Typhlotanais pereosetulosa, Larsen, Kim, 2011

Larsen, Kim, 2011, The tanaidacean assemblage from the Central Pacific Manganese Nodule Province. II. The genera Stenotanais and Typhlotanais (Crustacea), Zootaxa 3088, pp. 39-53 : 49-52

Typhlotanais pereosetulosa n. sp.

( Figs 6–7 )

Material examined. Holotype, female, dissected (MNHN-Ta 1035). Station Zone Ouest # 30, 12/06-2004, 09°33.81’N, 150°0.98’W, 5051 meters.

Diagnosis. Pereonite 2 longer than other pereonites. Antennule as long as carapace. Antenna article 2 and 3 with multiple setules; antenna article 4 short (about three times the length of article 3). Labrum lateral edges with spines. Cheliped carpus without row of small dorsal setae. Pereopod 1 coxa without anterior process. Pereopod 1–3 basis with multiple setules. Pereopods 2–3 merus and carpus without serrated distal margin. Pereopods 4–6 prickly tubercle comparatively small (smaller than half of carpus) not surrounded by spines. Distal pleopods with fewer setae than anterior pleopods. Uropodal endo- and exopod biarticulated.

Etymology. The species is named after the diagnostic character of the setation of the bases of pereopods 1–3.

Description. Female (body and appendages of holotype). Body length 1.6 mm.

Body ( Fig. 6 A) elongated, 7 times as long as wide. Cephalothorax longer than wide, with slightly rounded lateral margins. Pereonites all except pereonite 2, wider than long; pereonites1 and 6 subequal, shorter than other pereonites, almost twice as wide as long, longer than half of pereonite 2. Pereonite 2 longest, square. Pereonites 3 and 5 subequal. Pereonite 5 shorter than pereonite 4. Pleon 25% total body length. Pleonites 1–5 subequal. Pleotelson as long as combined length of last two pleonites, with flat apex.

Antennule ( Fig. 6 B) longer than cephalothorax. Article 1 slender, four times as long as wide, with two simple medial setae, one simple and two setulated distal setae. Article 2 shorter than 0.25 times of article 1, with two simple distal setae. Article 3 twice as long as article 2, with apical process and seven distal setae of which two are longer than article.

Antenna ( Fig. 6 C) about 60% as long as antennule. Article 1 wider than other articles, with scattered short thin setae. Article 2 with multiple setules on all margins, less than twice as long as article 3. Article 3 shorter than article 1, with multiple setules and one simple distal seta. Article 4 twice as long as article 2, with sparse setulation and three distal setae of which one is longer than rest of antenna. Article 5 marginally longer than article 2, with one simple distal seta. Article 6 minute, with four terminal setae.

Mouthparts: Labrum ( Fig. 6 D) with flat and setulose apex, lateral margins with conspicuous spines. Mandibles ( Figs 6 E–F) molar well developed, longer than incisor with distal spiniform denticles. Left mandible ( Fig. 6 F) incisor bifurcate; lacinia mobilis well developed and larger than incisor, with pointed outer corner. Right mandible ( Fig. 6 E) incisor blunt. Labium ( Fig. 6 G) with flat, sparsely setulose distal corners. Maxillule ( Fig. 6 H) endite with eight spiniform distal setae, palp not recovered. Maxilla ( Fig. 6 I) small, ovoid and featureless. Maxilliped ( Fig. 6 J): basis fused medially, with long distal seta near palp insertion; endite with two simple setae and serrated outer distal corners, no tubercles; palp article 1 naked; article 2 with three bipinnate distal setae on inner margin and proximal setulations, with one seta on outer margin; article 3 with four bipinnate setae on inner margin; article 4 less than half as wide as other articles, with one simple seta outer and five bipinnate distal inner setae. Epignath not recovered.

Cheliped ( Fig. 7 A) basis attached via triangular sclerite, distal part larger than proximal part, shorter than carpus, with one seta near carpus. Merus half as long as carpus, with one ventral seta. Carpus as long as propodus inclusive fixed finger, with two simple ventromedial setae, one small stout ventrodistal seta, and one short dorsodistal seta. Propodus (including fixed finger) more than twice as long as wide, with one seta at dactylus insertion. Fixed finger with two ventral and three inner setae, inner margin smooth. Dactylus naked.

Pereopod 1 ( Fig. 7 B) coxa without projections, with single seta. Basis six times as long as wide, with several setules on dorsal margin, with one dorsoproximal setulose seta. Ischium with one ventral seta. Merus marginally shorter than carpus, with one simple distal setae on each margin. Carpus sub-rectangular, longer than half of propodus, with two dorsodistal and two ventrodistal setae. Propodus less than twice as long as dactylus and unguis combined, with three dorso-subdistal setae, apical spine and one ventrodistal seta. Dactylus less than half as long as unguis, with single seta. Unguis with spatulated apex

Pereopod 2 ( Fig. 7 C) similar to pereopod 1 except dactylus and unguis shorter and unguis without spatulated apex.

Pereopod 3 ( Fig. 7 D) similar to pereopod 2.

Pereopod 4 ( Fig. 7 E) basis only marginally more robust than on pereopod 1–3, about 3 times longer than wide, apparently naked. Ischium with one ventral seta. Merus with proximal scales and two spiniform ventrodistal setae.

Carpus apparently with one dorsodistal spiniform seta and with prickly tubercle surrounded by spines. Propodus with two ventrodistal and one dorsodistal spiniform setae. Dactylus three times as long as unguis; both combined shorter than propodus.

Pereopod 5 ( Fig. 7 F) similar to pereopod 4 except: merus with one ventrodistal spiniform seta. Carpus with prickly tubercle surrounded by spines and one spiniform seta. Propodus with ventral setules and scales.

Pereopod 6 ( Fig. 7 G) similar to pereopod 4: Carpus with prickly tubercle surrounded by spines and one dorsodistal spiniform setae. Propodus with ventral setules and scales, two ventrodistal and three dorsodistal spiniform setae. Dactylus with row of ventral spines

Pleopods 1–3 ( Fig. 6 K) basal article naked; exopod with one plumose seta on inner margin and 12 plumose setae on outer margin, pronounced gap between proximal and other setae; endopod with 13 plumose setae on outer margin, pronounced gap between proximal and other setae.

Pleopods 4–5 ( Fig. 6 L), basal article naked; exopod with one plumose seta on inner margin and with only five plumose setae on outer margin, pronounced gap between proximal and other setae; endopod with 12 plumose setae on outer margin; pronounced gap between proximal and other setae.

Uropod ( Fig. 6 M) basal article 0.4 times as long as wide. Rami biarticulated, slender. Exopod 75% as long as endopod, article 1 with one small seta; article 2 with two dissimilar length distal setae of which one is longer than exopod. Endopod article 1 with two simple distal setae, article 2 with four distal setae of which two are longer than endopod.

Remarks. The new species key out to the ‘ mixtus’ group ( Hansen 1913) using the key of Błażewicz-Paszkowycz (2007:25) but differs by the pereopods 4 and 5 merus prickly tubercles being smaller (smaller than half of carpus) and the combined length of dactylus and unguis clearly shorter than propodus. The new species differ from T. mimosis by lacking the long dorsal setae on the first pereonite.

The new species is unique in having multiple small short setae on the pereopod 1 and 2 bases. Multiple small setae on the basis of the first pereopods are also recorded from T. aequiremis , and apparently only for pereopod 2 and; these are larger than in T. pereosetulosa which also differ in the number of uropod articles as well as several other characters.

The labrum spines is a somewhat unusual character but have been recorded from Paratyphlotanais alveolus Błażewicz-Paszkowycz (2007) but the uropodal endopod distal article of T. pereosetulosa is not shorter than the proximal and thus cannot be place in that genus.

The dissimilar structure of the pleopods is another interesting feature that has not been examined in sufficient detail among the Tanaidacea . Dissimilarity between pleopods have been observed in other tanaidaceanss to a greater ( Sphaeromapseudes - see Larsen (2011b) or lesser extent ( Zeuxo - Larsen et al. research in progress); also Błażewicz-Paszkowycz (2007) illustrates and even diagnoses dissimilar pleopods in Meromonakantha natatoris although not in the same specimen. However, most tanaidacean species are described as with “all pleopods similar” and it is doubtful if these appendages have been studied in sufficient detail in previous descriptions (even those by this author).

Figures

FIGURE 6. Typhlotanais pereosetulosa, female. Holotype. A, lateral view, scale bar 0.5 mm. B, antennule. C, antenna. D, labrum. E, right mandible. F, left mandible. G, labium. H, maxillule. I, maxilla. J, maxilliped. K, pleopod 3. L, pleopod 5. M. uropod. Scale bars 0.1 mm.

FIGURE 7. Typhlotanais pereosetulosa, female. Holotype. A, cheliped. B, pereopod 1. C, pereopod 2. D, pereopod 3. E, Pereopod 4. F, pereopod 5. G, pereopod 6. Scale bar 0.1 mm.