Ozestheria elliptica ( Sars, 1897 )

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 : 50-53

Ozestheria elliptica ( Sars, 1897)

Fig. 17

Estheria elliptica Sars, 1897: 12–17 , fig. 2.

Estheria elliptica – Sayce 1903: 252, 255. — Henry 1924: 122, 134. — Gurney 1927: 63–64.

Cyzicus ellipticus – Wolf 1911: 254. — Dakin 1914: 295.

Caenestheria elliptica – Daday 1914: 56, 96–98. — Richter & Timms 2005: 344–345 .

Eocyzicus ellipticus – Brtek 1997: 49.

Ozestheria elliptica – Rogers 2020: 23 .

Diagnosis

Ozestheria elliptica is characterized by a short condyle and wide occipital notch; a rounded ventral carapace margin; carapace ornamentation with large, well-developed polygonal reticulations; female rostrum with slightly drawn-out apex; 10 (female) antenna I lobes reaching to antenna II flagellomeres IV; 12 (female) antenna II flagellomeres; 22 or 23 complete thorax segments; ~28 small, unequally sized and spaced conical telsonic spines; no furcal setae.

Differential diagnosis

A morphological differentiation of O. elliptica , O. rubra , O. henryae sp. nov. and O. matuwa sp. nov. is difficult, though at least O. rubra , O. henryae and O. matuwa can be easily separated genetically via COI (no genetic data for O. elliptica available) ( Fig. 2 ). Sars’ (1897) illustration of O. elliptica shows interrupted and discontinuous polygonal mesh walls, which would distinguish this species from O. rubra , O. henryae and O. matuwa ; whether these represent inaccuracies in the drawing or a true ornamental feature will have to be evaluated in future studies. Ozestheria elliptica and O. henryae tend to be smaller (length up to ~ 7.5 mm, the other species up to ~ 9 mm) with a shorter male antenna I (reaching to antenna II flagellomeres V–VII [unknown for O. elliptica ], while reaching to about VII–X in the other species), a less strongly concave rostral ventral margin (in males) and more telsonic spines (> 20–30, and up to 16–28 though usually ~ 20 in the other two species). Ozestheria elliptica differs from O. henryae by having no setae on the furca and by all telsonic spines being subequal in length (vs mid and posterior spines slightly enlarged). Ozestheria rubra differs from O. matuwa in the number of complete thorax segments (22–23 vs 22–24) and the shape of the male rostrum apex, which is more strongly rounded in O. rubra . The four species differ in their geographic distributions: O. elliptica occurs in northern Western Australia, O. rubra occurs along the border region of Queensland and New South Wales as well as central Australia, O. matuwa in Western Australia and Ozestheria henryae in central Queensland.

The four species together can be easily distinguished from other species of Ozestheria by the elliptical shape of the carapace (with an evenly rounded ventral margin), the large polygonal, reticulating carapace ornamentation, polygonal secondary ornamentation within each polygon of the primary ornamentation and the relatively large number of telsonic spines. The very well-defined polygonal ornamentation on all wide growth bands clearly differentiates these four species from most other species with short and rounded condyles: O. berneyi , O. pellucida , O. sarsii , O. rufa , O. richteri sp. nov., and O. christiani sp. nov. Furthermore, the ornamentation of O. christiani is less regular, with the walls of single polygons often being intermittent or with small extensions reaching into the polygon’s center, and O. christiani has fewer antenna II flagellomeres (10–11 vs 12–16). Ozestheria rufa differs further by the lower number of telsonic spines. Ozestheria sarsii differs in the overall shape of the carapace, the shape of the female rostrum (rounded apex), the telson spination (larger number of spines), and O. paralutraria sp. nov. differs by its straight ventral carapace margin, the shape of the male and female rostrum and smaller telsonic spines. Ozestheria lutraria can be differentiated by the larger number of thorax segments (25–27 vs 22–24), the telsonic spines (fewer, usually smaller and less regularly spaced), irregular ornamentation on crowded growth bands and the secondary growth phase, and the carapace shape.

Material examined

None (the following description is based on the description of Sars and his detailed drawings, who studied a single adult female raised from dried sediments).

Type locality

Western Australia, shallow depression about 40 miles E of Roebuck Bay.

Description

Female

CARAPACE ( Fig. 17a ). Length 4.9 mm, height 3.0 mm (Sars reported a height of 3.2 mm but that probably included the umbo). Coloration dark reddish-brown, outer margin lighter. 25 growth lines, 14 widely spaced and 11 crowded.

CARAPACE SHAPE. Dorsal margin straight, rounded dorso-posterior corner. Posterior margin broadly rounded, suboval, supracurvate (b/H 0.38). Ventral margin widely rounded. Umbo position anterior (Cr/L 0.21).

CARAPACE ORNAMENTATION ( Fig. 17b ). Each growth band with large, well-developed reticulations, forming polygonal mesh across each growth band. Ornamentation uniform across all non-crowded growth bands, crowded growth bands with short radial lirae. Concentric ridges raised. Setae spiniform; preferentially preserved on ventral and posterior parts of the carapace.

HEAD ( Fig. 17c ). Condyle rounded, short, only weakly protruding; occipital notch wide. Condyle lacking anterobasal hump. Margin between condyle and ocular tubercle concave. Ocular tubercle well developed, forming obtuse (~120°) angle with rostrum. Anterior margin of rostrum straight to slightly concave. Apex with nearly rectangular angle, apex weakly drawn out and rounded. Antenna I long with 10 lobes, reaching to antenna II flagellomere IV. Antenna II with 12 flagellomeres.

THORAX. 22 or 23 thoracopod-bearing segments. Mid to posterior thoracopod-bearing segments with spine bearing dorsal extensions. Dorsal extensions increasing in size posteriorly over successive segments; spines mostly short, in posterior segments with fewer spines and central spines stouter but shorter.

TELSON ( Fig. 17d ). ~28 spines. First (anterior) spine enlarged. Spines conical or aciculate, subequally spaced, anterior spines smaller, spines of unequal size. Dorsal margin s-shaped: anteriorly slightly convex, posteriorly concavely curved. Right terminal claw slightly stronger curved than left.

FURCA ( Fig. 17d ). No proximal setae, a single conical spine. Distal part ¾ of furcal length, with numerous small denticles.

Distribution ( Fig. 17e )

Ozestheria elliptica is known only from its type locality in northern Western Australia.

Remarks

Richter & Timms (2005) suggested that syntypes may be housed in the Zoological Museum (Oslo). The respective collection holds three individuals labeled as Estheria elliptica ; however, the collection details do not match those of Sars and the respective species identification may be of more recent origin. No other contacted Norwegian (Natural History Museum University of Oslo, NTNU University Museum and Tromsø University Museum) or Australian (AM, MV, SAM and WAM) museum hosted potential types of this species.

The illustration of O. elliptica by Sars (1897) suggests interrupted and discontinuous polygonal mesh walls, which would distinguish this species from O. rubra , O. henryae sp. nov. and O. matuwa sp. nov. Sars did not mention such discontinuity in the polygonal mesh in his otherwise detailed description, suggesting that these represent inaccuracies in the drawing. This may be solved when the species is collected again.

Henry (1924) differentiated O. elliptica from O. rubra by a “marginal area of the carapace with crowded concentric striae” in the former. These so-called concentric striae are the crowded growth lines at the carapace’s outer margin (see Sars 1897: pl. 2). Henry did not observe or draw any crowded growth lines; however, they are present in the type specimen of O. rubra as well as in most other O. rubra specimens examined herein, showing that this character is not suitable for the distinction of the two species.

In the geometric morphometric analyses ( Fig. 5 ), O. elliptica is distinct from most other species and most similar to O. matuwa sp. nov. (68.6% probability) and O. rubra (21.1%). However, typicality scores were rather low with 0.28 and 0.11, respectively.

No genetic data is available for O. elliptica and also males are currently unknown.

The species has not been recorded since the first description by Sars (1897); all other reports are probably related to morphologically similar species (e.g., O. rubra , O. henryae sp. nov. or O. matuwa sp. nov.). Due to the clear geographic separation, it is unlikely that one of the species with similar morphological characteristics ( O. rubra , O. henryae or O. matuwa ) is conspecific with O. elliptica .

Figures

Fig. 17. Ozestheria elliptica (Sars, 1897). a–d. Original drawings by Sars (1897). a. Carapace. b. Carapace ornamentation. c. Head. d. Telson. e. Map (circle depicts the type locality).

Fig. 2 (next page). Bayesian phylogenetic analysis of COI.To reduce the number of terminals, only unique haplotypes were included from the Schwentner et al. (2015a) dataset; all newly sequenced specimens are included. Terminals are indicated by their respective collection numbers. Species partitions suggested by GMYC and ASAP are indicated, and for ASAP the two best-scoring partitions are indicated. Our final species interpretation closely followed the second best-scoring ASAP partition. In addition to the formal species name, the names used by Schwentner et al. (2015a) to identify genetically delimited species (e.g., A, B etc.; extended for the newly identified species, e.g., X1) are provided in parentheses.

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.