Poligarida beni, Bamber & Marshall, 2013

Bamber, Roger N. & Marshall, David J., 2013, Tanaidaceans from Brunei III. A New Genus and Two New Species of Shallow-water Sphyrapodids (Crustacea: Peracarida: Tanaidacea) from the South China Sea, Species Diversity 18, pp. 255-267 : 256-262

Poligarida beni sp. nov.

( Figs 1–4 )

Material examined. Holotype: ♀ ( BMNH 2013.177 ), Sample BU 3, 04°51′06″N 114°35′26″E, 20 m depth . Allotype: ♂ ( BMNH 2013.178 ), same data as holotype . Paratypes: 4♂♂, 14♀♀ (2 brooding, 6 with oostegites), 1 juvenile, 5 undetermined ( BMNH 2013.179 – 188 ), same data as holotype . 1♀ ( BMNH 2013.189 ), Sample B 4; 1♂, 1♀ ( BMNH 2013.190 – 191 ), Sample B 12; 1♂, 7♀♀ (2 brooding, 2 with oostegites) ( BMNH 2013.192 – 199 ), Sample B 13; all Station B, 04°51′06″N 114°35′26″E, 20 m depth . 1♂, 2♀♀ (1 brooding) ( BMNH 2013.200 – 202 ), Sample DA 1; 7♂♂, 24♀♀ (3 brooding, 8 with oostegites) ( BMNH 2013.203 – 212 ), Sample DA 2; all Station DA, 05°54′28.5″N 114°38′23.3″E, 20 m depth, sand .

Other material examined (retained by the author): 2 ♀♀ with oostegites (dissected), same data as holotype . 1♂, 1♀ (dissected), Sample DA1. 1♂, 1 brooding ♀ (dissected), Sample DA2.

Description. Female with oostegites (based predominantly on holotype). Body ( Fig. 1A ) glabrous, dorsoventrally flattened, holotype 2.0 mm long, five times as long as wide, narrower posteriorly. Cephalothorax subrectangular, 0.9 times as long as wide, anterior margin with conspicuous extended rostrum bearing two to four rounded distal tubercles ( Fig. 1C ). Eyes absent; eyelobes conspicuous. Pereonite 1 not fused to cephalothorax, one third as long as cephalothorax, laterally rounded; pereonite 2 as long as but narrower than pereonite 1; pereonite 3 as wide as pereonite 2, 1.8 times as long as pereonite 1, posteriorly expanded at coxal attachment, with triangular anterolateral apophyses; pereonite 4 as long as but just narrower than pereonite 3, 1.9 times as long as pereonite 1, with slight anterolateral apophyses (“shoulders”); pereonite 5 as long as pereonite 4, without apophyses; pereonite 6 shorter, 1.5 times as long as pereonite 1 (pereonites respectively 3.4, 3.0, 1.8, 1.5, 1.5 and 2.1 times as wide as long). Pleon 0.22 times as long as whole body; pleonites 4.8 times as wide as long, epimera held closely to body laterally, extended into posterior spine-like apophyses ( Fig. 1D ). Pleotelson semicircular, 0.3 times length of whole pleon, 0.6 as long as wide, with paired simple setae caudodistally.

Antennule ( Fig. 2A ) with proximal peduncular article robust, 3.4 times as long as wide, with three outer and three inner simple setae; second article one-third as long as first article, with single outer and inner simple setae; third article one-quarter as long as second, with inner distal seta; fourth article very short, naked. Accessory flagellum of two segments, distal segment twice as long as proximal segment and with two simple setae. Main flagellum of three segments, second segment longest, distal segment shortest and bearing two aesthetascs and three simple distal setae.

Antenna ( Fig. 2C ) with four-articled peduncle, squama absent; proximal article with inner expansion with denticulate margin, surface smooth; article 2 three times as long as wide, naked; article 3 short, 0.16 times as long as article 2, naked; article 4 elongate, 1.4 times as long as article 2, with fine, simple medial and distal setae. Flagellum of three segments.

Labrum ( Fig. 2D ) rounded, marginally setose. Left mandible ( Fig. 2E ) with pars incisiva and lacinia mobilis each bearing six rounded distal “teeth”, setiferous lobe bearing four slender, simple setae and one bifurcate seta, and pars molaris wide, flattened, distally bearing four slender setae; palp absent. Right mandible ( Fig. 2F ) with pars incisiva bearing two rounded distal teeth, and setiferous lobe bearing three slender setae and lanceolate spine resembling a lacinia mobilis. Maxillule ( Fig. 2G ) inner endite with three simple distal setae; outer endite with nine longer outer and two shorter central distal spines; palp absent. Maxilla ( Fig. 2H ) with outer marginal hook-like apophyses; outer lobe of moveable endite with five distal and two subdistal setae; inner lobe of movable endite with five simple setae; outer lobe of fixed endite with two simple, two bifurcate and two trifurcate spines; inner lobe of fixed endite with rostral row of 14 setae guarding one longer simple seta. Labium ( Fig. 2I ) with hook-like apophyses on outer margin, inner margins setulose, palp sparsely setose with one distal barbed spine. Maxilliped ( Fig. 2J ) basis apparently naked; palp article 1 with single short seta on outer margin and longer subdistal seta on inner margin; second palp article longer than wide, with five inner setae and single shorter outer distal spine; third palp article with six distally-tapering setae along expanded inner margin; fourth palp article with five distal and one subdistal setae. Maxilliped endite with three stout plumose outer setae, two inner coupling hooks, and five simple distal spines. Epignath ( Fig. 2K ) large, semicircular, with long, naked distal seta.

Cheliped ( Fig. 3A ) malleolate. Basis rounded, 1.6 times as long as wide, with one fine ventral-subdistal seta. Exopodite 3-articled, distal article with four plumose setae. Merus subrectangular but extending distally along ventral margin of carpus, with single midventral seta. Carpus 2.2 times as long as wide, with two longer proximal and one shorter subdistal simple setae on ventral margin, and one dorsal subdistal seta. Propodus massive, proximally overhanging carpus, 1.5 times as long as wide, with one mid-distal seta and combrow of two setae; fixed finger just shorter than palm, ventral margin with two setae, cutting edge of fixed finger with row of twelve triangular “teeth” and three submarginal setae; dactylus with sinuous cutting edge bearing four setae, three medial setae also present.

Pereopod 1 ( Fig. 3C ) much larger than remaining pereopods (overall length ∼ 1 mm), all spines with fine lateral denticulations. Coxa naked; basis relatively stout, 3.1 times as long as wide, with single ventrodistal seta; exopodite present, 3-articled, distal article with four distal plumose setae. Ischium compact, naked. Merus just over half as long as basis, with five distal setae and ventrodistal spine. Carpus 0.75 times as long as merus, with two proximal setae along ventral margin, single inner distal fine seta, three dorsal submarginal setae, and one dorsodistal and two ventrodistal spines. Propodus 0.8 times as long as carpus, dorsal margin with two setae and two spines, ventral margin with three spines. Dactylus slender, with three ventral denticulations, unguis one-third as long as dactylus, both together 1.3 times as long as propodus.

Pereopod 2 ( Fig. 4A ) half as long as pereopod 1; basis 5.8 times as long as wide with fine, simple ventrodistal seta. Ischium with one ventral seta. Merus half as long as basis, with one shorter and one much longer ventral setae. Carpus just shorter than merus, with three dorsal, one distal and three ventral marginal setae. Propodus as long as carpus, setation as carpus. Dactylus slender, with one middorsal and two ventrodistal setae, unguis short, both together as long as propodus. Pereopod 3 ( Fig. 4B ) similar to pereopod 2, but distal articles with one fewer ventral setae, dactylus with ventrodistal spine-like apophysis.

Pereopod 4 ( Fig. 4C ) similar to pereopod 2, but basis stouter, 4.8 times as long as wide. merus one-quarter as long as basis, with two ventrodistal setae; carpus 1.7 times as long as merus, with single ventral and two distal setae; propodus as long as carpus, with two ventral and one dorsal setae, distally with crown of five finely-denticulate curved setae; dactylus slender with ventrodistal apophysis, together with unguis longer than propodus. Pereopod 5 ( Fig. 4D ) similar to pereopod 3, but merus and carpus with two distal setae. Pereopod 6 ( Fig. 4E ) similar to but smaller than pereopod 5, propodus with three distal setae.

Pleopods ( Fig. 4F ) all alike. Basis elongate, with one inner-distal seta. Endopod as long as exopod, with one inner and four distal plumose setae; exopod of two segments, proximal segment with outer-distal plumose seta; distal segment with five distal plumose setae.

Uropod ( Fig. 4G ) biramous. Basis naked; exopod of three segments, reaching past distal end of second endopodal segment, distal segment longer than two proximal segments together, bearing two unequal setae; endopod elongate, as long as whole pleon, with nine segments, alternate segments with simple setae as figured.

Distinctions of male (predominantly based on allotype): Generally as female, body ( Fig. 1B ) more slender, apophyses on pereonites three and four more conspicuous than those of female; pleotelson subtriangular, caudally extend- ed. Pereopod 1 ( Fig. 1B ) proportionately larger than that of female. Dimorphism evident in antennule and cheliped. Antennule ( Fig. 2B ) with main flagellum of five segments, proximal two segments shorter than wide, each furnished distally with dense row of about 16 aesthetascs.

Cheliped ( Fig. 3B ) stouter than that of female, basis as long as wide, carpus 1.6 times as long as wide, propodus 1.4 times as long as wide with two distal setae; fixed finger 0.6 times as long as propodus, with expanded, denticulate cutting edge; dactylus longer than fixed finger, with eight setae along cutting edge.

Etymology. named after Ben Lovett, in gratitude for many enlightening discussions.

Remarks. Most morphological characteristics are discussed under remarks for the genus, above. In addition, Poligarida beni sp. nov. is unique within the Sphyrapodidae in having such pronounced anterolateral apophyses on the third pereonite (small apophyses are present in species of Sphyrapoides ).

The 73 specimens examined were from a total of 23 samples, representing an average density in the area of 31.7 individuals per m 2; analysis of the variance and mean of sample densities demonstrates that, based on the common dispersion parameter (k) of the negative binomial distribution [k = m 2 /(s 2 − m), where m is the mean and s 2 the variance], the population shows a highly aggregated distribution (k =0.7; 1/ k >>0). The overall male:female sex ratio was 0.31: 53% of the females had either oostegites or brood pouches.

In 50 samples from inshore (2 m depth) out to and including station DA (20 m depth), no individuals were found in waters shallower than 20 m. The shallow-water (2–8 m depth) samples off this same Brunei coast studied by Bamber et al. (2012) also contained no sphyrapodids. Previous surveys further offshore at 60 m depth (Bamber 1998) found no sphyrapodids at all, nor did surveys off the adjacent coasts of Sabah at 25–35 m depth ( Bamber and Sheader 2005). Poligarida beni appears to be a distinctly shallowwater species, but instability of the sediments at depths of 2 to 13 m, probably associated with the wave-base, precludes its colonization closer inshore, where total tanaidacean densities were between one half and one-quarter of the mean at 20 m depth.

Figures

Fig. 1. Poligarida beni sp. nov., A, female holotype; B, male allotype; C, variations in rostra, including (i) holotype and (ii) allotype; D, pleonal epimere. Scale: 1mm for A and B.

Fig. 2. Poligarida beni sp. nov., A, female antennule; B, male antennule; C, antenna; D, labrum; E, left mandible; F, right mandible; G, maxillule, with detail of distal spines of outer endite; H, maxilla; I, labium; J, maxilliped and endite; K, epignath. Scales: 0.1mm for A–C, 0.08mm for D–K.

Fig. 3. Poligarida beni sp. nov., A, female cheliped; B, male cheliped; C, female pereopod 1, with detail of denticulation of spine. Scale: 0.1mm.

Fig. 4. Poligarida beni sp. nov., A to E, pereopods 2 to 6 respectively (pereopod 4 with detail of denticulation of spine); F, pleopod (plumosity of all setae omitted); G, uropod. Scale: 0.1mm.