Australimnadia multifaciata, Timms, Brian V. & Schwentner, Martin, 2017

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 : 88-91

Australimnadia multifaciata sp. nov.

( Figs 5–7 )

Etymology. The specific epithet refers to the egg which has 8–10 distinct facets each with a few depressions and ridges.

Material Examined. Holotype: male, roadside pool 19.65 km S of Onslow , Western Australia, 21o48'36"S, 115o 06'33"E, 16 February 2009, BVT, WAM C5916 . Allotype: female, collected with holotype, WAM C5917. Paratypes: 1 male, 2 females, collected with holotype, WAM C5918.

Other material examined. 1 male, 15 females, collected with holotype WAM C5919; 1 male, collected with holotype, AM P91946; 1 female, collected with holotype, AM P91947.

Diagnosis. Egg non-spherical with 8–10 short facets each with few parallel ridges and depressions. Trunk segments 22 or 23. Second clasper with large palp bearing 2 palpomeres. Third thoracopod with palp of endite V almost 4 times longer than endite V. About 20–22 telsonic setae, separated into 2 subequal groups by insertion of telsonic filaments. Cercopod with about 40 long setae on proximal 80%.

Description. Egg. ( Fig. 1 C, D): mean diameter 176 µm, range 168–190 µm (n =10). Egg surface arranged in 8–10 facets, each with 4–6 grooves separated by rounded ridges arranged in short parallel sequences with facet surfaces meeting at angles>120°, at truncated depressions or at ends of set of depressions at angles <75° or occasionally>120° and marked by small ridge. Surface (tertiary) layer thin, particularly on ridges and covering thick spongiform layer.

Male. ( Fig. 5 A, C, E–G, J). Length 9.1 mm, height 6.5 mm. Head ( Fig. 3 C) smoothly humped posterodorsally with rounded ocular tubercle containing compound eye about 60% by volume. Pyriform frontal organ as long as ocular tubercle and separated from ocular tubercle by about its length. Anterior base of ocular tubercle meeting asymmetrically rounded rostrum at angle of about 85°. Rostrum protruding subequally as much as ocular tubercle, dorsally containing oval ocellus little smaller than compound eye. Labrum prominent, terminating in sharp setose apex. Labrum with prominent lobe midway on posterior surface.

First antenna ( Fig. 5 C) about twice as long as peduncle of second antenna and with about 15 sensory lobes subequal in size. Second antenna ( Fig. 5 E, F) with peduncle of about 12 annulations each, with spines dorsally and two rami, dorsal ramus with about 12 antennomeres and ventral ramus with about 14 antennomeres. Most antennomeres with about 4 spines dorsally and about 6 long setae ventrally. Proximally and apically, number of spines and setae more variable (spines 2–5; setae 4–7).

Carapace ( Fig. 5 A) off-white, opaque, oval, almost without dorsoanterior and dorsoventral angles. Dorsum evenly arched, maximum height at mid-length. Abductor muscle scar lying about 30° to horizontal body axis. No growth lines apparent.

Trunk segments 22. Dorsally, trunk segments XII–XXII each with few short setae or spines on posterior medial edges. Thoracopods I and II modified into claspers ( Fig. 5 J) essentially similar in structure. Palm trapezoidal with minor asymmetrical protrusion situated dorsomedially and near apical club base. Palm terminating in apical club medially and in expanded base of moveable finger laterally. Apical club longer than wide, but with thickening base and lateral insertion of small palp. Club with many short stout spines on terminal half medially and fewer long, jointed spines on lateral half. Moveable finger arcuate, terminating in blunt apex and with apical suctorial organ anteroventrally and rounded pits dorsally (in-situ). Long palp of 2 palpomeres and inserted terminally on palm; clasper 1 distal palpomere little longer than hand, but about twice as long on clasper 2 and 2.5 times length of hand. Distally, both palps with numerous setae marginally on flattened concave apical area. No spines or setae at palpomere joints.

Only thoracopod III described here ( Fig. 6) though thoracopods IV to at least XV with broadly similar structure. Endites each with numerous anterior ( AS) and posterior setae (PS). Endopod, exopod and flabellum each with posterior setae and naked epipodite. Endite I with about 45 apparently PS and about 12 apparently AS on medial margin, varying in size and complexity; 2 most basal short, stout and each with few short setulae; remaining approximately 10 or so setae are of 2 portions, increasing in length towards the centre, with basal portion stout, with few setulae, and with distal portion longer and plumose. Medial surface of endite I with thick row of setae along medial surface near medial margin. Endite II with about 35 AS and about 55 PS, endite III with about 17 AS and about 25 PS, endite IV with about 20 AS and about 20 PS, endite V with about 44 setae (presumably PS), 1 row transverse and 1 row apically. Endite V with cylindrical palp almost 3 times longer than endite V. Posterior setae similar throughout, geniculate, long and plumose. Anterior setae always geniculate and little longer than half PS, otherwise variable between endites: on endites II–IV, portion stout and plumose, but distal portion with cirrus. On endite II, base of cirrus with 3 or 4 pairs of blunt spines laterally, decreasing in size along each seta. Endopod with about 42 PS, distalmost with basal spiniform projection from endopod. Exopod and flabellum with numerous (ca. 80–100) presumably PS, most distal group (occupying about half exopod) on exopod with basal spiniform projection. Endopod, exopod and flabellum all long and narrow, each with acute apex. Epipodite fusiform, about 4/ 5 length of flabellum. Last few thoracopods very much smaller and reduced in complexity.

Telson ( Fig. 5 G) with about 21 dorsal spines on each side, mostly of even spacing and size; most spines slightly curved posteriorly, with setulae laterally. Anterior 10 spines in slightly convex row, basal surface of last 11 spines almost straight. Telson dorsal surface with mound at 10th spine supporting pair of setose telsonic filaments. Viewed dorsally, telsonic spines situated on U-shaped flange joined across midline anteriorly and open posteriorly; posterior surface high and near base of spines anteriorly utill insertion of telsonic filaments, but declivous posteriorly from this insertion with 11 posterior spines on sharp narrow ridge. Entire dorsal telsonic surface merging smoothly with posterodorsal surface of trunk segments, i.e., no steep rise to first telsonic spine.

Cercopod little longer than telson; dorsal and ventral margins almost parallel for about 80% of its length, with final 20% narrowing to sharp concave apex. Basal 80% of cercopod bearing about 40 long geniculate plumose setae dorsally, posteriormost much shorter than others. Distal 20% with cirrus of numerous short denticles dorsally on concave surface.

Female. Length 11.0 mm, height 8.0 mm. Head ( Fig. 5 D) largely as in male, though rostrum as prominent and even more asymmetrical; ocellus somewhat oval and almost as large as compound eye.

Carapace ( Fig. 5 B) similar to that of male, but anterodorsal and posterodorsal angles more noticeable while dorsal margin somewhat vaulted; carapace highest anteriorly at about 40% of its length.

First antenna ( Fig. 5 D) little longer than peduncle of second antenna and with about 9 sensory lobes of similar size. Second antenna as in male.

Trunk segments 23. Many segments with clumped dorsal setae/spines: none on segments I–IX, few on segments X and XI, many (mainly setae) on segments XII–XVII and few (mainly spines) in successively decreasing numbers and size on segments XVIII–XXIII. These setae/spines inserted on mounds along posterior portion of each segment, most noticeably on segments XII–XVII.

First 15 thoracopods all broadly similar to one another and to thoracopod III of male. None with endopodal palp. Remaining thoracopods serially smaller and reduced in complexity. Thoracopods on segments IX and X with long epipodal filaments to hold egg mass.

Telson ( Fig. 5 H) as in male, but with 23 dorsal spines each side.

Variation. In other specimens of Australimnadia multifaciata sp. nov. examined, some variation (ca 5%) in meristic characteristics was noted, as is often the case in clam shrimps ( Straškraba 1966) e.g., lobules on the first antennae numbered 14 rather than 15 in some males and eight rather nine in some females; antennomeres sometimes differing by one from the 12 and 14 stated, one male had 23 trunk segments instead of 22; telsonic spines varied from 21–23, and cercopod setae were always numbered near 40 (see below as this latter number is an important difference between A. multifaciata sp. nov. and A. grobbeni ).

Remarks. The two individuals studied of Australimnadia multifaciata sp.nov. had identical COI sequences. Uncorrected p -distances between A. multifaciata sp. nov. and A. grobbeni were 11.3 % for COI and 0.07 % for EF1a. None of the translated amino acid sequences featured stop codons or any amino acid substitutions.

Distribution and Conservation Status. Australimnadia multifaciata sp.nov. is known only from its type locality, a roadside pool 19 km south of Onslow, on the delta of the Ashburton River on the Pilbara coast. There are many turbid clay pans in the area, but only this deeper pool with clearer water harbours A. multifaciata sp. nov. It is possible the site is a singleton and given this species was not encountered in an intensive survey of the aquatic resources of the Pilbara ( Pinder et al. 2013), A. multifaciata sp. nov. could be a rare species and critically endangered according to ICUN criteria. The recent industrial development near Onslow nearby is of concern.

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 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 5. Australimnadia multifaciata sp. nov. A, male carapace; B, female carapace; C, male head, D, female head; E, male second antenna; F, antennomere; G, male telson; H, female telson; J, first clasper (with palp of second thoracopod). Scale bars 1 mm.