Australimnadia grobbeni ( Daday, 1925 ) Daday, 1925

Timms, Brian V. & Schwentner, Martin, 2017, A revision of the clam shrimp Australimnadia Timms and Schwentner, 2012 (Crustacea: Spinicaudata: Limnadiidae) with two new species from Western Australia, Zootaxa 4291 (1), pp. 81-98 : 83-88

Australimnadia grobbeni ( Daday, 1925) comb. nov.

( Figs 1–4 )

Limnadia grobbeni Daday, 1925: 150 (key), 167–170: fig. 119; Webb & Bell, 1979: 243; Brtek, 1997: 57 (list). Limnadia sp. B.— Schwentner et al., 2009: 723, tab. 1, fig. 1–3.

Australimnadia gigantea Timms & Schwentner, 2012: 984 –989, figs 2–4. [New synonym].

Type material. Lectotype. Female, New South Wales, collector and date unknown, but before 1925, ZCUV 2016/ 12/1. (The lectotype is damaged and not easily accessed: cercopods and antennae missing, and rostrum squashed beyond recognition).

Other material examined. Northern Territory: 1 female, lagoon near Darwin , 27 May 1913, G.F. Hill, NMV J54038 ; 2 males, 8 females, Berrimah, 2.5 km E along Stuart Highway, Knuckeys Lagoon , 12°26’20.6”S, 130°56’41.1”E, 23 February 2006, S. Richter, AM P88391 . New South Wales: 3 males, 4 females, Clarence River, Taloumbi , 29°31’54”S, 153°17’43”E, 7 Apr 2001, NSW State Fisheries, AM P80867 – 80869; 4 males, 5 females, Paroo, Bloodwood Station, Wirrania Swamp , 29°30’30.3”S, 144°51’1.5” E, 5 July 2016, BVT, AM P99542 . Queensland: 5 males, 5 females, Cape York, 51.5 km SE of Bamaga, a dune lake at Ussher Point , 11°09’53.8”S, 142°46’00.1”E, 8 July 1983, BVT, AM P88390, BVT ; 3 males, 2 females, 17 km ESE of Meandarra , from gilgai on south side of Surat Development Road, 27°21’18.9”S, 149°59’19.8”E, 7 July 2009, BVT, AM P88387–88389 [holotype, allotype and paratypes of A. gigantea Timms & Schwentner, 1925 ] ; 2 males, 2 females, 17 km ESE of Meandarra , data as above, QM W29148 [paratypes of A. gigantea Timms & Schwentner, 1925 ] . Victoria: 3 females, Melbourne, Kew rifle range, 22 October, 1912, unknown collector, NMV J54035 ; 1 male, 1 female, Barmah State Forest, washout into Murray River , 5 December 2000, M. Jones, NMV J62965 .

Diagnosis. Egg double discoid. Large limnadiid shrimp with 23 or 24 trunk segments, male with long palps on claspers, clasper I with two palpomeres, clasper II with three palpomeres. Usually 24 trunk segments. Both sexes with telson bearing 18–24 (usually 21–24) dorsal spines divided into two groups by insertion of telsonic filaments: an anterior 8–12 spines on convex edge and posterior 9–13 spines on concave edge. Cercopod with about 20–25 (usually 22–25) long plumose setae, without spines midlength.

Description. Egg. ( Fig 3 A–E). Non-spherical double discoid shape at most localities. Mean diameter about 236 µm, but measurements depending very much on point of measurement. Each disc consisting of elongated twisted facies of alternate ridges and grooves at right angles to axis; this ridge-groove system occupying ½ to almost all of disc width. Egg in Meandarra population appearing different from those in four other populations; although double discoid in shape, ridge-groove system much more widely spaced along axis with ridges narrow and ‘grooves’ wide.

Female lectotype. Rostrum probably rounded, (but squashed). Telson spines 23 or 24 in two groups separated by telsonic filament mid-length. Anterior group of 8–12 on convex margin, tending posteriorly curved; posterior group of 11–13 on concave margin, tending erect vertically. Telsonic ventroposterior margin rounded, hardly protruding. No other features discernible.

Male (based on types of A. gigantea ). Length 12.6 mm, height 9.0 mm. Head ( Fig. 1 F, 2B) with prominent ocular tubercle containing spherical compound eye, with asymmtetrical dorsal organ posterior by about its own height. Rostrum triangular, protruding subequally to ocular tubercle, apex rounded to acute. Ocellus shape variable shape, but largely cometiform.

First antennae ( Fig. 2 B) about 1.5 times longer than peduncle of second antenna, with ca.12 sensory lobes. Second antennae rami with 12–14 antennomeres, most with ca. 6 dorsal spines and 7 long ventral setae ( Fig. 2 C), except smaller apical antennomeres, and basal antennomeres.

Carapace ( Fig. 1 D, 2A) unevenly ovoid, with weakly vaulted dorsal surface, maximum height about one-third length from anterior, large larval surface, generally dark coloured even dorsal hinge, growth lines weakly expressed and numbering up to ca. 25. Umbone absent. Abductor muscle scar located away from carapace edge by its diameter, ovoid, at ca. 45° angle to horizontal axis.

Trunk segments and thoracopod pairs 24, sometimes 23. Thoracopods as described for A. gigantea and illustrated by Timms & Schwentner (2012: fig. 4). Segments X–XXIV with stout dorsal setae medioposteriorly on small mounds, many (about 7–15) on segments XII–XVIII and few on segments X–XI and XVIII–XIV, as described by Daday (1925).

Claspers ( Fig. 2 D) with palm trapezoidal, terminating in apical club medially and in expanded base of moveable finger (endopod) laterally. Club with small palp laterally, with apical setae terminally. Club apically with scaliform spines graduating laterally into long spines, providing griping surface for apical pits of finger ( Kaji et al.

2014). Moveable finger arcuate, terminating in blunt rounded apex with suctorial organ anterioventrally and rounded pits dorsally. Long palp inserted on dorsal edge of palm alongside finger base; clasper 1 with palp of two palpomeres and little longer than palm; clasper 2 with palp of three palpomeres and about twice as long as palm. Both palps distally with numerous setae marginally on flattened concave apical area. Palpomere junctions without spines or setae.

Telson ( Fig. 1 H, 2C) with 22–24 dorsal spines, each without adornment except denticle row on anterior surface of posterior spiniform projection, spine generally upturned; remaining spines in two groups separated by telsonic filament mid-length. Anterior group of 8–12 on convex margin, tending posteriorly curved; posterior group of 11– 13 on concave margin, tending erect vertically. Telsonic ventroposterior margin usually rounded, hardly protruding.

Cercopod ( Fig. 1 H, 2C) subequal in length to telson, sometimes straight, concave, or even weakly convex; array of 22–25 long plumose setae along 80–90% of its length; proximally, these setae longer than telson height (i.e. about 3 × cercopod diameter), distally somewhat shorter, often only about diameter of cercopod; spine at distal end of setalarray without spine. Distal 10–15% of cercopod narrowing to sharp apex, usually with weak cirrus of small denticles dorsally.

Female (based on types of A. gigantea ). Length 16.2 mm, height 12.7 mm. Head ( Fig 1 F, 2G) as in male but with triangular rostrum with rounded apex.

First antennae ( Fig. 2 G) subequal to peduncle length and with 6 or 7 lobules. Second antennae as in males.

Carapace as in male, but more vaulted.

Thoracopods as in male, but no claspers, with long epipodial filaments of thoracopods IX and X for holding eggs.

Telson and cercopods as in male.

Variation. With material from Cape York south to Melbourne (3000 km) and west to Darwin (1300 km), some variation in morphology can be expected ( Fig. 4 A–F), but it is not clinal. Carapace shape varies between sites, with those at Meandarra ( Fig. 2 A, F) more vaulted ventrally then is typical of other populations ( Fig 4 A). While there is minor variation in numbers of telsonic spines particularly in the anterior group (8–12), this set is not always distinctively curved (as in Fig. 4 B). The spiniform projection of the telson can be curved dorsally or protruding straight posteriorly. Cercopod setae basally are always 3–4 times its basal diameter but diminuation along the setal row can be minimal down to the length subequal to the cercopod diameter. An exception is the specimen Daday illustrated ( Fig. 1 H) which shows all cercopod setae short, about 1–1.5 times cercopod basal diameter. No significant variation was observed in head structure, antennae, or claspers, except to note that Daday (1925) recorded only 4 sensory lobes in the first antenna he examined (compared to 6 or 7 in all present specimens).

Individuals from Wirrania Swamp in the Paroo are smaller than usual (mean length males 10.5 mm, n = 4; females 12.0 mm, n = 5). Meristic features are a little fewer than in other populations: the second antennal flagellomeres have the most common arrangement as 5 dorsal spines and 6 ventral setae, telsonic spines range from 18–20 and cercopod setae from 20–22. Otherwise, they accord with the morphology of A. grobbeni as described above.

Remarks. The female syntype (ZCUV 2016/12/1) of Australimnadia grobbeni is herein designated as the lectotype to fix the identity of the species. Characteristics of the lectotype and type specimens of A. gigantea agree with Daday’s original description and diagrams of Limnadia grobbeni (illustrated in his figs 3F–J, and here repeated in Fig. 1 D–H)). The carapace is approximately the same across all specimens and the animal certainly large, the head also is approximately the same, but heads are usually not distinctive in limnadiids (and we note it is possible that Daday’s diagrams of male and female heads are reversed ― male heads in limnadiids almost always have a more-or-less triangular rostrum and the female rostrum rounded, yet Daday figures the female rostrum triangular and the male rostum rounded), but the telson is distinctive, though not identical in ornamentation to the lectotype (i.e., telson setae inserted at 8th telson spine, not the 10th, and the cercopod setae are of moderate length (ca 1–1.5 times cercopod diameter) instead of long (ca 3–4 times cercopod diameter). It is significant that the distinctive feature of L. grobbeni as determined from the lectotype and type description, namely the telson ornamention, matches exactly its counterpart in A. gigantea . No other limnadiid has such a distinctive arrangement of telson spines as Australimnadia, particularly this species. Comparison of the lectoype of L. grobbeni and types series of L. gigantea shows that the two nominal species are taxonomically indistinguishable and are therefore synonymised.

The egg of A. grobbeni is somewhat different from that what is now thought to be A. grobbeni at Meandarra but so similar to that of Limnadia lenticularis (see Fig. 4 F and Timms & Schwentner 2012: figs 2A, B), that no consistent differences are apparent. However, the difference in egg morphology within Australimnadia between the Meandarra and other populations is distinct enough to suggest a separate species, but their adult morphologies are the same (compare Timms & Schwentner 2012: fig. 3 for the Meandarra population with Figs 2 and 3 herewith of the Knuckeys Lagoon, Ussher Point and Taloumbi populations). The possibility of a mix-up in SEM labelling was explored and dismissed, so that the difference remains unexplained.

Distribution and Ecology. Australimnadia grobbeni occurs sporadically, both spatially and temporally, in eastern and northern Australia. It has only been seen once in Melbourne (in 1912) and given the subsequent urbanisation of the site, it could now be extinct so far south. The Meandarra site has been visited a few times and it seems the population only appears there after a major filling of the gilgai and expires well before drying. This site is shared with Paralimnadia queenslandicus Timms, 2016b , which occurs on any filling and is persistent. The Wirrania population grew from first filling in late May 2016 to adulthood by early July and stayed at about that size till late October after which it apparently disappeared even though the site did not dry till December 2016. Specimens were much damaged by attempted predation, with second antenna and/or cercopods often missing and carapace with large bites taken out.

Figures

FIGURE 1. Australimnadia grobbeni (Daday, 1925). A – C: female lectotype. D – H: redrawn from Daday (1925). A, head; B, telson; C, carapace; D, male carapace; E: female carapace lateral and dorsal views; F, male head; G, female head (Daday may have inadvertently reversed these figures); H, telson. Scale bars 1 mm.

FIGURE 2. Australimnadia grobbeni (Daday, 1925) from Meandarra Qld. A – E, holotype male (AM P 88387) and F – G, allotype female (AM P 88388) of A. gigantea Timms & Schwentner, 2012) A, male carapace; B, male head; C, male telson; D, male claspers 1 and 2; E, two setae on cercopod; F, female carapace; G, female head. Scale bars 1 mm.

FIGURE 3. SEMs of Australimnadia eggs. A – E: A. grobbeni (Daday, 1925). A, Knuckeys Lagoon, Darwin, NT; B, dune lake, Ussher Pt, Cape York, Qld; C, gilgai, Meandarra, Qld; D, pond, Taloumbi, NSW; E, swamp, Barmah Forest, Vic; F, Limnadia lenticularis Sars, North America. Scale bars 100 µm.

FIGURE 4. Australimnadia grobbeni. (Daday) A – C: from Taloumbi, NSW, AM P 80867 – 80869; A, male carapace; B, male telson; C, male head; D, from dune lake, Ussher Point, Cape York, Qld, AM P 88390, male telson; E, F from Knuckeys Lagoon, Darwin, NT, AM P 88391; E, male telson; F, female telson. Scale bars 1 mm.