Neotanais brevis, Wi, Jin Hee, Suh, Hae Lip & Yu, Ok Hwan, 2015

Wi, Jin Hee, Suh, Hae Lip & Yu, Ok Hwan, 2015, Description of two new species of Neotanais Beddard, 1886 (Crustacea, Tanaidacea) from KODOS area, Zootaxa 3926 (2), pp. 244-256 : 250-255

Neotanais brevis n. sp.

Figs 4–6

Material examined. Holotype: female collected from the east–central Pacific KODOS Area (St.1: 10° 29.979’N, 131°55.590’W, 5180 m depth), dissected and mounted on five slide glasses (MABIKCR00235166).

Diagnosis. Female. Pereonites 4 and 5 equal in length. Pleonites narrower than pereon. Pleonites without midventral spur and lateral setae. Pleotelson relatively long (length/width 1: 1.5). Cheliped carpus without ventral protrusion but with five dorsal setae and fixed finger bearing small dentiform processes along proximal margin. Small curved seta on pereopods 1–3 propodi with five ventral processes. Pleopod basis with one seta on each of dorsal and ventral margins. Uropod exopod slightly longer than first endopodal article.

Etymology. From the Latin for ‘narrow’; alluding to the pleonites that are narrower than pereon.

Description. Female. Non-ovigerous holotype. Body ( Fig. 4 A, B) length 6.7 mm, 1.7 times as long as wide.

Cephalothorax shorter than pereonites 1–2, 1.2 times as long as maximum width at proximal three-quarters, proximal margin with small rounded rostrum and with one disto-lateral setae on each side, without proximo-lateral keel and furrows.

Pereon ( Fig. 4 A) pereonites 1–6 with two lateral setae on each side. Pereonite 1 shortest, mid-lateral margin swollen, 0.5 times as long as cephalothorax. Pereonites 2–6 distolateral margin sub-square shaped, bearing pereopods on distolateral margins. Pereonites 1–2 combined longer than cephalothorax. Pereonites 5 as long as wide, longest. Pereonite 6 slightly longer than pereonite 1. Pereonites 1–6 proportional lengths 12.3: 16.9: 18.3: 19.5: 19.5: 13.5.

Pleon ( Fig. 4 A, B) 2.6 times longer than pereonite 6. Pleonites laterally convex, lateral margin without ornamentation, without mid-ventral spur ( Fig. 4 B). Pleonite 1 longest and pleonites 2–5 equal in length. Pleotelson ( Fig. 4 A, C) 0.4 times as long as whole pleon, 1.5 times as wide as long, uropod attached on distolateral margin at proximal to mid length: lateral margins bearing two short simple setae each, one ventral seta at distal surface, three short simple setae at distal margin; apex slightly protruded.

Antennule ( Fig. 4 D, E) proportional lengths 52.0: 16.0: 10.0: 10.7: 4.1: 3.6: 3.6. Article 1 elongate, 3.8 times as long as wide, longer than combined length of the remaining articles, with row of setules on proximal margin, and setules along ventroproximal margin, mid-dorsal margin with one broom seta, and six setae on distal margin. Article 2 with five broom setae and four setae on distal margin. Article 3 with four broom setae and one simple seta on distal margin. Article 4 without setae. Article 5 with one thick, four-segmented aesthetasc and three simple setae. Article 6 with one thick, four-segmented aesthetasc. Article 7 with three terminal setae and one seta at midregion.

Antenna ( Fig. 4 F) proportional lengths or articles 17.5: 17.5: 7.7: 14.9: 18.1: 9.0: 5.5: 6.0: 3.8. Article 1 with scale-like ornamentations and two rows of setules (arrowed in Fig. 4 F). Article 2 with two distal setae. Article 3 with one distal seta. Article 4 shorter than article 2, with one broom seta on distal margin. Article 5 longer than article 4, with five broom setae and two simple setae. Article 6 with three distal setae. Articles 7–9 each with two distal setae. Mouthparts ( Fig. 5 A–G) labrum not observed. Left mandible ( Fig. 5 A) incisor blunt and distally tapered, with dentiform processes along mid-ventral margin; lacinia mobilis broad, with four round dentiform processes along distal margin; setal row with one bipinnate spiniform seta and one unipinnate spiniform seta; molar processes broad, without teeth. Right mandible ( Fig. 5 B) incisor broad and distal margin sub-triangular; setal row with distally serrated spiniform seta and two bipinnate spiniform setae: ventral-most seta smallest (arrowed in Fig. 5 B); molar process with nine teeth on rim. Labium ( Fig. 5 C) similar to that of N. triqueturus . Maxillule ( Fig. 5 D) dorsal endite with ten distal spiniform setae. Maxilla ( Fig. 5 E) dorsal lobe of fixed finger with two bifurcated spiniform setae, five spiniform setae on distal margin, and one short simple seta on mid region; dorsal lobe of movable endite with two setules on dorsal margin.

Maxilliped ( Fig. 5 F, G) endite ventral margin with two bipinnate spiniform setae and with row of spinules, endite dorsal margin with seven pairs of spinules, dorso-proximal margin with two short spiniform setae and three short spiniform setae with serration on distal margin, one bipinnate seta on sub-distal region, dorsodistal margin with one long pinnate seta. Basis with one distal pinnate seta on ventral margin. Proximal palp article naked. Second palp article with five pinnate setae along ventral margin and one simple seta on dorso-distal corner. Third palp article with seven pinnate setae along ventral margin. Fourth palp article with eight bipinnate setae and three simple setae on distal margin. Epignath not observed.

Cheliped ( Fig. 4 G, H) basis broad, as long as wide. Ischium a narrow incomplete band, extending from distal margin of basis. Merus triangular, with one ventral simple seta. Carpus 1.8 times as long as wide, 1.2 times as long as basis, with two setae of unequal length on mid-region and one short seta on distal margin, dorsal margin with two proximal setae and three distal setae unequal in length. Propodus 1.9 times as long as wide, 1.6 times as long as basis, 1.4 times as long as carpus, with one seta near insertion of dactylus. Fixed finger cutting edge with five round ‘teeth’ and row of minute denticles along proximal margin (arrowed in Fig. 4 H); ventral margin with two setae of equal length, dorsal margin with one proximal seta, one on mid-region, one minute seta on mid-lateral region, and two distal setae on distal region. Dactylus much shorter than fixed finger, with seta on proximolateral margin, distal claw slightly longer than that of fixed finger.

Pereopod 1 ( Fig. 6 A) coxa with one slender seta. Basis with one minute simple seta, merus with four simple setae on distal margin. Carpus shorter than merus, with ten setae on ventral margin. Propodus as long as carpus, with six slender setae and one broom seta on dorsal margin, with six bipinnate setae on ventral margin, short spiniform seta on distal margin with five ventral irregular shaped processes (arrowed in Fig. 6 B). Dactylus ornamented with fine hairs and pointed process on disto-ventral margin (arrowed in Fig. 6 B). Unguis quarter length of dactylus. Dactylus and unguis combined longer than propodus.

Pereopod 2 ( Fig. 6 C) basis with two broom setae. Merus with three slender setae on distal margin. Carpus as long as merus, with six slender setae on dorsal margin, six slender setae on ventral margin, and one short simple seta on mid-distal margin. Propodus as long as carpus, with eight spiniform bipinnate setae on ventral margin, eight slender setae and one broom seta on dorsal margin. Dactylus and unguis combined shorter than propodus

Pereopod 3 ( Fig. 6 D) basis with three broom setae. Merus with two slender setae on distal margin. Carpus longer than merus, with five simple setae on ventral margin, five simple setae on dorsal margin Propodus slightly longer than carpus, with nine ventral bipinnate setae, six dorsal slender simple setae, and one dorsal broom seta. Dactylus and unguis shorter than propodus. Unguis half the length of dactylus.

Pereopod 4 ( Fig. 6 E) basis with five broom setae. Merus with two simple setae on ventral margin. Carpus much longer than merus, with eleven slender setae on ventral margin. Propodus as long as carpus, with six ventral setae, six dorsal setae, and one dorsal broom seta. Dactylus and unguis 1.7 times longer than propodus. Unguis 0.6 times as long as dactylus, ornamented with pointed extensions along mid-region (arrowed in Fig. 6 F).

Pereopod 5 ( Fig. 6 G) basis with four broom setae. Merus with three setae. Carpus much longer than merus, with three setae on ventral margin. Propodus as long as carpus, bearing six ventral setae, eight dorsal setae, and one dorsal broom seta.

Pereopod 6 ( Fig. 6 H) basis with one broom seta. Merus with two setae on distal margin. Carpus shorter than merus, with four ventral setae, one short mid-distal seta, and four dorsal setae. Propodus as long as carpus, bearing two dorsal setae, two distal setae, three ventral setae, and five blunt bipinnate spiniform setae on ventrodistal margin (arrowed in Fig. 6 I).

Pleopod 1 to 5 ( Fig. 6 J) all alike. Basis with one ventral plumose seta and one dorsal plumose seta. Exopod first article with one plumose seta on dorso-distal corner; second article 2.4 times as long as first article, bearing four distal plumose setae. Endopod much longer than exopod, with one plumose seta on dorsal margin, four distal plumose setae, and two inner plumose setae on ventral margin.

Uropod ( Fig. 4 A, I) biramous. Basis 0.6 times as pleotelson. Exopod with two articles, first article with one simple seta, second article twice as long as first article, 1.3 times as long as first endopodal article, with two distal setae. Endopod with nine articles, article 1 naked, article 2 with small seta, article 3 naked, article 4 with two dorsal setae, article 5 with one seta, article 6 with two long simple setae and one plumose seta, article 7 with one short seta, article 8 naked, and article 9 with six setae on tip.

Remarks. Neotanais brevis n. sp. corresponds closely with the ‘ micromopher -group’, characterized by pleonites narrower than the pereon, a cheliped carpus without a ventral process, and a uropod endopod with nine articles. The group consists of N. micromopher Gardiner, 1975 and N. dinotomer Gardiner. In particular, the following morphological characteristics of N. micromopher match those of N. brevis : cheliped dactylus shorter than the fixed finger and the pleonite basis with one ventral seta and one dorsal seta as in N. dinotomer and the pleonite without a mid-ventral spur, a slightly longer uropod than pleon, and the length to width ratio of the first article of the antennule (3.8: 1). However, both species of the micromopher -group differ from N. brevis by the following characteristics: a short pleotelson (length: 1: 2 vs. 1: 1.5, respectively), the wider pereonites of a rectangular shape, the number of inner setae on the maxilliped endite (two vs. four and five), and the pleotelson fused to pleonite 5. On the other hand, the characters of long pleotelson (length:width <1:1.5), slightly longer uropod compared to the pleon, and the pleonite without a mid-ventral spur are shown in N. robustus Wolff, 1956 described by Gardiner (1975) and N. antarcticus Kussakin, 1967 . However, both species can also be differentiated from N. brevis by their relatively longer cephalothorax measurement compared to the combined length of pereonites1–2, relatively broad pereonites, and a uropod with an exopod half the length of endopod article 1.

Morphological comparison between eight species within Neotanais from the east–central Pacific. Currently, eight species of Neotanais have been described from the eastern central Pacific, including the two new species examined in the present study, and the morphological comparisons between them are given in Table 2. Although the characteristics do occasionally overlap, the comprehensive comparisons of these characteristics do definitively identify the eight distinct species. As an example, the pereon to pleon length ratios were similar in N. triqueturus , N. americanus , N. pacificus , and N. capillus ; however, the combination of the remaining characteristics given in Table 2 separates the four species. In addition, some characteristics exist only in one or two species. The relative length of the dactylus to the fixed finger of the cheliped was shorter in N. americanus and N. capillus while it was longer only for N. pfaffi . The proximal denticles on the fixed finger of the cheliped were only seen in N. capillus . The dorsal and ventral setae of the pleopod basis showed the fewest number (1, 1, respectively) in N. brevis and the greatest number for N. pfaffi (5, 7, respectively) and N. calcarulus (8, 2, respectively). The dorsal setal number for the cheliped carpus varied greatly. Although N. americanus and N. calcarulus showed the same setal number on the cheliped carpus, the presence/absence of ventral process on the cheliped carpus differentiates them. The combination of the length of each pereonite, the presence/absence of mid-ventral spur on the pleonites, the pleotelson length to width ratio, and the length ratio of the uropod to pleotelson also differentiated each species in the eastern central Pacific and the result proved N. triqueturus and N. brevis to be new species.

Figures

FIGURE 4. Neotanais brevis n. sp., holotype female. A, holotype, dorsal view; B, pleon, lateral view; C, pleotelson; D, antennule; E, antennule articles 5 – 7; F, antenna, G, cheliped; H, cheliped chela; I, uropod. Scale bars are given in mm.

FIGURE 5. Neotanais brevis n. sp., holotype female. A, left mandible; B, right mandible; C, labrum; D, maxillule; E, maxilla; F, maxilliped; G, maxilliped, endite. Scale bars are given in mm.

FIGURE 6. Neotanais brevis n. sp., holotype female. A, pereopod 1; B, pereopod 1, dactylus and unguis; C, pereopod 2; D, pereopod 3; E, pereopod 4; F, pereopod 4, dactylus and unguis; G, pereopod 5; H, pereopod 6; I, pereopod 6 propodus, distal part; J, pleopod. Scale bars are given in mm.