Zeuxo (Parazeuxo) andaminimus, Bamber, Roger N & Chatterjee, Tapas, 2010

Bamber, Roger N & Chatterjee, Tapas, 2010, The new and the old: littoral tanaidomorph Tanaidacea (Crustacea: Peracarida) from the Andaman Islands, Indian Ocean, Zootaxa 2558, pp. 17-32 : 26-31

Zeuxo (Parazeuxo) andaminimus sp. nov.

Figs 5–7

Material examined: 1Ƥ, holotype ( NMWZ.2010.001.0007), 13, allotype ( NMWZ.2010.001.0008), 8ƤƤ, 13, 5 preparatory 33, 9 neuters, 2 juveniles, paratypes ( NMWZ.2010.001.0009), 1Ƥ, 23 (dissected, not retained), intertidal sediments among macroalgae ( Padina sp.), Burmanalla (11°33.45’N; 92°43.78’E), South Andaman Island, December 2005; coll. TC. 1Ƥ with oostegites, 1 brooding Ƥ, 6 neuters, 10 mancae, paratypes ( NMWZ.2010.001.0010), 3ƤƤ, 333, 4 neuters, 6 mancae, paratypes ( NMWZ.2010.001.0011), Wandoor (11°40.55’N, 92°45.12’E), Port Blair, South Andaman Island, salinity 35.5‰, intertidal sediments among macroalgae ( Halimeda opuntia ), December 2005; coll. TC. 1 Ƥ, 13, Wandoor, among macroalgae, are kept in second author’s personal collection.

Description of female: typical small Zeuxo ( Fig. 5 A), holotype 1.5 mm long, body 5.3 times as long as wide, dorsally with black mottling (as figured) particularly between the eyes, also on cephalothorax, pereonites, pleonites 1 to 3, pleotelson, proximal antennule article and distal cheliped articles (in preserved material). Cephalothorax subrectangular, with convex lateral margins, tapering towards anterior, 1.1 times as long as wide, with slight rounded rostrum, eyes present, pigmented. Cephalothorax about as long as pereonites 1–3 together; single lateral setae at one-third and two-thirds the length of the cephalothorax. Six free pereonites, rounded laterally, with one (pereonite 1), two (pereonites 2, 3 and 6) or three (pereonites 4 and 5) simple lateral seta on each side; pereonite 1 shortest, half as long as pereonite 2; pereonites 2 and 3 subequal, pereonites 4 and 6 subequal and slightly longer than pereonite 3; pereonite 5 longest, 1.5 times as long as pereonite 3 (all pereonites respectively 4.4, 2.1, 2.1, 1.8, 1.3 and 1.7 times as wide as long). Pleon of five free pleonites, and pleotelson; pleonites each with one (rarely two) lateral seta on each side but no transverse latero-dorsal rows of setae; pleonites 1 to 3 bearing pleopods, pleonites 2 and 3 subequal in length and shorter than pleonite 1; pleonites 4 and 5 shorter and narrower, about one-third as long as pleonite 2, without pleopods. Pleotelson ( Fig. 6 G) pentangular, twice as wide as long, with paired lateral and paired laterodistal setae on each side, and paired distal setae.

Antennule ( Fig. 5 B) of four articles; proximal article twice as long as wide with outer distal tuft of three simple and one penicillate setae, inner distal pair of simple setae; second article 0.45 times as long as first with outer distal tuft of two simple and two penicillate setae, inner distal pair of simple setae; third article twothirds as long as second, distally with single simple and penicillate outer setae, and two shorter and one much longer simple inner setae; distal article very small, with four distal setae and two aesthetascs.

Antenna ( Fig. 5 C) of seven articles, first article naked; second article 1.3 times as long as first, with single dorsal and ventral setae; third article as long as first, naked; fourth article as long as second article, with three simple distal setae; fifth article just longer than fourth, with three simple distal setae; sixth article one third as long as fourth, with two distal setae; seventh article very small with five distal setae.

Labrum (not figured) typical of the genus, hood-shaped, rounded, setulose. Left mandible ( Fig. 5 D) with narrow, linguiform lacinia mobilis with minute accessory tooth, right mandible ( Fig. 5 E) with smaller, triangular lacinia mobilis with minute accessory tooth; pars molaris of each mandible robust, rugose. Labium ( Fig. 5 G) wide, all lobes finely setose distally, labial palp present but without articulation. Maxillule ( Fig. 5 F) with eight distal spines, finely rugose outer margin, palp with three shorter and one longer distal setae; maxilla ovoid, simple, naked. Maxilliped ( Fig. 5 H) basis naked; proximal palp article with outer seta, second palp article with outer seta, three longer inner setae, and two curved distal setae; third article with eight simple inner setae, distally in two rows; fourth article with seven distal and one outer subdistal simple setae. Maxilliped endites with two coarsely-plumose setae and setulose distal margin. Epignath ( Fig. 5 I) typical of genus, reniform with distal spine and finely setose distal margin.

Cheliped ( Fig. 6 A) comparatively robust, basis 1.65 times as long as wide with subdistal ventral seta; merus ventrally with two subdistal seta and one mesial seta near dorsal margin; carpus 1.6 times as long as wide, with single dorsodistal and three midventral setae; propodus with two short mid-distal setae between fingers; fixed finger three ventral setae three distal setae, and four blunt setae along cutting edge; dactylus with fine spinules along cutting edge and single mid-dorsal seta.

Pereopod 1 ( Fig. 6 B) longer than other pereopods; coxa with two setae on slight rounded apophysis; ischio-basis 3.4 times as long as wide, with single dorsoproximal and ventrodistal simple setae; merus 0.3 times length of basis; carpus one-third longer than merus; propodus nearly twice as long as carpus; dactylus with distinct, slender, longer unguis, both together 0.85 times as long as propodus. Pereopod 2 ( Fig. 6 C) ischio-basis 2.5 times as long as wide, with single dorsoproximal and ventrodistal simple setae; merus less than half length of basis with two ventrodistal and one small dorsodistal setae; carpus compact, shorter than merus, with dorsal and ventral distal setae and three anterodistal and two posterodistal slender tooth-like spines, largest spine less than half as long as propodus; propodus 1.6 times as long as carpus, with single dorsodistal and ventral subdistal setae, but without ventrodistal spine; dactylus plus unguis as long as carpus. Pereopod 3 ( Fig. 6 D) similar to pereopod 2 but merus with short ventrodistal spine, carpus with four anterodistal spines.

Pereopod 4 ( Fig. 6 E) ischio-basis 3.1 times as long as wide, with two ventrodistal setae; merus 0.9 times as long as carpus, with one dorsodistal seta, and single ventrodistal spine and seta; carpus with three anteroventral and two posteroventral short tooth-like spines, and two dorsodistal setae; propodus 1.3 times as long as merus, with ventral microtrichia; dactylus and unguis fused into a claw, curved, about half as long as propodus, with lateral comb of four spinules. Pereopod 5 (not figured) as pereopod 4. Pereopod 6 ( Fig. 6 F) as pereopod 4, but carpus with four anterodistal spines, propodus with distal row of seven pointed leaf-like spines, claw with lateral comb of five spinules.

Pleopod ( Fig. 6 H) basis with one inner and five (pleopods 1 and 2) or three (pleopod 3) outer plumose setae; exopod with 22 plumose setae along outer edge; endopod with one inner and 11 outer plumose setae, distally with shorter, stout, articulate seta.

Uropod ( Fig. 6 G) uniramous, of four segments plus basis, segments about twice as long as wide, subequal in length.

Description of male: larger and stouter than female, allotype ( Fig. 7 ) 1.74 mm long, 4.25 times as long as wide; cephalothorax as long as wide, pereonite 2 as long as pereonite 1, pereonites 4 to 6 equal in length. No significant sexual dimorphism in any appendages, but antennule with three aesthetascs.

Etymology: a euphonic combination from the first four letters of Andaman Islands, the type locality, and minimus from the Greek minys —small, alluding to the unusually (for the subgenus) small size of adults of the present species.

Remarks. The genus Zeuxo was analyzed comprehensively by Sieg (1980), and a more up-to-date context given to the taxonomic problems within the Anataini by Bird (2008). With only one inner seta on the pleopod endopod, one dorsal (tergal) seta on the merus of pereopods 4 to 6, and a relatively-slight rounded apophysis on coxa 1, the present species falls within Sieg’s (1980) subgenus Parazeuxo . Since Sieg (1980), the only additional species of Parazeuxo described were by Bamber & Bird (1997), Bamber (2006, 2008) and Edgar (2008), giving the following list of 12 species:

Zeuxo (Parazeuxo) amiti Bamber, 2008 Z. (P.) belli Edgar, 2008

Z. (P.) cloacarattus Bamber, 2006 Z. (P.) coralensis Sieg 1980

Z. (P.) exsargasso Sieg 1980

Z. (P.) kurilensis ( Kussakin & Tsareva 1974) Z. (P.) maledivensis Sieg 1980 Z. (P.) mooneyi Edgar, 2008

Z. (P.) russi Edgar, 2008

Z. (P.) phytalensis Sieg 1980

Z. (P.) seurati (Nobili 1906)

Z. (P.) zorro Bamber & Bird 1997

The only previously-described species of Parazeuxo with a five-segmented uropod (basis plus four segments) in the adult are Z. (P.) kurilensis , Z. (P.) maledivensis and Z. (P.) exsargasso . All of these species are conspicuously larger (body-length 2.5 mm or more) than Z. (P.) andaminimus sp. nov.; indeed, the only recorded species of Parazeuxo with an adult body length of less than 2 mm are Z. (P.) amiti , a species with a seven-segmented uropod, and Z. (P.) mooneyi (known only from the male), a species with a four-segmented uropod.

The new species is further distinct from Z. (P.) kurilensis and Z. (P.) maledivensis , as those species have a much wider lacinia mobilis on the right mandible, a proportionately longer proximal antennule article (especially in the male), six maxillule-palp setae, and three setae on the coxa 1 apophysis. Unlike Z. (P.) andaminimus , Z. (P.) exsargasso has the lacinia mobilis reduced to an unarticulated tooth on the left mandible, a proportionately longer proximal antennule article, more numerous spinules in the comb-rows of the ungues of pereopods 4 to 6, only three maxillule-palp setae, and two inner setae on the pleopod endopod.

No species of the Anatanaini has been recorded previously from the Bay of Bengal, although Sieg (1980) suggests that both Z. (P.) maledivensis and Z. (P.) coralensis have rather unlikely widespread distributions which include the Maldives and Japan.

Figures

FIGURE 5. Zeuxo andaminimus sp. nov., female, A, holotype, dorsal; B, antennule; C, antenna; D, left mandible; E, right mandible; F, maxillule and maxilla; G, labium; H, maxilliped; I, epignath. Scale line = 0.4 mm for A, 0.1 mm for B to I.

FIGURE 6. Zeuxo andaminimus sp. nov., female, A, cheliped; B, pereopod 1; C, pereopod 2; D, pereopod 3; E, pereopod 4; F, pereopod 6; G, pleotelson and right uropod; H, pleopod (most setae shown only by their bases). Scale line = 0.1 mm.

FIGURE 7. Zeuxo andaminimus sp. nov., male allotype, dorsal. Scale line = 0.5 mm.