Actenos kalimantus, Bamber, Roger N., 2013

Bamber, Roger N., 2013, Tanaidaceans from Brunei, IV. The Families Kalliapseudidae, Pagurapseudopsidae, Parapseudidae and Apseudidae (Crustacea: Peracarida: Tanaidacea: Apseudomorpha), with descriptions of a new genus and six new species, Zootaxa 3734 (4), pp. 401-441 : 414-419

Actenos kalimantus sp. nov.

Figs 6–9

Material: 1♀, holotype (BMNH 2013.835), 05°21′25"N 111°26′30"E, 90 m depth, sand; 3♀♀, 1 juvenile, paratypes (BMNH 2013.836–839), 05°21′08"N 111°26′25"E, 90 m depth, sand; 1♀ with oostegites, dissected (retained), 05°20′58"N 111°26′15"E, 90 m depth, sand.

2♂♂, 2♀♀ (one with oostegites), 05°22′21"N 111°27′30"E, 70 m depth, sand (lost).

Description of female: Body ( Fig. 6 A) slender, 9.5 times as long as wide, dorsoventrally flattened, elongate, holotype 7.4 mm long (tip of rostrum to posterior of pleotelson). Cephalothorax subrectangular with convex margins, as long as wide, with pronounced rostrum extended as a minute apophysis, eyelobes distinct, eyes pigmented. Pereonite 1 one-third as long as cephalothorax, wider anteriorly, naked; pereonite 2 twice as long as pereonite 1, laterally expanded over attachment of coxae of pereopod 2; pereonite 3 subrectangular, similar in configuration to pereonite 2, 2.3 times as long as pereonite 1; pereonites 4 to 6 wider posteriorly, laterally expanded over attachment of pereopod coxae, marginally sparsely setulose; pereonite 4 as long as long as pereonite 3; pereonites 5 and 6 just shorter, 0.9 times as long as pereonite 3 (all pereonites respectively 2.9, 1.2, 0.9, 0.9, 1.0 and 1.0 times as wide as long). Pleon one third of whole body length, pleonites trapezoid, just over half as long as pereonite 6, and about 1.4 times as wide as long, with numerous lateral marginal simple setae. Pleotelson subrectangular, about one-quarter length of pleon, 1.4 times as long as wide, with numerous lateral marginal simple setae.

Antennule ( Fig. 6 B) proximal peduncle article 5.6 times as long as wide, outer margin with proximal tuft of penicillate setae, inner and outer margins with numerous simple setae. Second article twice as long as wide, 0.3 times length of first article, with inner and outer simple setae. Third article about 0.4 times as long as second article, 0.9 times as long as wide, with four simple distal setae. Fourth article 0.6 times as long as third article, wider than long. Main flagellum of 16 to 17 segments, single aesthetasc present on antepenultimate segment; accessory flagellum shorter than main flagellum, of fourteen segments.

Antenna ( Fig. 6 C) with naked proximal peduncle article bearing inner rounded apophysis. Second article 0.8 times as long as first, with two inner-distal tooth-like apophyses and small outer subdistal seta, elongate squama bearing four marginal setae. Third article 0.4 times as long as second article, about half as long as wide, with outer seta. Fourth article similar to third article; fifth three times as long as fourth article, with outer seta. Flagellum of perhaps 14 segments, segmentation obscure.

Labrum not recovered, epistomal apophysis conspicuous, up-curved. Left mandible ( Fig. 7 A, B) with six rounded “teeth” on pars incisiva, five rounded “teeth” on lacinia mobilis; setiferous lobe with three trifurcate, two simple and two spatulate setae, pars molaris stout, distally with complex rugosity and extended into substantial rugose and denticulate flange; palp of three articles, proximal article with eight distal setae; second article with four setae in distal half; third article with two mesial and five distal setae. Right mandible as left but without lacinia mobilis. Labium ( Fig. 7 C) not setose, palp with inner and outer fine lateral setules and two simple distal spines, slight inner apophysis. Maxillule ( Fig. 7 E) inner endite with proximal outer apophysis and four distal forked setae; outer endite with ten distal spines and two subdistal setae, outer margin finely setose distally; palp of two articles, distally with five setae. Maxilla ( Fig. 7 D) typical of subfamily, outer margin denticulate, moveable endite outer lobe with two subdistal and five distal setae, inner lobe with six setae and one subdistal denticulate spine; fixed endite outer lobe with simple and trifurcate distal spines, inner lobe with two longer setae and rostral row of about 20 setae. Maxilliped basis and palp ( Fig. 7 F) with simple setae, some setae with flagelliform tips; first palp article with two inner setae, smaller outer seta; second palp article with inner margin bearing numerous shorter curled setae and proximal straighter setae, three longer and three shorter outer distal setae; third palp article with three shorter and five longer inner setae; fourth palp article with seven setae around distal margin. Maxilliped endite ( Fig. 7 G) distal margin with outer simple setae and inner pointed or spatulate spines. Epignath ( Fig. 7 H) large, subrectangular, with simple distal spine.

Cheliped ( Fig. 8 A) slender. Basis 3.2 times as long as wide, ventrally with two fine setae. Exopodite threearticled; article 2 naked, article 3 with four plumose setae. Merus with midventral tuft of five setae and ventrodistal group of seven setae. Carpus very slender, six times as long as wide, ventrally with six marginal and two submarginal setae, six dorsal to dorsodistal setae. Chela slender, palm twice as long as wide with simple seta near base of dactylus; fixed finger 1.8 times as long as palm, curved, with five ventral setae, cutting edge without apophyses but with row of curved setae. Dactylus with three mid-dorsal setae, no apophyses on cutting edge, unguis not distinct.

Pereopod 1 ( Fig. 8 B) distal articles generally bearing tapering longer setae. Coxa with small apophysis bearing one slender distal spine and three adjacent setae. Basis 2.8 times as long as wide, with seven ventrodistal setae exceeding distal margin of ischium; exopodite conspicuous, article 2 with naked, article 3 with six plumose setae. Ischium with four ventrodistal setae. Merus 0.6 times as long as basis, wider distally, with single ventrodistal spine and numerous dorsal and ventral marginal setae, dorsodistal setae 1.4 times as long as merus. Carpus compact, just shorter than merus, with two ventral spines amongst full row of marginal setae, inner-dorsal and dorsodistal fine setae, dorsodistal margin with array of eleven elongate tapering setae exceeding tip of propodus in length. Propodus as long as carpus, ventral margin with five spines interspersed with tapering setae, dorsal margin with row of ten tapering setae but no spine. Dactylus and unguis ( Fig. 8 E) fused, distally appearing cleft, with eight ventral denticulations.

Pereopod 2 ( Fig. 8 C) basis 4.5 times as long as wide, with two ventrodistal setae. Ischium almost as long as wide, with three ventrodistal setae. Merus one-quarter length of basis, with one fine dorsodistal and six ventrodistal setae. Carpus 1.9 times as long as merus, with marginal and submarginal rows of setae and midventral slender spine, no dorsodistal spine. Propodus 0.7 times as long as carpus, with fine ventrodistal setae and six dorsodistal setae. Dactylus and unguis fused, together 0.7 times as long as propodus, distally appearing cleft (as pereopod 3, see Fig. 8 E), with ventroproximal denticulation. Pereopod 3 ( Fig. 8 D) similar to pereopod 2, but without dorsodistal seta on merus; propodus with three ventral submarginal tubercles bearing short spine; claw ( Fig. 8 E) as on pereopod 2.

Pereopod 4 ( Fig. 9 A) basis 3.4 times as long as wide with four fine ventral-marginal and one ventrodistal setae, three mid-dorsal penicillate setae. Ischium with four ventral setae. Merus one-quarter length of basis, with two ventral setae. Carpus 2,3 times as long as merus, with setation similar to that of pereopods 2 and 3. Propodus 0.6 times as long as carpus, with similar ornamentation to that of pereopod 3 and in addition dorsal penicillate seta. Dactylus and unguis ( Fig. 9 D) fused, together shorter than adjacent setae and 0.6 times as long as propodus, not cleft but with subdistal denticulation. Pereopod 5 ( Fig. 9 B) similar to pereopod 4, but basis with two penicillate setae, ventral margin naked, propodus without penicillate seta, dactylus and unguis as on pereopod 6 ( Fig. 9 D), not fused. Pereopod 6 ( Fig. 9 C) similar to pereopod 5, but basis without penicillate setae, carpus with ventrodistal spinose tubercle; propodus with dorsoproximal penicillate seta but without ventral-distal row of spines; dactylus and unguis ( Fig. 9 D) not fused, dactylus with fine ventrodistal seta.

Pleopods ( Fig. 9 E) alike. Basis with five inner and five outer plumose setae; rami linguiform, exopod shorter than endopod and with 24 plumose setae along inner and distal margins; endopod with 22 marginal plumose setae, inner proximal seta separated from others.

Uropod ( Fig. 6 D) biramous. Basis with three outer and one inner-distal setae. Exopod of eight segments; endopod missing on all specimens.

Male: similar overall to female. Antennule not recovered. Cheliped similar to that of female. Antenna (not figured) peduncle articles 2 and 3 fused, flagellum showing secondary segmentation, with ~ 10 aesthetascs per segment.

Etymology: from Kalimantan, the Indonesian name for Borneo (adjectival).

Remarks: Actenos kalimantus sp. nov. is a significantly larger species than A. marshalli , and from deeper waters, but does show the consistent features (for the genus) of fused (and bifurcate) claws on the anterior pereopods, including pereopod 1, an array of long dorsal-marginal setae (but no spine) on the carpus and propodus of pereopod 1, and no spine-row on the propodus of pereopod 6. Other consistent features are the up-curved epistomal apophysis, the expanded distal flange on the mandibular molar, and the posterolateral expansion of the pleonites where the pleopods attach; in this species the expansion is also more exaggerated on the pereonites. The greater size of this species accounts for the more numerous segments in the antennal and antennular flagella and the uropod exopod, as well as the larger number of setae on, for example, the pereopod ischia and the maxillular palp. The present species is distinguished from both of its congeners by the complex denticulation of the claw of pereopod 1 and the greater number of segments in the flagella of the antennule, and from A. tenuicorporeus by the lack of a dorsal spine or longer ventral setae on the basis of the cheliped and the lack of anterolateral pointed apophyses on the pereonites, inter alia.

Actenos kalimantus was taken at 70 to 90 m depth in sand off the north-coast of Brunei.

Figures

FIGURE 6. Actenos kalimantus gen. et sp. nov., A, holotype female, dorsal; B, antennule; C, antenna; D, left uropod (endopod broken). Scale line = 1.0 mm for A, 0.4 mm for B to D.

FIGURE 7. Actenos kalimantus gen. et sp. nov., A, left mandible; B, alternative view of molar; C, labial palp; D, maxilla; E, maxillule; F, maxilliped; G, maxilliped endite; H, epignath. Scale line = 0.2 mm.

FIGURE 8. Actenos kalimantus gen. et sp. nov., A, female cheliped; B, pereopod 1; C, pereopod 2; D, pereopod 3, with detail of spinose tubercle; E, claws of pereopods 1 and 3. Scale line = 0.4 mm for A to D, 0.1 mm for E.

FIGURE 9. Actenos kalimantus gen. et sp. nov., A, pereopod 4; B, pereopod 5; C, pereopod 6; D, claws of pereopods 6 and 4; E, pleopod (plumose nature of all setae not shown, for clarity). Scale line = 0.4 mm for A to C and E, 0.1 mm for