Liljeborgia (Liljeborgia) clytaemnestra, D'Acoz, Cédric D'Udekem, 2012

D'Acoz, Cédric D'Udekem, 2012, The genus Liljeborgia in the Mediterranean Sea, with the description of a new species (Crustacea: Amphipoda: Liljeborgiidae), Zootaxa 3310, pp. 51-65 : 52-62

Liljeborgia (Liljeborgia) clytaemnestra sp. nov.

( Fig. 1–6 )

Nicippe pallida . — Della Valle, 1893: 658 (in part), not pl. 1 fig. 1; not pl. 19 fig. 35–52.

Lilljeborgia Della Vallei. — Chevreux, 1911: 204, pl. 13 fig. 7–11 (in part).

Lilljeborgia cf. brevicornis . — Ledoyer, 1968: 194, pl. 1 fig.c.

Liljeborgia dellavallei . — Geldiay et al., 1971: 375 (in part), fig. 1–3. — Ledoyer, 1977: 371 (?). — Krapp-Schickel, 1989: 465 (in part), fig. 315.

Liljeborgia sp. 4 d'Udekem d'Acoz, 2010: 178 –179, 181, fig. 63.

Type material. Malta, off Qawra/St Paul's Bay, 35°57'N 014°25'E, station AF 01/03, 50 m, slightly gravelly muddy sand, 0.1 m 2 Van Veen grab, January 2003: 1 very small specimen (PARATYPE), coll. Joseph Borg, RBINS, INV. 100998; Malta, off Qawra/St Paul's Bay, 35°57'N 014°25'E, station AF 03/04, 50 m, slightly gravelly muddy sand, 0.1 m 2 Van Veen grab, March 2004: 1 specimen (PARATYPE mounted on 3 slides in Euparal), coll.

Joseph Borg, RBINS, INV. 100997; 110201 /1-3; Malta, off Qawra/St Paul's Bay, 35°57'N 014°25'E, station AF 06/ 0 7, 50 m, slightly gravelly muddy sand, 0.1 m 2 Van Veen grab, June 2007: 4 specimens (PARATYPES), coll. Joseph Borg, RBINS, INV. 100996; Malta, off Qawra/St Paul's Bay, 35°57'N 014°25'E, station AF 11/01, 50 m, slightly gravelly muddy sand, 0.1 m 2 Van Veen grab, November 2001: 7 specimens (PARATYPES), coll. Joseph Borg, RBINS, INV. 100994; Malta, off Qawra/St Paul's Bay, 35°57'N 014°25'E, station AF 4/02, 50 m, slightly gravelly muddy sand, 0.1 m 2 Van Veen grab, April 2002: 8 specimens (HOLOTYPE male mounted on 8 slides in Euparal, RBINS, INV. 100999 /1-8, PARATYPE female on 3 slides in Euparal, RBINS INV. 101000 /1-3 and 6 PARATYPES in alcohol, RBINS, INV. 100995), coll. Joseph Borg; Italy, Naples area, Vervece, 40°37'07"N 014°19'29"E, 'Corallina' [i.e. presumably coralligenous bottom], 55–60 m, no date: 5 specimens (PARATYPES), leg. G. Krapp-Schickel, RBINS, INV. 69584.

Type locality. Off Qawra/St Paul's Bay, Malta, 35°57'N 014°25'E, 50 m depth, slightly gravelly muddy sand.

Etymology. Kλυταɩμνήστρα (latinized herein as Clytaemnestra ), twin sister of Helen and femme fatale of the Greek mythology. The name of a twin figure with a difficult personality has been coined because the new taxon belongs to a group where species are extremely similar and problematic to separate from each other. The name is a noun in apposition.

Description. Head: rostrum acute, eye large, of variable shape (broadly and irregularly reniform in holotype), with well-developed ommatidia, eye black in alcohol in specimens preserved for a few years, fading after a long preservation; anterior lobe of head rounded, not producing beyond rostrum.

Antenna 1: major flagellum with 20 articles; accessory flagellum with 11 articles.

Antenna 2: article four of peduncle with 4 groups of slender dorsomedial spines, 1 dorsodistal group of setae, two groups of ventrolateral setae and 5 narrow distal ventrolateral spines; article five with 9 groups of dorsomedial setae but without dorsomedial spines, with a distal ventrolateral spine; flagellum with 16 articles.

Epistome: not acute.

Lower lips: lobes with medial tooth.

Mandible: left lacinia mobilis large with anterior margin with 6 triangular teeth (the two medial ones partly fused); right lacinia mobilis distinctly smaller than left one, with anterior margin distinctly denticulate and with one medium-sized medial triangular tooth; ultimate raker spine of incisor process of normal stoutness; molar process with only 3 setae; article one of palp without setae, distinctly shorter than article two (ratio length article one / article two = 0.63), 2.47 x as long as wide; article two with setae on distal 0.3, 3.72 x as long as wide; article three very long, 4.07 x as long as wide, 0.72 x as long as article two.

Maxilla 1: article two of palp with 4 long setae on anterior margin, 9 spines on posterior and apical margin (proximal ones long and slender) and 6 facial setae; outer plate with 7 spines, of which some are denticulate; inner plate with a single seta.

Maxilla 2: outer plate with 2 well-developed setae on anterior margin.

Maxilliped: article one of palp without distal outer dorsal setae, article two without non-distal setae on outer margin; article three with 4 isolated setae on anterior border, article four (dactylus) slender on all its length, with anterior and posterior margins strongly curved and 0.64 x as long as article three; outer plate with 8 well-spaced slender and very long spines on posterior border (penultimate spine distinctly curved, with slight angular discontinuity), and 7–9 slender medio-facial setae; inner plate with 3 anterior spines (of normal stoutness, of size decreasing posteriorly) and 7 setae.

Gnathopod 1: coxa trapezoidal and rather narrow, with anterior medial setae, with posterior border weakly concave, with small anterior and posterior tooth or notch; merus with 2 groups of setae and distal tooth; carpus process with 3–4 groups of setae, tip of carpus reaching 0.29–0.32 of propodus, not very distant from propodal group of strong spines; propodus 1.90 to 2.00 x as long as wide; group of spines on proximal 0.37–0.45 of propodus (most distal spine used as reference point), these spines being rather small; palm border forming a regular curve, without teeth; with hooked spines on outer row narrowly spaced (36 [male] or 32 [female] hooked outer spines, and no outer setae); dactylus with 7–8 teeth.

Gnathopod 2: coxa rectangular, broad (1.2–1.3 x as long as wide), with anterior and posterior notch/tooth (notches well distant); merus with 2–3 groups of setae and with distal tooth; carpus process with 5–6 groups of setae; tip of carpus reaching 0.28–0.29 of propodus, almost reaching distal pre-palmar strong spine; propodus 1.95–1.98 x as long as wide; group of spines on the proximal 0.33–0.34 of propodus (most distal spine used as reference point); these spines are of normal length; palm border curved and convex, margin smooth; palm with hooked spines of outer row widely spaced (13 [male] to 15 [female] outer hooked spines and 9 [male] or 6 [female] outer setae); dactylus with 12 to 15 teeth. Gnathopod 2 larger than gnathopod 1; ratio length of propodus of gnathopod 2 / length of propodus of gnathopod 1: 1.45 (male) or 1.36 (female), surface of propodus of gnathopod 2 / surface of propodus of gnathopod 1: 2.12 (male) or 1.82 (female).

Pereiopod 3: coxa rectangular and narrow (2.10 x as long as wide), with 2 anterior and 1 posterior notches (notches very close to each other); merus 1.11 x as long as carpus and 0.79 x as long as propodus; posterior border of merus with 6 isolated setules and anterior border with distal setule; posterior border of carpus with 5 isolated non-distal setules and a third distal setule paired with a medium-sized seta; anterior border of carpus with 3 isolated setules; propodus with 11 posterior isolated spines (distal one paired with a spinule), of which the length is slightly increasing towards tip (length of longest posterior propodal spines 0.63 x as long as width of propodus); anterior border of propodus with 4 isolated non-distal setules and a pair of distal setules; dactylus long, slender, almost straight, 0.63 x as long as carpus and 0.44 x as long as propodus.

Pereiopod 4: coxa of normal width (1.42 x as long as wide), with anterior and posterior border parallel, with ventral border weakly convex, with 6 normally developed crenulations on posterior border and 1 ventral notch associated with a seta; merus 1.12 x as long as carpus and 0.81 x as long as propodus; posterior border of merus with 6 isolated setules and anterior border with 2 isolated setules; posterior border of carpus with 4 isolated nondistal setules and a fourth distal setule paired with a medium-sized seta; anterior border of carpus with 2 isolated setules; propodus with 10 posterior isolated spines (distal one paired with a spinule), of which the length is slightly increasing towards tip (length of longest posterior propodal spines 0.63 x as long as width of propodus); anterior border of propodus with 2 isolated setules and distal tuft of very short setules; dactylus long, slender, almost straight, 0.56 x as long as carpus and 0.41 x as long as propodus.

Pereiopod 5: coxa with small posterior tooth; basis broad (1.48–1.62 x as long as wide), with anterior and posterior border convex; anterior border with 10–11 small conical spines (distal one paired with or replaced by a medium-sized spine), posterior border with 11–13 well-developed serrations, distal border produced into a rounded lobe; ischium with 1–2 spines paired with a short seta on anterodistal corner; merus with 5 groups of 1–3 anterior spines, and 4 short posterior spines or pairs of spines; carpus with 3 anterior groups of articulated structures including long setae and 2–3 medium-sized spines, and with posterodistal pair of spines; carpus 0.89 x as long as merus; carpus + propodus 1.81 x as long as merus; propodus with 8 isolated small anterior spines and with long medial setae; dactylus distinctly curved and of normal stoutness, with tip entire, 0.27 x as long as propodus.

Pereiopod 6: coxa with small posterior tooth; basis broad (1.42–1.49 x as long as wide), with anterior and posterior border convex; anterior border with 9–12 small conical spines (distal one paired with or replaced by a medium-sized spine), posterior border with 13 (adult) or 9 (immature) strong serrations, distal border produced into a rounded lobe; ischium with medium-sized spine paired with short seta on anterodistal corner; merus with 4– 5 anterior groups of 1–3 spines and 5 posterior spines or pairs of spines; carpus with 3 anterior medium-sized spines or groups of spines of which 2 are associated with long setae arising more medially, with posterodistal group of spines; carpus 0.71 x as long as merus; propodus with 5 anterior spines or pairs of spines, with about 6 posterior groups of long thin setae; dactylus almost straight, slender, with tip entire, 0.41 x as long as propodus.

Pereiopod 7: coxa with small posterior notch; basis broad (1.24 x as long as wide), with anterior and posterior border convex; anterior border with 9 small conical spines (distal one paired with medium-sized spine), posterior border with 13 strong serrations, distal border produced into a low rounded lobe; ischium with pair of spines on anterodistal corner; merus with 6 anterior groups of long spines and 6 posterior groups of 1–2 spines; merus 3.67 x as long as wide and 0.90 x as long as basis; carpus 1.02 x as long as merus; dactylus straight, very long and slender, entire, 0.88 x as long as propodus.

Pleonite 1: posterodorsal area produced into 3 small teeth of which the median one is the longest; epimeron 1 with normally developed posteroventral tooth, with posterior border distinctly convex; without anterior setae, with a posterior setule.

Pleonite 2: posterodorsal area produced into 3 small teeth of which the median one is the longest; epimeron 2 with normally developed posteroventral tooth, with posterior border almost straight.

Pleonite 3: posterodorsal area toothless; epimeron 3 with small posteroventral tooth, with posterior border scarcely convex.

Urosomite 1: with small or very small posterodorsal tooth; ventrofacial border with 1 spine; peduncle of uropod 1 with medial distal corner rounded, with 6 dorsolateral spines of which the proximal one is fairly long (not extremely long) and exhibits no sexual dimorphism, and with 1 dorsomedial distal spine; outer ramus with 4–5 medium-sized stout outer spines and 5–6 short stout medial spines; inner ramus with 2–4 short stout outer spines and 7–8 stout medium-sized medial spines.

Urosomite 2: with small to minute posterodorsal tooth (development variable); peduncle of uropod 2 with 1 long dorsolateral distal spine, with 1 dorsomedial distal spine; outer ramus with 4–5 well-developed stout outer spines and no medial spine; inner ramus with 2–3 short stout spines on outer border and with 7–8 stout mediumsized spines on medial border.

Urosomite 3: without posterolateral tooth on each side, without posterodorsal spine on each side; outer ramus of uropod 3 with 3–4 short outer spines; inner ramus with 2–3 short stout spines on outer border, with 3 well-developed spines on medial border; rami subequal and longer than peduncle.

Telson: cleft to 0.78 of its length; medial tooth of each lobe a bit shorter than outer tooth; interdental spine overreaching outer tooth by 0.50 of its length, 0.48 times as long as telson; medial apical teeth of telson with 1– 2 setules.

Size. 7 mm.

Distribution and ecology. Specimens from Malta and Naples have been examined. Chevreux (1911) illustrated specimens of ' L. dellavallei ' from Bône, Algeria, which presumably also belong to L. clytaemnestra sp. nov. Specimens of ' L. cf. brevicornis ' from the area of Marseille recorded by Ledoyer (1968) and Bellan-Santini & Ledoyer (1973) probably also belong to L. clytaemnestra sp. nov. The species is presumably not uncommon and widely distributed throughout the Mediterranean Sea. The specimens examined were found on gravelly muddy sand and on coralligenous bottoms, between 50 and 60 m. The bathymetric and ecological distribution of L. clytaemnestra sp. nov. is probably wider, but it is replaced by L. dellavallei in Posidonia meadows.

Remarks. Della Valle (1893) recorded two varieties of ' Nicippe pallida ( Spence Bate, 1857) ' from the Bay of Naples: a reddish one from the military harbour and a grayish and more slender one from the sandy bottoms in front of the biological station. The propodus of the pereiopod 4 of the specimen illustrated by Della Valle (1893) has two very long distal spines (these spines being much longer than the proximal ones) (Della Valle, 1893: pl. 19 fig. 50) and short spines on the tip of the telson (Della Valle, 1893: pl. 19 fig. 43). Stebbing (1906) erected a new species, L. dellavallei Stebbing, 1906 , on the basis of Della Valle's (1893) account of ' Nicippe pallida ' but he did not examine any specimens himself. Concerning Mediterranean Liljeborgia species, most subsequent authors recognized only L. dellavallei , and from 1975 onwards also the distinctive but rare, L. psaltrica Krapp-Schickel, 1975 . The only noticeable exceptions were Ledoyer (1968) and Bellan-Santini & Ledoyer (1973), who recognized a L. cf. brevicornis as distinct from L. dellavallei . Recently, d'Udekem d'Acoz (2010) provided a new detailed illustrated account of a species identified as L. dellavallei after a careful examination of Della Valle's (1893) figures. Also recorded were a few specimens in mediocre condition slightly departing from the morphology of true L. dellavallei , provisionally named Liljeborgia sp. 4. Examination of new samples of ' Liljeborgia sp. 4', kindly provided by Joseph Borg (University of Malta), confirmed that it is distinct from L. dellavallei . The species is described herein as L. clytaemnestra sp. nov. Ecological information available on the types of L. clytaemnestra sp. nov. suggests that it is probably identical to the grayish variety of ' Nicippe pallida ' recorded by Della Valle (1893).

Complete illustrations of L. dellavallei are given by d'Udekem d'Acoz (2010), but essential features of that species are illustrated again herein (fig. 7) for an easier comparison with L. clytaemnestra sp. nov. The most reliable difference between L. clytaemnestra sp. nov. and L. dellavallei is the posterior ornamentation of the propodus of pereiopods 3–4. In L. clytaemnestra sp. nov., the size of the spines scarcely increases towards tip, whilst in L. dellavallei , the size of spines dramatically increases towards tip. In L. clytaemnestra sp. nov., the spines are also narrower and the most distal long spine is immediately followed by a much shorter one, which is not observed in L. dellavallei . The distal spine of each lobe of the telson is about 0.5 times as long as telson in L. clytaemnestra sp. nov., but about 0.2 times (or less) in L. dellavallei . In L. clytaemnestra sp. nov., the dorsolateral border of the peduncle of uropod 1 exhibits a fairly long spine followed by slightly shorter spines in adult males (and in females and juveniles), whilst in L. dellavallei , it exhibits an immensely elongated spine followed by much shorter spines in adult males (that spine is just a bit longer in females and immatures). There are also other less striking differences. On the mandibular palp of L. clytaemnestra sp. nov., the setae extend to the distal third, whilst in L. dellavallei they are restricted to the tip of article 2. Article 3 of palp is also longer in L. clytaemnestra sp. nov. than in L. dellavallei . The posterior spines of the outer plate of the maxilliped are longer in L. clytaemnestra sp. nov. (0.7 times as long as spatulate part of outer plate) than in L. dellavallei (0.5 times). Pereiopods 3–4 are more slender in L. clytaemnestra sp. nov. than in L. dellavallei . Finally the posterodorsal teeth of the segments of the pleon are as a rule a bit less developed in L. clytaemnestra sp. nov. than in L. dellavallei .

L. clytaemnestra sp. nov. is actually more similar to two northeastern Atlantic species, the British L. pallida ( Spence Bate, 1857) and especially the Scandinavian L. brevicornis ( Bruzelius, 1859) than to the Mediterranean L. dellavallei (see d'Udekem d'Acoz (2010) for complete illustrations of these species). The eyes of L. clytaemnestra sp. nov. preserved in alcohol for a few years are black, as in L. pallida , but not as in L. brevicornis , where they are weakly pigmented. In L. clytaemnestra sp. nov., article 2 of the mandibular palp has setae on distal third of article 2, whilst setae are restricted to tip in the two other species. Article 3 of the mandibular palp is also longer in L. clytaemnestra sp. nov. (4 times as long as wide) than in the two Atlantic species (less than 3 times as long as wide). The spines of the outer plate of the maxilliped are longer in L. clytaemnestra sp. nov. (0.7 times as long as spatulate part of outer plate) than in the two other species (0.4–0.55 times). The usual number of teeth on the dactylus of gnathopod 1 is 7–8 in adult L. clytaemnestra sp. nov. versus 8–12 in adult L. pallida and 4–7 (most commonly 5) in adult L. brevicornis . The most distal spine of the propodus of P3–P4 is reduced in L. clytaemnestra sp. nov. and L. brevicornis , but not in L. pallida . The serration of the posterior border of the basis of P7 is much stronger in L. clytaemnestra sp. nov. than in the two other species. Finally, in L. clytaemnestra sp. nov., the spines of the lobes of the telson are longer (0.5 times as long as telson) than in L. pallida (0.1–0.25 times) and about the same size as in L. brevicornis (0.4 times). These differences are extremely slight, so that, in the absence of molecular data, the distinctness between these taxa is somewhat debatable. However, in the author's opinion, it is preferable, at least for the time being, to formally consider the Mediterranean form as separate from L. brevicornis and L. pallida rather than proposing uncertain synonymies or using informal names, possibly leading to confusion.

It is impossible to compare L. clytaemnestra sp. nov. with its African relative L. mixta Schellenberg, 1925 , since the species has been described after a too immature specimen (only 3 mm long). Thus, L. mixta should be considered as a nomen dubium.

Finally it appears that juvenile L. clytaemnestra sp. nov. and L. dellavallei exhibit striking similarities with the Atlantic diminutive species, L. kinahani ( Spence Bate, 1862) . For example, they have smaller and more rounded eyes and the posterior border of the propodus of P3–P4 has setules instead of spines, as in L. kinahani . L. kinahani is much smaller than any other European Liljeborgia species and all the characters of the species, as described by d'Udekem d'Acoz (2010), are possibly related to its small size. Actually, there is no clear evidence that L. kinahani is a valid species, and the synonymy of L. kinahani and L. pallida (both species described based on British specimens) seems increasingly likely.

Figures

FIGURE 1. Liljeborgia clytaemnestra sp. nov., Malta, off Qawra / St Paul's Bay, sta. AF 4 / 02. A, D – H, male holotype (7 mm); B, female paratype (7 mm); C, juvenile (about 2 mm). A, head with antennae; B, eye; C, upper part of head with eye; D, lower lip; E, right Md; F, tip of right Md; G, tip of left Md; H, left Mx 1; I, right Mx 2.

FIGURE 2. Liljeborgia clytaemnestra sp. nov., Malta, off Qawra / St Paul's Bay, sta. AF 4 / 02, male holotype (7 mm). A, Mxp; B, Mxp plates; C, telson.

FIGURE 3. Liljeborgia clytaemnestra sp. nov., Malta, off Qawra / St Paul's Bay, sta. AF 4 / 02. A – D, male holotype (7 mm); E – F, female paratype (7 mm). A, E, left Gn 1; C, F, left Gn 2; B, palm of left Gn 1; D, palm of left Gn 2.

FIGURE 4. Liljeborgia clytaemnestra sp. nov., Malta, off Qawra / St Paul's Bay, sta. AF 4 / 02. A – D, male holotype (7 mm); E, juvenile (2 mm). A, right P 3; B, propodus and dactylus of right P 3; C, right P 4; D, propodus and dactylus of right P 4; E, propodus and dactylus of left P 3.

FIGURE 5. Liljeborgia clytaemnestra sp. nov., Malta, off Qawra / St Paul's Bay. A – D, F, sta. AF 4 / 02, E, sta. AF 3 / 04. A – C, male holotype (7 mm); D, female paratype (6 mm); E, immature specimen (3.6 mm); F, juvenile specimen (about 2 mm). A, left P 5; B, left P 6; C, left P 7; D, left P 5; E, right P 6 (inverted); F, right P 7 (inverted).

FIGURE 6. Liljeborgia clytaemnestra sp. nov., Malta, off Qawra / St Paul's Bay, sta. AF 4 / 02. A, D, F, G, H, male holotype (7 mm); B, C, E, female paratype (7 mm). A, pleosome; B, posterodorsal border of pleonite 1 in lateral view; C, posterodorsal bor- der of pleonite 2 in lateral view; D, E, urosome; F, right U 1; G, right U 2; H, right U 3.