.

Other material examined. Western Australia: 22 males, 27 females, Coomberdale , near Moora , pan dissected by Coomberdale West Road, 30°28’01.7”S, 115°59’04.9”E, 7-9-2011, BVT, WAM C61752 ; 2 males, 2 females, Watheroo , Railway Road pan on east side of by railway, 30°13’27.6”S, 116°04’47.9”E, 7-9-2011, WAM C61753 .

Diagnosis. Egg spherical with numerous, close set, narrow, spongiform spikes. Male rostrum protruding about twice as far as ocular tubercle. Cercopod with about 10–12 setae, length subequal to its basal width. Male second clasper palp with about 5 short setae at palpomere junction. Triangular ventroposterior angle of telson clothed in denticles.

Description. Male: Head ( Fig. 16 B) with ocular tubercle prominent, compound eye occupying about 80%. Rostrum protruding about twice as far as ocular tubercle and consisting of about three times its volume. Rostrum projecting at right angles from its base; apex rounded. Ocellus about half size of compond eye, lying at base of rostrum. Dorsal organ posterior to eye by about threequarters its length, pedunculate and asymmetrical and about threequarters height of ocular tubercle.

First antennae ( Fig. 16 B) about one and a half times length of peduncle of second antennae; with about 10 lobes, each with numerous short sensory setae. Second antennae with spinose peduncle; dorsal flagella with 9 antennomeres and ventral flagella with 10 antennomeres. Dorsally with 1–3 short spines; ventrally with 1–6 longer setae. Basal and distal antennomeres with minimal spines, while setae maximal distally.

Carapace ( Fig. 16 A) elongated oval, pelucid, with about 3 growth lines. Adductor muscle scar at about 45° to carapace long axis.

Eighteen pairs of thoracopods. Claspers ( Fig. 16 D) with palm trapezoidal with distinct rounded expansion distomedially. Apical club spherical with many stout spines pointing medially. Small palp with many short thin spines apically on gripping area. Finger arcuate with blunt apex bearing many rounded pits ventrally. Long palp of first clasper inserted on apical edge of palm with 3 palpomeres and with about 4 stout setae medially at basal palpomere junction and many thin, limp setae on flattened palaform apical area. Long palp of second clasper also with 3 palpomeres, though second division indistinct and with about 5 stout setae medially at basal palpomere junction. Palp of first clasper about 1.25 × length of palm and 2 × length in second clasper.

Thoracopods. Other thoracopods of typical structure for Paralimnadia , decreasing is size and complexity posteriorly. Dorsal surface of trunk with 1 or 2 short spines medoposteriorly on each of posterior 12 trunk segments.

Telson ( Fig. 16 C) posterior spine rows with about 14 pairs of spines, with anteriormost spine about twice next few, and remainder forming uneven row. Spines with spinules. Telsonic filaments originating from mound little higher than dorsal floor of telson positioned near fourth spine. Dorsal floor of telson posterior to mound sloping steeply posterior to mound then with slightly convex surface to base of cercopod. Cercopods almost as long as posterior margin of telson; basal 50% hardly narrowing to small spine then rapidly narrowing to acute apex. About 11 long setae, most little longer than diameter of cercopod on basal half, with many tiny denticles dorsolaterally on apical quarter. Setae geniculate and plumose, much more so on distal section than on basal. Ventroposterior corner of telson with small triangular denticlulate protrusion.

Female. Head ( Fig. 16 F) with ocular tubercle prominent, compound eye occupying about 90%. Rostrum a rounded prominent bulge, protruding little less than ocular tubercle; basal part occupied by large ocellus, about 60% size of compound eye. Dorsal organ posterior to eye by about threequarters its height, pedunculate and asymmetrical and about threequarters the height of ocular tubercle.

First antennae ( Fig. 16 F) little shorter than peduncle of second antennae, with 7 lobes each with many short sensory setae. Second antennae largely as in male, though both flagellum with 9 antennomeres.

Carapace ( Fig. 16 E) as in male, though more vaulted dorsally.

Thoracopods. Eighteen pairs of thoracopods of typical Paralimnadia structure. Trunk dorsum with 3–9 setae terminally, these setae few, short and stout on last few segments, numerous and longer on segments 8–15 and anterior trunk segments 1–7 naked.

Telson ( Fig. 16 G) as in male, though with 19 pairs of posterior row spines.

Egg ( Fig. 11 G, H) consisting of numerous (60–80) elongated triangular to polygonal based pyramidal/ sublamellar projections around a central sphere. Each projection extremely spongiform. Overall diameter 325 µm at Coomberdale and 395 µm at Watheroo (each n = 5) with a total range of 316 to 412 µm.

Variability. While there is little difference in the morphology of animals from the two sites (e.g., slightly different telsonic denticle numbers, which are different between the sexes), the eggs look different, the pyramidal projections being of different sturdiness in the two sites. However, basic structure is similar so the two populations are considered conspecific.

Differential diagnosis. Paralimnadia hyposalina n. sp. shares a relatively large male rostrum (i.e., significantly greater ocular tubercle) bearing a rounded apex with some populations of P. stanleyana , most P. cygnorum , most P. monaro n. sp., and most P. westraliensis n. sp., but these species all have a noticeable projection on the distomedial surface of the clasper palm, whereas P. hyposalina n. sp. does not. Concerning cercopod setae, which are often diagnostic, P. hyposalina n. sp. has about 10–12 short setae of even length like P. saxitalis n. sp., but the later has only two palpomeres on the long palp of clasper I whereas P. hyposalina n. sp. has three. The presence of denticles on the triangular angle beneath the cercopod base is unusual, though they are present in some species of Eulimnadia (Timms 2015) . The egg is unique, with 60–80 triangular to polygonal projections within a general spherical shape.

Distribution and ecology. This species is known only from hyposaline ponds in the Coomberdale–Watheroo area north of Moora, Western Australia ( Fig. 4 ). Most occurrences were in the 5–10 g /L range with highest at 14 g / L.

Figures

FIGURE 4. Map of Australia showing distributions of all species with insert of details of Sydney region, especially for sites of P. stanyleyana.

FIGURE 11. Scanning electron micrographs of eggs. A-B, Paralimnadia ammolophos n. sp., C, P. bishopi n. sp., D-F, P. flavia n. sp., G-H, P. hyposalina n. sp., I-J, P. monaro n. sp., K-L, P. montana n. sp. A from Brooms Head, NSW, AM P 99008; B from Shelly Beach, NSW, AM P 99007; C from Cape Bedford, Qld, AM P 99359; D from Radom Springs, NT, AM P 98911; E from Larrimah, NT, AM P 98999; F from near Kununurra, WA, WAM C 61749; G from Coomberdale, WA, WAM C 61751; H from Watheroo, WA, WAM C 61753; I from near Berridale, NSW, AM P 99011; J from Manderley Pool, NSW, AM P 47129; K from Glencoe Lagoon, NSW, AMP 99014; L from Emu Rk Tarn, NSW, AM P 47132. Scale bars 0.1 mm.

FIGURE 16. Paralimnadia hyposalina n. sp.: A – D, male, WAM C 61750; E – G, female, WAM C 61751. A, carapace; B, head; C, telson; D, 2 nd clasper; E, carapace; F, head; G, telson. Scale bars 1 mm.