Zeuxo normani ( Richardson 1905 )

Edgar, Graham J., 2008, Shallow water Tanaidae (Crustacea: Tanaidacea) of Australia, Zootaxa 1836 (1), pp. 1-92 : 47-52

Zeuxo normani ( Richardson 1905)

( Figs 22–24 )

Material examined. Two males, five females (two ovigerous) ( NMV J56611 ), Mrs Macquarie’s Chair , Sydney Harbour, NSW, fucoid algal washings, 1 April 1993, low water mark. One male , eight females, one juvenile, Kettering, Tas, pylon scrapings, collected by Aquenal Pty Ltd ( Aquenal 2003), 9 Jul 2003, 2 m depth; one male, 13 juveniles ( NMV J57286 ), Murohama , Otsuchi Bay, Japan, Zostera marina bed, collected by I. Takeuchi, 6 June 1990, 2 m depth .

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

Description. FEMALE

Body ( Fig. 22 ). Length to 2.5 mm in length; preserved specimens with dark pigmentation covering most of cephalothorax, chelipeds, and articles 1 and 3 of antennule, lighter pigmentation on pereon and pleon.

Cephalothorax rounded and narrowing anteriorly in dorsal view, length slightly greater than 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 about length of pleonite 2; posterior margin with pair of short setae central between pair of long setae, two simple setae and pappose seta anterior to articulation with uropod, three long simple setae posterior on lateral margin.

Antennule ( Fig. 22 ). Total length extends three fifths length of cephalothorax, with article 1 about three times longer than wide, with three two or three pappose setae and two simple setae two-fifths distance along outer margin and about three pappose and four long simple setae distally; article 2 about one-third length of article 1, about twice as long as wide, with about two pappose and six simple setae distally; article 3 length similar to width, about two-third length of article 2, with about four setae distally; article 4 greatly reduced and cap-shaped, with about six long setae and three or four aesthetascs.

Antenna ( Fig. 22 ). Article 1 as long as wide, lacking setae; article 2 twice length of article 1, length about 1.5 times width, with about two 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 about five long distal setae; article 5 four-fifths length of article 4, with five or six simple and pappose setae distally; article 6 length similar to width, with about three simple setae; seventh article reduced to small terminal cap with about 15 long setae.

Mouthparts ( Fig. 23 ). Labrum distally carpeted by fine setules.

Left mandible with large lacinia mobilis, with undulating margin and large denticulate seta at base, pars incisiva smooth and acute, pars molaris broad and corrugated; right mandible with lacinia mobilis reduced to peg-like process with two denticulate setae at base, pars incisiva with blunt apex, pars molaris broad and corrugated.

Labium with inner and outer lobes covered by fine setules near distal margins, outer lobe with pointed terminal process and with very fine spines projecting from proximal lateral margins.

Maxillule endite with eight large terminal spiniform setae and cluster of fine setae on outer margin near base of spines; palp with five to seven long setae.

Maxilliped coxa and basis not joined medially; coxa with two small proximo-medial setae; basis 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 of similar length to long setae on inner margin of palp; palp with four articles, article 1 as long as wide with seta on outer margin, article 2 slightly longer than article 1 with single seta on outer margin, four or five very long setae extending distally in a row from midway along inner margin and three long distal setae, article 3 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 fringed by fine setules.

Cheliped ( Fig. 22 ). Basis longer than wide with one distal seta near ventral margin and one seta adjacent to articulation with merus; merus triangular with three setae three-quarters distance along ventral margin and two medial setae; carpus similar in length to basis, longer than wide, with about five setae distal near ventral margin, about four distal dorsal setae and one seta one-third distance along dorsal margin; propodus with five to six setae on ventral margin, about seven long setae extending as comb along inner margin of fixed finger, and group of three or four setae plus large pappose seta near articulation with dactylus; dactylus with row of about 10 very short setae along ventral margin, unguis short and solid, about one-fifth total length of dactylus.

Pereopod 1 ( Fig. 24 ). Coxa produced anteriorly into bulge with four 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 distal setae, seta two-thirds distance along dorsal margin and pappose seta two-thirds distance along ventral margin; unguis two-thirds length of dactylus.

Pereopods 2 and 3 ( Fig. 24 ). 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 seta and two simple setae distal on ventral margin, and one simple seta distal on dorsal margin; carpus two-thirds length of merus, with about four serrated spiniform setae along distal margin with dorsal spiniform seta largest; propodus 1.6 times length of carpus; unguis three-fifth length of dactylus.

Pereopods 4 and 5 ( Fig. 24 ). Similar; basis width about one-third length; merus with a pair of large spiniform setae and two simple setae distal near ventral margin; carpus with two parallel rows of three or four serrated spiniform setae around distal margin; propodus 1.4 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. 24 ). Basis width about one-quarter length; merus with a pair of large spiniform setae and two simple setae distal near ventral margin; carpus with parallel rows of three spiniform setae around distal margin; propodus with distal comb-like row of about six flattened denticulate setae and pair of very long simple setae and pappose seta; dactylus with lateral comb-like rows of about ten setae.

Pleopods 1–3 ( Fig. 24 ). Similar; basal article length similar to width, with five or six plumose setae along outer margin and one plumose seta on inner margin; exopod with about 28 plumose setae on outer margin; endopod with two to four plumose setae on inner margin, large terminal circumplumose seta and about twelve plumose setae along outer margin.

Uropod ( Fig. 24 ). Six or seven articles, fewer on immature animals; basal article length about twice width, with about five distal setae; articles 2, 3, 4 and 5 similar in length, with two to five distal setae; terminal article similar in length to preceding article, with about seven very long simple terminal setae and pappose seta.

MALE. Similar to female, other than

Body ( Fig. 22 ). Cephalothorax pear-shaped in dorsal view with concavity in margin.

Antennule ( Fig. 22 ). Article 1 about 3.5 times longer than wide; article 3 length almost twice width; article 4 with three or four projecting aesthetascs.

Cheliped ( Fig. 22 ). All articles proportionately wider than in female; basis and carpus length similar to width; dactylus with unguis about one-tenth total length of dactylus.

Distribution. Sydney, NSW; Hobart and Kettering, Tas; California to British Columbia, Japan ( Sieg 1980b). 0–5 m depth.

Remarks. Following Sieg (1980b), species of Zeuxo are primarily distinguished from each other on the basis of shape of mandibles, morphology and setation of coxa of pereopod 1, number of uropod articles, number of antennule aesthetascs, and arrangement of spiniform setae on pereopods and plumose setae on pleopods. These characters on Australian specimens attributed here to Zeuxo normani agree well with specimens of Zeuxo normani examined from Otsuchi Bay, Japan, although reaching a smaller maximum length. Australian animals mature at ca. 2 mm length, whereas Japanese animals at the same body size typically are immature, with uropods four- rather than six-segmented at that size. Animals in both regions possess similar distinctive pigmentation, with the cephalothorax markedly darker than the rest of the body.

Other than a few minor details of setation, the appearance of Australian animals conforms with descriptions of North American Zeuxo normani , including type material from Monterey, California ( Richardson 1905; Sieg 1980b). Specimens in all regions possess similar mandibles, a strongly projecting lobe on the coxa of pereopod 1 with four associated setae, similar pleopod setation, relatively few aesthetascs on antennule, and maxilliped endite with long projecting circumplumose setae. Australian specimens differ from those described by Sieg (1980b) in possessing two rather than one setae at the base of the maxilliped, and up to seven rather than four long terminal setae on the maxillule palp.

The wide geographic distribution of this species, encompassing both Northern and Southern Hemispheres, indicates the likelihood that it has been transported by shipping across ocean basins. Whether the species moved from the Northern to Southern Hemisphere or vice versa remains conjectural. Zeuxo normani has an extensive range along the southeastern Australian coast, albeit within estuaries, as well as occurring commonly off the Pacific coast of North America and Japan. Despite Z. normani having been initially reported in North America in 1905, no useful descriptions of tanaids were made from the Australian coast prior to that time, nor during the subsequent century. Thus, the species may well have been present in Australia since prior to historical times but unreported.

The sole tanaid previously described within the Australian range of Z. normani , Tanais tenuicornis Haswell (1881) , cannot presently be assigned to genus, let alone species, because the original description is poor and type material is lost ( Springthorpe & Lowry 1994). Sieg (1980b) regards T. tenuicornis as nomina dubia with affinities to the tribe Anatanaini (i.e., Anatanais , Zeuxoides or Zeuxo ). Although possibly a species of Zeuxo , this enigmatic tanaid is unlikely to be conspecific with Z. normani given that its reported size (1/ 4 inch = 6 mm) is much greater than the maximum size of locally observed specimens of Z. normani (2.5 mm).

Figures

FIGURE 22. Zeuxo normani. Sydney Harbour, NSW. Female dorsal, male dorsal (pigmentation not shown), antennules (A1), antennae (A2), chelipeds (CH), pleotelson (Plt). Scale units 0.1 mm (appendages) and 1 mm (dorsal).

FIGURE 23. Zeuxo normani. Sydney Harbour, NSW. Labrum (L), left mandible (Mdl), right mandible (Mdr), labium (La), maxillule (Mx), maxilliped (Mxp), epignath (E). Scale units 0.1 mm.

FIGURE 24. Zeuxo normani. Sydney Harbour, NSW. Pereopods 1–6 (P1–P6), pleopod (Pl), uropod (U). Scale units 0.1 mm.