Zeuxo kirkmani, Edgar, 2008

Edgar, Graham J., 2008, Shallow water Tanaidae (Crustacea: Tanaidacea) of Australia, Zootaxa 1836 (1), pp. 1-92 : 58-63

Zeuxo kirkmani n. sp.

( Figs 28–30 )

Material examined. Holotype. Female ( NMV J56149 ), 2.8 mm Seven Mile Beach, WA, 2 m depth, Amphibolis antarctica washings, 1 May 1986.

Paratypes. Two males, three females ( NMV J56150 ), holotype location .

Other material. One male, five females ( NMV J57285 ), Cliff Head, WA, 1 m depth, Amphibolis antarctica washings, 1 May 1986 ; two males, one female, Bickley Point , Rottnest Island, WA, 0.5 m, Amphibolis washings, 10 Jan 1991 .

Diagnosis. With characters of genus. Dorsal surface with dark purplish pigmentation extending from cephalothorax to pleotelson; antennule article 1 about 2.8 times (female) and 3.5 times (male) longer than wide, terminal article with two to four (female) and four or five (male) aesthetascs; left mandible with lacinia mobilis reduced, peg-like and acutely pointed, right mandible with lacinia mobilis reduced to thorn; pereopod 1 coxa produced anteriorly into bulge with six setae; pleopod basal article with six setae on outer margin, one seta on inner margin, endopod with three setae on inner margin; uropod with six articles in mature individuals; sexually dimorphic.

Description. FEMALE

Body ( Fig. 28 ). Length to 3.5 mm; preserved specimens with dark purplish pigmentation extending from cephalothorax to pleotelson and on chelipeds, pereopods, antenna and articles 1 and 3 of antennule.

Cephalothorax rounded and narrowing anteriorly in dorsal view, longer than wide.

Pereon occupies about 57% 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, 5 and 6 similar, nearly twice length of pereonite 3.

Pleonites together one-fifth as long as body; pleonites 1, 2 and 3 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 similar length to pleonite 2; posterior margin with pair of short setae central between pair of longer setae, three or four setae anterior to articulation with uropod, long simple seta on lateral margin.

Antennule ( Fig. 28 ). Total length extends three-fifths length of cephalothorax, with article 1 about 2.8 times longer than wide, with two setae one-third distance along outer margin and about four pappose setae and about five long simple setae distally; article 2 about one-third length of article 1, about 1.5 times longer than wide, with two or three pappose setae and about six simple setae distally; article 3 length almost twice width, about two-third length of article 2, with one or two pappose setae and about four simple setae distally; article 4 greatly reduced and cap-shaped, with about ten long simple setae and two to four aesthetascs.

Antenna ( Fig. 28 ). Article 1 as long as wide, lacking setae; article 2 twice length of article 1, length about 1.5 times width, with two small setae 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 five long distal setae; article 5 four-fifths length of article 4, with about four simple setae and pappose seta distally; article 6 length similar to width, with about six long setae; seventh article reduced to small terminal cap with about ten long setae.

Mouthparts ( Fig. 29 ). Labrum with setulose fringe.

Left mandible with lacinia mobilis reduced, peg-like and acutely pointed, with thorn at base, pars incisiva smooth and acute, pars molaris broad and corrugated; right mandible with lacinia mobilis reduced to bifurcated thorn, pars incisiva with broad bifurcated apex, 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 margin.

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

Maxilliped coxa and basis not joined medially; coxa with two or three long proximo-medial setae; basis with fine marginal spines and a distal pair of simple setae; endite with fine spines on margin, two small spiniform setae distal near medial margin, three small spiniform setae medial on distal margin, and two circumplumose setae near medio-distal margin that are about one-quarter length of simple setae on inner margin of palp; palp with four articles, article 1 as long as wide with simple seta distal on outer margin and fine marginal spines, article 2 slightly longer than article 1 with single seta distal on outer margin, six to eight very long setae extending distally in a row from midway along inner margin, article 3 considerably smaller than article 2, fringed with about ten long setae along inner margin, article 4 similar in length to article 3 but two-thirds 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. 28 ). 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 five setae distal near ventral margin, three distal dorsal setae and one seta one-third distance along dorsal margin; propodus with five or six setae ascending in size along ventral margin, about seven long setae extending as comb along inner margin of fixed finger to dorsal margin of dactylus when dactylus closed, and group of two or three setae plus large pappose seta near articulation with dactylus; dactylus with row of about nine very short setae along ventral margin, unguis short and solid, about one-fifth total length of dactylus.

Pereopod 1 ( Fig. 30 ). Coxa produced anteriorly into pronounced bulge with six setae; basis length approximately four 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 setae near distal ventral margin and two setae near distal dorsal margin; unguis two-thirds length of dactylus.

Pereopods 2 and 3 ( Fig. 30 ). Similar; basis width one-quarter length, length slightly less than merus, carpus and propodus together; merus two-fifths length of basis, with one short spiniform setae and two to four simple setae distal on ventral margin and one simple seta distal on dorsal margin; carpus two-thirds length of merus, about eight 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. 30 ). Similar; basis width about one-third length; merus with a pair of large spiniform setae and two or three simple seta distal on ventral margin; carpus with two adjacent rows of about five serrated spiniform setae around distal margin; propodus 1.5 times length of merus, with about three 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 five flattened setae.

Pereopod 6 ( Fig. 30 ). Basis width about one-third length; merus with a pair of large spiniform setae and two or three simple seta distal on ventral margin and two or three simple setae dorsal near distal margin; carpus with parallel rows of about six spiniform setae around distal margin; propodus with distal comb-like row of about twelve flattened denticulate setae and dorso-distal group of two long simple setae and pappose seta; dactylus with lateral comb-like rows of about six flattened setae.

Pleopods 1–3 ( Fig. 30 ). Similar; basal article length similar to width, with six plumose setae along outer margin and one plumose seta on inner margin; exopod with about 30 plumose setae along outer margin; endopod with three plumose setae on inner margin, large terminal circumplumose seta and about 16 plumose setae along outer margin.

Uropod ( Fig. 30 ). Six articles, fewer on immature animals; basal article length about four times width, with about six distal simple setae; articles 2, 3, 4 and 5 similar in length, with about four distal simple setae and one or two pappose seta; terminal article length slightly less than preceding article, with about six long terminal simple setae and a pappose seta.

MALE. Similar to female, other than

Antennule ( Fig. 28 ). Total length extends four-fifths length of cephalothorax; article 1 about 3.5 times longer than wide; article 4 with four or five projecting aesthetascs.

Cheliped ( Fig. 28 ). 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 after Hugh Kirkman in recognition of his contribution to marine conservation and studies of seagrass communities in Western Australia.

Distribution. Southwestern Australia, from Dongara to Perth, WA. 0–5 m depth.

Remarks. Zeuxo kirkmani can be distinguished from other tanaids by the combination of characters outlined in the diagnosis, and the presence of six setae on the coxa of pereopod 1, a greater number than for other known Australian species of Zeuxo . Its dark purplish coloration, which extends fully across the dorsal surface, is also unique among known tanaids, allowing this species to be identified without dissection.

Figures

FIGURE 28. Zeuxo kirkmani n. sp. Seven Mile Beach, WA. Female dorsal (holotype), male dorsal (paratype; pigmentation not shown), antennules (A1), antennae (A2), chelipeds (CH), pleotelson (Plt). Scale units 0.1 mm (appendages) and 1 mm (dorsal).

FIGURE 29. Zeuxo kirkmani n. sp. Seven Mile Beach, WA. Labrum (L), left mandible (Mdl), right mandible (Mdr), labium (La), maxillule (Mx), maxilliped (Mxp), epignath (E). Scale units 0.1 mm.

FIGURE 30. Zeuxo kirkmani n. sp. Seven Mile Beach, WA. Pereopods 1–6 (P1–P6), pleopod (Pl), uropod (U). Scale units 0.1 mm.