Zeuxo russi, Edgar, 2008

Edgar, Graham J., 2008, Shallow water Tanaidae (Crustacea: Tanaidacea) of Australia, Zootaxa 1836 (1), pp. 1-92 : 74-79

publication ID	https://doi.org/ 10.11646/zootaxa.1836.1.1
persistent identifier	https://treatment.plazi.org/id/676CB04D-FFDB-FFB7-FF32-FF55F874358F
treatment provided by	Felipe
scientific name	Zeuxo russi
status	sp. nov.

Treatment

Zeuxo russi View in CoL n. sp.

( Figs 37–39 View FIGURE 37 View FIGURE 38 View FIGURE 39 )

Material examined. Holotype. Female ( NMV J56145 View Materials ), 1.8 mm, Australian Institute of Marine Science Beach , Cape Cleveland, Qld, 1 m depth, Sargassum washings, 24 July 1996.

Paratypes. Three males, four females (four ovigerous) ( NMV J56146 View Materials ), holotype location .

Other material. Four males, twelve females, 16 juveniles, Purtaboi Island , Qld (17º56’S, 146º08’E), 2 m, macrophyte washings, 25 Sep 1999 GoogleMaps ; five females, three juveniles, Mandalay Point , Qld (20º16’S, 148º44’E), 2 m, macrophyte washings, 26 Sep 1999 GoogleMaps ; one female, Shoal Point , Qld (21º00’S, 149º09’E), 1 m, macrophyte washings, 27 Sep 1999 GoogleMaps ; eleven females, one juvenile, Slade Point , Qld (21º05’S, 149º13’’E), 2 m, macrophyte washings, 27 Sep 1999 ; four females (2 ovigerous), 13 juveniles, Diggers Camp , NSW (29°19’S 153°17’E), 1 m depth, 29 Sep 1999 GoogleMaps ; five females, three males, Cliff Head , WA, 0-3 m depth, 3 March 1986 ,

Diagnosis. With characters of genus. Dorsal surface with dark pigmented stripes behind eyes and near posterior margin of pereonites; antennule article 1 about 2.2 times (female) and just over 3.0 times (male) longer than wide, terminal article with three or four (female) and eight to ten (male) aesthetascs; left mandible with lacinia mobilis reduced and peg-like with roundly-indented tip, right mandible with lacinia mobilis lacking; pereopod 1 coxa produced anteriorly into slight bulge with one or two setae; pleopod basal article with four to seven 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. 37 View FIGURE 37 ). Length to 2.9 mm; preserved specimens with fine spots coalescing as band of pigment along posterior border of pereonites, anterior of cephalothorax and, to a lesser extent, lateral margins.

Cephalothorax trapezoidal in dorsal view; length similar to width and slightly more than one-fifth body length.

Pereon occupies about 53% 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 one-fifth as long as body; pleonites 1, 2 and 3 decreasing in length and width, each about four-fifths 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, three or four setae anterior to articulation with uropod, two or three long simple setae posterior on lateral margin.

Antennule ( Fig. 37 View FIGURE 37 ). Total length extends three-fifths length of cephalothorax, with article 1 about 2.3 times longer than wide, with three pappose setae one-third distance along outer margin and two or three pappose setae and about three long simple setae distally; article 2 about one-third length of article 1, about 1.2 times longer than wide, with two or three pappose setae and about four simple setae distally; article 3 length similar to width, about two-third 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 ten long simple setae and three or four aesthetascs.

Antenna ( Fig. 37 View FIGURE 37 ). Article 1 as long as wide, lacking setae; article 2 1.5 times length of article 1, length about 1.5 times width, with small 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 three 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. 38 View FIGURE 38 ). Labrum with setulose fringe.

Left mandible with lacinia mobilis reduced and peg-like with roundly-indented tip, 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 four or five long setae.

Maxilliped coxa and basis not joined medially; coxa with small proximo-medial seta; basis lacking fine marginal setae, with a short distal seta; endite setulose around distal margin, with two small spiniform setae distal near medial margin, two small spiniform setae medial on distal margin and two circumplumose setae near distal margin that are considerably shorter than 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 teeth, article 2 slightly longer than article 1 with single seta distal on outer margin, three to five very long setae extending distally in a row from midway along inner margin and three long distal setae, article 3 considerably smaller than article 2, fringed with about nine 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. 37 View FIGURE 37 ). 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 similar in length to basis, longer than wide, with three setae distal near ventral margin, three distal dorsal setae and one seta one-third distance along dorsal margin; propodus with five or six setae midway along ventral margin, about seven long setae extending as comb along inner margin of fixed finger to above dactylus when dactylus closed, and group of three or four setae plus large pappose seta near articulation with dactylus; dactylus with row of three or four very short setae along ventral margin, unguis short and solid, about one-fifth total length of dactylus.

Pereopod 1 ( Fig. 39 View FIGURE 39 ). Coxa produced anteriorly into slight bulge with one or two 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 three simple setae and pappose seta near distal margin, two setae two-thirds distance along dorsal margin and pappose seta two-thirds distance along ventral margin; unguis half length of dactylus.

Pereopods 2 and 3 ( Fig. 39 View FIGURE 39 ). Similar; basis width one-quarter length, length slightly less than merus, carpus and propodus together; merus two-fifths length of basis, with two short spiniform setae and two simple setae distal on ventral margin and one simple seta distal on dorsal margin; carpus two-thirds length of merus, about six 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. 39 View FIGURE 39 ). Similar; basis width about one-third length; merus with a pair of large spiniform setae and simple seta distal on ventral margin; carpus with two adjacent rows of about four serrated spiniform setae around distal margin; propodus 1.5 times length of merus, with seta 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 seven flattened setae.

Pereopod 6 ( Fig. 39 View FIGURE 39 ). Basis width about one-third length; merus with a pair of large spiniform setae and simple seta distal on ventral margin and two simple setae distal on dorsal margin; carpus with parallel rows of four spiniform setae around distal margin; propodus with distal comb-like row of about seven flattened denticulate setae and dorso-distal group of two long simple setae and pappose seta; dactylus with lateral comb-like rows of about seven setae.

Pleopods 1–3 ( Fig. 39 View FIGURE 39 ). Similar; basal article length similar to width, with four to seven plumose setae along outer margin and one plumose seta on inner margin; exopod with numerous plumose setae along outer margin; endopod with one plumose seta on inner margin, large terminal circumplumose seta and numerous plumose setae along outer margin.

Uropod ( Fig. 39 View FIGURE 39 ). Six or seven articles, fewer on immature animals; basal article length about twice width, with about five distal simple setae; articles 2, 3, 4 and 5 similar in length, with two to six distal setae including pappose seta; terminal article length slightly less than preceding article, with numerous very long terminal setae.

MALE. Similar to female, other than

Body ( Fig. 37 View FIGURE 37 ). Cephalothorax almost triangular in dorsal view.

Antennule ( Fig. 37 View FIGURE 37 ). Total length extends five-sixths length of cephalothorax, with article 1 just over three times longer than wide; article 4 with eight to ten terminal aesthetascs.

Cheliped ( Fig. 37 View FIGURE 37 ). All articles proportionately wider than in female; basis and carpus length similar to width; dactylus with unguis about one-tenth total length of dactylus.

Etymology. Named in recognition of contributions to tropical marine conservation and ecology by Garry Russ.

Distribution. Northern Australia, from Dongara, WA, to Coffs Harbour, NSW. 0–3 m depth.

Remarks. Morphological and setal characters in Zeuxo russi are largely similar to those in the Hawaiian and Gambier Island species Zeuxo seurati ( Nobili 1906) , as described by Miller (1940) and Sieg (1980b); however, female Z. russi possess three or four rather than two aesthetascs on antennules, and lack the small thorn on the lacinia mobilis of left mandible. Differences in setation between Z. russi and Z. seurati include fewer distal setae on antennule articles, five rather than four long terminal setae on maxilla palp, five rather than three setae on ventral margin of fixed finger, and two rather than one spinous setae on merus of pereopods 2 and 3. Most mature Z. russi possess six uropod articles; however, an occasional mature specimen examined from both Cliff Head and Cape Cleveland possessed seven articles. Setation differs in minor details between specimens of Z. russi collected at different sites across northern Australia. For example, the number of setae on the outer margin of the basal article of pleopods varied from four to seven on animals studied at Cliff Head, and five to seven for Cape Cleveland animals.

Zeuxo russi possesses a characteristic pigmentation pattern, which includes a dark mask behind the eyes and dark stippled stripes posterior on the dorsal surface of pereonites. The species occurs abundantly in shallow algal habitats around tropical and subtropical Australian coasts, and is particularly prevalent in association with Sargassum plants growing near low tide mark.