Neotanais bicornutus, Araújo-Silva, Catarina L., Froufe, Elsa & Larsen, Kim, 2015

Araújo-Silva, Catarina L., Froufe, Elsa & Larsen, Kim, 2015, Two new species of family Neotanaidae (Peracarida: Tanaidacea) from the Antarctic and Mid-Pacific Oceans, Zootaxa 4018 (4), pp. 535-552 : 537-543

Neotanais bicornutus sp. nov.

( Figs 1–3 )

Material examined. Holotype: female with oostegites ( ZMHK 45086), body total length: 9.7 mm, ANT XIX-3 ANDEEP I Sta. 42-2/EBS-SUPRA, 59º 24’ 10’’ S, 57º 21’ 15’’ W, 27 January 2002, depth 3683 m.

Allotype: copulatory male (damaged, partly dissected—ZMHK 45088), body total length: 20.6 mm, ANDEEP II Sta. 140-8/EBS-Supra, 58° 9’ 35’’ S, 24° 32’ 14’’ W, 22 March 2002, depth 2947 m.

Paratype: one female without oostegites, body total length: 5.21 mm (dissected, body partially preserved - ZMHK 45087), same locality of allotype.

Etymology. The name reflects the presence of two projections found on the dorsal male chelipedal propodus, similar to a " cornus ”, i.e. horn, in Latin.

Diagnosis. Female, with oostegites: body six times as long as wide. Cephalothorax marginally longer than first two pereonites combined, no apparent rostrum or setae. Pereonites rectangular, without setae. Pleonites narrower than pereon and pleotelson, pleon lateral epimera with three plumose setae, mid-ventral keel very weekly pronounced. Pleotelson 0.6 times as long as wide, no setation. Antennule as long as cephalothorax, article 1 about 3.3 times as long as wide. Maxilliped basis broad, without proximal seta, endite with three spiniform and one bipinnate inner distal setae. Cheliped carpus with two simple ventral setae and about 15 simple dorsal setae. Uropod attachment slightly posterior to mid-length, basal article about 2.7 times as long as article 1 of endopod, exopod biarticulate, marginally shorter than endopod article 1.

Male, copulatory male: larger than female, about 7.2 times as long as wide. Body with no apparent setae. Cephalothorax about 1.5 times as long as the first two pereonites combined. Pereonites rectangular, without setae. Pleon and pleotelson naked, uropod attached mid-length on pleotelson. Antennule 0.8 times as long as cephalothorax, article 1 about 7.5 times as long as wide. Maxilliped basis robust, naked. Endite naked. Palp of four slender articles with one simple seta on article 3 and four simple distal setae on article 4. Cheliped sclerite, basis, ischium and merus naked; carpus about 1.5 times as long as cephalothorax, widening distally with one large ventral protuberance bearing one strong spine; propodus with two long dorsal projections; fixed finger with an innermedial deep groove and a tooth distally. Uropod endopod article 1 with 8–10 fine setae proximal to mid-length on outer margin.

Description. Female. Body based on female holotype and appendages from dissected paratype. Body ( Fig. 1 A, B): heavily calcified, dorsoventrally flattened, about six times as long as wide. Cephalothorax: about 1.2 times as long as wide and 1.1 times as long as the first two pereonites combined, no apparent rostrum or setae. Pereon: about 4.1 times as long as wide, 60% of total body length, no dorsal relief. All pereonites rectangular, no plumose or simple setae; pereonite 1 shortest, 0.4 times as long as wide; pereonites 2–6 subequal: 0.7, 0.76, 0.81, 0.87, 0.68 times as long as wide, respectively. Pleon: about 1.8 times as long as wide, 20% of total body length; all pleonites subequal, narrower than pereon and slightly narrower than pleotelson, lateral epimera with about three plumose setae, mid-ventral keel very weekly pronounced ( Fig. 1 D). Pleotelson 0.6 times as long as wide, no apparent setation; uropod attachment slightly posterior to mid-length.

Antennule ( Fig. 2 A): as long as cephalothorax. Article 1 longest, about 3.3 times as long as wide, with one setulose and four simple distal setae. Article 2 about three times shorter than article 1, with four simple distal setae. Article 3 about 1.2 times as long as wide, 1.6 times shorter than previous article, with two simple distal setae. Article 4 1.2 times as long as article 3 and three times as long as wide, naked. Articles 5–7 marginally shorter than article 4, with one simple and one annulated aesthetasc on article 5; article 6 with one annulated aesthetasc; article 7 with three simple distal setae.

Antenna ( Fig. 2 B): marginally shorter than antennule (0.8 times). Article 1 broader than others articles, about 1.6 times as long as wide and, as long as articles 3 and 4 combined, naked. Article 2 slender than article 1, about 2.6 times as long as wide, with two simple distal setae. Article 3 as long as wide and, as long as articles 7–8 combined, 0.4 times as short as article 2, with one simple distal seta. Article 4 about two times as long as wide, naked. Article 5 marginally longer than article 2, about 3.3 times as long as wide, with two simple distal setae. Article 6 about 1.2 times as long as article 3, naked. Articles 7 and 8 both short, with three and five simple distal setae, respectively.

Mouthparts ( Fig. 2 C–J): labrum ( Fig. 2 C) subtriangular, with several fine setules at the tip, anterior lateral margins depressed. Mandibles ( Fig. 2 D, E) molar with several distal pointed denticles. Left mandible ( Fig. 2 D) incisor longer than lacinia mobilis, with several blunt denticles, setal row with two spiniform- serrated setae; lacinia mobilis well developed with four crenulated denticles. Right mandible ( Fig. 2 E) incisor with several blunt crenulated denticles, setal row with four spiniform- serrated setae. Labium ( Fig. 2 H) palp elongated with several setules at tip and two small spiniform setae, lobes with distal and lateral rows of setules. Maxillule ( Fig. 2 F, G) outer endite ( Fig. 2 F) with eight spiniform distal setae as well as several fine lateral setae; inner endite ( Fig. 2 G) one long and two short bipinnate setae and one short spiniform seta. Maxilla ( Fig. 2 I) inner lobe of fixed endite with several distal setae; outer lobe with two spiniform setae; inner lobe of movable endite with three spiniform setae, outer lobe with two spiniform and three bifurcate spiniform setae.

Maxilliped ( Fig. 2 J) endite with three inner distal spiniform setae, one bipinnate spiniform and several fine setae along the distal margin. Basis broad, palp pedestal (see Larsen 2005: 11) with one long simple distal seta. Palp article 1 naked, as long as article 3; article 2 shortest, with one outer distal simple seta and six inner simple setae; article 3 about 1.4 times as long as article 2, with eight simple inner setae; article 4 slender and longest than the other articles, four times as long as wide, with three pinnate and four simple setae. Epignath not recovered.

Cheliped ( Fig. 1 C): sclerite rectangular (illustrated on Fig. 1 B). Basis tapering distally, about 1.1 times as long as wide, naked. Ischium very short, hardly visible. Merus with one simple seta. Carpus about 1.1 times as long as basis, about twice as long as wide; with two simple ventral setae and, 15 simple setae along dorsal margin. Propodus slightly shorter than basis, no setae. Fixed finger with one simple inner proximal seta, three distal and two on outer margin next to unguis; dactylus shorter than fixed finger with two short spines in the inner margin.

Pereopod 1 ( Fig. 3 A): coxa small, naked. Basis slender, about 4.1 times as long as wide, slightly longer than the three next articles combined, with four dorsoproximal and two plumose ventral setae. Ischium with two simple setae. Merus about 1.5 times as long as carpus, with two bipinnate medial setae. Carpus shortest, about 1.7 times as long as wide, with three simple medial setae, one spiniform- serrated distal and, three long- bipinnate distal setae. Propodus as long as dactylus and unguis combined, about 2.9 times as long as wide, with one setulose medial, two simple distal, one spiniform- serrated hook-like, and four spiniform- bipinnate setae. Dactylus and unguis thin, naked.

Pereopod 2 ( Fig. 3 B): articles with similar length and armament as pereopod 1 except: basis with two ventral and one setulose dorsal setae. Carpus about 0.8 times as long as merus, with four simple medial setae. Propodus with seven spiniform- bipinnate ventral setae. Dactylus with one fine simple proximal seta; unguis broken.

Pereopod 3 ( Fig. 3 C): articles with similar length to pereopod 2 except: coxa with one simple seta. Basis about three times as long as wide, with two dorsal and one ventral setulose setae. Carpus about 1.2 times as long as merus, with three simple medial and four bipinnate ventral setae. Propodus with three simple distal setae.

Pereopod 4 ( Fig. 3 D): coxa absent. Basis about 4.2 times as long as wide, with one dorsoproximal and three setulose ventral setae. Ischium with three simple setae. Merus shortest, about 0.8 times as long as carpus, with three bipinnate distal setae. Carpus marginally shorter than propodus, with six bipinnate and one small simple distal setae. Propodus as long as dactylus and unguis combined (without the terminal seta), with five spiniform bipinnate, three simple and one setulose setae. Dactylus with denticles arranged in a ring around the insertion of unguis; unguis slender with two ventral rows of small spines.

Pereopod 5 ( Fig. 3 E): articles with similar length to pereopod 4 except: basis with two setulose ventral setae.

Pereopod 6 ( Fig. 3 F): articles with similar length to pereopod 5 except: basis with one setulose dorsoproximal seta. Ischium with two simple setae. Merus with two bipinnate distal setae. Carpus with five bipinnate distal and three simple setae. Propodus with seven bipinnate, two simple and about five spiniform serrated setae next to dactylus insertion.

Pleopods ( Fig. 1 E): basal article about 1.6 times as long as wide, with three plumose setae. Exopod with 13 plumose setae. Endopod with three inner and eleven outer plumose setae.

Uropod ( Fig. 2 K): basal article naked, about 2.7 times as long as article 1. Endopod (damaged) with five articles. Articles 1–4 bearing one to four simple setae, except article 4, naked. Article 5 longer, bearing five simple distal setae. Exopod biarticulate, marginally shorter than article 1 of endopod, with one simple seta each article.

Description. Copulatory male allotype. Body ( Fig. 1 F): heavily calcified, no apparent setae. Dorsoventrally flattened, about 7.2 times as long as wide. Cephalothorax: about 1.4 times as long as wide and 1.5 times as long as the first two pereonites combined, with visible rostrum, with two strong anterolateral spines. Pereon: about 3.7 times as long as wide, about 50% of total body length. All pereonites rectangular, no plumose or simple setae; pereonite 1 shortest, 0.3 times as long as wide; pereonites 2 and 3 subequal, 0.5 and 0.7, respectively; pereonites 4 and 5 similar; pereonite 6 about 0.6 times as long as wide. Pleon: no mid-ventral spur ( Fig. 1 G); about 1.6 times as long as wide, 30% of total body length; all pleonites subequal, as wide as cephalothorax and pereonite 1, lateral epimera with no seta. Pleotelson ( Fig. 1 I) about 0.6 times as long as wide, no apparent seta; uropod attachment mid-length on pleotelson.

Antennule ( Fig. 2 L): damaged. Article 1 longest, 0.8 times as long as cephalothorax, about 7.5 times as long as wide, with five proximal and six simple subdistal setae. Article 2 about 2.1 times as long as wide, twice as long as articles 3 and 4 combined, with five simple medial setae. Article 3 naked. Article 4 short bearing several aesthetascs. Other articles missed.

Mouthparts and maxilliped ( Fig. 2 M): all reduced, except: maxilliped basis robust, longer than wide, naked. Endite naked. Palp article 1 naked, short; article 2 about 2.2 times as long as article 1, naked; article 3 about 1.3 times as long as article 2, with one simple proximal seta; article 4 longest, about 1.2 times as long as article 3, with four simple distal setae.

Cheliped ( Fig. 1 H): sclerite (not illustrated), naked. Basis short, naked. Ischium shaped as a narrow incomplete band extending from under the merus. Merus short, naked. Carpus 1.5 times as long as cephalothorax, widening distally, with one simple seta and one visible protuberance bearing one long strong spine on ventral side. Propodus with two strong dorsal projections and a third less visible (next to dactylus insertion), with slight crenation and one simple seta next to dactylus insertion. Fixed finger inner margin with one simple seta, one deep groove medial and one tooth distally. Dactylus marginally longer than fixed finger, with three proximal denticles and a row of denticles distally.

Uropod ( Fig. 1 I): basal article attached at mid-lateral margin, about 1.2 times as long as article 1 of endopod. Endopod damaged, article 1 with 8–10 fine setae proximal to mid-length on outer margin. Exopod biarticulate, half size of endopod article 1, with one simple seta on each article.

Pleopods (not illustrated): basal article apparently naked. Exopod with two apparent articles (at least a fusion line), first article bearing three and second with about 25–30 plumose setae. Endopod with about 30 inner and three plumose outer setae.

Remarks. The specimens of Neotanais bicornutus sp. nov. were collected in the Antarctic Ocean and when compared to Gardiner’s (1975) Neotanais scheme, it mostly resembles with the " robustus " group, which hitherto held N. robustus Wolff, 1956b , N. antarcticus Kussakin, 1967 and N. tuberculatus Kudinova-Pasternak, 1970 . Gardiner (1975) recognized this group based mainly on copulatory male characters, although identification of neotanaid males to species is difficult owing to their strong sexual polymorphism (Larsen & Błażewicz- Paszkowycz 2003; Larsen 2005). Males are also frequently larger than females and show sexual dimorphism in the proportions of the cephalothorax and the shape of the cheliped ( Bamber 2007).

The male of N. bicornutus shares many characters with the " robustus " group by having a pleotelson about 1.5 times as wide as long (1.4 times in N. robustus , 1.7 in N. antarcticus ), the pleonites are broad and rounded laterally in dorsal view, lateral epimera without apparent seta, and they also bear a strong ventral spine arising from a protuberance on the cheliped carpus ( Fig. 1 H). However, N. bicornutus differs from the " robustus " group by having a dorsally naked cheliped carpus (while there are four setae in N. tuberculatus , five in N. antarcticus and apparently two or three tiny setae in N. robustus ). The uropod endopod article 1 has 8–10 fine setae proximal to mid-length on outer margin, while these setae are lacking in the " robustus " group, but are found in N. hadalis Wolff, 1956a and N. mesostenoceps Gardiner, 1975 . It further differs in having a cheliped propodus with two strong and long dorsal projections; within the " robustus " group only in N. robustus are there propodus projections, one small dorsal and one longer ventral. The propodal dorsal crest is very slight in N. bicornutus , while in other species this character is rather pronounced.

The females vary mainly in the number of setae on the dorsal margin of the cheliped carpus; N. bicornutus has about 15 setae, while there are nine in N. robustus , three in N. antarcticus and seven in N. tuberculatus . Also, the pleonal epimera have three plumose setae, while the other " robustus " group species apparently lack this feature. Neotanais bicornutus also resembles the Antarctic species N. krappschickelae Larsen & Błażewicz-Paszkowycz, 2003 , in having a ring of spines on the unguis of pereopods 4–6 and the many dorsal setae on the cheliped carpus (about 24 setae in N. krappschickelae and 15 setae in N. bicornutus ). However, they can be easily distinguished by the number of the plumose setae on almost all pereopod articles of both genders, the number of setae on the first antennule article (about eleven plumose [described as bipinnate] in N. krappschickelae while N. bicornutus has two simple and two plumose setae), the epimera setae (absent in N. krappschickelae while N. bicornutus has three), the body size as well as other characters.

Figures

FIGURE 1. Neotanais bicornutus sp. nov., female with oostegites (ZMHK 45086): A, holotype habitus dorsal view; B, holotype habitus lateral view. Female paratype (ZMHK 45087): C, cheliped; D, pleon and pleotelson; E, pleopod. Copulatory male allotype (ZMHK 45088): F, habitus dorsal view; G, pleon; H, cheliped; I, pleotelson and uropod. Scale bars: A, B, F, H = 2 mm; C = 0.5 mm; D, E = 0.2 mm; G, I = 1 mm.

FIGURE 2. Neotanais bicornutus sp. nov., female paratype: A, antennule; B, antenna; C, labrum; D, left mandible; E, right mandible; F, maxillule, outer endite; G, maxillule, inner endite; H, labium; I, maxilla; J, maxilliped; K, uropod; copulatory male allotype: L, antennule and antenna; M, maxilliped. Scale bars: A – J = 0.2 mm; K = 0.5 mm; L, M = 2 mm.

FIGURE 3. Neotanais bicornutus sp. nov., female paratype: A, pereopod 1; B, pereopod 2; C, pereopod 3; D, pereopod 4; E, pereopod 5; F, pereopod 6. Scale bars: A, C – F = 0.5 mm; B = 0.2 mm.