Actenos marshalli, 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 : 409-414

Actenos marshalli sp. nov.

Figs 3–5

Type material: 1♀, holotype (BMNH 2013.820), 4♂♂, 23♀♀ (one with oostegites), 13 neuters, paratypes (BMNH 2013.821–830), Station B13, 04°51′06"N 114°35′26"E, 20 m depth, sand; March 2009. 1♂, 1♀, paratypes (BMNH 2013.831–832), Station B5, 04°51′06"N 114°35′26"E, 20 m depth, sand; March 2009. 2♂♂, paratypes (BMNH 2013.833–834), Site DA1, 05°54′28.5"N 114°38′23.3"E, 20 m depth, sand; March 2009.

Other material: 4♀♀ (two brooding), Station S18, 04°41′30"N 114°27′13.5"E, 7.5 m depth, sand; coll. March 2009. 1♂, 6♀♀, Station S14, 04°42′39"N 114°26′24.6"E, 12.7 m depth, sand; coll. March 2009. 1♂, 4♀♀, Site DA2; 2♀♀, Site DA-R; both Station DA, 05°54′28.5"N 114°38′23.3"E, 20 m depth, sand; March 2009.

Description of female: Body ( Fig. 3 A) glabrous, dorsoventrally flattened, elongate, 8.6 times as long as wide, holotype 3.3 mm long (tip of rostrum to posterior of pleotelson). Cephalothorax subrectangular, just longer than wide, with pronounced rostrum extended as a slender apophysis, eyelobes distinct, eyes pigmented. Pereonite 1 more than half as long as cephalothorax, wider anteriorly, with single anterolateral setae, pereonite 2 half as long as cephalothorax, laterally convex; pereonite 3 almost hexagonal, 1.1 times as long as pereonite 1; pereonites 4 to 6 wider posteriorly, pereonite 4 longest, 1.2 times as long as long as pereonite 3; pereonite 5 as long as pereonite 3, pereonite 6 as long as pereonite 2 (all pereonites respectively 1.6, 1.6, 1.2, 0.9, 1.0 and 1.5 times as wide as long). Pleon one third of whole body length, pleonites of similar form to, and three-quarters as long as, pereonite 6, and about 1.8 times as wide as long. Pleotelson subrectangular but distally rounded, about one fifth length of pleon, slightly longer than wide.

Antennule ( Fig. 3 B) proximal peduncle article 4.3 times as long as wide, outer margin with proximal tuft of penicillate setae and row of longer simple setae in distal half, two inner simple setae. Second article 2.2 times as long as wide, 0.4 times length of first, with inner-distal penicillate and simple setae, outer margin with row of longer simple setae in distal half. Third article about 0.4 times as long as second article, 0.8 times as long as wide, with three simple distal setae. Fourth article 0.8 times as long as third article, wider than long, with outer distal simple seta. Main flagellum of eight or nine segments, single aesthetasc present on antepenultimate segment; accessory flagellum of nine or ten segments, longer than main flagellum.

Antenna ( Fig. 3 C) with naked first peduncle article. Second article 1.25 times as long as first, naked, elongate squama bearing six marginal setae. Third article 0.6 times as long as second article, about half as long as wide, with two inner-distal spine-like apophyses. Fourth article four times as long as third article, twice as long as wide, naked; fifth article just shorter than fourth article, 2.5 times as long as wide, with two outer setae. Flagellum of eight segments.

Labrum ( Fig. 3 D) rounded, simple, naked; epistomal apophysis ( Fig. 3 E) conspicuous, hooked. Right mandible ( Fig. 3 F) with five rounded “teeth” on pars incisiva; setiferous lobe with one trifurcate, two bifurcate and three simple setae, pars molaris stout, distally with complex rugosity and extended into substantial rugose flange; left mandible ( Fig. 3 G) as right but with dentate lacinia mobilis; palp of three articles, proximal article with four distal setae; second article with one mesial and two distal setae; third article with five distal setae and one subdistal seta. Labium ( Fig. 3 H) with sparse outer serrations, not setose, palp with inner and outer fine lateral setules and two simple distal spines, slight inner apophysis. Maxillule ( Fig. 3 I) inner endite with inner-proximal apophysis but no outer apophysis, and four distal setae; outer endite with ten distal spines and two subdistal setae, outer margin finely setose distally; palp of two articles, distally with two setae. Maxilla ( Fig. 3 J) generally typical of subfamily, outer margin smooth, moveable endite outer lobe with two subdistal and five distal setae, inner lobe with five setae and two subdistal denticulate spines; fixed endite outer lobe with simple and trifurcate distal spines, inner lobe with three longer setae and rostral row of 16 setae. Maxilliped basis and palp ( Fig. 3 K) with simple setae; first palp article with single inner seta, no outer seta; second palp article with inner margin bearing numerous shorter curled setae and three longer setae, outer distal seta reaching tip of fourth article; third palp article with three shorter and four longer recurved inner setae; fourth palp article with four setae around distal margin. Maxilliped endite distal margin with outer simple setae and inner blunt spines. Epignath ( Fig. 3 L) large, subrectangular, with simple distal spine.

Cheliped ( Fig. 4 A) slender. Basis twice as long as wide, ventrally with proximal spine-like apophysis, central curved spine, ventrodistal seta and longer simple seta in proximal half. Exopodite three-articled; second article naked, third article with four plumose setae. Merus fusiform in outline, with ventrodistal group of three setae.

Carpus very slender, 5.5 times as long as wide, ventrally with four marginal and four submarginal setae, five dorsodistal setae. Chela slender, palm 1.5 times as long as wide with single dorsal, ventral and distal setae and simple seta at base of dactylus; fixed finger 1.5 times as long as palm, curved, with longer proximal and shorter distal ventral setae, cutting edge without apophyses but with three shorter and one longer curved setae. Dactylus with three mid-dorsal setae, with two fine setules but no apophyses on cutting edge.

Pereopod 1 ( Fig. 4 B) with longer setae on distal articles generally tapering. Coxa with broad apophysis bearing one longer and one shorter distal spines, and two adjacent fine setae. Basis 2.5 times as long as wide, with three ventrodistal setae exceeding distal margin of ischium; exopodite conspicuous, article 2 with fine distal spinule, article 3 with five plumose setae. Ischium with two ventrodistal setae. Merus 0.6 times as long as basis, wider distally, with single dorsodistal spine and three adjacent setae, row of four midventral longer setae, one ventrodistal spine. Carpus compact, just shorter than merus, with two ventral spines amongst five marginal setae, one dorsodistal spine with two adjacent setae, dorsodistal margin with eight elongate tapering setae exceeding tip of propodus in length. Propodus as long as carpus, ventral margin with four spines interspersed with tapering setae, dorsal margin with row of six tapering setae but no spine. Dactylus and unguis fused, distally appearing cleft, with ventral denticulation.

Pereopod 2 ( Fig. 4 C) basis three times as long as wide, with two elongate ventrodistal setae. Ischium almost as long as wide, with ventrodistal seta. Merus one-quarter length of basis, with three ventrodistal setae. Carpus 1.7 times as long as merus, with three ventrodistal setae and dorsodistal slender curved spine as long as propodus. Propodus three-quarters length of carpus, with two ventrodistal setae and slender, curved dorsodistal spine. Dactylus and unguis fused, together longer than propodus, distally appearing cleft, with ventrodistal seta. Pereopod 3 ( Fig. 4 D) similar to pereopod 2, but without slender dorsodistal spines on carpus and propodus; carpus with row of five ventral setae in distal half and two dorsodistal setae; propodus with four ventral setae and four distal setae.

Pereopod 4 ( Fig. 4 E) basis 3.3 times as long as wide with two ventrodistal setae. Ischium with one ventral seta. Merus one-quarter length of basis, with five ventral setae in distal half. Carpus 2,2 times as long as merus, with mid-ventral seta and ventrodistally with array of five longer setae. Propodus two-thirds length of carpus, with five distal and two ventral-subdistal setae. Dactylus and unguis fused, together 1.2 times as long as propodus, not cleft but with dorsodistal denticulation. Pereopod 5 ( Fig. 4 F) similar to pereopod 4, but carpus more-densely setose, dactylus and unguis not fused. Pereopod 6 ( Fig. 4 G) similar to pereopod 5, but merus with dorsodistal seta; propodus without ventral-distal row of lanceolate spines.

Pleopods ( Fig. 5 D) alike. Basis with three inner and four outer plumose setae; rami linguiform, exopod shorter than endopod and with 13 plumose setae along inner and distal margins; endopod with eleven marginal plumose setae, inner proximal seta separated from others.

Uropod ( Fig. 5 A) biramous. Basis with two outer-distal setae. Exopod of four segments; endopod missing on all specimens.

Mature male: generally similar to female. Cheliped missing from specimen.

Antennule ( Fig. 5 B) more robust, proximal peduncle article 2.8 times as long as wide, more-densely setose than that of female; second article half as long as first; fourth article longer than third, naked. Main flagellum secondary segmentation, each segment apart from distal two with dense array of 10 to 12 aesthetascs; accessory flagellum longer than main flagellum, with nine segments.

Antenna ( Fig. 5 C) proximal peduncle article as long as wide, with slight inner-distal apophysis; second and third articles fused, with inner-distal spine-like apophyses and squama bearing five marginal setae; fourth article one-third as long as first article and half as long as wide; fifth article about as long as first article and as long as wide. Flagellum showing secondary segmentation, all segments other than distal segment with array of 10 to 12 aesthetascs.

Subadult male: Antennule similar to that of female, but main flagellum showing preliminary stages of secondary segmentation. Antenna ( Fig. 5 E) proximal article compact, second and third articles not fused, proximal flagellar segments showing preliminary stages of secondary segmentation. Cheliped as that of female.

Etymology. Named after Dr David Marshall of the Universiti Brunei Darussalam in gratitude for hospitality and support in Brunei and for his collaboration on the study of the tanaidaceans of Brunei.

Remarks. Distinctions of Actenos marshalli sp. nov. from species in other pakistanapseudin genera are discussed under the generic remarks above. The distinct spine on the coxa of pereopod 1 (not a spine-like apophysis as found in the Apseudinae ) also appears to be unique in the Pakistanapseudinae . In addition, the long dorsodistal spines on the carpus and propodus of pereopod 2 are unusual, but are a specific character, being absent in the second species of the genus described below and in A. tenuicorporeus . Similar spines are found on pereopod 2 in Pakistanapseudes taylorae BłaŻewicz-Paszkowycz & Bamber, 2012 (q.v.), but in that species they occur on the merus and carpus.

Actenos marshalli was taken together with other shallow-water pakistanapseudins, which can be difficult to identify in mixed samples owing to the propensity of these taxa to autotomize their limbs. In practice, the whole animal is recognizable by the conspicuous array of setae on the dorsal margins of the carpus and propodus of pereopod 1, the central point on the rostrum (which may be down-curved), and the conspicuous epistomal apophysis.

Actenos marshalli was taken over a depth range of 7.5 to 20 m, at an average density of 1.7 individuals per m2 (at the stations where it occurred). Over all the material identified, the female:male sex ratio was about 3:1.

Figures

FIGURE 3. Actenos marshalli gen. et sp. nov., female: A, holotype dorsal; B, antennule; C, antenna; D, labrum; E, epistomal apophysis; F, right mandible (molar viewed distally); G, left mandible; H, labium; I, maxillule; J, maxilla; K, maxilliped and endite; L, epignath. Scale line = 1.0 mm for A, 0.25 mm for B and C, 0.2 mm for D to L.

FIGURE 4. Actenos marshalli gen. et sp. nov., female: A, cheliped; B to G, pereopods 1 to 6. Scale line = 0.2 mm.

FIGURE 5. Actenos marshalli gen. et sp. nov.: A, uropod exopod; B, mature male antennule; C, mature male antenna; D, pleopod (plumose nature of all setae not shown, for clarity); E, subadult male antenna. Scale line = 0.2 mm.