Zeuxoides lasti, Edgar, 2008

Edgar, Graham J., 2008, Shallow water Tanaidae (Crustacea: Tanaidacea) of Australia, Zootaxa 1836 (1), pp. 1-92 : 29-35

Zeuxoides lasti n. sp.

( Figs 13–15 )

Material examined. Holotype. Male ( NMV J56139 ), 4.2 mm, Governor Island, Bicheno , Tasmania (41°53’S 148°17’E), 10 m depth, kelp ( Lessonia corrugata ) holdfast, 20 May 1993.

Paratypes. Ovigerous female ( NMV J56140 ), holotype location .

Diagnosis. With characters of genus. Antennule article 1 about 2.5 times longer than wide in both sexes, terminal article with five or six (female) and twelve (male) aesthetascs; left mandible with lacinia mobilis tooth-shaped and only slightly reduced, right mandible with lacinia mobilis reduced and thorn-like; pereopod 1 coxa with three setae; pleopod basal article with six to eight setae on outer margin, one seta on inner margin, endopod with four setae on inner margin; uropod with seven articles in mature individuals.

Description. FEMALE

Body ( Fig. 13 ). Length to 4.5 mm; preserved specimens with mottled pigmentation extending prominently from cephalothorax to pleotelson and on chelipeds, antennae and antennules.

Cephalothorax rounded and narrowing anteriorly in dorsal view, length about equal to width and slightly more than one quarter body length.

Pereon occupies about 52% of total length; pereonites with several setae along anterio-dorsal and lateral margins; pereonite 1 length about five times width; pereonite 2 and 3 similar, 1.5 times length of pereonite 1; pereonites 4 and 5 largest, about twice length of pereonite 2, pereonite 6 three-quarters length of pereonite 5.

Pleonites together one sixth as long as body; pleonites 1 and 2 similar, together as long as pereonite 6, with long plumose setae extending from margins part way on to the dorso-lateral surface; pleonite 3 slightly shorter than pleonite 2; pleonites 4 and 5 similar, together as long as pleonite 3.

Pleotelson about one-third length of pleonites; posterior margin with pair of short setae central between pair of long setae, about five long and two short setae anterior to articulation with uropod.

Antennule ( Fig. 13 ). Article 1 about 2.4 times longer than wide, three small pappose setae and about three long setae along outer margin and two clusters of several simple setae with single pappose seta distally; article 2 about one-third length of article 1, length about equal to width, with clusters of about five simple setae and about five simple setae plus pappose seta distally; article 3 about half length of article 2, with about five setae distally; article 4 greatly reduced and cap-shaped, with numerous long setae and five or six aesthetascs.

Antenna ( Fig. 13 ). Article 1 as long as wide, lacking setae; article 2 almost twice length of article 1, with two to four small setae on outer margin and two distal setae; article 3 half length of article 2, lacking setae; article 4 twice length of article 3, with several long distal simple setae and a pappose seta; article 5 two-thirds length of article 4, with about four simple distal setae and two pappose setae; sixth and seventh articles greatly reduced, much wider than long, with numerous long setae.

Mouthparts ( Fig. 14 ). Labrum carpeted by fine setae, longest setae associated with distal lateral margins.

Left mandible with lacinia mobilis tooth-shaped and only slightly reduced, with two large basal denticulate setae, pars incisiva smooth and rounded, pars molaris broad and corrugated; right mandible with lacinia mobilis reduced and thorn-like, with two large basal denticulate setae, pars incisiva smooth and blunt, pars molaris broad and corrugated.

Labium with inner and outer lobes covered in fine setae distally, outer lobe with small elongate terminal process and small spines projecting from proximal lateral margins.

Maxillule endite with eight large terminal spiniform setae, long simple seta, and cluster of fine setae on outer margin near base of spinous setae; palp with six long simple setae.

Maxilliped coxa and basis not joined medially; coxa with two large proximo-medial setae; basis finely setose marginally, with three distal setae; endite finely setulose marginally, with two short spiniform setae distal near medial margin, two short spiniform setae medial on distal margin, and two distal scythe-shaped circumplumose setae that are considerably shorter than setae on inner margin of palp; palp with four articles, article 1 slightly wider than long with two long setae distally on outer margin, article 2 slightly longer than article 1 with single seta on outer margin, four or five long setae extending distally in a row from midway near inner margin, three long distal setae and three long setae on distal margin, article 3 slightly shorter in length than article 2, fringed with two rows of about seven long setae along inner margin, article 4 approximately two-thirds length of article 3 with two rows of about six long setae distally on inner margin and single seta on outer margin.

Epignath with terminal circumplumose seta and fringed by fine setules.

Cheliped ( Fig. 13 ). Sclerite with two distal setae near dorsal margin; basis longer than wide with two distal setae near ventral margin; merus triangular with group of about four setae two-thirds distance along ventral margin, one or two setae central; carpus similar in length to basis, with four to six setae distal on ventral margin, distal dorsal group of four or five setae, and single seta one-third distance along dorsal margin; propodus similar in length to carpus, with large terminal spiniform seta, about seven setae midway along ventral margin, about ten setae near dorsal margin of fixed finger and three simple setae and single 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. 15 ). Coxa produced into anterior process with three setae; basis length approximately five times width; merus about one-quarter length of basis; carpus 1.5 times length of merus; propodus almost length of merus and carpus together, with about six setae near distal ventral margin, long seta near distal dorsal margin and pappose seta; unguis three-fifths length of dactylus.

Pereopods 2 and 3 ( Fig. 15 ). Similar; basis width between one-third and one-quarter length, slightly shorter than merus, carpus and propodus together, dorso-distal corner projecting over merus; merus two-fifths length of basis, with two short spiniform setae and three simple setae distal on ventral margin and simple seta dorso-distally; carpus between one-half and two-thirds length of merus, eight to ten serrated spiniform setae along distal margin with dorsal spiniform seta longest; propodus 1.5 times length of carpus, with pappose seta, several distal setae and three setae evenly spaced along ventral margin; unguis three-fifths length of dactylus.

Pereopods 4 and 5 ( Fig. 15 ). Similar; basis width almost half length, dorso-distal corner projecting over merus; merus two-fifths length of basis, with two short spiniform setae and about three simple setae distal on ventral margin and about four simple seta dorso-distally; carpus with two parallel rows of six or seven serrated spiniform setae around distal margin; propodus 1.2 times length of merus, with about four setae on ventral margin and pappose seta plus two long simple setae distal near dorsal margin; unguis merged into claw-like dactylus, with lateral comb-like row of about six flattened setae.

Pereopod 6 ( Fig. 15 ). Carpus with two parallel rows of about seven serrated spiniform setae along distal margin; propodus with distal comb-like row of about twelve flattened denticulate setae and dorso-distal group of about five slightly longer denticulate setae and several long simple setae; dactylus with lateral comb-like row of about eight flattened setae.

Pleopods 1–3 ( Fig. 15 ). Similar; basal article with six to eight plumose setae along outer margin and one plumose seta on inner margin; exopod with numerous plumose setae along outer margin; endopod with four plumose setae along inner margin, large terminal circumplumose seta and about eighteen plumose setae along outer margin.

Uropod ( Fig. 15 ). Seven articles; basal article length nearly twice width, with about six very long distal setae; article 2 half length of basal article; articles 3, 4, 5 and 6 with length similar to article 2, up to eight long simple setae distally and occasional pappose seta; article 7 reduced to about one-third length of article 6, with numerous very long terminal setae.

MALE. Similar to female, other than

Antennule ( Fig. 13 ). About 12 aesthetascs projecting from terminal article.

Cheliped ( Fig. 13 ). Articles with greater width relative to length than female, basis length equal to width.

Etymology. Named after Peter Last, in recognition to his contribution to studies of Tasmanian marine species and habitats.

Distribution. Tasmania. 1–10 m depth.

Remarks. Zeuxoides lasti closely resembles Zeuxoides spongicola , a tanaid recorded from the southwestern coast of Africa ( Sieg, 1980b). Features shared by these two species include similarities in level of reduction of lacinia mobilis of mandibles, form of pereopod 1 coxa, number of aesthetascs on antennule, and number of setae on maxillule palp. Zeuxo lasti differs from Z. spongicola primarily by possessing a relatively short article 1 of antennule, with a length/breadth ratio of 2.4 compared to 4 for Z. spongicola , an extra uropod article, and two rather than one denticulate setae associated with the lacinia mobilis of the left mandible. The Australian species also possesses more setae on antennules, antennae and pleotelson, and four plumose setae on the inner margin of the pleopod endopod.

With the exception of Zeuxoides casanunda , Z. lasti can be distinguished without dissection from other Australian species in Zeuxoides and the closely-related genus Zeuxo because of conspicuous plumose setae that extend around lateral margins onto the dorsal surface of pleonites 1 and 2. It differs from Zeuxoides casanunda , the only previously reported species in this genus from Australia ( Bamber 2005), in lesser reduction of lacinia mobilis of right mandible, greater number of antennule aesthetascs, and more numerous spiniform setae on carpus of pereopods 2-6.

Figures

FIGURE 13. Zeuxoides lasti n. sp. Governor Island, Tas. Female dorsal (paratype), male dorsal (holotype; pigmentation not shown), antennules (A1), antennae (A2), chelipeds (CH), pleotelson (Plt). Scale units 0.1 mm (appendages) and 1 mm (dorsal).

FIGURE 14. Zeuxoides lasti n. sp. Governor Island, Tas. Labrum (L), left mandible (Mdl), right mandible (Mdr), labium (La), maxillule (Mx), maxilliped (Mxp), epignath (E). Scale units 0.1 mm.

FIGURE 15. Zeuxoides lasti n. sp. Governor Island, Tas. Pereopods 1–6 (P1–P6), pleopod (Pl), uropod (U). Scale units 0.1 mm.