Nannoniscus antennaspinis, Brandt, Angelika, 2002

Brandt, Angelika, 2002, New species of Nannoniscidae (Crustacea, Isopoda) and Saetoniscus n. gen. from the deep sea of the Angola Basin, Zootaxa 88, pp. 1-36 : 28-35

Nannoniscus antennaspinis n. sp. (Figs. 17­22)

Holotype female of 1.8 mm, ZMH, Nr. K­40110, station 348, 28.7.2000, 16°18.1'S 05°27.2'E ­ 16°19.3'S 05°27.2'S, 5389 m.

Paratype male of 1.8 mm, ZMH, Nr. K­40111, station 348, 28.7.2000, 16°18.1'S 05°27.2'E ­ 16°19.3'S 05°27.2'S, 5389 m.

Type locality: Angola Basin, Atlantic, 5389 m.

Distribution: only known from type locality.

Etymology: named for the long lateral spine on third peduncular article of antenna.

Description: habitus of holotype female illustrated in Fig. 17: Body dorsally smooth, without setae or elevations, and also without setules on lateral margins of pereonites and pleotelson. Lateral and caudal margins of pleotelson smooth, without spines or notches, lateral margins slightly rounded, laterocaudally acuminating after two thirds of length and extending into a rounded caudal apex. Cephalothorax broader than long, (Fig. 17), without rostrum, frontomedial margin of head straight, lateral margins of cephalon smooth and straight, eyes lacking; antennae inserting frontolaterally. Coxae not visible in dorsal view. Pereonites 1 ­ 4 only with slightly frontally directed laterofrontal margins, pereonite 1 very short, pereonites 2­4 increasing in length, 4 longest, pereonites 5­7 decreasing in length. Pleonites all fused with pleotelson. Pleotelson slightly broader than long.

Al article 1 (Fig. 17) rectangular, twice as long as broad, with 1 distal feather­like seta and two setae; article 2 1.4 times as long as first, with 3 lateral setae and 4 distal featherlike setae; article 3 shortest, ring­like, without setation. 2 flagellar articles, first one with acute spine­like projection, with 2 feather­like setae on top of this projection; last one bulbous, round oval, with 1 seta.

A2 article 1 (Fig. 17) short, about triangular in shape, without setae; article 2 slightly longer than 1, with 1 seta; article 3 about as long as 1 and 2 together, with 1 medial seta and 1 long, produced lateral spine­like extension, bearing 1 seta; article 4 as long as one, with 1 medial seta; article 5 slightly longer than articles 1­4 together, with 4 setae and 1 feather­like distal seta; article 6 as long as 5, with 8 setae and one distal feather­like seta; flagellar article 1ongest, as long as peduncular articles 1 and 2, with 2 setae; following 11 flagellar articles decreasing in width, with 1­3 setae, last article with 7 setae.

Mandibular palps comparably short, not reaching the distal tip of the pars incisiva, palp inserted proximally of mandibular body ( Fig. 18 ), consisting of 3 articles; article 1 longest, with 1 simple distal seta in rMd, article 2 slightly shorter than 1, with 2 ventral setae, article 3 with 3 distal setae. Incisor of IMd with 5, of rMd also with 5 teeth, lacinia mobilis of IMd 5 teeth. Setal rows with 6­10 setae. Molars small, short, acuminating, bearing a tuft of 8 long, slightly serrated setae. RMd without lacinia mobilis.

Mxl lateral margin of inner endite (Fig. 17) without setae, distally with tuft of many slender setae. Tip of lateral endite with 11 serrated spines, medial margin without, outer margin with setules.

Mx 2 outer margins of lateral and inner endites ( Fig. 18 ) with few long setules, inner margin of inner endite setose, with 2 rows of 5 fringed setae distally. 3 strong setae of varying lengths on lateral and medial endites.

Mxp epipod ( Fig. 18 ) short, bare, reaching to mid of second palpal article. First palpal article short, rectangular, with 1 seta, second one 5 times as long as first, with 2 medial and 1 lateral setae, medial margin of the 3rd palpal article with 3 setae on serrated margin; article 4 slightly longer than 1, half as wide as third, with 3 setae, and article 5 slightly shorter and narrower than 4, with 3 simple distal setae. 2 coupling hooks medially on endite. Endite distally reaching to mid of third palpal article, with 1 fan­like seta.

Pereopods ( Figs. 18­19 ) similar in shape; P1 shortest, posterior pereopods longer than anterior. P1 ( Fig. 18 ) of female with few setae. Basis longest article, with 5 setae; ischium with 1 ventral and 2 dorsal setae; merus with 2 ventral, 1 lateral, and 2 dorsal setae distally; carpus 0.6 basis length, with 2 ventral setae of different lengths and 1 ventral sensory seta, one dorsal seta, propodus slightly shorter than carpus, distally slightly narrowing, with 4 simple distal setae and 1 distoventral sensory seta; dactylus with 2 distal claws, dorsal one more than twice as long as ventral and 2 long slightly fringed medial setae as well as another 4 setae distolaterally on article.

P1 ­ 7 ( Figs. 18­20 ) bases longest article, with 5­7 simple and 3­6 dorsal feather­like setae of varying lengths. Ischium of all pereopods with 0­4 dorsal setae and 1­3 ventral setae; merus shorter (0.8) than ischium, with 1­2 distodorsal setae and 1­3 ventral setae; carpus slightly shorter than propodus in P2­4, in P5­7 about as long as propodus, with 2­3 ventral sensory setae in P2­4, and simple ventral setae in P5­7, distodorsally of carpus and propodus 1 feather­like seta; propodus similar to carpus, but fewer setae. P5 with a long and slender sensory proximodorsal seta; dactylus shortest article, 0.3 as long as propodus, with 2 claws of different lengths, 4 distodorsal setae and 2 setae inserted between claws.

Plp2 of female ( Fig. 19 ) operculiform, long ovate, with few lateral short and longer caudal setae.

Plp3 exopod ( Fig. 19 ) round oval, laterally and medially surrounded by small setules, distally bearing 1 apical long seta. Endopod twice as long as exopod, with 3 fringed long setae.

Plp 4 ( Fig. 19 ) with bare, broad­oval endopod. Exopod slightly shorter than endopod and slender (a fourth as wide as endopod), laterally with some short setules and distally with a long fringed seta.

Plp5 ( Fig. 19 ) only one small oval lobe without setation.

Uropod ( Fig. 20 ) long with quadrangular sympod which is about as long as exopod, bearing a laterodistal protrusion and 1 long seta; exopod half as long as endopod, with 2 long setae, endopod slightly broader than exopod, with 7 feather­like setae of different lengths and 2 setae.

Differences in paratype male ( Figs. 21­22 ):

General habitus very similar, but pereonite 1 slightly longer and 7 shorter, laterocaudal notches of pleotelson less rounded than in female ( Fig. 21 ).

A1 ( Fig. 21 ), first peduncular article shorter than in female, second article only with 3 feather­like setae, first flagellar article with only 1 feather­like seta.

A2 ( Fig. 21 ) broken off in this male, but third article with a stronger and shorter spine in male than in female.

Mandibles ( Fig. 21 ) very similar, in left mandibular incisor with more teeth in male, right mandibular incisor very similar in both sexes.

No differences could be observed in the male maxillula, maxilla and maxilliped.

Pereopods ( Fig. 21­22 ) of male ( Fig. 21 ) with slightly fewer setae. P1 basis with 1 distodorsal feather­like seta. P2 with only 1 feather­like seta on basis, otherwise very similar. P3 and 5 were broken off in male. P4 also with only 1 feather­like seta dorsally on basis, distodorsal feather­like seta of propodus missing in male. P6 with at least 3 long and slender setae dorsally on propodus (which is broken off in male), in female there is only 1 long distal one. P7 of male similar, but bearing less setae and distoventrally of propodus 3 comb­like structures.

Plp 1 ( Fig. 22 ) long and slender, damaged proximally, at least 5 times as long as distal width, tips rounded in ventral view. Pleopod 2 ( Fig. 22 ) sympod length 2.4 width. Lateral margin slightly rounded with 3 distolateral plumose setae. Endopod inserting at 0.4 sympod length from distal tip. Stylet two thirds as long as sympod, only slightly bent. Exopod, rounded, small, bare, with distal tuft of fine setae. Plp 3 ( Fig. 22 ) very similar to that of female, but endopod more rounded in male.

Remarks

Nannoniscus Sars, 1870 is most probably a paraphyletic genus which needs to be revised in the future. Most species of Nannoniscus do not have antennal spines, like Nannoniscus bidens Vanhöffen, 1914 ( Brandt, 1992) and can therefore easily be differentiated from the new species. The most similar species which also bears a long antennal spine is N. intermedius Siebenaller & Hessler, 1981 . The long spine of N. intermedius , however, is inserted medially on the second antennal article, and not laterally on the third as in N. antennaspinis . Moreover, the first pereonite of N. antennaspinis is very short and not as much frontally directed as in N. intermedius . The caudolateral spines on pleotelson of N. intermedius are missing in N. antennaspinis .

Figures

FIGURE 18: Nannoniscus antennaspinis n. sp., holotype female of 1.8 mm length, right mandible, detail of left mandible, maxilla, maxilliped, pereopods 1, 2.

FIGURE 19: Nannoniscus antennaspinis n. sp., holotype female of 1.8 mm length, pereopods 3 ­ 5, pleopods 2 ­ 5.

FIGURE 20: Nannoniscus antennaspinis n. sp., holotype female of 1.8 mm length, pereopods 6, 7, uropod.

FIGURE 21: Nannoniscus antennaspinis n. sp., paratype male of 1.8 mm length, antennule, basal articles of antenna, left mandible and detail of right mandible, pereopods 1, 2, 4, 7, uropod.

FIGURE 22: Nannoniscus antennaspinis n. sp., paratype male of 1.8 mm length, pereopod 6, pleopods 1 ­ 3.