Paralimnadia monaro, 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: 482-485

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Paralimnadia monaro

n. sp.

Paralimnadia monaro   n. sp.

( Figs. 4 View FIGURE 4 , 11 View FIGURE 11 , 17 View FIGURE 17 )

Etymology. The name for this species is taken from the district name, the Monaro   plateau, so that specific epithet ‘monaro’ is a noun in apposition.

Type material. Holotype: AM P99011 View Materials , male, length 8.1 mm, height 4.8 mm, New South Wales, 11.7 km north of Berridale , roadside pond on ‘ Stoneleigh,’ 36°15’41.4”S, 148°47’42.1”E, 14 March 2010, BVT GoogleMaps   . Allotype: AM P99012, female, length 9.0 mm, height 5.7 mm, collected with holotype. Paratypes: AM P99013, 5 males, 8.9 × 5.7 mm, 8.8 × 5.1 mm, 8.3 × 5.0 mm, 7.9 × 4.8 mm, 7.9 × 4.8 mm, 5 females, 9.5 × 6.7 mm, 8.9 × 6.0 mm, 8.7 × 5.1 mm, 8.4 × 5.8 mm, 7.8 × 5.1 mm, collected with holotype.

Other material examined. New South Wales, 4 males, 3 females, near Berridale, AM P55642 View Materials   ; 14 males, 26 females, 18.6 km west of Cooma , pan on ‘ Manderley,’ 36°14’53.6”S, 148°53’ 22.0”E, 1 February 1996, BVT, AM P47129 View Materials GoogleMaps   ; 4 males, 2 females,‘ Cow pool’ on ‘ Manderley,’ 36°14’53.1”S, 148°53’22.1”E, 3 March 2010, M. Schwentner, AM P82784 View Materials GoogleMaps   .

Diagnosis. Egg consists of 2 bands of ridge-groove sets at right angles. Male rostrum significantly larger (ca. 2 ×) than ocular tubercle and with rounded apex. About 15 telsonic denticles and <10 cercopod setae. Basal segment of cercopod setae with few setules or none.

Description. Male: Head ( Fig. 17 View FIGURE 17 B) with ocular tubercle prominent, the compound eye occupying about 80%. Rostrum large, protruding about twice the ocular tubercle, broadly triangular but with rounded apex and base extended ventrally. Ocellus somewhat smaller than compound eye and lying at base of rostrum. Rostrum with curved growth lines between ocellus and apex. Dorsal organ posterior to eye by about its height, pedunculate and asymmetrical and about half as high as ocular tubercle.

First antennae ( Fig. 17 View FIGURE 17 B) almost twice the length of peduncle of second antennae, and with 10 lobes, each with numerous short sensory setae. Second antennae with spinose peduncle and dorsal flagellum with 12 antennomeres and ventral flagellum with 13 antennomeres, and dorsally with 0–3 short spines and ventrally with 0–5 longer setae. Distal antennomeres with minimal spines and maximal setae.

Carapace ( Fig. 17 View FIGURE 17 A) elongated oval, partially opaque, light cream-coloured. Valves with many pigment cells fairly evenly distributed. About 5 growth lines visible. Adductor muscle scar at about 45° to carapace long axis, only visible when animal removed from carapace.

Thoracopods. Eighteen pairs of thoracopods. Claspers ( Fig. 17 View FIGURE 17 D) with palm trapezoidal with distinct rounded projection distomedially. Apical club spherical with many stout spines pointing medially. Small palp with many short thin spines apically. Finger arcuate with blunt apex bearing suctorial disc anteriordorsally and many rounded pits ventrally. Both long palps of claspers inserted on apical edge of palm, each with 2 palpomeres, but with thin band in distal palpomere suggesting possible split into third palpomere. Palpomere junctions inerm and many limp filiform setae on flattened palaform terminal area. Long palp of first clasper about 1.5 × length of palm and 2 × length in second clasper. Other thoracopods of typical structure for Paralimnadia   , decreasing is size and complexity posteriorly. Last 7 segments dorsally with short spine medially.

Telson ( Fig. 17 View FIGURE 17 C) spine rows with about 15 pairs of spines, with shortest centrally and longest at each end of row. Spines with spinules. Telsonic filaments originating from mound little higher than dorsal floor of telson positioned near fourth spine. 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 spinal row of telson, the basal 50% hardly narrowing to small spine then greatly narrowed to acute apex. About 7 cercopod setae, each subequal in length to basal diameter of cercopod and many tiny denticles dorsolaterally on apical half. Setae geniculate with only distal portion plumose. Ventroposterior corner of telson rounded and hardly protruding.

Female: Head ( Fig. 17 View FIGURE 17 F) with ocular tubercle prominent, with compound eye occupying about 80%. Rostrum a rounded prominent bulge subequal in prominence to ocular tubercle. Middle basal part of rostrum occupied by large ocellus, about 80% 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. 17 View FIGURE 17 F) somewhat shorter than the peduncle of the second antennae, with four small lobes each with many short sensory hairs. Second antennae largely as in male.

Carapace ( Fig. 17 View FIGURE 17 E) as in male, though more vaulted dorsally.

Thoracopods. Eighteen thoracopods of typical Paralimnadia   structure. Trunk dorsum with segments 1–9 naked, segments 10–14 with 9–13 spines medioterminally and segments 15–18 with 3–7 spines medioterminally. Thoracopods 9 and 10 with long flabellum dorsally.

Telson ( Fig. 17 View FIGURE 17 G) as in male, though with 19 pairs of posterior row spines. Cercopod also of similar structure as in males, but 10 or 11 setae, most subequal to basal diameter of cercopod.

Egg ( Fig. 11 View FIGURE 11 I, J). Egg essentially cubicular with flared lamellae on edges, each surface about 100 µm long, diameter about 190 µm (range 176–218 µm, n = 10). Egg surface with 2 rows of ridges and grooves wrapped around each other, usually at right angles, neither forming complete ring, whole egg approximately cubicular. Row edges flared.

Variability. The distinctive head morphology among males is consistent within and between sites, and the numbers of antennal lobes and antennomeres rarely varies from 10 and 12 or 13 respectively. However, the number of telsonic spines is particularly variable among males with numbers ranging from 12 to 16, though the size variation along the row is almost invariant. Female’s telsonic spines are less variable. In the Manderley pan population, the cercopod setae are about twice the basal cercopod diameter (instead of being subequal) and number 8 or 9 in males and 12 in females. The palps of the clapsers are generally as described for the holotype, but some specimens have three palpomeres on the large palp.

Differential diagnosis. The egg is unique within Paralimnadia   , though the double structure of two bands of ridge-groove sets wound around at right angles to each other is reminiscent of the egg of Eulimnadia vinculuma   in southwestern Australia (Timms 2015). The relatively large male rostrum (i.e., significantly greater ocular tubercle) and with a rounded apex is similar to those in some populations of P. stanleyana   , most P. cygnorum   , all known P. hyposalina   n. sp. and in most P. westraliensis   n. sp. Large differences in telsonic spines can be used to differentiate P. stanleyana   (<12) and P. westraliensis   n. sp. (>25) from P. monaro   n. sp. (ca. 15), but P. cygnorum   and P. hyposalina   n. sp. have about 14–18 so are not distinguished. Paralimandia hyposalina   n. sp. and particularly P. monaro   n. sp. have few or no setules on the basal segment of the cercopod setae, whereas all other species of Paralimandia have many. Their eggs and distributions, however, are very different (see text).

Distribution and ecology. This species occurs in small ponds on both granite and basalt on the Monaro   plateau in southeast New South Wales ( Fig. 4 View FIGURE 4 ).