Limnadopsis brevirostris Schwentner, Timms & Richter, 2012, sp. nov.
Creators: name: Schwentner, Martin
name: Timms, Brian V.
name: Richter, Stefan
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Branchiopoda
Diplostraca
Limnadiidae
Limnadopsis
Limnadopsis brevirostris

description: Limnadopsis brevirostris sp. nov.
(Figure 1 g, h, 8, 9)
Limnadopsis sp. ‘Lagoon’: Schwentner et al. 2011
Etymology. The name is an amalgamation of the Latin ‘brevus’, meaning small, and rostrum, a body part (originally named for the likeness to the extended bow of a ship), and refers to the unusually small rostrum in the male.
Type locality. Queensland, unnamed lagoon 52 km north of Taroom near Palm Tree Creek, 25o 12’ 54.2”S, 149o 34’ 34.5”E, 13.ii.2010.
Type material. Holotype 3 AM P.86807 (GenBank JQ424944); allotype Ƥ AM P.86806 (GenBank JQ424943); paratypes 4 3 AM P.86810, AM P.86811, AM P.86812, AM P.87799; 4Ƥ AM P.86808, AM P.86809, AM P.86813, AM P.87798 (GenBank JQ424945 - JQ424951).
Description
Male (Holotype, AM P86807) (Figs. 1 g, 8a, b, c, d)
Carapace. Length 10.2 mm; height 6.0 mm, length/height ratio 1.70 (Figs. 1 g, 8a). Five evenly spaced growth lines on posterior and ventral two-fifths of carapace; growth lines indistinct particularly anteriorly, surface between them smooth without structure, translucent in posterior and ventral two-fifths. Dorsal margin slightly convex with no depression near umbo, latter poorly developed and hardly visible; no dorsal serration, dorso-anterior corner indistinct with angle of about 140°, dorso-posterior angle more distinct also about 140°, anterior and posterior margins protruding from dorsal angles and markedly convex, ventral margin broadly convex.
Head. Mound containing the eye protruding about half the diameter of compound eye, frontal organ pyriform and posterior to eye by a distance about 1.5 times eye diameter and protruding a little less than diameter of eye (Fig. 8 b). Rostrum equilateral triangular, length subequal to frons length, and rostrum length/basal width nearly equal. Angle between rostrum and anterior surface of head about 100o, apex rounded, rostrum filled with a triangular naupliar eye. First antenna with nine lobes (Fig. 8 b) and a little shorter than peduncle of second antenna. Peduncle of second antenna with eleven discernable segments, numbers of antennomeres variable with range between 13 and 16 (some may have broken off); most antennomeres, except the most apical, with three to four spines ventrally and four to six long setae anteriorly (Fig. 8 c).
Trunk comprising 25 segments, decreasing in size posteriorly; ten most anterior segments without dorsal armature, next five segments with one or two weak setae each, then eight segments with a small spine, leaving the last segment spineless. Claspers typical of Spinicaudata in general structure (Olesen et al. 1996) and spines at tip of moveable finger as described by Schwentner et al. (2011), no medial tumidity on hand of clasper (Fig. 8 d).
Telson: Bearing 15 dorsal spines on each dorsal ridgeline, first spine a little larger than following spines, these vary in size with the most posterior spine being enlarged and curved dorsally (Fig. 8 e); one preceding smaller spine originates at base of enlarged spin; most spines smooth though last large one with small denticles dorsally. Caudal filaments inserted between fourth and fifth spine. Floor of telson decreasing evenly from filament insertion to base of furca.
Furca. Each ramus bearing three long setae on basal fifth overlapping with about nine spines spaced more or less equidistantly along basal two-thirds of the ramus, spines varying in size with last being largest (Fig. 8 e); all spines less than half the width of furcal ramus. Distal third of ramus covered dorsally by small denticles. Basal two thirds of ramus slightly curved, but distal third strongly curved dorsally. No spine or protrusion beneath the basal articulation.
Female (Allotype, AM P86806) (Figs. 1 h, 8f, g, h, j)
Carapace. Length 9.4 mm, height 6.1 mm, length/height ratio 1.54 (Figs. 1 h, 8f). Three almost complete evenly spaced growth lines on posterior and ventral carapace, plus two partial growth lines on posterior carapace with same spacing as outer three. Dorsal margin slightly convex, but more than in male, dorso-anterior and dorsoposterior angles and shape of anterior, posterior and ventral carapace as in male.
Head as in male, except that rostrum less protruding; length of rostrum about one third of frons length and equilateral in shape, apex rounded as in male, rostrum length <basal width (Fig. 8 g). Angle between rostrum and anterior surface of head about 125o. First antenna and second antennae as in male, but second antenna with 14–16 antennomeres though with similar spines and setae as in male.
Trunk composed of 24 segments, dorsal armature a little different from male: anteriormost seven segments without armature, next nine segments with few setae, then two segments with two spines, followed by four segments with one spine, and the last segment without armature (Fig. 8 h).
Telson bearing 14 dorsal spines on each dorsal ridgeline (Fig. 8 j). Filaments inserted at fourth spine, otherwise as in male.
Furca. Structure same as in male, but with four basal setae and eight spines on basal two-thirds of each ramus (Fig. 8 j).
Variability. Some males have a shorter rostrum than the holotype, but never longer (Fig. 9 a). In rare cases only 24 trunk segments may be present. The dorsal trunk armature of the segments varies, though it always features numerous posterior segments with single dorsal spines and a few middle segments with setae, the exact number of each is variable though there are always about twice as many spined segments as segments bearing setae. Telsonic dorsal spines vary from 14–16 (Fig. 9 b), basal furca setae sometimes number four rather than three and furcal spines may number only eight. Even when nine are present, one may be much smaller. The scales on the tip of the movable finger of the male claspers are always bifid, with the dorsal part slender and the ventral part triangular. The number of scales varies from one to three, if three scales are present, they are arranged in a triangle (Schwentner et al. 2011).
Females exhibit some variability with the rostrum a little longer and at less of an angle (120o to the anterior surface of the head) in some specimens, though it is always distinctly shorter than in males (Fig. 9 d). Occasionally the first antenna may have eight or ten lobes (Fig. 9 d), but it is always of a similar length to that in males. Dorsal trunk armature is variable as in males, but females tend to have more spines and setae than males, though about the same number of spined segments and segments with setaed segments. Telsonic spine and setal numbers vary as in males (Fig. 9 e).
Genetic diversity within L. brevirostris is low. Both uncorrected p – distance and K2P corrected distance for COI are only 0.0–0.9% (based on 15 specimens).
Distribution: So far this species is known only from its type locality.
Remarks. Limnadopsis brevirostris sp. nov. is morphologically best defined by the number of growth lines, the nature of the male rostrum, and the adornment of the furcal rami. Growth lines average five in mature specimens, significantly fewer than in almost all other species of Limnadopsis. The nearest minimum is about seven to eight in L. tatei, but this species is easily distinguished from L. brevirostris sp. nov. by the presence of dorsal serration, absent in L. brevirostris sp. nov. The male rostrum is the smallest in relation to head size of all species of Limnadopsis, with a broad and blunt apex and a length/basal width ratio approaching one, compared to <0.8 in other species (calculated from figures in Timms 2009). Setae and spine numbers on the furca are the most defining character: no other species has three to four basal setae and eight to nine spines spread along the basal two-thirds of the furca. In most Limnadopsis species there are>9 basal setae and <6 spines clumped mid length (Timms 2009).
Many species of Limnadopsis exhibit marked sexual dimorphism, but this is minimal in L. brevirostris. The rostrum differs in length between males and females, as it does in all species of Limnadopsis, and there is a small difference between the sexes in the shape of the carapace, with the female dorsum slightly more convex than the male, as in L. minuta (Timms 2009).
The collection of L. brevirostris studied contained a single egg-bearing female. The eggs were lost during critical point drying, so unfortunately, no SEM images of the eggs are available. Nevertheless, the presence of an eggbearing female suggests that the specimens in this population were reaching maturity at the time of sampling. The specimens studied were adult or nearly adult. The morphological variation observed and molecular genetic differentiation described by Schwentner et al. (2011) clearly supports L. brevirostris as a distinct species.
description: Published as part of Schwentner, Martin, Timms, Brian V. & Richter, Stefan, 2012, Description of four new species of Limnadopsis from Australia (Crustacea: Branchiopoda: Spinicaudata), pp. 42-64 in Zootaxa 3315 on pages 53-60, DOI: 10.5281/zenodo.210812