Limnadopsis occidentalis, Timms, 2009

Timms, Brian V., 2009, A Revision of the Australian Endemic Clam Shrimp Genus Limnadopsis Spencer & Hall (Crustacea: Branchiopoda: Spinicaudata: Limnadiidae), Records of the Australian Museum 61 (1), pp. 49-72 : 63-64

Limnadopsis occidentalis n.sp.

Figs. 2F , 5J , 12

Types. Holotype 3 WAM C39336, allotype ♀ WAM C39337, paratypes, 23, 2♀, WAM C39338. Type locality: Western Australia, N of Carnarvon, Boolathana Station , unnamed claypan, 24°38'34"S 113°59'35"E, 15.iii.1995, S.A. Halse.

Other material: Western Australia: 23, 8♀, 58.6 km south of Roebourne , small pools adjacent to creek, 20°48'S 117° 6'E, 25.vi.1964, C. Pugh, AM P55651 ; 13, 131 mile post, road to Port Headland via Woodstock , waterhole, 21°12'S 118°48'E, 26.vi.1964, C. Pugh, AM P55650 ; 63, 2♀, E of Kalbarri, Coolcalalaya Station , unnamed clay pan, 27°31'29"S 115°05'14"E, S.A. Halse, 15.iii.1995, WAM C39339 ; c. 40 km south of Mullewa, Tardan, Christian Brothers College , dam, 28°43'S 115°49'E, 25.vii.1999, J. McRae & A. Pinder, DEC, Woodvale, SPS185 ; 1♀, via Laverton , 20 km west near highway, samphire swamp, 28°36'S 122°13'E, 17.ii.2003, B. Datson, WAM C39340 .

Habitat and distribution. Limnadopsis occidentalis lives in a variety of temporary fresh waters, including claypans and floodplain pools, all in northwestern Western Australia.

Etymology. The species name is derived from the Latin occidens referring to the direction of the setting sun, and hence “west” an appropriate epithet for a species found in the west of Australia as opposed to its closely related species L. parvispinus , which is found in eastern Australia.

Male. Carapace ( Fig. 12A ) oval, 11 mm by 6 mm, L:D ratio = 1.8. Dorsal margin weakly convex with highest point at about one-third length, slight depression anterior to umbo and distinct dorsoposterior angle. Dorsal margin almost smooth, but with slight serrations at many growth lines, mainly posteriorly. Growth lines 11, weakly expressed. Carapace weakly granulated within, but presenting a smooth yellow-buff surface in preserved condition.

Head ( Fig. 12B ) with pyriform organ posterior to eye mound and about as high as latter. Anterior sides of eye mound and rostrum both straight and meeting at a distinct angle of about 110°. Rostrum elongated triangular, about as long as anterior surface of head, apex rounded and slightly flexed downward. Naupliar eye triangular, its axis aligned similarly to that of rostrum. Length of first antenna subequal to that of peduncle of second antenna, and former bearing 7 lobules. Second antenna with 12 apparent peduncular segments and 15–16 flagellomeres on flagella, most middle segments with 5–7 spines, 2 of which sometimes grouped apically.

Trunk segments 25 in number, each bearing pair of thoracopods, these decreasing in size posteriorly, and anterior two pairs modified as claspers. Posterior dorsal armature comprising 1–3 spines on small protuberances on each of last 7 segments, and a few setae on preceding 6 segments. Claspers of normal structure for Limnadopsis , with one spine apically on the movable finger, and prominent, asymmetrical protrusion midway along anterior edge of hand.

Telson ( Fig. 12C ) with two rows of 13 dorsal spines each. Most anterior spine about 1.5 times the size of next spine, most posterior spines smaller and sharper than anterior spines, and spines in middle of row more widely spaced than anterior or posterior spines. Two telsonic setae inserted on protuberance situated about one quarter of way along dorsal side of telson. Caudal claws about 8 times longer than wide, with long, almost straight basal section of even width and much shorter, curved apical part tapering to a sharp apex. Basally, cercopods bearing about 12 setae mediodorsally, most of them being a little longer than width of claw, followed by 3 short spines inserted almost dorsally, the posteriormost the largest. Curved, tapered apical part of cercopods bearing many short denticles dorsally.

Female. Carapace ( Fig. 12D ) oval, 11 mm by 7 mm, L:D ratio 1.57. Dorsal margin more convex than in male and also with distinct depression in umbo area. Dorsal margin largely smooth, but minor serrations present posteriorly at junctions of growth lines. Growth lines 9, weakly expressed.

Head ( Fig. 12E ) typical for females of Limnadopsis , with short triangular rostrum. Six lobules on first antenna. Second antenna as in male.

Telson ( Fig. 12F ) similar to that of male, but with 15 telsonic spines in each row, and six spines on caudal claws.

Eggs ( Fig. 5J ) round, about 175 µm in diameter (range 170–178 µm; n = 5) with short deep grooves, aligned at most in pairs, otherwise set at various angles to one another. Intergroove areas smooth and internally frothy.

Variability. Considerable variability was noted in representatives of the six populations studied. Growth lines vary from 9 to12, but they are invariably weakly expressed and meet the dorsal margin in at most weak dorsal serrations posteriorly. First antennal lobules vary from 6 to 9, with males of a given population generally having one more than females. On the telson, the dorsal spines vary from 12 to16 per row, with a mean of 13; and the spines on the caudal claws range from 2 to 6, usually about 4.

Comments. This species is similar to L. parvispinus . Despite wide variation in many features of both species, there are many differences between the two, including: (a) fewer telsonic spines in L. occidentalis (about 13–15 per row compared to about 18–22); (b) A slight anterior depression in the dorsal carapace margin of L. occidentalis while in L. parvispinus the margin is straight or slightly convex; (c) the differently shaped eggs, round in L. occidentalis and with the grooves ungrouped or at most in pairs, compared to cylindrical to muffin-shaped in L. parvispinus with multiple parallel grooves in the outer cortex; (d) most flagellomeres have six dorsal spines in L. parvispinus , but five in L. occidentalis ; (e) fewer setae and fewer spines on the caudal claws in L. occidentalis (ca 12 setae in L. occidentalis and c. 15 in L. parvispinus ; 2–6 spines in L. occidentalis and 4–9 spines in L. parvispinus ); and (f) usually one fewer lobule in the first antenna in L. occidentalis (6–9, verses 7–10 in L. parvispinus ).

Figures

Fig. 2. Photographs of whole specimens of species of Limnadopsis. (A) L. birchii; (B) L. tatei; (C) L. parvispinus; (D) L. minuta; (E) L. multilineata; (F) L. occidentalis; (G) L. paradoxa; (H) L. pilbarensis. Scale bars 5 mm.

Fig. 5. SEMs of eggs. (A) Limnadopsis birchii, Twin Pans, Currawinya National Park, Qld; (B) L. birchii, Bluebush Bore Swamp, via Carnarvon, WA; (C) L. multilineata, Mitchell River Falls, Kimberley, WA; (D) L. tatei, Bloodwood Station, Paroo; (E) L. tatei, near Laverton, WA; (F) L. pilbarensis, Chichester Range, WA; (G) L. parvispinus, Bloodwood Station, via Bourke, NSW; (H) L. parvispinus, Coolringdon Station, via Cooma, NSW; (J) L. occidentalis, Boolathana Station, via Carnarvon, WA; (K) L. paradoxa, Sieda Farm, Grass Patch, WA; (L) L. paradoxa, East Lake Bryde, via Newdegate, WA; (M) L. minuta, Keep River National Park, NT. Scale bars 50 µm.

Fig. 12. Limnadopsis occidentalis n.sp., Boolathana Station, via Carnarvon, WA. Male: (A) carapace; (B) head; (C) telson. Female: (D) carapace; (E) head; (F) telson. For clarity some growth lines of the carapace are incompletely shown anterior to umbo. Scale bars 1 mm.