Leptestheria brevirostris Barnard, 1924

Rogers, D. Christopher, Tladi, Murphy, Wasserman, Ryan J. & Meyer-Milne, Elizabeth, 2021, Review of the southern African Leptestheriidae (Branchiopoda: Spinicaudata) I: redescription of Leptestheria brevirostris Barnard, 1924 with comments on diagnostic characters, Zootaxa 4974 (2), pp. 258-266 : 260-264

Leptestheria brevirostris Barnard, 1924

(fig. 1)

Barnard, 1924: 227, 1929; Brendonck 1999, Brtek 1997, 2002, Garcia & Perreira 2003, Rogers 2020, Emami-Khoyi et al. 2021.

Material examined. In addition to the type material below, the following material was examined: Botswana, Central District, 8.14km south of Palapye, 22° 35’ 55.50” S; 27° 7’ 51.78” E, natural pool in sandstone rock outcrop, on the Botswana International University of Science and Technology ( BIUST) campus; 7♂ - 22♀ (18 ovigerous), 3 Dec 2018, M. Tladi; Republic of South Africa, Northern Cape, Augrabies Falls National Park , depressional pools in Moon Rock outcrop, 27 Jan 1993, 1♂, cultured from dry sediment, M. Hamer, University of Natal , AM LEN 156 B.

Type material. Namibia, Otjozondjupa Region , 20°30’59.8”S 17°13’59.9”E, Waterberg Tops, ~ 70km E of Otjiwarango. One female with eggs, one juvenile. 1920, R. W.E. Tucker, collector; catalogue number MB-A006738, at the South African Museum , Republic of South Africa .

Diagnosis. Leptestheria brevirostris is readily separated from all other African members of the genus by the greatly abbreviated rostrum, which has a length that is roughly 0.6x the length of the head from the ocular tubercle to the base of the occipital condyle ( Fig. 1A ). In all other African species, the lengths are subequal ( Fig. 2A ). The male telson is unique among the Spinicaudata in that the posterior telson spiniform projections are directed dorsoposteriorly, and are subparallel to the telson spine rows ( Fig. 1F ). Male L. brevirostris is also unique in that the first claspers are different in form from the second ( Fig. 1B–D ). The second clasper ( Fig. 1D ) possesses a longitudinal, subrectangular lamellar projection on the base of the endopod just lateral of a line between the base of the endopod medial bend and the base of endite IV.

Redescription. Male. Form in general typical for the family and genus. Carapace length average 5.9 mm (range, 5.1– 6.2 mm).

Head broadly rectangular ( Fig. 1A ). Ocular tubercle rounded, projecting not more than 0.25x the width of the eye above the frons. Contiguous compound eyes large, subspherical, ~0.85x ocular tubercle width. Naupliar ocellus subtriangular, lying just posterior to rostrum apex. Rostrum abbreviated, length ~0.6x distance between ocular tubercle and occipital condyle base. Rostral spine slightly arcuate, curving anteriorly, length ~0.7x eye length. Angle between rostrum and frons ~100°. Frontal organ at base of occipital condyle. Occipital condyle conical, elongate; length subequal to distance between ocular tubercle and occipital condyle base.

First antennae posterior to rostrum; length ~1.4x second antennal peduncle ( Fig. 1A ). Distal three fourths bearing a longitudinal row of large rounded lobes; lobes are smooth and inerm, irregularly spaced, more crowded distally. Distalmost lobe on anterior portion of first antenna apex.

Second antenna typical for genus ( Fig. 1A ), 2.0 to 2.5x head length. Second antennal peduncle subcylindrical, subequal in length to head, bearing seven to ten anterior transverse ridges, each margined with spines. First through penultimate ridges with single row of spines. Distalmost transverse ridge with scattered elongate spines. Lateral and posterior peduncle surfaces smooth and inerm. Second antennal anterior flagellum (exopod) with six or nine flagellomeres. Exopod flagellomere I campaniform, widening distally; distal margin ringed with aciculate spines. Exopod flagellomere II campaniform, widening distally; anterior surface with a few short, scattered spines, posterior surface with three recurved long spines; distal margin with three or four anterior spines. Exopod flagellomere III clavate, widening distally; anterior surface distally with four or six scattered aciculate spines; posterior surface with four or six long slightly curved spines and at least one short spine. Remaining exopod flagellomeres clavate with anterior surface distally bearing two to six scattered aciculate spines. Posterior flagellum (endopod) with eight or nine flagellomeres, subequal in length to exopod. Endopod flagellomeres subcylindrical; posterior surface with a subdistal rounded protrusion bearing three to 15 filiform elongate setae. Endopod flagellomeres I and II posterior surface proximal to rounded protrusion with three filiform setae in a longitudinal row.

Carapace form typical for the genus, with broadly rounded anterior and posterior margins, and the dorsal and ventral margins relatively straight; length width ratio ~1.8. Umbone present and obvious. Growth lines clear and prominent, narrow, and slightly projecting. Growth line intervals ( Fig. 1E ) with surface sculpture of raised mesh lines defining shallowly depressed rounded, roughly rectangular to oblong polygons. Carapace posterior third with three to four polygons longitudinally per large interval between growth lines. Adductor muscle scar broad, oblong; length ~2x width.

Fourteen to eighteen pairs of thoracopods. Thoracopods I and II modified as claspers ( Figs. 1B–D ).

Thoracopod I ( Figs. 1B, C ) endite III produced as rigid hamulus (‘tumidity’ in Schwentner et al. 2012), length 2x basal width, apically rounded rectangular, and separated by a distance subequal to its length from the base of endite IV. Endite IV (‘thumb’) subcylindrical, length subequal to width; apex flat, transverse, covered in dense aciculate denticulae; endite IV outgrowth (‘small palp’) projecting distomedially from side of endite IV; length~ 1.5x basal width, apically rounded subrectangular. Endopod (‘finger’) proximally conical; distal portion subcylindrical, with distal portion bending basally ~150° with apex directed to endite IV. Endopod apex rounded, covered apically and at contact region with endite IV with small rounded denticulae. Endite V (‘large palp’) cylindrical, slightly shorter in total length than endopod, with apex rounded, slightly expanded, and bearing short scattered filiform setae.

Thoracopod II ( Fig. 1D ) endite III produced as rigid hamulus; length subequal to basal width, apically rounded triangular, and situated at base of endite IV. Endite IV (‘thumb’) subcylindrical; length ~2.5x width; apex flat, transverse, covered in dense aciculate denticulae; endite IV outgrowth (‘small palp’) projecting distomedially from side of endite IV, length~ 1.5x basal width, apically rounded subrectangular. Endopod (‘finger’) proximally conical, with a large subrectangular lamella projecting from subconical base longitudinally, just lateral of a line from the base of the distal endopod cylindrical portion and the base of endite IV. Endopod distal portion subcylindrical, with distal portion arcing 90° with apex directed to endite IV. Endopod apex subacute, covered apically and at contact region with endite IV with small rounded denticulae. Endite V (‘large palp’) as for thoracopod I.

Thoracopods II or III through X or XI each bearing dorsally elongated subcylindrical flabellum; posterior limbs lack elongated flabellae. Body segments posterior to eleventh thoracopod pair dorsally with transverse ridge each bearing a transverse row of simple setae, diminishing in length serially in posterior abdominal segments.

Telson ( Fig. 1G ) with posterior surface ridges reflexed anteriorly over telson dorsal portion. Posterior ridges with 26 to 32 spines each; spines simple, aciculate, separated by a distance subequal to spine length. Anterior most spines directed anterodorsally, with next spines directed dorsally, and subsequent spines directed posteriorly. Spine length ~3x spine basal width. Posterior ridges extending to posterior spiniform projections with spines spaced 4–5x spine length; spine length 5–6x basal width, and spine rows only extending to base of distal third of spiniform projection. Telson filaments between fourth, fifth, or sixth spine pairs. Both telson posterior spiniform projections directed dorsoposteriorly, subparallel to telson spine rows. Telson lacking a ventral spiniform projection.

Cercopods projecting posteriorly from the ventroposterior surface of the telson. Cercopod length subequal to telson spiniform projection. Cercopod nearly straight with slight arc at the ventral margin, with slightly sinuous dorsal margin. Cercopod medial surface with a longitudinal row of short aciculate spines. Spine length ~2x basal width, spines separated by 2–4x spine length. Cercopod spine row terminates at base of distal tenth.

Female. General form as in male with following exceptions: carapace length average 3.4 mm (range, 3.0– 4.6 mm).

Thoracopods X and XI with epipodal flabellae extended as long filaments for carrying eggs.

Telson ( Fig. 1H ) with posterior surface ridges produced dorsally. Posterior ridges with 26 to 32 spines each; spines simple, aciculate, separated by a distance subequal to spine length. Spine pairs directed posteriorly. Spine length ~2–4x spine basal width. Posterior ridges extending to posterior spiniform projections with spines spaced 2–3x spine length, and spine rows only extending to base of distal third of spiniform projection. Telson filaments between second, third, or fourth spine pairs. Telson posterior spiniform projection directed posteriorly.

Egg. Spherical, unornamented, ~250μm in diameter.

Amplexus. One pair in the lot are in amplexus, with amplexus being single file as in certain Australian endemic Limnadiidae ( Rogers et al. 2012) . This form of amplexus has not been reported outside the Limnadiidae .

Differential diagnosis. Leptestheria brevirostris is readily separated from all congeners by the form of the rostrum, the form of the male telson, the form of the male second clasper, and to a lesser extent the form of the occipital condyle ( Fig. 1 ).

The rostrum in L. brevirostris is extremely short in both sexes compared to all other Leptestheria species , with the rostrum length approximately 0.6x the length of the head from the ocular tubercle to the base of the occipital condyle. In all other African species, and most other species globally, the lengths are subequal or longer than the distance between the ocular tubercle and the occipital condyle base. The few exceptions are limited to aberrant or unique individuals within a given population of a species that otherwise has a longer rostrum. Halloy (1979) presents a female L. titicacae Harding, 1940 (as L. tucumanensis ), with an abbreviated rostrum and Karande & Inamdar (1960) depict a male specimen of L. nobilis Sars, 1900 (as Leptestheriella gigas ) with a short rostrum. Similarly, in Marinček & Petrov’s (1992) paper on Leptestheria dahalacensis (Rüppell, in Straus-Dürckheim, 1837) (presented by them as L. saetosa ), the authors depict variation within and between populations and illustrate two specimens with an atypically abbreviated rostrum. However, in all these species the typical form has the rostrum proportionally longer than in L. brevirostris .

It is not uncommon for the telsons to be sexually dimorphic in Leptestheria , but nowhere is the dimorphism as pronounced as in this species. The male telson in L. brevirostris is unique among the Spinicaudata in that the posterior telson spiniform projections are directed dorsoposteriorly, and subparallel to the posterior telson surface. No other Leptestheria , let alone any other described spinicaudatan has the telson in this form.

Male L. brevirostris is also unique in that the second clasper possesses a longitudinal, subrectangular lamellar projection on the base of the endopod just lateral of a line between the base of the endopod medial bend at the base of endite IV. Leptestheria orientalis Spandl, 1925 from Borneo has a low, rounded projection at the endopod base. Rogers et al. (2016) described L. serracauda , depicting this species with an angular projection at the base of endite IV on the first clasper.

The occipital condyle length varied in our material from 0.6x to 1.2x the length of the distance between the ocular tubercle and the occipital condyle base, with an average of 1.0x. In our comparative material of other species, the occipital condyle length ranged from 0.4 to 0.6x, with an average of 0.5x.

The mitochondrial genome of L. brevirostris was recently published ( Emami-Khoyi et al. 2021), and will be useful in future molecular studies as more leptestheriid taxa are similarly sequenced.

Distribution. Namibia in Otjiwarango, Botswana in Central District, and Republic of South Africa in Northern Cape at Augrabies National Park. Surveys between these areas for additional localities should be undertaken.

Habitat. Rock pools (gnammas); depressions in sandstone that fill with water from seasonal rainfall. These rock pools are dry most of the year. The typical wet season for all three sites is December through February.

The geology of the underlying rock at the locality in Botswana is characterized by medium to coarse size quartzarenites and arkose, with presence of feldspars and lenses of conglomerate to micro conglomerate. The area is characterised by rocky outcrops of the Tswapong Formation ( Ermanovics et al., 1978) and holds numerous rock pools. The site in South Africa is a gneiss dome.

Figures

FIGURE 1. Leptestheria brevirostris. A, male head, left lateral view. B, male right thoracopod I clasper medial view. C, male left thoracopod I clasper lateral view. D, male left thoracopod II clasper lateral view. E, carapace outline, left valve. F, carapace growth line interval ornamentation (two intervals). G, male telson, left lateral view. H, female telson, left lateral view. Scale bars: A–E 2mm; F, G 4mm.

FIGURE 2. A, Leptestheria rubidgei, male head, left lateral view. B, male telson, left lateral view. C–E, Leptestheria rubidgei, carapace growth line interval ornamentation (two intervals), various examples. F, Leptestheria striatoconcha, carapace growth line interval ornamentation (two intervals). G, Leptestheria rubidgei, carapace growth line interval ornamentation (two intervals), example. Scale bars: A 2mm; B 4mm; C–G 2mm.