Ozestheria sarsii ( Sayce, 1903 )

Schwentner, Martin & Hethke, Manja, 2025, Revision of the Australian Ozestheria Schwentner & Richter, 2015 (Crustacea: Branchiopoda: Spinicaudata) fauna, with the descriptions of 27 new species, European Journal of Taxonomy 992, pp. 1-172 : 135-138

Ozestheria sarsii ( Sayce, 1903)

Fig. 43

Estheria sarsii Sayce, 1903: 252–253 , 256, fig. 35.

Cyzicus sarsi – Wolf 1911: 254.

Cyzicus sarsii – Dakin 1914: 295.

Caenestheria sarsi – Daday 1914: 55, 57–59, fig. 2. — Richter & Timms 2005: 344.

Eocyzicus sarsii – Brtek 1997: 50.

Ozestheria sp. T – Schwentner et al. 2015a: figs 2, 6.; 2020: figs 1–2.

Ozestheria sarsii – Rogers 2020: 24 .

Estheria sarsii – Henry 1924: 122, 134.

Diagnosis

Ozestheria sarsii is characterized by a short condyle and a wide occipital notch; a rounded ventral carapace margin; carapace ornamentation dorsally on carapace pit-like, in following growth bands with medium to large polygonal reticulations; male rostrum with convex anterior margin, apex strongly rounded with right angle, ventral margin concave; 13–16 (male) or 14 (female) antenna I lobes reaching to antenna II flagellomeres V–VII (male) or IV (female); 11–14 (male) or 13 (female) antenna II flagellomeres; 23–24 complete thorax segments; telson with 12–22 spines, anterior spines small and conical, posteriorly increasing in size and aciculate, few larger spines interspersed; 5–8 furcal setae.

Differential diagnosis

Ozestheria sarsii can be easily differentiated from most other species by the shape and ornamentation of the carapace as well as the telson spination. The morphologically most similar species are O. lutraria , O. rufa , O. paralutraria sp. nov. and O. christiani sp. nov. Ozestheria lutraria has more thorax segments (25–28 vs 24) and can grow larger (up to ~ 14 mm). The carapace ornamentation of O. rufa contains smaller, more irregular and less distinct polygonal reticulations, which transition into nodulous, highly anastomosing lirae from about mid carapace, and the apex of the female rostrum of O. rufa is less rounded and more angular and the male rostrum has a small, wing-like flange antero-dorsally on the anterior margin. Ozestheria christiani can be differentiated by its carapace ornamentation, whose medium to large polygonal reticulations are partly intermittent and with small projections into the polygon’s center. Ozestheria paralutraria differs by having more thorax segments (25 vs 23–24), a more dorsal widest extension of the posterior carapace margin (b/H 0.36–0.38 vs 0.48–0.50) and by the shapes of the male and female (drawn out into pointed tip vs rounded) rostrum.

Type material

Holotype AUSTRALIA – Western Australia • ♂; Murchinson, Lauke Aurean ; Jan. 1896; J.T. Markes leg.; MV J203 .

Other material examined

AUSTRALIA – Western Australia • 2 ♂♂; Lindsay Gordon Lagoon, SW of Lorna Glen Homestead; 26°15′45.2″ S, 121°29′51.2″ E; 18 Mar. 2014; K. Quinlan leg.; WAM C78008 , C80200 • 1 ♀; same data as for preceding; NHMW-ZOO-CR-28495

Additional material (not examined)

AUSTRALIA – Western Australia • 1 juv.; Urumurdah Lake, near Lake Way ; 26°40′11.5″ S, 120°20′22.6″ E; 2009; B.V. Timms leg.; reared from sediment; AM P. 91436 .

Type locality

Western Australia, Murchinson, Lauke Aurean [the locality of this lake is unknown].

Description

Males

CARAPACE ( Fig. 43a–c, e ). Length 7.7–8.7 mm (HT: 7.8 mm), height 4.2–4.6 mm (HT: 4.2 mm). Coloration light yellow-brownish, crowded growth bands lighter (HT: yellowish; color could be faded). 14–21 (HT: 14) growth lines, 13–16 (HT: 13) widely spaced and 1–6 (HT: 1) crowded.

CARAPACE SHAPE. Dorsal margin straight, distinct dorso-posterior corner. Posterior margin broadly rounded, suboval, equicurvate (b/H 0.49–0.50, HT: 49). Ventral margin widely rounded, posteriorly complanate. Umbo position submedian (Cr/L 0.26–0.28, HT: 0.27).

CARAPACE ORNAMENTATION ( Fig. 43f–g ). Larval valve and following growth bands with pit-like shallow medium reticulations (under SEM polygonal reticulations). From mid carapace, the reticulations become wider (large in last few non-crowded growth bands) and more pronounced, forming a polygonal mesh across each growth band with each polygon usually being a pentagon, hexagon or heptagon. The floor of each polygon with minute, pit-like depressions (best seen under SEM). Within growth bands ventral polygons (close to the following concentric ridge) dorso-ventrally compressed and decreasing in size. Crowded growth bands with irregular, granular ornamentation. Concentric ridges raised, with pitted/ polygonal ornamentation. Setae spiniform; preferentially preserved on ventral parts of the carapace, setal pores in single line along all growth lines under SEM.

HEAD ( Fig. 43h–i ). Condyle rounded, short, only weakly protruding; occipital notch wide. Condyle lacking anterobasal hump. Margin between condyle and ocular tubercle straight to weakly convex. Ocular tubercle weakly to well developed, forming nearly rectangular to obtuse (~120°) angle with rostrum. Anterior margin of rostrum strongly convex. Apex strongly rounded, acute (~70°) to nearly rectangular. Ventral margin of rostrum with notch anteriorly; concave about half-length, pointing apex slightly downwards. Naupliar eye subtriangular, small (HT: naupliar eye not visible, may be faded). Antenna I long with 13–16 (HT: 16) lobes, reaching to antenna II flagellomeres V–VII (HT: VI). Antenna II with 11–14 (HT: 11) flagellomeres.

THORAX. 23–24 (HT: 24) segments, 23–24 (HT: 23) thoracopod-bearing and one or no posterior limbless segment not reaching dorsal margin. Mid to posterior thoracopod-bearing segments with spine bearing dorsal extensions. Posterior segments without dorsal extension or spines.

THORACOPOD III (only WAM C78008; Fig. 43n ). Endite I short and curved dorsally. Endites II–V broad, decreasing in size. Endite V palp two-segmented, basal segment shorter than endopod. Exopod ventral extension shorter in extension to endopod, dorsal extension wide, narrowing distally, overreaching epipod. Epipod long, cylindric.

TELSON ( Fig. 43k–l ). 12–22 spines (HT: 12) spines. First (anterior) spine enlarged. Spines conical, irregularly spaced, anteriormost spine large, following spines small, one larger spine about ⅔ of telson length; posteriorly spines slightly thinner and more drawn out and increasing in size (last ~⅓ of telson). Dorsal margin straight or slightly convex anteriorly. Left or right (HT: left) terminal claw more strongly curved.

FURCA ( Fig. 43k–l ). Proximally with dorsomedial longitudinal row of 5–8 (HT: 7) setae, row ending distally in a single conical spine. Distal part ½ of furcal length, with numerous small denticles.

Female

Overall appearance as in males. Carapace ( Fig. 43d ) length 7.8 mm, height 4.2 mm; 18 growth lines, 15 widely spaced and 3 crowded; Cr/L 0.24 and b/H 0.48. Anterior margin of rostrum slightly convex; apex strongly rounded, acute angle (~80°); ventral margin weakly concave, with small notch anteriorly ( Fig. 43j ). Antenna I with 14 small lobes, lobes smaller than in males; reaching to antenna II flagellomere IV. Antenna II with 13 flagellomeres. 24 segments, 24 thoracopod-bearing and no posterior limbless segment not reaching dorsal margin. Telson with 18 dorsal spines; left and right terminal claws equally curved ( Fig. 43m ). Furca with 5 setae.

Distribution ( Fig. 43o )

Ozestheria sarsii is known from its type locality in western Western Australia and two localities in central Western Australia.

Remarks

The original type series comprises only a single male specimen, with no genetic information. In the geometric morphometric analyses of carapace shape ( Fig. 5 ), O. sarsii is distinct from most other species and most similar to O. sp. T ( Schwentner et al. 2015a) and O. rufa . The species assignment classified O. sarsii as O. sp. X10 (probability 97.3%; which probably represents O. rufa ; Supp. file 1_4.10) or O. sp. T (probability 2.7%), though the classification was not supported by the very low typicality scores (0.02 and 0.003). The type specimens of O. sarsii and O. rufa differ considerably in their general morphology (e.g., shape male rostrum, telson spination and carapace ornamentation). Ozestheria sarsii has an overall strong morphological resemblance to Ozestheria sp. T (sensu Schwentner et al. 2015a) (e.g., the carapace ornamentation and shape, the shape of the male head and rostrum, the number of growth lines and thorax segments) and their geographic distribution is similar, supporting their conspecifity. The holotype of O. sarsii differed from the other specimens mainly in the shape of the ventral carapace margin (which was more strongly curved, and which might have resulted in the low probability scores in the classification; however, in O. sp. T this character was variable, ranging from straight to slightly curved) and the strong curvature of the left telsonic claw. The latter is only rarely observed in Ozestheria , though we interpret it as an individual aberration rather than a diagnostic feature.

Figures

Fig. 43. Ozestheria sarsii (Sayce, 1903). a–e. Carapace. a. Male, holotype (MV J203). b. Male (WAM C78008). c. Carapace, Dorsal view male, holotype (MV J203, right valve only). d. Female (NHMW- ZOO-CR-28495). e. Male (WAM C80200), SEM. f–g. Carapace ornamentation (positions marked in a and e by rectangles). f. Mid-dorsal carapace, male (WAM C80200), SEM. g. Mid-carapace, male, holotype (MV J203). h–j. Head (antennae not shown). h. Male, holotype (MV J203). i. Male (WAM C78008). j. Female (NHMW-ZOO-CR-28495). k–m. Telson. k. Male, holotype (MV J203). l. Male (WAM C78008). m. Female (NHMW-ZOO-CR-28495). n. Male, third left thoracopod (WAM C78008). o. Distribution map (produced in ArcMap 10.7; see caption Fig. 7 for sources). Scale bars: a–e =1 mm; f =0.1 mm; g–j, n= 0.5 mm; k–m= 0.2 mm.

Fig. 5. Morphometrics of short-condyled species. Scores on upper PC1 and PC2 of Fourier shape coefficients of 248 outlines, including 233 new individuals and 15 historic type specimens, four of which are drawings ofOzestheria elliptica (Sars, 1897),O. lutraria (Brady, 1886) andO. berneyi (Gurney, 1927). One of the drawings of O. berneyi corresponds to the studied syntype. The names used by Schwentner et al. (2015a) to identify genetically delimited species (e.g., C, D etc.; extended for the newly identified species, e.g., X1) are provided. New specimens are represented by convex hulls, type specimens by data points. lower. Mean shape of each species, calculated based on up to 73 individuals per species.