Zeuxo Templeton 1840, n.comb.
Creators: name: Bird, Graham J
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Tanaidacea
Tanaididae
Zeuxo

description: Zeuxo Templeton, 1840
Species included (New Zealand and Australasian species in bold): Zeuxo (Parazeuxo) coralensis Sieg; Z. (P.) exsargasso Sieg; Z. (P.) kurilensis Kussakin & Tsareva; Z. (P.) phytalensis Sieg; Z. (P.) seurati (Nobile); Z. (P.) zorro Bamber & Bird; Zeuxo (Zeuxo) angua Bamber; Z. (Z.) fresii Sieg; Zeuxo (Z.) holdichi Bamber; Z. (Z.) nannioggae Bamber; Z. (Z.) normani Richardson; Z. (Z.) novaezealandiae (Thomson) n.comb.; Z. (Z.) paranormani Sieg; Z. (Z.) simonsiensis Sieg; Z. (Z.) vanhoeffeni Sieg; Z. (P.) cloacarattus Bamber; Z. belli Edgar; Z. kirkmani Edgar; Z. mooneyi Edgar; Z. odoughertyae Edgar; Z. russi Edgar; Z. shepherdi Edgar.
Zeuxo remains the most speciose of the Tribe Anatanaini. The two subgenera recognised by Sieg (s.g. Zeuxo and s.g. Parazeuxo) were based on differences in the presence/absence of a process on the pereopod-1 coxa (with: Zeuxo, or without: Parazeuxo), one (Parazeuxo) or two (Zeuxo) tergal setae on the merus of pereopods 4–6, and the number of inner setae on the pleopod endopod (one: Parazeuxo, three or four: Zeuxo). Intrageneric species discrimination is based on character states expressed by the antennule, mandibles, pereopods (coxa and setation), pleopods, uropods, etc.
It is quite possible that Aviatanais Bamber, 2005 (Tribe Pancolini) is a close relative of these two genera, differing only in the partial fusion of pleonite-5 with the pleotelson, a character also seen in some specimens of Pancoloides moverleyi Edgar (Bird ined.). The reduced nature of the outer labial processes is also not beyond the range shown by some species of Zeuxo and Zeuxoides and exposes the inherent weakness in the current classification of subfamilies and tribes (see above). The increasingly species-rich genus Zeuxo is possibly polyphyletic and a challenge to Linnaean classification, but only a careful phylogenetic or molecular analysis can confirm the existence of discrete monophyletic (or potential genera) within this taxon.
Zeuxo (Zeuxo) novaezealandiae (Thomson, 1879) n.comb. Figs 1–6
Tanais novae-zealandiae: Thomson (1879): 417 –418, plate XIXX figs 5–6; Thomson (1880): 207, fig.3; Chilton (1909): 606, 609.
Tanais novae-zealandiae: Tattersall (1921): 198, plate I figs. 1–5 non Tanais novaezealandiae Thomson.
Tanais novae-zeelandiae Nierstraz (1913): 23 lapsus calami.
Tanais novaezealandiae: G.O. Sars (1882): 24; G.O. Sars (1886): 311; Fincham (1974): 7, 8 (probable synonymy); Rainer (1981): 16 (table 2), 17 (table 3), 18 (table 4).
Tanais neo-zelanica: Thomson & Chilton (1885): 151.
Anatanais novae-zealandiae: Stephensen (1936): 371
Anatanais novaezealandiae: Sieg (1980): 157–162, fig. 43 non Tanais novaezealandiae Thomson
[Restricted synonymy and bibliography largely confined to tracking nomenclatural changes and/or reference to distribution records. Many of the other references in the extensive bibliography given by Sieg (1980, 1983b) are secondary and derivative].
Diagnosis. Zeuxo with antennule slender, 2.3–2.7 times longer than broad, article-2 twice as long as broad. Right mandible with peg-like lacinia mobilis and setal row of two small spines; left mandible with tooth-like lacinia mobilis and small bifid accessory spine. Pereopod-1 coxa with prominent, three or four-dentate spur; pereopods 2–3 with seven to nine carpal spines; pereopods 4–6 with 12–14 carpal spines. Pleopod basis with five inner and 13 outer plumose setae; exopod with eight inner plumose setae. Uropod five or sixarticled (rarely seven-articled). Sexual dimorphism moderate, copulatory male with longer antennule and chelae more robust and with straighter incisive margins.
Material examined. Neotype (here designated): one preparatory Ψ, Rainer Stn B12, (NMNZ Cr. 012181).
Associated material: one ɗ, Rainer Stn C11, (NMNZ Cr. 012183); ten small prep. ΨΨ (NMNZ Cr. 012185), ten large prep. ΨΨ (NMNZ Cr. 012184), ten prep. ɗɗ, (NMNZ Cr. 012186), ten ɗɗ (NMNZ Cr. 012187), five large neuters/non-ovigerous ΨΨ, (NMNZ Cr. 012188) - all from Stn B12; one ɗ,?G.M. Thomson material, (NIWA.44928).
Additional material: one neuter, two prep. ΨΨ (NIWA.27335); one ovigerous Ψ (NIWA.27337); one prep. Ψ (NIWA.27340); one neuter? one prep. Ψ (NIWA.27343); 26 individuals (NIWA.27344); one prep. Ψ (NIWA.27347); one neuter? (NIWA.27350); ca.460 individuals, Ports-NZ 1 CHT 191-TN (NIWA.44893); 393 individuals, Ports-NZ 1 CHT 193-TN (NIWA.44894); three ɗɗ, Ports-NZ 1STW067-TN (NIWA.44895); 14 prep. ΨΨ, 16 ovig. ΨΨ, 22 ɗɗ, ca. 22 others, Ports-NZ 1STW069-TN (NIWA.44896); twelve ovig. ΨΨ, 13 prep. ΨΨ, 17 ɗɗ, Ports-NZ 1STW070-TN (NIWA.44897); twelve individuals, Ports-NZ 1STW071-TN (NIWA.44898); 15 neuters, four ovig. ΨΨ, two prep. ɗɗ, eleven ɗɗ, Ports-NZ 1STW120-TN (NIWA.44899); one neuter, two ΨΨ, Ports-NZ 1STW162-TN (NIWA.44900); one ɗ, Ports-NZ 1STW284-TN (NIWA.44901); one ɗ, Ports-NZ 1STW309-TN (NIWA.44902); three neuters, two prep. ΨΨ, two ɗɗ, Ports-NZ 1STW347-TN (NIWA.44903); ca. 16 individuals, Ports-NZ 1STW349-TN (NIWA.44904); four neuters, one prep. Ψ, three ɗɗ, Ports-NZ 1STW352-TN (NIWA.44905); three neuters, eleven prep. ΨΨ, one ovig. Ψ, four prep. ɗɗ, four ɗɗ, plus ca.40 individuals, SA-3498 (NMNZ Cr. 012147); twelve neuters, five prep. ΨΨ, one ovig. Ψ, four ɗɗ, F24 (NMNZ Cr. 012172); three neuters, four prep. ΨΨ, two prep. ɗɗ, one ɗ, two indeterminate stage (indet.), McArthur Stn 4.1.1; 18 neuters, 29 prep. ΨΨ, six ovig. ΨΨ, 15 prep. ɗɗ, 18 ɗɗ, McArthur Stn 4.2.4; two neuters, one prep. Ψ, one ɗ, McArthur Stn 5.2.4; one neuter, four prep. ΨΨ, four prep. ɗɗ, two ɗɗ; McArthur Stn 5.3.7; one neuter, three prep. ΨΨ, one ovig. Ψ, one ɗ, (NMNZ Cr.12150); 39 neuters/indet., 138 prep. ΨΨ, 81 prep. ɗɗ, 68 ɗɗ, Rainer Stn B12 (NMNZ Cr.004371); 13 neuters, nine prep. ΨΨ, three ovig. ΨΨ, seven ɗɗ, Rainer Stn C10; 20 neuters, 24 prep.Ψ, five ovig. ΨΨ; four prep. ɗ, eleven ɗɗ, two indet., Rainer Stn C11.
Description. Preparatory female: Body (Fig 1 A, C) fairly stout, 5.7 times longer than broad (neotype), length 2.66–7.51 mm (neotype 6.38 mm). Purple-brown pigmentation on most of the dorsal surface including antennules and dorsum of cheliped propodus, patterned with un-pigmented lacunae (spots and patches). Cephalothorax just longer than pereonites 1–3, slightly longer than broad, with narrow distal margin and shallow convex rostrum; eye-lobes conical; several small setae just posterior to eye. Pereon 53% of body length; pereonite-1 shortest, with coxal process of pereopod-1 clearly visible in dorsal view; pereonites 2–3 progressively longer; pereonites 4–5 shorter than broad, sub-hexagonal in outline; all pereonites with small lateral setae. Pleon (Fig. 1 B) 21% of body length, pleonites 1–3 progressively smaller, with about three simple setae dorso-laterally, from one (pleonite-1) to ten (pleonite-3) plumose lateral setae and about six plumose setae in dorso-lateral group; pleonites 4–5 with one (pleonite-4) or two unequal lateral setae and two dorsal setae. Pleotelson (Fig. 1 B) about as long as pleonites 4–5, with two unequal lateral setae, with weakly triangular apex bearing two long setae, and each termino-lateral margin with three setae (one pinnate).
Antennule (Fig. 2 A). Four-articled; two-thirds length of carapace, slender; article-1 58% of total length, 6.6 times longer than broad (mid-point) and 2.3–2.65 times longer than article-2 (2.6 times, neotype), with setulose inner basal margin, four simple setae and about three pinnate setae in distolateral group and one pinnate and two simple setae in disto-medial group; article-2 twice as long as broad, with about seven simple and four pinnate distal setae; article-3 0.8 times as long as article-2, three times as long as broad, with four distal simple setae, and one pinnate seta; article-4 small and cap-like, with about five long simple setae, one short pinnate seta and three long, semi-annulated aesthetascs; other setation as figured. Antenna (Fig. 2 B). Sevenarticled; about 0.8 times as long as antennule; article-1 as long as broad, with small dorsal setules; article-2 over twice as long as previous article, with dorsal setules and two distal and two medial setae; article-3 short, with dorso-distal seta; article-4 as long as article-2 but 2.8 times longer than broad, with medial seta and about seven simple and one pinnate distal setae; article-5 shorter than article-4, with about three simple and five pinnate setae; article-6 small but with about seven long setae (over-reaching those of article-7); article-7 very small, almost obscured by setal insertions, with about five long setae, one short seta and at least one pinnate seta.
Labrum (Fig. 3 A). Typical of genus, hood-shaped, highly setulose distally. Mandibles (Figs 3 B–C). Well calcified, strong, typical of genus, molars with highly ridged grinding surface set with pectinate setae; right mandible with small conical lacinia mobilis and setal row of two small spines; left mandible with tooth-like lacinia mobilis and setal row of one small bifid spine. Labium (Fig. 3 D). Typical of genus, with conical inner lobes set with numerous distal setules and combs; outer lobes with setose outer margin and conical process, also setose. Maxillule (Fig. 3 E). Typical of genus, palp with eight long terminal setae; endite with minutely setulose distal margin, group of small distal setae and nine spiniform terminal setae, at least five being pectinate. Maxilliped (Fig. 3 F–H). Large, with cardiform bases, each with posterior lobe bearing four setae and a disto-ventral seta; endites almost reaching end of palp article-2, with rounded and heavily setose lateral margin, two coupling hooks, two short, strong medial setae and two longer pectinate disto-medial setae; palp highly setose, article-1 with lateral setulose margin and simple seta; article-2 longer, with lateral seta, eight long disto-medial setae and two disto-medial pectinate setae; article-3 with double row (each eight or nine) of medial setae,; article-4 narrow, with proximal setae, one disto-lateral seta, about three finely pectinate terminal setae and double row (each six or seven) of disto-medial setae. Epignath (Fig. 3 J). Typical of genus, with setulose margin and one terminal seta.
Cheliped (Figs 4 A–B). Stout, separated from carapace by a triangular sclerite; basis with well rounded free posterior margin, with one ventral seta; merus subtriangular, with three unequal ventral setae; carpus 1.8 times as long as broad, with one proximal dorsal seta, four disto-dorsal setae and six ventral/lateral setae; propodus as long as carpus, just over twice as long as broad, with two unequal setae near lateral dactylar insertion and one large pectinate seta on medial face; fixed finger with five ventral setae, two medio-distal setae and seven lateral setae near incisive margin, this being weakly convex and finely ridged; dactylus tapering to narrow point, with numerous stout peg-like setae on incisive margin and one disto-medial seta.
Pereopod-1 (Fig. 5 A–B). More slender than pereopods 2–3; coxa with prominent anterior spur with three cusps and five unequal setae; ischio-basis 4.7 times longer than broad, with two simple and one pinnate proximal setae, and one terminal seta; merus with one small ventral and one longer dorsal seta; carpus subrectangular, longer than merus and twice as long as broad, with three distal setae; propodus as long as merus and carpus together, with two dorsal setae and five disto-ventral setae, as well as some smaller distal setules; dactylus and unguis together 0.75 times as long as propodus, dactylus with small accessory seta.
Pereopod-2 (Fig. 5 C). Coxa annular, with seta; ischio-basis just over three times as long as broad, with proximal simple and two pinnate setae, and two unequal terminal setae; merus larger than carpus, with numerous michrotrichia on ventral margin, one stout spine, four ventral setae and one dorsal seta; carpus just over half length of merus, 1.3 times longer than broad, with many michrotrichia, seven complex spines, three ventral and two dorsal simple setae; propodus half as broad as carpus, 1.5 times as long, with many michrotrichia, five ventral setae and two unequal dorsal setae; dactylus and unguis two-thirds length of propodus, dactylus shorter than unguis, with small accessory seta.
Pereopod-3 (Fig, 5D). Similar to pereopod-2 but merus and propodus slightly shorter.
Pereopod-4 (Figs 5 E–G, 6C). Ischio-basis stouter than pereopods 2–3, 2.3 times as long as broad, with dorsal and ventral pinnate setae, and two terminal setae; merus more slender than pereopods 2–3, with michrotrichia, three dorsal setae, two ventral setae and three complex spines; carpus about two-thirds length of merus, with many michrotrichia, five distal setae and two rows (five and seven) of complex spines; propodus just longer and narrower than, carpus, with ventral setules/michrotrichia, two ventral setae, one dorso-distal pinnate seta, two large dorso-distal setae and two smaller distal setae; claw strongly hook-shaped, proximal ventral margin spinose, and with double row of spiniform comb setae.
Pereopod-5 (Fig. 5 H). Similar to pereopod-4 but ischio-basis with additional pinnate seta, merus with two ventral spines, carpus with fourteen complex spines.
Pereopod-6 (Figs 5 I–J). Similar to pereopod-5, but ischio-basis with fewer pinnate setae, propodus with three ventral setae and distal comb of about 20 blade-like setae.
Pleopod (Fig. 6 A). All pleopods similar in size; basal article with five inner and thirteen outer marginal setae; endopod with six proximal inner and 24 outer marginal setae; exopod with about 50 outer marginal setae; all setae pinnate.
Uropod (Fig. 6 B). Six-articled, basal article as long as articles 2–3 together; articles 2–6 all longer than broad, with both long simple setae and pinnate setae (as figured).
[N.B. Small preparatory female. As above but antennule (Fig. 2 C) stouter; pereopod-1 coxa (Fig.6 D) with fewer cusps and setae; pereopods 4–6 (Fig. 6 E–G) with fewer carpal spines and propodal blade spines; pleopod (Fig. 6 H) basis with one inner and seven outer plumose setae, exopod with four inner and 15 outer setae, endopod with 35 setae; uropod (Fig. 6 I) five-articled. Length ca. 3 mm].
Neuter/non-ovigerous female. As preparatory female or small preparatory female (depending on size) but without conical oostegite buds attached posterior to pereopods 4. Antennule article 1:2 ratio wider (1.9–2.6). Uropod four, five or six-articled. Length 1.33–6.41 mm.
Ovigerous female. As preparatory female, but more dorso-ventrally compressed, with two ovisacs attached behind pereopod-4. Uropod six-articled. Length 4.05–6.13 mm.
Preparatory male. Very similar to female, but with two genital cones (Figs 6 J–K) on ventrum of pereonite 6, even if visible only as unraised pores in early moult stages. Antennule article 1:2 ratio 2.3–3.0. Cheliped (Fig. 4 C) shows some degree of enlargement (especially carpus in early stages) depending on size. Uropod four or five-articled, rarely six-articled. Length 2.6–4.60 mm.
Copulatory male (Fig. 1 D). Generally as female but cephalothorax slightly more triangular; pereon slightly broader; distinct genital cones on pereonite-6. Antennule (Fig. 2 D) longer than in female, 0.8 times as long as cephalothorax, article-1 4.6 times as long as broad, 2.6–3.3 times longer than article-2 (neotype male figured) terminal article with four aesthetascs. Cheliped (Figs 4 D–E) proportionately much larger, carpus stouter, 1.4 times longer than broad; fixed finger with straighter incisive margin and dactylus without ventral setae and with broader, more medial insertion into propodus. Uropod five or six-articled. Length 3.23–5.42 mm.
Manca. Not known as yet.
Distribution: Comprehensive records are not yet available but the current distribution in New Zealand appears to be southerly, extending from the Snares, Stewart Island (Fincham 1974), Fjiordland (Dusky Sound), Otago Harbour (Rainer 1981), and Papanui Inlet (Banks Peninsula), Wellington and the Chatham Islands. Habitat is primarily intertidal and shallow muddy-sand but a few records are from under stones or among hydroids (Table 1). Population densities of up to 15,000 m -2 have been recorded (McArthur pers.comm.).
Remarks: Compared to A. novaezealandiae sensu Sieg (1980) the Otago species is more slender, has longer antennules, and has a quite different mandible structure. The prominent digitate pereopod-1 coxal spur is very similar to that of Z. shepherdi but similar processes occur throughout the genera Anatanais, Zeuxo and Zeuxoides although it is not clear if cusps or digitations have been properly observed. Its body shape and slen- der antennules are similar to those of A. lineatus but the antennule ratio and strong sexual dimorphism (at least for chelipeds) really preclude its inclusion in Anatanais (as defined by Sieg).
Of the Australian Zeuxo species, Z. odoughertyae and Z. kirkmani are very close matches in terms of the number of uropod articles and in mandible structure, the mandible of the first actually being identical. However, compared to Z. odoughertyae, Z. novaezealandiae has shorter pereonites 1–3, a different antennal setation, a more slender cheliped carpus, a longer pereopod-1 coxal spur, more carpal spines on pereopods 4–6 and has a different pleopod setation (basis with five inner and 13 outer, endopod with six inner setae, as against one, nine and five respectively). These numeric comparisons are made with some caution in view of allometric changes but individuals of Z. novaezealandiae of 4 to 5 mm length (for comparison with the Z. odoughertyae female of 4.5 mm) have five or six-articled uropods (but proportionately more of the latter), and only one has been recorded with the seven-articled uropod state described for the Australian species. In view of the zoogeographic relationships it might be hypothesised that Z. novaezealandiae and Z. odoughertyae are sibling species, derived from a common ancestor, or that the first possibly originated from the second.
As outlined above, the identity of G.M. Thomson’s species is clouded by several factors, so that establishing neotypes is highly problematical – indeed, this may have led Sieg (1980) to base his redescription and change of generic attribution on only a single specimen from the subantarctic Auckland Islands. Thomson’s original drawing is recognisable only as a species of Tanaidae and probably represents a male, with enlarged chelipeds. The relatively long article-1 of the antennule is typical of some male Zeuxoides species and the females and males of some Zeuxo. The uropods appear to be biramous but are probably drawn showing the two uniramous uropods simultaneously; these are shown as being at least five or six-articled but not with sufficient clarity to indicate whether the terminal article is very short or ‘cap-like’ (Zeuxoides) or normal (Zeuxo). Ultimately, no unequivocal identification can be made solely from Thomson’s description and drawings of Tanais novaezealandiae. That a species of Zeuxo is common and abundant in Otago Harbour would appear to lean the decision towards this identity, although a few Zeuxoides specimens are also present in the samples. Additionally, two specimens of Zeuxoides aka n.sp. were recorded from Dunedin Harbour (the precise type locality) in the recent Ports of NZ survey and Zeuxoides rimuwhero n.sp. also appears frequently in shore collections from the Portobello Marine Biology Station/Otago Harbour area, largely made by D.E. Hurley. Of greater significance, a sample of Tanaidae designated as being Thomson’s material has recently been returned to New Zealand (NIWA, Wellington) from the collections of Karl Lang and Jurgen Sieg. No label with collection data remained so the precise provenance cannot be validated, but the sample includes several Zeuxoides specimens and a single Zeuxo. The last is a male with enlarged chelipeds and is of a general shape and size compatible with Thomson’s original drawing and it is not impossible that this is indeed the ‘lost’ holotype.
A more practical consideration relates to usage in the literature and in unpublished records, i.e. whether the Zeuxo or one of the Zeuxoides species is more likely to have been assigned the identity Tanais (or Anatanais) novaezealandiae. This is not a particularly critical issue, as relatively few exist. More significantly, the species identified by Sieg as Anatanais novaezealandiae is clearly not the same as Otago Harbour specimens. Furthermore, an incomplete, partly dissected Zeuxo specimen (from the NIWA collection) collected from the Auckland Islands, identified by J. Sieg and labelled as “ Zeuxo limeniskos “ (a nomen nudum) – appears to be Z. novaezealandiae and supports the contention that he redescribed a different species.
It remains to be discovered if more abundant North Island records of Z. novaezealandiae exist. Also, the specimens from the distant Chatham Islands seem to be externally the same species, although molecular/DNA analysis might reveal if this population is genetically distinct from the main New Zealand populations.
description: Published as part of Bird, Graham J, 2008, Untying the Gordian Knot: on Tanais novaezealandiae Thomson (Crustacea, Tanaidacea, Tanaidae) from New Zealand, with descriptions of two new Zeuxoides species, pp. 1-36 in Zootaxa 1877 on pages 7-18, DOI: 10.5281/zenodo.184126