Venusticrus thor, 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 : 543-550

Venusticrus thor sp. nov.

( Figs 4–6 )

Material examined. Holotype: female with oostegites (MNHN-IU-2014-10184), body total length: 6.6 mm, BIONOD EBS-Supra Sta. 12–51, 12º 18’ 44’’N, 118º 8’ 2’’W, 11 April 2012, depth 4274 m.

Allotype: copulatory male (MNHN-IU-2014-10185), body total length: 10.6 mm, same locality as holotype.

Paratypes: one female with oostegites (MNHN-IU-2014-10186), (dissected), body total length 7.1 mm, same locality as holotype. One female, manca II (MNHN-IU-2014-10187) body total length: 2.2 mm, same locality as holotype. Two females with oostegites (used for DNA extraction, 28S - KT592230 , KT592231 ; COI - KT592232 , KT592233 ), same locality as holotype. One female, manca II; one female, without oostegites (MNHN-IU-2014-10188), BIONOD EBS-Supra Sta. 12–80, 14º 3’ 23’’N, 130º 2’ 23’’W, 21 April 2012, depth 4986 m.

Etymology. The name reflects the strong shape of male cheliped dactylus and fixed finger, as if holding a hammer, like the god Thor from Nordic mythology. Noun in apposition.

Diagnosis. Female with oostegites. Body with pigmentation along the pereonites and pereopods, no apparent setae. Cephalothorax as long as the first two pereonites combined, with no apparent rostrum or setae. Pleonites lateral epimera with three plumose setae, ventral keel weekly pronounced. Labrum subtriangular, naked; maxilliped endite with five setulose spiniform distal setae, pedestal palp with one long distal seta, and basis with two simple proximal long setae. Cheliped carpus with about twelve simple dorsal setae; propodus with a distal margin curved and pointed crenulated at tip. Uropod attached mid-length on ventral margin, basal article about 1.8 times as long as article 1 of endopod; exopod biarticulate, half as long as endopod article 1.

Male (copulatory): see diagnosis of Venusticrus .

Description. Body based on female holotype and appendages from dissected paratype.

Body ( Fig. 4 A, B): heavily calcified, dorsoventrally flattened, about 7.9 times as long as wide, with pigmentation along the pereonites and pereopods; no apparent setae. Cephalothorax: about 1.3 times as long as wide, as long as the first two pereonites combined; no apparent rostrum or setae. Pereon: about 4.6 times as long as wide, about 57% of total body length. All pereonites rectangular; pereonite 1 shortest, about 0.5 times as long as wide; pereonite 2–5 similar. Pereonite 6 slightly short than previous pereonite, about 0.8 times as long as wide. Pleon ( Fig. 5 K): about 2.4 times as long as wide, about 28% of total body length; all pleonites subequal, with three plumose setae on lateral epimera, ventral keel present but blunt and soft. Pleotelson ( Fig. 5 L): rounded, marginally wider than long (1.1 times), uropod attached to mid-length on ventral margin.

Antennule ( Fig. 5 A): marginally longer than cephalothorax. Article 1 longest, about 2.9 times as long as wide, about three times as long as article 2, with two plumose subdistal and two simple distal setae. Article 2 slightly longer than articles 3, about 1.7 times as long as wide, with two plumose and three simple distal setae. Article 3 about 1.4 times as long as wide, as long as article 4, naked. Article 4 as long as articles 5–7 combined, with three simple distal setae. Article 5 and 6 subequal with one annulated aesthetasc each. Article 7 with three simple distal setae.

Antenna ( Fig. 5 B): about 1.5 times as long as antennule. Article 1 broader than other articles, as long as wide, as long as articles 3 and 4 combined, naked. Article 2 longest, about 3.5 times as long as wide and 3.8 times as long as article 3, with one fine spiniform distal and one plumose setae. Article 3 as long as wide, with one plumose distal seta. Article 4 about 1.8 times as long as article 3, with one plumose distal seta. Article 5 about 2.5 times as long as wide, marginally shorter than articles 6 and 7 combined, with two strong and four short simple setae, one setulose distal seta. Article 6 about 2.8 times as long article 7, with four simple distal setae. Articles 7–9 subequal, bearing three, two and four simple distal setae, respectively.

Mouthparts ( Fig. 5 C–J): labrum ( Fig. 5 C) subtriangular, naked. Mandibles ( Fig. 5 D, E) heavily calcified, molar with several pointed distal denticles. Left mandible ( Fig. 5 D) incisor with about five blunt denticles, setal row with two serrated setae; lacinia mobilis marginally longer than incisor with one or two blunt crenulated denticles. R ight mandible ( Fig. 5 E) incisor with several blunt distal denticles, setal row with two serrated setae. Labium ( Fig. 5 H): palp elongated with several setules at tip, with two outer denticles and two inner small spiniform setae, lobes with distal and lateral setules. Maxillule ( Fig. 5 F, G) outer endite ( Fig. 5 F) with seven spiniform and three bipinnate distal setae; inner endite ( Fig. 5 G) with one plumose and three short spiniform distal setae. Maxilla ( Fig. 5 I) with several setules on ventral and lateral margins; inner lobe of fixed endite with several simple distal setae; outer lobe with two spiniform and three bifurcate spiniform setae; inner lobe of movable endite with three spiniform setae; outer lobe with two bipinnate and three spiniform setae.

Maxilliped ( Fig. 5 J) endite with five inner distal setulose spiniform setae and, several fine simple setae. Basis about 1.8 times as long as wide, with two proximal long simple setae, palp pedestal with one long simple distal seta. Palp article 1, marginally longer than article 2 (about 1.1 times), about 1.6 times as long as wide, naked; article 2 shortest, about 1.3 times as long as wide, with one simple outer distal seta and about five simple inner setae; article 3 longest, about 1.5 times as long as article 2, and about 2.2 times as long as wide, with five simple inner setae; article 4 slender, about 2.7 times as long as wide, with five pinnate and five simple setae. Epignath not recovered.

Cheliped ( Fig. 4 C): sclerite rectangular (illustrated on Fig. 4 B). Basis about 1.7 times as long as wide, naked. Ischium short, hardly visible. Merus subtriangular, with one simple seta. Carpus marginally longer than basis, about 2.2 times as long as wide, with two simple ventral setae and, about 12 simple dorsal setae. Propodus slightly shorter than basis, with a distal margin curved and pointed crenulated at tip, with one simple seta at the dactylus insertion. Fixed finger with one simple inner proximal seta, three simple inner distal and two on outer margin next to unguis, inner margin with three to four blunt denticles; dactylus marginally shorter than fixed finger, with one simple inner proximal seta.

Pereopod 1 ( Fig. 6 G): coxa small, naked (not illustrated). Basis about three times as long as wide, about 1.7 times as long as merus, with three short setulose proximal setae. Ischium with two simple setae. Merus about 1.3 times as long as carpus, with two simple distal and one bipinnate setae. Carpus marginally shorter than propodus, about 1.9 times as long as wide, with two spiniform, three bipinnate, one spiniform- serrated distal and, six simple setae. Propodus as long as dactylus and unguis combined, about 2.7 times as long as wide, with one setulose medial, three simple, one pinnate, five bipinnate and one hook-like spiniform serrated setae. Dactylus with one simple proximal short seta; unguis naked.

Pereopod 2 ( Fig. 6 H): articles with similar length to pereopod 1 except: basis marginally broader, about 2.2 times as long as wide, with two setulose proximal setae. Carpus about 1.5 times as long as merus. Propodus with six bipinnate and six simple setae. Dactylus marginally longer than propodus.

Pereopod 3 ( Fig. 6 I): articles with similar length to pereopod 2 except: coxa with one setulose seta. Basis with three setulose setae. Carpus as long as propodus with seven simple setae. Propodus with five bipinnate setae. Dactylus about 1.4 times as long as propodus.

Pereopod 4 ( Fig. 6 J): coxa absent. Basis as long as carpus and propodus combined, about 3.9 times as long as wide, with two setulose proximal setae. Ischium with two simple setae. Merus shortest, about 0.6 times as long as carpus, with one bipinnate and two simple distal setae. Carpus marginally longer than propodus and about 2.4 times as long as wide, with six bipinnate and five simple setae. Propodus half size of dactylus and unguis combined, with one setulose, six bipinnate and three simple setae. Dactylus with distal bilobate and finely serrated terminal shield at insertion of unguis; unguis slender, with two fine ventral rows of setae.

Pereopod 5 ( Fig. 6 K): articles with similar length to pereopod 4 except: basis broader, about 2.5 times as long as wide. Carpus with twelve bipinnate and one simple fine distal setae. Propodus with seven bipinnate and three simple setae.

Pereopod 6 ( Fig. 6 L): articles with similar length to pereopod 5 except: basis with one setulose proximal seta. Carpus with eight bipinnate and one simple fine distal setae.

Pleopods ( Fig. 5 M): basal article short and stout, with three plumose setae. Exopod with about 17 plumose setae. Endopod with three inner and 15 outer plumose setae.

Uropod ( Fig. 4 D): basal article naked, about 1.8 times as long as article 1 of endopod. Endopod with 14 articles. Articles 1–3 naked, subequal. Article 4 with one pair of plumose and other pair of simple setae. Article 5 with one simple seta. Article 6 with one plumose seta and three simple setae. Articles 7, 9 and 11–13 subequal, naked. Article 8 as article 4. Article 10 with one plumose and three simple setae. Article 14 one plumose, four simple setae and one aesthetasc. Exopod biarticulate, half the length of endopod article 1, with one simple seta on each article.

Manca II ( Fig. 4 E, F). Body ( Fig. 4 E) female paratype, length 2.2 mm, not calcified, about six times as long as wide; no apparent pigmentation, naked. Cephalothorax: as adult female. Cheliped ( Fig. 4 F): sclerite rectangular. Basis about 1.2 times as long as wide, naked. No apparent ischium. Merus as adult female. Carpus with six simple dorsal and two ventral setae. Propodus with a distal margin very curved and pointed at tip, almost as reaching dactylus. Fixed finger and dactylus with similar setation as adult female paratype. Pereopods 1–6 (not illustrated) apparently as adult female but with less spiniform bipinnate setae on propodus. Uropods damaged.

Description. Copulatory male allotype. Body ( Fig. 6 A, B): heavily calcified, no apparent setae. Dorsoventrally flattened, about 8.1 times as long as wide. Cephalothorax: anterior margin relatively broad, widening posteriorly, about 2.2 times as long as wide and 1.2 times as long as the first three pereonites combined, naked, no apparent rostrum. Pereon: about 4.6 times as long as wide, about 49% of total body length. All pereonites pentagonal, no plumose or simple setae; pereonite 1 shortest, about 0.5 times as long as wide; pereonites 2 and 6 subequal, about 0.8 and 0.7 times as long as wide, respectively; pereonites 3–5 subequal, marginally longer than wide; pereonite 6 with two tiny genital cone (only one illustrated, Fig. 6 B). Pleon: about 2.3 times as long as wide, 24% of total body length. All pleonites subequal, lateral margin rounded, with one fine simple seta. Pleotelson ( Fig. 6 C): marginally wider than long, naked.

Antennule ( Fig. 6 D): article 1 longest, about 0.6 times as long as cephalothorax, about 6.6 times as long as wide, with one medial and four simple distal setae. Article 2 about 2.8 times as long as article 3, with one simple distal seta. Article 3 as long as articles 5 and 6 combined, naked. Article 4 rounded at basis bearing several long aesthetascs, about 2.6 times as long as wide. Articles 5 and 6 bearing one long aesthetasc each. Article 7 with three simple setae at tip.

Antenna ( Fig. 6 E): about 0.8 times as long as antennule. Article 1 broader than following articles, about 1.8 times as long as wide, naked. Article 2 slender, about 5.7 times as long as wide, about 1.1 times as long as articles 3–5 combined, with one simple subdistal seta. Article 3 as long as article 7, with one simple distal seta. Article 4 marginally shorter than article 6, naked. Article 5 about 3.3 times as long as wide, with two plumose and a row (7– 10) of subdistal setae. Article 6 about 0.8 times as long as articles 7–9 combined, with two simple distal setae. Articles 7 marginally longer than article 8, both naked. Article 9 shortest, with six simple distal setae.

Mouthparts and maxilliped: all reduced.

Cheliped ( Fig. 6 B): sclerite rectangular, apparently naked. Basis stout. Ischium shaped as a narrow incomplete band extending from under the merus. Merus short, naked. Carpus long as in " robustus " group, but thinner and without protuberance or a long strong spine on ventral margin, about 1.9 times as long as cephalothorax, with two ventral simple setae. Propodus about 0.6 times as long carpus, about 4.8 times as long as wide, with two simple distal setae. Fixed finger reduced, with several blunt denticles on inner and outer margins bearing three and two simple setae, respectively. Dactylus long, about 2.6 times as long as fixed finger and slightly shorter than propodus (0.9 times), with a row of distal blunt denticles on inner and outer margins, naked.

Pleopods ( Fig. 6 F): basal article about 1.2 times as long as wide, naked. Exopod with two apparent articles (at least a fusion line), article 1 with three small and one long plumose setae, article 2 with about 17 plumose setae. Endopod with about 16 inner and four plumose outer setae.

Uropod ( Fig. 6 C): basal article attached mid-length on ventral margin. Endopod article 1 with several fine setae proximal to mid-length on outer margin, other articles missed. Exopod biarticulate, with two simple distal setae.

Remarks. Venusticrus thor sp. nov. is the fourth described species of Venusticrus and the first record for the Pacific Ocean. The new species is similar its congeners in having characters such as: several dorsal setae on the cheliped carpus (more than ten), the type of armament on the dactylus at the unguis insertion of pereopods 4–6 (see Fig. 6 J–L), the cheliped propodus with a dorsodistal margin that is long, curved and pointed at its tip (also seen in V. insolitus and V. rotermundiae ), and by the uropods attached mid-length on the ventral margin of the pleotelson— a diagnostic character for Venusticrus .

The females in the Neotanaidae family are known to have a very conservative morphology so often require a combination of characters to distinguish them. With the exception of V. glandurus , which differs from its congeners mainly due to the antennule article 1 and the number of plumose setae on the pereopods and uropods, the females of V. rotermundiae and V. insolitus share many characters with V. thor . However they can be separated from V. t ho r as this new species has the following unique character combination: body length about 7.9 times as long as wide (nine times in V. insolitus and V. rotermundiae ); pleonal lateral epimera with three setae (one or two in V. insolitus and absent in V. rotermundiae ), pleon with a very weak straight mid-ventral keel (pronounced and posteriorly directed in V. glandurus and V. insolitus ); antennule article 1 about 2.9 times as long as wide (3.1 times in V. insolitus and 2.7 times in V. rotermundiae ), with two simple and two plumose setae (with several setulose setae in V. rotermundiae and five simple setae in V. insolitus ); maxilliped endite with five inner distal setulose spiniform setae (two in V. insolitus and three setulose spiniform and several tiny spiniform setae in V. rotermundiae ), pereopods 1–6 number and type of seta; uropod basal article about 1.8 times as long as endopod article 1 (1.2 times in V. glandurus , 1.5 times and in V. rotermundiae ); uropod exopod half size of endopod article 1 (1.5 times as long as endopod article 1 in V. insolitus , 0.8 in V. rotermundiae and 0.4 in V. glandurus ).

The first record of a Venusticrus male was made by Gardiner (1975: 154) under the species V. insolitus . However, the author reported the male as non copulatory and just described the main characters without providing illustrations. The second record of a Venusticrus male was by Weigmann & Guerrero-Kommritz (2009: 28), when describing V. rotermundiae . The authors reported the specimen as damaged and lacking the chelipeds and accordingly did not illustrate or describe the specimen fully. To redeem this, a diagnosis and illustrations of a Venusticrus male are presented here. In addition, Weigmann & Guerrero-Kommritz (2009: 28), cited a "rudimental oostegites on pereopods 1 to 4" that was not found in the allotype of V. thor . Finally, a row of fine simple setae (about 8–10) was observed proximal to mid-length on the outer margin of the uropodal endopod article 1 (see Figs. 1 I and 6C). This character was previously found in N. mesostenoceps and N. hadalis and is well illustrated by Gardiner (1975: 69, fig. 27D; 75, fig. 32B, respectively). It is unclear if this character has been missed in other previous descriptions, hence should be carefully observed when describing new species of Venusticrus or Neotanais .

All previous species of Venusticrus (including V. rotermundiae ) were collected in the Atlantic Ocean, with the bathymetric distribution between 4460–5139 m.

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 4. Venusticrus thor sp. nov., female with oostegites (MNHN-IU- 2014 - 10184): A, holotype habitus dorsal view; B, holotype habitus lateral view; female paratype (MNHN-IU- 2014 - 10186): C, cheliped; D, uropod; manca female paratype (MNHN-IU- 2014 - 10187): E, habitus dorsal view; F, cheliped. Scale bars: A, B, E = 1 mm; C, D, F = 0.5 mm.

FIGURE 5. Venusticrus thor 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, pleon and pleotelson; L, detail of pleotelson and uropod ventral attachment; M, pleopod. Scale bars: A, L = 0.5 mm; B – J, M = 0.2 mm; K = 1 mm.

FIGURE 6. Venusticrus thor sp. nov., copulatory male allotype (MNHN-IU- 2014 - 10185): A, habitus dorsal view; B, habitus lateral view; C, pleotelson and uropods; D, antennule; E, antenna; F, pleopod; female paratype: G, pereopod 1; H, pereopod 2; I, pereopod 3; J, pereopod 4; K, pereopod 5; L, pereopod 6. Arrow in Fig. 6 B indicates one of two genital cone. Scale bars: A, B = 2 mm; C – F = 0.2 mm; G – L = 0.5 mm.