Meromonakantha natatoris, Błażewicz-Paszkowycz, 2007

Błażewicz-Paszkowycz, Magdalena, 2007, Figure 6. Typhlotanais Compactus, Female A In Family Nototanaidae Sieg, 1976 And Typhlotanaidae Sieg, 1984, Zootaxa 1598, pp. 1-141 : 11-15

Meromonakantha natatoris n. sp.

( Figs 2–4 )

Material examined: Holotype: female, ( K 41350 ), ANT XXII/3 , PS 67/81-8-E, 70°32.02'- 70°32.19'S, 14°35.05'– 14°35.13'W, depth 4392– 4385 m, epibenthic sledge, 24 Feb 2005 ; Paratypes: one female ( K 41351 ), the same locality ; one female dissected on slides, ( K 41352 ), ANT XXII/3 , PS 67/81-9, 70°32.94'– 70°33.15'S, 14°34.40'– 14°32.74'W, depth 4390–4392 m, Agassiz trawl, 24 Feb 2005 .

Diagnosis: Body long, 7.5 times as long as wide. Carapace 1.4 times as long as wide. Pereonite-1 shorter than pereonite-2, with proximal seta on each side. Pleon as long as pereonites 4–5 combined, each pleomere with single lateral seta. Antennule article-3 three times as long as article-2. Chela clearly shorter than cheliped carpus. Pereopod-1 propodus longer than merus and carpus combined. Pleopod exopod normal or reduced to oval squama. Uropod exopod clearly shorter than endopod.

Etymology: Natator (Latin) = ‘swimmer’. Named after its “swimming” habitus.

Description: Non-ovigerous female. Body length 1.5 mm ( Fig. 2A, B ), 7–8 times as long as wide. Cephalothorax 20% of overall length, 1.4 times as long as wide. Pereonite-1 three times as wide as long, with single lateral seta and with strong sternal hook; pereonites 2–6 of similar size, 1.2 times as long as wide; pereonite-2 trapezoidal, narrower caudally; pereonites 3–4 hexagonal; pereonites 5–6 trapezoidal, narrower proximally. Pleon almost 20% of body length, each pleomere with single lateral seta.

Antennule ( Fig. 3A ): Little shorter than carapace; article-1stout, twice as long as wide, with two long setae medially, one long seta distally and with three pinnate setae distally; article-2 with two long (reaching beyond end of article-3) simple setae and one pinnate seta distally; article-3 three times as long as article-2, with terminal spur and four setae distally.

Antenna ( Fig. 3B ): Article-1 short; article-2 twice as long as article-3, with one long (reaching beyond half of article-4) and one short simple setae; article-3 with long (reaching end of article-4) simple seta; article- 4 1.5 times as long as article-5, with two short simple setae and three pinnate setae distally; article-5 with single distal seta; article-6 with five simple setae.

Mouth parts: Labrum ( Fig. 3C ) hood-shaped, covered by numerous minute setae. Mandible ( Fig. 3D, E ) stout; molar process well-developed, with crenulated, well-calcified edges; lacinia mobilis well-developed, crenulated. Maxillule and maxilla lost during dissection. Maxilliped ( Fig. 3G ) coxa absent; bases fused, without seta; endite with seta and two tubercles distally; palp four-articled, article-1 naked; article-2 wedge-shaped with three strong short setae on inner margin and one minute seta on outer margin; article-3 elongated, with four strong setae on inner margin, article-4 slender (over twice as long as wide) with six strong setae terminally.

Cheliped ( Fig. 3H ): Basis 1.6 times as long as wide; merus triangular, with long ventral seta; carpus almost three times as long as broad, with two dorsal setae and two setae ventrally, one of which is twice as long as the other; propodus and fixed finger shorter than carpus, about half as broad as long; dactylus about half length of whole; fixed finger inner margin well-calcified, with three setae distally and with two simple setae ventrally.

Pereopod-1 ( Fig. 4A ): Of walking type; basis shorter than rest of articles combined, with simple seta proximally; ischium short with one seta; merus as long as carpus, with one seta distally; carpus with four setae distally; propodus longer than merus and carpus combined length, with one dorsal and one ventrally setae subdistally; dactylus and unguis combined 0.7 times as long as propodus; unguis almost twice as long as dactylus.

Pereopod-2 ( Fig. 4B ): Of walking type; coxa with one simple seta; basis shorter than rest of articles combined, naked; ischium with one seta; merus as long as carpus, with one simple and one spiniform setae distally; carpus with three spiniform setae distally; propodus longer than merus and carpus combined, with one short ventral seta and one long dorsal seta sub-distally; dactylus and unguis combined half as long as propodus.

Pereopod-3 ( Fig. 4C ): Similar to pereopod-2, but propodus a little longer than carpus, both propodal setae short.

Pereopod-4 broken.

Pereopod-5 ( Fig. 4D ): Basis walking type, 2.5 times as long as wide, with two pinnate setae ventrally; ischium with two setae; merus almost as long as carpus, with strong spiniform seta distally; carpus with two spiniform setae (small and large) and three setae (two long, one short) distally; propodus a little longer than carpus with one spiniform seta ventrally; dactylus broken.

Pereopod-6 ( Fig. 4E ): Similar to pereopod-4; dactylus four times as long as unguis.

Pleopods 1–5 ( Fig. 4G ): Basal article naked. Endopod with eighteen setae. Exopod four times as long as wide, with seven pinnate outer setae and one inner seta. Large gap between most proximal seta and the others in both rami.

Uropod ( Fig. 4H ): Endopod two-articled; proximal article 0.6 times length of ramus, with seta distally; distal article tipped by four long seta. Exopod two-articled, a little longer than endopod proximal article with one seta distally; distal article tipped by one long and one short setae.

Distribution: Antarctic: Eastern Weddell Sea, at abyssal depths of 4385–4392 m.

Remarks: One of three specimens of Meromonakantha natatoris n. sp. had the exopod of the pleopods vestigial ( Fig. 4F ) while the two others had them normally developed ( Fig. 4G ). As all studied specimens had the same body length, the presence of residual pleopods in the only one of them cannot be explained by age of the animals. Also no gonopores or cones could be observed in any of those three specimens so the character cannot be explained by sexual dimorphism. Either these are three females, one of which has incompletely developed pleopods, or one is an immature animal at a moult stage just before maturity.

The slender, relatively long (slightly shorter than carapace) antennule, narrow pereonite-1, long pereopod- 1 propodus, and relatively short uropod exopod, distinguish Meromonakantha natatoris n. sp. from the other members of the genus. A controversial character is the spiniform setae on merus and carpus of pereopods 2 and 3 in the new species, where the other species usually have only simple setae. The peculiar body habitus, hook-like setae on merus and carpus of pereopods 4–6, presence (in specific stages) of large hyposphaenium (pereonal hook) and slender uropods support including the new species in Meromonakantha .

Figures

FIGURE 2. Meromonakantha natatoris n. sp., holotype, adult female. A) lateral view; B) dorsal view. Scale = 0.1 mm.

FIGURE 3. Meromonakantha natatoris n. sp., female paratype. A) Antennule; B) Antenna; C) Labrum; D) Left mandible; E) Right mandible; F) Labium; G) Maxilliped; H) Cheliped. Scale: A, B, H = 0.1 mm; C–G = 0.01 mm.

FIGURE 4. Meromonakantha natatoris n. sp., female paratype. A) Pereopod-1; B) Pereopod-2; C) Pereopod-3; D) Pereopod-5; E) Pereopod-6; F) Pleopod with rudimental exopod; G) Pleopod with regular exopod; H) Uropod. Scale = 0.1 mm.