Nymphodora fletcheri ( Paul & George, 1975 ) Kaiser, Stefanie, 2009

Kaiser, Stefanie, 2009, Nymphodora gen. nov., a new genus of Nannoniscidae Hansen, 1916 (Isopoda, Asellota, Janiroidea) from the high Arctic *, Zootaxa 2096 (1), pp. 371-380 : 373-378

Nymphodora fletcheri ( Paul & George, 1975) comb. nov.

( Figs 1–3 )

Mirabilicoxa fletcheri Paul & George, 1975: 166–168 ; Chelibranchus fletcheri Kussakin, 1999: 314 .

Holotype: 1 ♀ (preparatory, 2.8 mm), Canada Basin , 84°52.9’N, 110°27’W, 1740 m, USNM No. 143607.

Diagnosis. Cephalothorax frontally vaulted, antennae inserting frontolaterally in a deep fault next to strongly produced anterolateral triangular projections; pereonite 1 slightly longer than second, pereopod 1 more robust but shorter than pereopods 2–7. Pereonites 6, 7 and pleotelson fused dorsally; pleotelson without posterolateral spines. Uropods biramous, endopodite long, projecting posterior margin of pleotelson; exopodite minute (modified after Paul & George 1975).

Description. Habitus of holotype female ( Figs 1A, B ): body dorsoventrally slightly flattened, 4.3 times longer than pereonite 2 width (i.e. 0.7 mm incl. coxal plates), surface with several fine setule. Cephalothorax ( Figs 1A, C ) about 1.3 times wider than long, length 0.2 times body length. Antennae inserting in a deep fold next to anterolateral triangular projections. Anterior margin strongly vaulted medially. Coxae not visible in dorsal view. Tergits laterally expanding in marginal flanges. Body gradually flattening from pereonites 1–5. Pereonite 1 width 3.1 times length, pereonites 1–3 of similar width and length; pereonite 2 widest, pereonite 4 longest, 1.5 times pereonite 1 length, width 2 times length; pereonite 5 about 2.3 wider than long. Pereonites 6, 7 and pleotelson fused dorsomedially, anterior margin of pereonite 6 strongly concave. Pereonite 7 short, length 0.6 pereonite 6 length. Pleotelson ( Fig. 3D ) length 0.2 of body length, 1.2 times longer than wide, with few small setae. Lateral margins straight, posterior margin tapering distally. Uropods ( Fig. 3E ) inserting close to the anus valves.

Antenna 1 ( Fig. 2A ) length 0.1 times body length, with 5 articles. Article 1 widest, article 2 longest; article 3 minute; article 4 with a triangular lateral projection tipped with a long, simple seta, 1.4 times longer than wide, with 1 long broom seta laterally; article 5 bulbous, 2.1 times longer than wide, length 4.9 times article 3 length, with a small, robust sensory seta terminally.

Antenna 2 ( Fig. 2B ) 0.5 of body length, with 6 peduncular and 12 flagellar articles. Peduncular articles 1–4 short. Article 5 somewhat shorter and more robust than article 6. Article 6 long and slender, twice as long as flagellar article 1, with few small setae and 1 small broom seta laterally, with 1 simple, slender and 1 more robust seta and 2 long and 2 short broom setae distally. Flagellum length 0.8 peduncle length, articles with 1–4 simple setae of varying size distally; terminal article with 6 long, slender setae.

Pereopod 1 ( Fig. 2C ) more robust than pereopods 2–7. Basis length 4.4 times width; with 8 small, simple setae ventrally. Ischium length 0.4 times basis length, 2 times longer than wide. Merus length 0.6 times ischium length, 1.4 times longer than wide; with 1 unequally bifid seta distodorsally and with 1 long unequally bifid distally setulate seta and 1 small seta distoventrally. Carpus length 0.7 times merus length, 2.4 times longer than wide; with 2 short, simple setae dorsally, with 3 robust unequally bifid and 2 long unequally bifid distally setulate setae ventrally. Propodus nearly as long as carpus, 2.8 times longer than wide; with 1 long simple seta and 1 unequally bifid distally setulate seta dorsally, with 2 robust, unequally bifid setae, 2 simple setae of varying size and a fringe of short setae, membranously embedded, ventrally. Dactylus length 0.6 times propodus length, 3.3 times longer than wide; with 4 fine setae of varying size medially and a fringe of setae, membranously embedded, ventrally. Ungius length 0.3 times dactylus length; with 2 short, cuspidate setae and 2 slender setae of varying size in between.

Pereopods 2–4 ( Figs 2D–F ). Basis of pereopod 2 length 4.5 times width, in pereopods 3–4 basis length 5.7 times width; pereopods 3–4 with 7 small, simple setae ventrally. Ischium length 0.4 times basis length. Ischium of pereopods 2–3 with 2 simple setae dorsally and 3 simple setae ventrally. Ischium of pereopod 4 more slender than of pereopods 2–3, length 3 times width; with 1 simple setae dorsally. Merus of pereopods 2–4 length 0.7 times width. Merus of pereopod 2 length 1.5 times width; with 4 simple setae of varying size dorsally and 2 simple setae ventrally. Merus of pereopods 3–4 length 2.1 times width; pereopod 3 with 3 simple setae dorsally and 2 small simple setae ventrally. Merus of pereopod 4 with each 1 simple seta dorsally and ventrally. Carpus of pereopods 2–3 length 4.3 times width. Carpus of pereopod 2 with 3 short simple setae dorsally, with 4 robust unequally bifid setae, 1 somewhat longer, slender seta and a fringe of small setae, membranously embedded, ventrally. Carpus of pereopod 3 with 5 slender simple setae of varying size dorsally and 3 robust unequally bifid setae and a fringe of small simple setae, membranously embedded, ventrally. Carpus of pereopod 4 very slender, 7.8 times longer than wide; with 4 small simple setae dorsally and 3 robust unequally bifid setae and a fringe of small setae, membranously embedded, ventrally. Propodus and dactylus of pereopod 2 missing. Propodus of pereopods 3–4 length 6.6 times width; pereopod 3 and 4 with 3–4 slender simple setae dorsally and with 3–4 robust unequally bifid setae and a fringe of setae, membranously embedded, ventrally, pereopod 4 with 1 long slender seta distoventrally. Dactylus of pereopod 3 very slender, length 7.3 times width; with 3 slender setae of varying size medially and with fringe of setae, membranously embedded, ventrally. Ungius with 2 robust cuspidate setae of varying size and 2 somewhat longer slender setae in between. Dactylus of pereopod 4 length 5.3 times width; with 3 slender setae of varying size medially. Unguis with 2 robust cuspidate setae of varying size and 2 somewhat longer slender setae in between.

Pereopods 5–7 ( Figs 3A–C ): Basis of pereopods 5–6 length 6 times width, of pereopod 7 length 5 times width; basis of pereopod 5 with 1 long broom seta and 1 long simple seta dorsally and with 4 somewhat smaller simple setae ventrally. Ischium of pereopods 5–7 length 3 times width, pereopod 5 with 2 simple setae ventrally; pereopod 7 with 2 simple setae dorsally. Merus of pereopods 5 and 7 length 2 times width; pereopod 5 with 1 long simple seta dorsally and 2 somewhat shorter simple setae ventrally; pereopod 7 with 1 simple seta dorsally and 1 small unequally bifid seta ventrally. Merus of pereopod 6 slender, length 2.6 times width. Carpus of pereopod 5 length 5.1 times width; with 4 simple setae dorsally, with 3 robust unequally bifid setae decreasing in size distally and a fringe of small setae, membranously embedded, ventrally. Carpus of pereopod 6 length 6.4 times width; with 2 simple setae dorsally, with 4 robust, unequally bifid setae increasing in size distally and with a fringe of small setae, membranously embedded, ventrally. Carpus of pereopod 7 length 3.9 times width; with 2 simple setae dorsally and with 3 simple setae ventrally. Propodus of pereopod 5 length 6.6 times width; with 3 simple setae dorsally, with 3 robust unequally bifid setae and a fringe of small setae, membranously embedded, ventrally. Propodus of pereopod 6 very slender, length 8.8 times width; with 3 robust unequally bifid setae and a fringe of small setae, membranously embedded, ventrally. Propodus of pereopod 7 length 4.7 times width; with 1 simple seta dorsally and with 2 robust unequally bifid setae and a fringe of small setae, membranously embedded, ventrally. Dactylus of pereopods 6–7 damaged. Dactylus of pereopod 5 length 7.4 times width. Ungius with 1 long seta, 1 short robust cuspidate seta and 2 somewhat longer, slender setae in between.

Pleopod 2 (operculum, Fig. 3D ) nearly round, almost as long as wide, lateral margins with numerous small setae.

Uropods ( Fig. 3E ) biramous. Protopodite rectangular, as long as wide. Exopodite minute, with 2 long, simple setae. Endopodite length about 25 times exopodite length, 4.7 times longer than wide, length 3.5 times protopodite length; with 4 long broom setae and 2 long simple setae distally.

Type locality. Canada Basin, north west of Queen Elizabeth Islands.

Distribution. Only known from type locality.

Etymology.`Nymphe´ (greek) is feminine and refers to a Greek natural deity.`Doris` (lat.), feminine, is an allegory for ocean. The name refers to the inhabited realm and the head structure of the species resembling a hexapod nymph.

Remarks. A redescription of Nymphodora fletcheri comb. nov. was necessary due to the previously inaccurate description of the pereonites 6, 7 and pleotelson, uropods and antennae. Paul & George (1975) first assigned the species to the genus Mirabilicoxa , which is characterised by the following synapomorphies (cf. Hessler 1970): pleotelson widest anteriorly, with posterolateral spines; uropod uniramous or biramous with rudimentary exopodite; propodus of pereopod 1 without robust setae, carpus of pereopod 1 with a row of robust, unequally bifid setae; coxae strongly produced in male, though visible in dorsal view in female.

Kussakin (1999) transferred the species to the desmosomatid genus Chelibranchus Mezhov, 1986 . However, the existence of this genus is doubted, as Mezhov (1986) defined it on the basis of two badly damaged specimens, which were even less accurately described ( Brix 2006). Nymphodora gen. nov. differs from Chelibranchus as follows: 5-segmented antenna 1 with bulbous terminal article; pereonites 6, 7 and pleotelson fused, posterior margin of pleopod 2 (operculum) strongly rounded, uropods biramous (in Chelibranchus with 4-segmented antenna 1, terminal article not enlarged, free pereonites and pleotelson, posterior margin of operculum strongly concave, uniramous uropods). The new genus ( Nymphodora ) bears characters with a greater affinity to Nannoniscidae than to Desmosomatidae , i.e. bulbous terminal article of the 5-segmented antenna 1, coxae not dorsally visible, inserting ventrally, fused pereonites 6, 7 and pleotelson, uropods inserting close together (cf. Wägele 1989; Wilson 2008).

Nymphodora can be distinguished from all other genera of this family by the fusion of the pereonites 6, 7 and pleotelson. It most closely resembles Panetela Siebenaller & Hessler, 1981 . The latter can be distinguished from the new genus as follows: all pereonites free; body length more than 5 times pereonite 2 width, pereopod 6 with natatory setae. Nymphodora also resembles Nannoniscus Sars, 1870 ; the latter can be distinguished from the new genus by the following characters: pereonites 6 and 7 fused (not in all species); ventral spines on pereonite 7 or operculum. Due to the described differences between these similar species, Nymphodora fletcheri cannot be assigned to either Nannoniscus Sars, 1870 or Panetela Siebenaller & Hessler 1981 .

Siebenaller & Hessler (1981) noted that the genus Nannoniscus is characterised by plesiomorphies (antenna 1 with bulbous terminal article; pereopods 1 and 2 equally robust; fusion of pereonites 6 and 7) rather than apomorphies and needs to be revised. In a recent review on Nannoniscidae, Wilson (2008) modified the generic diagnosis of Nannoniscus and transferred some species in other genera of the family. However, the generic diagnosis given by Wilson (2008) cannot be applied to all species in the genus. For example, N. ovatus Menzies & George 1972 is still included in the genus despite possessing uniramous uropods. Thus, the genus Nannoniscus still lacks a comprehensive revision.

Nymphodora fletcheri most closely resembles Panetela compacta Malyutina & Kussakin, 1996 by the shape of the habitus, cephalothorax, uropods and operculum, as well as the setation and proportions of the pereopods. The latter species differs from N. fletcheri by the following characters: terminal article of antenna 1 length 3.5 times width (2.1 times in N. fletcheri ); propodus of pereopod 3 with 3 unequally bifid setae ventrally (while N. fletcheri possess 4 unequally bifid setae); carpus of pereopod 4 length 5.1 times width (in N. fletcheri length 7.8. times width); no ventral fringe of setae on propodus and carpus of pereopods 4–6, carpus of pereopods 7 with 1 robust unequally bifid seta ventrally ( N. fletcheri with 3 simple setae); uropod’s exopodite length 0.14 times endopodite length (in N. fletcheri endopodit length 25 times exopodit length).

Nymphodora fletcheri is also very similar to the female of Nannoniscus arctoabyssalis Just, 1980 in the shape of the habitus, cephalothorax, pereopod 1 and the lateral view of pereonite 7. Nannoniscus arctoabyssalis can be distinguished from Nymphodora fletcheri as follows: body surface and pereopods with numerous setae ( N. fletcheri with just few setae); pereonites 6 and 7 fused (in N. fletcheri pereonites 6, 7 and pleotelson fused); pereonite 3 widest (in N. fletcheri pereonite 2 widest); uropods completely covering anus valves (uropods of N. fletcheri just partly covering anus valves); uropods with relatively long exopodite (about half of endopodite length).

Malyutina & Kussakin (1996) discussed the arguable classification of P. compacta in Panetela due to the relatively wide habitus and the short pereonite 6, 7 and pleotelson. Wilson (2008) discussed the shape of the rostral crest more resembling Joeropsidae or Acanthaspidiidae , but proposed a position in Nannonicidae due to the bulbous form of the terminal article of antenna 1, and the shape of the molar process. A further classification was not possible, though, as the holotype was dissected (cf. Wilson 2008).

Figures

FIGURE 1. Nymphodora fletcheri (Paul & George, 1975) comb. nov., holotype female (USNM No. 143607); A, habitus, dorsal view; B, habitus, lateral view; C, cephalothorax, lateral view. Scale bar: A, B = 1000 µm, C = 500 µm.

FIGURE 2. Nymphodora fletcheri (Paul & George, 1975) comb. nov., holotype female (USNM No. 143607); A, A1; B, A2; C–F, P1–4. Scale bar: A, B = 100 µm, C–F = 200 µm.

FIGURE 3. Nymphodora fletcheri (Paul & George, 1975) comb. nov., holotype female (USNM No. 143607); A–C, P5–7; D, Plt ventrally, Plp 2; E, Urp. Scale bar: A–C = 200 µm, D = 500 µm, E = 100 µm.