Zeuxo shepherdi, Edgar, 2008

Edgar, Graham J., 2008, Shallow water Tanaidae (Crustacea: Tanaidacea) of Australia, Zootaxa 1836 (1), pp. 1-92 : 79-84

publication ID	https://doi.org/ 10.11646/zootaxa.1836.1.1
persistent identifier	https://treatment.plazi.org/id/676CB04D-FFDC-FFAA-FF32-FA85F8BB3687
treatment provided by	Felipe
scientific name	Zeuxo shepherdi
status	sp. nov.

Treatment

Zeuxo shepherdi View in CoL n. sp.

( Figs 40–42 View FIGURE 40 View FIGURE 41 View FIGURE 42 )

Diagnosis. With characters of genus. Dorsal surface with light mottled pink pigmentation; antennule article 1 about 2.3 times longer than wide, terminal article with eight aesthetascs; left mandible with lacinia mobilis reduced and peg-like, right mandible with lacinia mobilis reduced to thorn; pereopod 1 coxa produced anteriorly into pronounced digitate bulge with four or five associated setae; pleopod basal article with eight setae on outer margin, two setae on inner margin, endopod with six plumose setae on inner margin; uropod with six articles in mature individuals. Sexes similar.

Material examined. Holotype. Male ( NMV J56137 View Materials ), 4.4 mm, Cape Jaffa, SA (36°50.646’S 139°41.360’E), 16 m depth, within gastropod shells attached to macroalga, 13 Mar 1996. GoogleMaps

Paratypes. Five males, two females, one adult not removed from gastropod shell, five indeterminate animals ( NMV J56138 View Materials ), holotype location .

Description. FEMALE.

Body ( Fig. 40 View FIGURE 40 ). Large, length to 5.4 mm; preserved specimens with light mottled pink pigmentation extending most prominently on cephalothorax, propodus of chelipeds, antennae and articles 1 and 3 of antennules.

Cephalothorax rounded and narrowing anteriorly in dorsal view, with slight medial inflection, length slightly less than width and about one-fifth body length.

Pereon occupies about 48% of total length; pereonites with several setae along anterio-dorsal and lateral margins; pereonite 1 length about one-fifth width; pereonite 2 slightly shorter then pereonite 3 but otherwise 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 slightly in length and width, each about four-fifths length of preceding segment; pleonites 4 and 5 together as long as pleonite 3.

Pleotelson length similar 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, two or three long setae dorso-laterally.

Antennule ( Fig. 40 View FIGURE 40 ). Article 1 about 2.3 times longer than wide, with small pappose setae and simple setae along lateral margin and numerous simple and pappose setae distally; article 2 about two-fifths length of article 1, with numerous simple and pappose setae distally; article 3 about two-third length of article 2, with about five setae distally; article 4 greatly reduced and cap-shaped, with numerous long setae and eight aesthetascs.

Antenna ( Fig. 40 View FIGURE 40 ). Article 1 as long as wide, lacking setae; article 2 slightly longer than wide, about 1.5 times length of article 1, with two small setae on lateral margin and two setae distally; article 3 half length of article 2, lacking setae; article 4 twice length of article 3, with about eight long simple setae and pappose seta distally; article 5 three-quarters length of article 4, with five or six simple setae and three or four pappose setae distally; article 6 length similar to width, with several long setae; seventh article reduced to small terminal cap with numerous long setae.

Mouthparts ( Fig. 41 View FIGURE 41 ). Labrum distally carpeted by fine setules.

Left mandible with lacinia mobilis peg-like and possessing spiniform seta at base, pars incisiva smooth and acute, pars molaris broad and corrugated; right mandible with lacinia mobilis reduced to thorn with spiniform seta, pars incisiva smooth, rounded and slightly bifurcated, pars molaris broad and corrugated.

Labium with inner and outer lobes covered by fine setae near distal margins, outer lobe with small 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 long setae.

Maxilliped coxa and basis not joined medially; basis with three or four long setae distally; endite with two small spiniform setae medially, two or three spiniform setae medio-distally and two pappose setae distally; palp with four articles, article 1 slightly longer than wide with three long setae distally on outer margin, article 2 slightly longer than article 1 with three setae distal on outer margin, six or seven very long setae extending distally in a row from midway along inner margin to outer margin and two long setae distally, article 3 smaller than article 2 and fringed with two rows of six to eight long setae along inner margin, article 4 slightly shorter than article 3 and half width, with a long seta distally on outer margin, and two adjacent rows of four to six setae distally on inner margin.

Epignath with relatively small terminal circumplumose seta and fringed by fine setules.

Cheliped ( Fig. 40 View FIGURE 40 ). Basis slightly longer than wide with two setae near distal ventral margin; merus triangular with about six setae three-quarters distance along ventral margin and three setae central; carpus similar in length to basis, with five setae distal on ventral margin, four distal dorsal setae and single seta midway along dorsal margin; propodus similar in length to carpus, with large terminal spiniform seta, about seven setae midway along ventral margin increasing in size in distal direction, about 12 setae along dorsal margin of fixed finger and five simple setae and long pappose seta near articulation with dactylus; dactylus with row of very short setae along ventral margin, unguis short and solid, about one-fifth total length of dactylus.

Pereopod 1 ( Fig. 42 View FIGURE 42 ). Coxa produced anteriorly into pronounced digitate bulge with four or five associated setae; basis length approximately four times width; merus about one-quarter length of basis; carpus slightly longer than merus; propodus length similar to merus and carpus together, with row of eight setae near distal ventral margin, pappose seta two-thirds distance along dorsal margin and long distal dorsal seta; unguis half length of dactylus.

Pereopods 2 and 3 ( Fig. 42 View FIGURE 42 ). Similar, basis length approximately three times width, length less than merus, carpus and propodus together; merus two-fifths length of basis, with short spiniform distal ventral seta, four simple adjacent setae, and simple distal dorsal seta; carpus two-thirds length of merus, eight to ten ser- rated spiniform setae along distal margin with dorsal spiniform seta largest; propodus slightly longer than carpus; unguis more than half length of dactylus.

Pereopods 4 and 5 ( Fig. 42 View FIGURE 42 ). Similar; basis length double width; merus with two distal ventral spiniform setae; carpus with two adjacent rows of five and seven serrated spiniform setae around distal margin; propodus length similar to carpus, with about five long simple setae and pappose seta on distal margin; unguis merged into claw-like dactylus, with lateral comb-like rows of about six flattened setae that project across the ventral margin.

Pereopod 6 ( Fig. 42 View FIGURE 42 ). Basis length 2.5 times width; merus with two distal ventral spiniform setae and about five simple setae; carpus with two adjacent rows of five and seven spiniform setae; propodus with distal comb-like row of about twelve flattened denticulate setae and more dorsal group of about six longer denticulate setae; dactylus with lateral comb-like row of about eight flattened setae that project well across the ventral margin.

Pleopods 1–3 ( Fig. 42 View FIGURE 42 ). Similar; basal article with eight plumose setae along outer margin and two plumose seta on inner margin; exopod with numerous plumose setae along outer margin; endopod with six plumose setae along inner margin, large terminal circumplumose seta and numerous plumose setae along outer margin.

Uropod ( Fig. 40 View FIGURE 40 ). Six articles; basal article length slightly twice width, with two distal groups of three setae; articles 2, 3, 4 and 6 length about half length of article 1, each with distal pappose seta and simple setae that increase in number in distal direction; article 5 length 1.5 times that of adjacent articles.

MALE. Similar to female.

Etymology. Named in honour of Scoresby Shepherd for contributions to South Australian marine science and conservation.

Distribution. Only known from the type locality off Cape Jaffa, SA. 16 m depth.

Remarks. Assignment of this tanaid to genus is complicated by an overlap in characters used to distinguish the three genera ( Anatanais , Zeuxo and Zeuxoides ) of the tribe Anatanaini of Sieg (1980b), a grouping to which Zeuxo shepherdi belongs. Zeuxo shepherdi differs from other species of Zeuxo in possessing numerous (eight) terminal aesthetascs on the antennules and greater setation on pleonites, from species of Zeuxoides in possessing an elongate terminal uropod article, and also from both these genera in lacking sexual dimorphism. The extent of sexual dimorphism within Zeuxo is, however, variable, ranging from strong to barely present, while the maximum number of antennule aesthetascs and number of pleonite setae for known Zeuxo species approaches that seen in Z. shepherdi ; consequently Z. shepherdi is assigned to Zeuxo , but with an expanded generic diagnosis.

Zeuxo shepherdi differs from species of Anatanais in its strongly digitate coxa of pereopod 1, presence of numerous terminal aesthetascs on the antennules, two rather than one setae on inner margin of pleopod basis, and six rather than two plumose setae on the inner margin of the pleopod endopod. Sieg (1980b) also regards a relatively short antennule first article (i.e. approximately twice second article length) as an important characteristic of Anatanais . The ratio of first to second antennule article length is about 2.5 in Z. shepherdi , greater than in Anatanais , similar to Zeuxoides , and less than in Zeuxo .

Regardless of assignation to Zeuxo , Z. shepherdi is most similar in general morphology to the New Zealand species Anatanais novaezelandiae amongst known taxa, as figured by Sieg (1980b). Characters shared between these species include reduced lacinia mobilis of right mandible (albeit more reduced in Z. shepherdi than A. novaezelandiae ), robust antennule, maxillule palp with four or five long setae, six segmented uropod, numerous setae on outer margin of basal article of pleopods, lack of sexual dimorphism, and strongly produced lobe on coxa of pereopod 1 (see Sieg 1980b).

Zeuxo shepherdi sits inside the aperture of small gastropod shells within a hole encircled by cemented sand grains, a similar habit to that shown by species of the apseudomorph tanaidacean genus Pagurapseudes . The shells themselves are bonded to macroalgae or sessile invertebrates.