Pseudotanais (Pseudotanais) stiletto Bamber

Bamber, Roger N, Bird, Graham, Błażewicz-Paszkowycz, Magdalena & Galil, Bella, 2009, Tanaidaceans (Crustacea: Malacostraca: Peracarida) from soft-sediment habitats off Israel, Eastern Mediterranean, Zootaxa 2109, pp. 1-44 : 34-39

Pseudotanais (Pseudotanais) stiletto Bamber sp. nov.

Figures 15–17

Material examined. Holotype: 1 female (NHM.2008.4840), station RFI 2, off the coast of Israel, 31º53.328’N 034º32.853’E, 58 m depth, fine mud, 14 September, 2006. Allotype: 1 male (NHM.2008.4841), station RFI 4, 31º54.193’N 0 34º33.241’E, 59 m depth, 20 October 2007. Paratypes: 5 females (NHM.2008.4842–4846), same sample as holotype; 9 specimens (NHM.2008.4847–4856), 1 female with oostegites, dissected, station RFI 1, 31º53.640’N 0 34º33. 0 69’E, 57 m depth; 3 specimens (NHM.2008.4857–4859), station RFI 3, 31º53.842’N 0 34º33.300’E, 57 m depth; 6 specimens (NHM.2008.4860–4865), station RFI 4, 31º54.193’N 0 34º33.241’E, 59 m depth; 4 specimens (NHM.2008.4866–4869), station RFI 5, 31º53.633’N 034º33.251’E, 55 m depth; 7 specimens ( TAU AR 28433), 1 female dissected, station RFI 7, 31º48.809’N 034º28.892’E, 62 m depth; all 14 September, 2006; all fine mud. 5 specimens ( TAU AR 28434), RFI 2; 4 specimens ( TAU AR 28435), RFI 4; 1 specimen ( TAU AR 38436), RFI 5; 14 specimens ( TAU AR 38437), RFI 7; all 0 3 May 2007. 2 females (NHM.2008.4870–4871), RFI 1; 6 females (4 brooding) (NHM.2008.4872–4877), RFI 2; 7 females (NHM.2008.4878–4884), RFI 3; 11 females (NHM.2008.4885–4894), RFI 4; 6 females (NHM.2008.4895–4900), 1 male (dissected), RFI 5; 101 specimens (NHM.2008.4901–4910), RFI 7; all 20 October 2007.

Other material: 11 specimens, HMI 18, 31° 52.059’N 034° 38.151’E, 28.1 m depth; 6 specimens, HMI 19, 31° 52.447’N 034° 38.468’E, 27.2 m depth; 2 specimens, HMI 34, 31° 52.367’N 034° 38.573’E, 25.5 m depth; 10 specimens, HMI 64, 31° 52.648’N 034° 38.509’E, 27.9 m depth; all 20 October 2007.

Diagnosis: member of the ‘ forcipatus -group’ of Pseudotanais (P.) sensu Bird & Holdich (1989) , but with distinct black eyes and a single-segmented uropod endopod. Male with posterior pereopods much longer than anterior pereopods, and bearing elongate, corrugated dactylus.

Description of female: small Pseudotanais , holotype length 1.07 mm, body ( Figure 15 A) 4.5 times as long as wide, colour translucent white, eyes black. Cephalothorax subtriangular, 1.2 times as wide as long, longer than any pereonite, naked; eyes present, pigmented. Six free cylindrical pereonites, pleonites 3 to 6 with small anterolateral seta on each side; pereonites 1 and 2 equal in length, shortest, pereonite 3 almost twice as long as pereonite 2, pereonites 4 and 5 subequal, 2.5 times as long as pereonite 3, pereonite 6 shorter, only three times as long as pereonite 2 (all pereonites respectively 6.4, 6.4, 3.6, 1.4, 1.4 and 2.2 times as wide as long). Pleon of five free subequal pleonites bearing pleopods plus pleotelson; pleonites 7.5 times as wide as long; at least pleonites 1 to 3 with simple lateral seta on each side. Pleotelson semicircular, short, 3 times as long as pleonite 5, half as long as wide, naked.

Antennule ( Figure 15 B) of three articles, proximal article 3.8 times as long as wide, with outer medial and distal setae longer than article width, and two proximal penicillate setae; second article half as long as first, with outer distal seta as long as article and paired smaller inner distal setae; third article just longer than second, with four distally bifurcate and one simple distal setae.

Antenna ( Figure 15 C) of six articles, proximal article compact, naked; second article with fine dorsodistal seta; third article 1.3 times as long as second with fine dorsodistal seta; fourth article curved, twice as long as third, with four distal simple setae; fifth article just longer than third with distal seta; sixth article minute with five distal setae.

Labrum ( Figure 15 D) rounded, setose. Left mandible ( Figure 15 E) with triangular, crenulate lacinia mobilis, pars molaris a very slender spike with simple point; right mandible ( Figure 15 F) with lacinia mobilis fused to a small process. Labium, and maxillule and maxilla ( Figure 15 G) typical of the genus, maxillule palp with two unequal distal setae. Maxilliped ( Figure 15 H, I) endites almost entirely fused, with slight distal tubercles but no setae; palp first article naked, second article with two simple inner setae, third with three inner and one submarginal setae, fourth article with four distal, one subdistal and one outer simple setae; distal margin of endites naked. Epignath ( Figure 15 J) simple, linguiform.

Cheliped ( Figure 16 A) forcipate, basis 1.5 times as long as wide, naked; merus subtriangular, with single midventral seta; carpus 2.3 times as long as wide, with two midventral setae, and dorsodistal and dorso-subproximal single setae; propodus palm longer than fixed finger, with ventral seta proximal to fixed finger and four anterior spines; fixed finger slender, cutting edge with three distal setae; unguis slender; dactylus naked.

Pereopod 1 ( Figure 16 B) slender; coxa simple, naked; basis 5.8 times as long as wide, naked; ischium with single small seta; merus half as long as carpus, with ventrodistal seta; carpus with single inner distal seta; propodus 1.2 times as long as carpus; dactylus with distinct, slender, longer unguis, both together 0.9 times as long as propodus.

Pereopod 2 ( Figure 16 C) relatively compact, basis 5.3 times as long as wide with single dorsoproximal seta; ischium with single small seta; merus and carpus equal in length, merus with paired ventrodistal setae, carpus with single dorsodistal seta, inner-distal seta and large, spatulate ventrodistal spine; propodus 1.5 times as long as carpus, with distal spine longer than dactylus, dactylus plus unguis half length of propodus. Pereopod 3 ( Figure 16 D) similar to but smaller than pereopod 2 (total length 73% of that of pereopod 2), propodus only just longer than carpus.

Pereopod 4 ( Figure 16 E) articulation of coxa with sternite obscure; basis 3.6 times as long as wide, naked; ischium with single small seta; merus and carpus of equal length, merus with two fine ventrodistal simple spines and dorsodistal seta, carpus with single dorsodistal seta, inner-distal seta and spatulate ventrodistal spine; propodus 1.4 times as long as carpus with one distal and paired ventrodistal setae, and distal penicillate seta; dactylus and unguis fused into claw, curved, together one-third as long as propodus. Pereopod 5 ( Figure 16 F) as pereopod 4 but without propodal penicillate seta. Pereopod 6 ( Figure 16 G) as pereopod 4, but propodus with two simple distal setae.

Pleopods ( Figure 16 H) all alike, with naked basis, endopod larger than exopod, with eight distal plumose setae; exopod with four longer and one shorter distal plumose setae.

Uropod ( Figure 15 K) basis naked, endopod of one segment with five distal setae, exopod of two segments, together 0.7 times as long as endopod, proximal segment with single outer seta, distal segment with paired unequal setae.

Description of male: body ( Figure 17 A) smaller and more compact than female, allotype 0.66 mm long, 4 times as long as wide. Cephalon tapering less than that of female, proportionately longer, as long as wide. Eyes large, black. Pereonite 1 shortest, pereonite 2 slightly longer, pereonites 3 to 5 subequal (pereonite 4 longest, twice as long as pereonite 2), pereonite 6 as long as pereonite 2 (all pereonites respectively 6, 4.3, 2.4, 2.3, 2.5 and 4.3 times as wide as long). Pleotelson short, distally produced, three times as wide as long.

Antennule ( Figure 17 B) peduncle more compact than that of female; first article 1.22 times as long as wide with four paired fine ventral setae and single dorsodistal seta; second article almost as long as first and with single dorsodistal seta, long midventral seta and adjacent penicillate seta; third article just longer than wide and less than half length of second, with two dorsal setae; flagellum of four segments, first segment very short, much wider than long, with five or six ventral aesthetascs, second segment much longer than wide and longer than third peduncle article with four ventrodistal aesthetascs, third segment 0.8 times as long as second, with four aesthetascs, fourth article as long as second, with two distal aesthetascs and four setae. Antenna similar to that of female.

Mouthparts not studied.

Cheliped ( Figure 17 C) with basis and carpus more compact than those of female, merus with two ventral setae, carpus with single ventral seta, propodus with distal comb-row of eleven spines, fixed finger with two distal setae on cutting edge; dactylus slender and sinuous, unguis not obviously distinct; forcipate nature of chela less obvious.

Pereopod 1 ( Figure 17 D) similar to that of female, but apparently without setae. Pereopod 2 ( Figure 17 E) more slender than that of female, basis six times as long as wide, merus shorter than carpus, spatulate carpal spine narrower; propodus with corrugated dorsal and ventral margins, dactylus plus unguis two-thirds as long as propodus. Pereopod 3 as pereopod 2.

Posterior pereopods much longer than anterior pereopods. Pereopod 4 ( Figure 17 F) 1.7 times as long as pereopod 2, basis four times as long as wide, ischium with single distal seta, merus with paired distal setae, carpus 1.5 times as long as merus and naked, propodus 1.1 times as long as carpus with three distal setae; dactylus long and slender, 2.7 times as long as unguis, both together 1.8 times as long as propodus. Carpus, propodus and dactylus with corrugated dorsal and ventral margins. Pereopods 5 and 6 ( Figure 17 I) as pereopod 4, but merus with short ventrodistal spine, carpus with paired distal setae.

Pleopods ( Figure 17 G) with rami slightly wider than those of female, distal setae nearly three times as long as rami. Uropods ( Figure 17 H) similar to those of female.

Etymology: named after the slender Italian dagger (diminutive of the Italian stylo, from the Latin stylus), with reference to the extremely fine mandibular pars molaris.

Remarks. With the spatulate (blade-like) spine on the carpus of pereopods 2 to 6, P. s t i l e t t o sp. nov. is a member of the nominate subgenus of Pseudotanais , and, with the diastema between the dactylus and fixed finger of the chela, it belongs to the Pseudotanais ‘ forcipatus -group’ sensu Bird and Holdich (1989) , a suite of species also consistently showing a simple-pointed mandibular pars molaris and the ventral seta on the cheliped propodus proximal to the fixed finger origin. Sieg (1977) and Bird and Holdich (1989) gave comprehensive reviews of the species of Pseudotanais from the northeast Atlantic and Mediterranean regions. Since that time, the only two new species of the subgenus Pseudotanais which have been described are P. (P) baresnauti Bird, 1999 and P. (P.) nipponicus McLelland, 2007 (P. (P) californiensis Dojiri & Sieg, 1997 probably = P. abyssi Hansen 1913 ), neither of which are members of the ‘ forcipatus -group’.

Of the six previously-described species of the ‘ forcipatus -group’, only P. mexicoplos Sieg, 1988 , from the Gulf of Mexico, has eyes. However, that species, as all of the other five, has two segments in the uropod endopod. The only species of Pseudotanais described previously from the Mediterranean are P. (P) macrochelis Sars 1882, P. (P) mediterraneus Sars 1882 and P. (P) unicus Sieg 1977, of which only P. (P) mediterraneus has eyes, none have a 1-segmented uropod endopod, nor are they members of. the ‘ forcipatus - group’.

Mature males of Pseudotanais are rarely recorded: Bird and Holdich (1989) found only preparatory males in their extensive north-east Atlantic material, while Sieg (1977) had a mature male only for P. forcipatus . The antennular structure of that male is similar to that of P. stiletto , and interestingly, the chela of that nominate species of the “ forcipatus -group” is not forcipate, as found with the present species. However, the posterior leg dimorphism shown by P. stiletto was not present in P. forcipatus . The male of P. “ californiensis ” described by Dojiri and Sieg (1997) again shows a similar antennule morphology, but the chela is forcipate, and the posterior pereopods do not show extreme dimorphism. Only the male “ Pseudotanais sp.” of Kudinova- Pasternak (1970), again with the typical male antennule, appears to show longer, more slender posterior pereopods with an elongate dactylus (but a distinct cheliped, and different antennular peduncle proportions from P. stiletto ).

All the specimens were found in deeper inshore waters, between 25 and 62 m depth, towards the south of the survey area.

Figures

FIGURE 15. Pseudotanais (P.) stiletto sp. nov., A, holotype female, dorsal; B, antennule; C, antenna; D, labrum; E, left mandible; F, right mandible; G, maxillule and maxilla; H, maxilliped endite; I, maxilliped; J, epignath; K, uropod. Scale line = 0.3 mm for A; 0.1 mm for B to K.

FIGURE 16. Pseudotanais (P.) stiletto sp. nov., A, cheliped, B to G, pereopods 1 to 6 respectively; H, pleopod. Scale line = 0.1 mm.

FIGURE 17. Pseudotanais (P.) stiletto sp. nov., male, A, allotype, dorsal; B, antennule; C, left cheliped; D, pereopod 1; E, pereopod 2; F, pereopod 4; G, pleopod; H, uropod; I, pereopod 6. Scale line = 0.2 mm for A; 0.1 mm for B to I.