Zeuxo belli, Edgar, 2008

Edgar, Graham J., 2008, Shallow water Tanaidae (Crustacea: Tanaidacea) of Australia, Zootaxa 1836 (1), pp. 1-92 : 53-58

Zeuxo belli n. sp.

( Figs 25–27 )

Material examined. Holotype. Female ( NMV J56147 ), 1.8 mm, Coral Beach, Qld, (20º17’S 148º48’E), 2 m depth, 26 Oct 1999.

Paratype. One male, three females, two juveniles ( NMV J56148 ), 1.6 mm . Holotype location.

Other material. Six females, four juveniles, Mandalay Point, Qld (20º16’S, 148º44’E), 2 m, macrophyte washings, 26 Sep 1999.

Diagnosis. With characters of genus. Dorsal surface with dark chromatophore-like flecks; antennule article 1 about twice (female) and 2.5 times (male) longer than wide, terminal article with four (female) and seven or eight (male) aesthetascs; left mandible with lacinia mobilis reduced peg-like and acutely pointed, right mandible with lacinia mobilis lacking; pereopod 1 coxa produced anteriorly into slight bulge with two or three setae; pleopod basal article with six setae on outer margin, one seta on inner margin, endopod with one seta on inner margin; uropod with six or seven articles in mature individuals; sexually dimorphic.

Description. FEMALE

Body ( Fig. 25 ). Length to 2.5 mm; preserved specimens with numerous dark chromatophore-like flecks on cephalothorax, pereonites, pleonites and pleotelson, flecks not coalescing as band of pigment but disproportionately present behind eyes of some individuals (as indicated in Fig. 25 male).

Cephalothorax rounded and narrowing anteriorly in dorsal view, slightly longer than wide one-quarter body length.

Pereon occupies about 51 % of total length; pereonites with several setae along anterio-dorsal and lateral margins; pereonite 1 length about one-fifth width; pereonites 2 and 3 similar, almost twice length of pereonite 1; pereonites 4 and 5 similar, about 1.5 times length of pereonite 3; pereonite 6 about three-quarters length of pereonite 5.

Pleonites together about one-fifth as long as body; pleonites 1, 2 and 3 slightly decreasing in length and width, each about five-sixths length of preceding segment; pleonites 4 and 5 similar, together as long as pleonite 3.

Pleotelson 1.5 times length of pleonite 2; posterior margin with pair of short setae central between pair of long setae, about four setae anterior to articulation with uropod, two long simple setae posterior on lateral margin.

Antennule ( Fig. 25 ). Total length extends two-thirds length of cephalothorax, with article 1 length twice width, with one to three pappose setae one-third distance along outer margin and two or three pappose setae and about four long simple setae distally; article 2 about one-third length of article 1, about 1.2 times longer than wide, with two pappose setae and about four simple setae distally; article 3 length almost twice width, about three-quarters length of article 2, with two or three pappose setae and about four simple setae distally; article 4 greatly reduced and cap-shaped, with about seven long simple setae and four aesthetascs.

Antenna ( Fig. 25 ). Article 1 as long as wide, lacking setae; article 2 1.5 times length of article 1, length about 1.5 times width, with seta midway on outer margin and two setae distally; article 3 half length of article 2, lacking setae; article 4 twice length of article 3, with four long distal setae; article 5 four-fifths length of article 4, with about three simple setae and two pappose setae distally; article 6 length similar to width, with about six long setae; seventh article reduced to small terminal cap with about eight long setae.

Mouthparts ( Fig. 26 ). Labrum with setulose fringe.

Left mandible with lacinia mobilis greatly reduced, peg-like and acutely pointed, lacking accessory seta, pars incisiva smooth with blunt apex, pars molaris broad and corrugated; right mandible with lacinia mobilis and accessory seta lacking, pars incisiva smooth and acute, pars molaris broad and corrugated.

Labium with inner lobe setulose; outer lobe setulose on distal margin, with pointed terminal process and with very fine spines projecting from proximal lateral margins.

Maxillule endite with eight large terminal spiniform setae, setulose on outer margin near base of spines; palp with about seven long setae.

Maxilliped coxa and basis not joined medially; basis lacking fine marginal setae, with a distal seta; endite setulose around distal margin, with two short flat setae on distal margin and two circumplumose setae near distal margin that are half length of setae on inner margin of palp; palp with four articles, article 1 wider than long with seta distal on outer margin, article 2 with single seta distal on outer margin, four long setae extending distally in a row from midway along inner margin and two long distal setae, article 3 fringed with about eight long setae along inner margin, article 4 similar in length to article 3 with similar width, with a long seta distal on outer margin, a long terminal seta, and two adjacent rows of about five setae distal on inner margin.

Epignath with terminal circumplumose seta and fringe of fine setules.

Cheliped ( Fig. 25 ). Basis longer than wide with one distal seta near ventral margin and one seta adjacent to articulation with merus; merus triangular with two setae two-thirds distance along ventral margin; carpus slightly longer than basis, longer than wide, with three setae two-thirds distance along ventral margin, three distal dorsal setae and one seta one-third distance along dorsal margin; propodus with five to six setae midway along ventral margin, about seven long setae extending along dorsal margin of fixed finger as comb to just above ventral margin of dactylus when dactylus closed, and group of three or four setae plus large pappose seta near articulation with dactylus; dactylus with row of about ten very short setae along ventral margin, unguis short and solid, about one-sixths total length of dactylus.

Pereopod 1 ( Fig. 27 ). Coxa produced anteriorly into slight bulge with two or three setae; basis length approximately five times width; merus about one-quarter length of basis; carpus 1.5 times length of merus; propodus length similar to merus and carpus together, with about six simple setae near distal margin and seta two-thirds distance along ventral margin; unguis three-fifths length of dactylus.

Pereopods 2 and 3 ( Fig. 27 ). Similar; basis width one-quarter length, length slightly less than merus, carpus and propodus together; merus two-fifths length of basis, with one spiniform setae and two or three simple setae distal on ventral margin and one simple seta distal on dorsal margin; carpus two-thirds length of merus, two rows of about three serrated spiniform setae along distal margin with dorsal spiniform seta largest; propodus 1.5 times length of carpus; unguis half length of dactylus.

Pereopods 4 and 5 ( Fig. 27 ). Similar; basis width about one-third length; merus with a pair of large spiniform setae and two simple setae distal on ventral margin, two simple setae distal on dorsal margin; carpus with two adjacent rows of about four serrated spiniform setae and two long simple setae near distal margin; propodus 1.5 times length of merus, with one or two setae distal near ventral margin and pappose seta plus two long simple setae distal near dorsal margin; unguis merged into claw-like dactylus, with comb-like lateral rows of about nine flattened setae.

Pereopod 6 ( Fig. 27 ). Basis width about two-fifths length; merus with a pair of large spiniform setae and two simple setae distal on ventral margin, two simple setae distal on dorsal margin; carpus with two parallel rows of about four spiniform setae around distal margin; propodus with distal comb-like row of about nine flattened denticulate setae and dorso-distal group of two long simple setae and pappose seta; dactylus with lateral comb-like rows of about ten setae.

Pleopods 1–3 ( Fig. 27 ). Similar; basal article length similar to width, with six plumose setae along outer margin and one plumose seta on inner margin; exopod with about 25 plumose setae along outer margin; endopod with one plumose seta on inner margin, large terminal circumplumose seta and about 13 plumose setae along outer margin.

Uropod ( Fig. 27 ). Six or seven articles, fewer on immature animals; basal article length about twice width, with about six distal simple setae; article 2 longer than more distal articles, length similar to basal article, with about three simple setae and a plumose seta; article 3 half length of article 2, with about four simple setae and a plumose seta; articles 4 and 5 similar, length slightly longer than article 3, with about four simple setae and a plumose seta; terminal article two-thirds length of preceding article, with about seven very long terminal setae.

MALE. Similar to female, other than

Antennule ( Fig. 25 ). Total length slightly less than length of cephalothorax, with article 1 about length 2.5 times width; article 4 with seven or eight projecting aesthetascs.

Cheliped ( Fig. 25 ). All articles proportionately wider than in female; basis and carpus length similar to width; dactylus with unguis about one-eighth total length of dactylus.

Etymology. Named in memory of Stuart Bell in recognition of his contribution to, and enthusiasm for, marine science.

Distribution. Central Qld. 2 m depth.

Remarks. This species is very similar to both Zeuxo russi and the Hawaiian and Gambier Island species Zeuxo seurati (Nobili) , with synapomorphies that include number of setae on pleopods and maxilla, form and setation of pereopod 1 coxa, number of uropod articles, number of antennule aesthetascs, and loss of lacinia mobilis of left mandible. Zeuxo belli and Z. russi differ most obviously in their distinctive dorsal pigmentation patterns, with Z. belli possessing dark irregular speckles and Z. russi a mask anteriorly on the dorsal surface behind the eyes and dark pigmented bands posterior on body segments. Patterns of pigmentation on the dorsal surface of Z. seurati have not been described. The three species also differ in body proportions—with Z. belli the more elongate species in body, antennules and antennae—and in the arrangement of setae on maxillipeds and chelipeds, including comb setae along the cheliped fixed finger of Z. belli that are half the length of comparable setae in Z. russi and Z. seurati .

Figures

FIGURE 25. Zeuxo belli n. sp. Coral Beach, Qld. Female dorsal (holotype), male dorsal (paratype), antennules (A1), antennae (A2), chelipeds (CH), pleotelson (Plt). Scale units 0.1 mm.

FIGURE 26. Zeuxo belli n. sp. Coral Beach, Qld. Labrum (L), left mandible (Mdl), right mandible (Mdr), labium (La), maxillule (Mx), maxilliped (Mxp), epignath (E). Scale units 0.1 mm.

FIGURE 27. Zeuxo belli n. sp. Coral Beach, Qld. Pereopods 1–6 (P1–P6), pleopod (Pl), uropod (U). Scale units 0.1 mm.