Gammarus sywulai, Grabowski & Wysocka & Mamos, 2017

GAMMARUS SYWULAI View in CoL SP. NOV.

( FIGS 3, 4)

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Diagnosis: Medium-sized species. It may be distinguished from other Lake Ohrid species by the following combination of characters: (1) mesosome and metasome smooth and unarmed, epimeral plates armed with spines only, (2) urosome elevated and slightly compressed laterally, armed with spines only, (3) antennae slender, poorly setose, antenna I with short two-segmented accessory flagellum, antenna II without calceoli, (4) pereopods III–IV poorly setose, pereopods V–VII armed with spines only, and (5) uropod III with endopodit shorter than half of the exopodit, both armed with spines and few very short simple setae.

Materials examined: More than 100 individuals, both males and females, from several localities in different parts of Lake Ohrid, FYR Macedonia. Ohrid (offshore), N41.1109, E20.7890, depth of 20–30 m: many individuals coll. 21 September 2012 GoogleMaps , 7 ind. coll. 11 June 2011; vicinity of Ohrid – Hotel Gorica (offshore), N41.0886, E20.7957, depth of 20–30 m: 11 ind. coll. 3 June 2007 GoogleMaps ; Sveti Naum (offshore), N40.9142, E20.7405, depth of 20 m, 5 ind. coll. 11 June 2011 GoogleMaps , 5 ind. coll. 23 September 2012; Gradiste (offshore), depth of 20–30 m: 20 ind. coll. 11 June 2011 , many individuals coll. 25 September 2012; Pestani (offshore), N41.0160, E20.8083, depth of 20–37 m: 1 ind. coll. 25 September 2012 GoogleMaps ; Sveti Zaum (offshore), N40.9489, E20.7743, depth of 20–30 m: 2 ind. coll. 11 June 2011 GoogleMaps ; Kaliste (offshore), N41.1502, E20.6512, depth of 20–30 m: 12 ind. coll. 11 June 2011 GoogleMaps .

Type: Holotype: An adult male individual collected on 21 September 2012, body length of 10 mm, as well as the DNA voucher (extracted DNA in buffer) deposited in Museum and Institute of Zoology Polish Academy of Sciences. Catalogue number: MIZ 11/2016/1; GenBank accession numbers: KX233065 View Materials for cox I, KX233236 View Materials for 16S rRNA. Paratypes were deposited in Museum and Institute of Zoology Polish Academy of Sciences: five specimens fixed in 96% ethanol, collected from type locality on 11 June 2012 (catalogue numbers: MIZ 11/2016/2-MIZ 11/2016/6).

Type locality: Lake Ohrid, Ohrid (offshore), FYR Macedonia, N41.1109, E20.7890, depth of 20–30 m. GoogleMaps

Distribution and habitat: The species is endemic to the ancient Lake Ohrid and member of the local endemic species flock (sensu Wysocka et al., 2013). It is found throughout the lake, usually at a depth range of 20–40 m, predominantly in the beds of Dreissena shells.

Etymology: This new species is named to honour and commemorate the late prof. dr. hab. Tadeusz Sywula (1939–2004), of the University of Gdansk, who lost his life in a car accident in FYR Macedonia during a scientific expedition to the lake. He was a prominent Polish carcinologist specializing in ostracods and initiated our scientific interests in Lake Ohrid biota.

Description: Male: Medium-sized species with robust body, length up to 12 mm. Head ( Fig. 3a): Lateral lobes rounded; eyes medium-large, oval, about as long as the diameter of antenna I. Antenna I ( Fig. 3b): About half of the body length. Peduncle segments subsequently shorter with third segment about half length of the first one. Main flagellum with 20–25 segments. Accessory flagellum with 3 segments (exceptionally 4 segments in some largest individuals). Both peduncle and flagellum with few groups of short simple setae, only rarely and slightly exceeding the diameter of underlying segments. Antenna II ( Fig. 3c): Peduncle and flagellum segments slender. Gland cone rather straight and slender, slightly exceeding the distal end of the third peduncle segment. Fifth peduncle segment slightly longer than the fourth one, each armed with 1–3 groups of short simple setae, rarely longer than the diameter of underlying segments. Flagellum relatively short, up to 10 segmented, without calceoli, with a row of short ventral setae, never forming a regular brush. Mandibular palp ( Fig. 3d): First segment unarmed. Second segment with ventral setae: in the proximal part 2–3 setae shorter than the diameter of the segment, in the distal part 5–8 setae up to 2.5× longer than the diameter of segment. The third segment is armed with 2 groups of long A-setae, a regular comb of 25–28 D-setae and 5–6 long E-setae. Maxillipedes ( Fig. 3e): Inner plate with three apical teeth intermixed with number of slightly longer setae, ventral margin without setae. Outer plate with a row of 5–6 apical setae, ventral margin with a row of 9–10 teeth accompanied by some setae of similar length. Palp well developed. Gnathopod I ( Fig. 3f): Coxal plate rather rectangular, slightly dilated in the distal part, with rounded distal corners, each incised and equipped with one short seta. Basis with several long setae along the anterior and posterior margin. Ischium, merus and carpus with posterodistal groups of simple setae. Propodus pyriform with a few groups of setae along anterior margin and one apical group of setae. Palm oblique, setose, with one medial palmar spine and one angle spine, posterior palmar margin with 5 groups of small spines intermixed with rather short setae. Dactylus very robust. Gnathopod II ( Fig. 3g): Coxal plate slightly narrowing distally, with rounded distal corners, each incised and equipped with one short seta. Anterior margin of basis with few long setae in the proximal part and short setae in the distal part, posterior margin with several long setae. Ischium, merus and carpus with posterodistal groups of simple setae. Propodus trapezoid, widening distally. Anterior margin naked with one apical group of setae. Palm concave, setose, with one medial palmar spine and two angle spines. Posterior palmar margin with a dense brush of robust setae. Pereopod III ( Fig. 4a): Anterior and distal margin of the coxal plate slightly convex, posterior margin straight. Distal corners rounded, each incised and equipped with one short seta. Pereopod poorly setose. Basis with several long setae on the anterior and posterior margin, longer than the diameter of segment. Ischium with groups of setae on posterodistal corner. Anterior margin of merus is armed with 1–2 spines and one anterodistal spine accompanied by a few short setae, posterior margin with few groups of short setae (shorter than the diameter of segment) and a posterodistal group of longer setae. Carpus with naked anterior margin and one anterodistal spine accompanied by few short setae, posterior margin with 1–2 groups of spines accompanied by a few short setae and with a posteroapical group of spines and setae. Propodus with naked anterior margin and anteroapical group of setae, posterior margin with 3–4 spines accompanied by setae up to 2× longer than the spines. Dactylus robust with one seta at joint of unguis. Pereopod IV ( Fig. 4b): Coxal plate dilated distally. Distal corners rounded, each incised and equipped with one short seta. Basis with several long setae along the anterior and posterior margins, one anterodistal spine and posterodistal group of setae. Ischium with groups of setae on posterodistal corner. Anterior margin of merus armed with 1–2 spines and one anterodistal spine accompanied by a few short setae, posterior margin with a few groups of short setae (shorter than the diameter of segment) and a posterodistal group of few setae. Carpus with naked anterior margin and one anterodistal spine accompanied by a few short setae, posterior margin with one to two groups of spines accompanied by a few short setae and with a posteroapical group of spines and setae. Propodus with naked anterior margin and anteroapical group of setae, posterior margin with 3–4 spines accompanied by setae up to 2× longer than the spines. Dactylus robust with one seta at joint of unguis. Pereopod V ( Fig. 4c): Basis with a subrectangular shape, posterior margin slightly concave, posterodistal lobe well developed, posterior margin with 4–6 very short setae, anterior margin with 2–3 spiniform setae, 4–5 spines intermixed with fine setae and one group of apical spines and short setae. Ischium with anterodistal group of spines intermixed with relatively short setae. Merus, carpus and propodus with robust spines on both margins, sometimes intermixed with relatively short setae. Dactylus robust with one seta at joint of unguis. Pereopod VI ( Fig. 4d): Similar to PV, but slightly longer and wider, posterior margin convex, posterodistal lobe less prominent with strong spines at posteroinferior corner. Ischium to propodus armed with robust spines and very few short setae. Pereopod VII ( Fig. 4e): Basis wider than in PVI with spine and seta at posteroinferior corner. Further articles armed same as in preceding pereopods. Urosome ( Fig. 4f): Elevated and slightly compressed laterally. First and second urosomite with one dorsomedial and two dorsolateral groups of robust spines (2–2–2 and 3–2–3). Third urosomite only with one dorsolateral spine on each side (1–0–1). Uropod III ( Fig. 4g): Peduncle with 2–4 distal spines. Inner ramus (endopodit) shorter than half of the outer ramus (exopodit). Both rami poorly armed with a few groups of spines intermixed with simple short setae. First article of outer ramus tipped with 5–6 distal spines intermixed with slightly longer setae. Second article of outer ramus longer than the distal spines and setae of the first article. Epimeral plates ( Fig. 4h): First epimeral plate with 1 spine at the anterodistal margin, posterodistal margin notched with 2 spines. Second epimeral plate with 1 spine at the laterodistal surface, posterodistal margin slightly notched. Third epimeral plate with 3 spines at the laterodistal surface, posterodistal corner with long sharply pointed notch. Telson ( Fig. 4i): Deeply cleft, poorly setose. Each lobe with 2–3 apical strong spines intermixed with few short setae, very few short subapical setae sometimes present. Female: Apart from the usual secondary sexual characters, that is, the presence of oostegites and lack of penes as well as slightly more intense setation of appendages, females do not show any detectable differences in external morphology.

Variability: Morphology of G. sywulai is stable with respect to features such as absence of calceoli, poor armature of antennae, pereopods and uropod III as well as compression, elevation and armature of urosomites. Only limited variability associated most probably with postembryonic developmental changes was observed. Larger individuals tended to have higher number of flagellum segments in antennas I and II, as well as more and longer setae on all appendages. Such variability is typical for most species of this genus ( Karaman & Pinkster, 1977a, b, 1987).

Molecular diagnostic characters: BOLD analysis of species diagnostic characters revealed eight diagnostic and two partial characters for cox I as well as two diagnostic characters for 16S rRNA (details in Table 2).