Eulimnogammarus etingovae, Moskalenko & Neretina & Yampolsky, 2020

Moskalenko, Victoria N., Neretina, Tatiana V. & Yampolsky, Lev Y., 2020, To the origin of Lake Baikal endemic gammarid radiations, with description of two new Eulimnogammarus spp., Zootaxa 4766 (3), pp. 457-471 : 462-465

Eulimnogammarus etingovae sp. nov.

( Fig. 1A , Fig. 2 )

Holotype: female, body length 11 mm. South Baikal , near Kultuk, 51.696N, 103.874E, depth 10–20 m, dredge on sandy substrate, August 2013. Numerous paratypes of both sexes, same location and date. Holotype location: Zoological Museum , Moscow State University, Moscow, Russia. Paratypes: ETSU museum of Natural History, Johnson City, TN, USA and Baikal Museum, Listvyanka, Russia. See Supplementary materials for holotype museum ID.

Etymology. The species is named after Anna Etingova who participated in the collection of the holotypes.

Diagnosis. The species can be distinguished from other Eulimnogammarus spp . by a 1-articulate accessory flagellum, sparse setation on rami of uropod III, lack of calceoli, lack of setae on uropods I and II and of plumose setae on uropod III and presence of spines only on the last two body segments.

Description. Description is based on female holotype and two male paratypes. No sexual dimorphism noted other than the presence of brood chamber in females and slightly weaker gnathopods I in female. Body slender, smooth, 8–11 mm, red when alive, with yellow spots on the posterior half of the head segment. Small spines on the last two segments of the urosome, setae on the last segment of pleosome and the first segment of urosome. Eyes kidney-shaped, white with black spots (black in preserved material). Rostrum very short, rounded, antennal sinus shallow ( Fig. 1A ).

Antennae I short (1/4 body length) with the first peduncle article about 2/3 as long as the head segment and the length ratio of peduncle segments 1:0.6:0.4, carrying small setae on the distal end of each segment of peduncle and main flagellum. Flagellum consists of 9-12 articles. Accessory flagellum 1-articulate, very short, often barely visible ( Fig. 2A ). Antennae II shorter than I, peduncle articles carrying rare single setae, flagellum consists of 6 articles carrying short setae. No calceoli found ( Fig. 2B ).

Mouthparts typical for subgenus Eurybiogammarus ( Bazikalova 1945) . Basal article of mandible palpus with- out setae, terminal article slightly shorter than the subterminal one; the comb is much shorter than the apical setae ( Fig. 2C ). Outer plate of maxillae I carries hooks with up to 5 teeth, inner plate triangle with dense pennate setae ( Fig. 2D ). Maxillae II ( Fig. 2E ) and maxillipedae ( Fig. 2F ) as in any Eulimnogammarus spp .

Gnathopods I with weak, almond-shaped, weakly setose propodus with 8 pairs of spines on posterior margin ( Fig. 2G ), and with a group of weak setae at the base of the dactylus, somewhat more powerful in males. Gnathopods II with even weaker, heavily setose subrectangular elongated propodus with oblique palmar edge and a group of spines at the palmar-posterior corner ( Fig. 2H ).

Pereopods short, stalky, with short spines and few setae, coxal plates short, rounded, with short setae on the posterior edge. Basipodite of pereopode VII with a large, round lobe extending distally in a rounded protrusion that reaches to the distal end of the next segment ( Fig. 2I ). Posterior edge serrated, with a weak seta under each notch. Uropods I and II with spines. Pleopods of typical gammarid morphology, with 2 small (50 microns) retinacles on the basal article, each equipped with 4-5 bumps on the convex side and 1-2 hooks on the concave side.

Uropod III elongated, nearly bare, peduncle with 2 groups of 3-4 spines, outer ramus 2-2.5 times longer than the peduncle, 2-articulate, with 3 short spine and 1-3 weak simple setae on the outer margin, no spines or setae on the inner margin, 4-5 spines and a few setae at the distal end, spines reaching to ½ of the length of the triangle 2 nd article ( Fig. 2J ). Inner ramus narrow, about 2/3 as long as the outer ramus, narrow and slightly curved, completely bare, except for 1 spine and 2-3 setae at the distal end. Telson cleft to the base with 1-3 short spines at the tip of branches ( Fig. 2K ).

Remarks: this species shares morphological affinities with both Echiuropus (1-articulate accessory flagellum, sparse to no setation on rami of uropod III) and Eulimnogammarus (2-articulate outer ramus of uropod III). It is similar to Eulimnogammarus aheneus and Eulimnogammarus similis , but it has neither calceoli, nor setae on uropods I and II nor plumose setae on uropod III. Similar to E. hyacynthus , but is smaller, red rather than blue and has spines only on the last two body segments. Differs from all other Eulimnogammarus spp . except the next species by having a 1-articulate accessory flagellum and by the structure of uropod III. Molecular phylogeny places this species basally within the paraphyletic genus Eulimnogammarus , with possible affinities to either the genus Macropereiopus which clusters within Eulimnogammarus ( Naumenko et al. 2017; Fig. 5 below), or to the Echiuropus which is basal to Baikal clade 2 ( Naumenko et al. 2017; Supplementary Fig. 1 ), depending on the nucleotide vs. amino acid sequences of the protein coding genes analyzed. This species is different from the next one by weak gnathopods, inner branch of uropod III longer than 2/3 of the outer branch, no setation on antennae II, uropod III and telson and a more protruding distal lobe on pereopod VII basipodite.

Figures

FIGURE 1. Whole body outline of two newly described species. A: Eulimnogammarus etingovae sp. nov. B: Eulimnogammarus tchernykhi sp. nov. Bar = 1 mm.

FIGURE 2 Eulimnogammarus etingovae sp. nov. Holotype, female. A: antenna I* (inset: accessory flagellum enlarged); B: antenna II; C: palpus of mandible; D: maxilla I*; E: maxilla II; F: maxilliped; G: propodus of gnatopod I; H: propodus of gnatopod II; I: basipodit of pereopod VII; J: uropod III; K: telson. * - composite images. Bars = 0.1 mm.

FIGURE 5. Bayesian reconstruction of basal branching events of Baikal endemic radiation based on nucleotide sequences of 16S, 18S and 28S rRNAs, COI and elongation factor 1α. Symbols and bars as on Fig. 4.