Sinelobus barretti, Edgar, 2008

Edgar, Graham J., 2008, Shallow water Tanaidae (Crustacea: Tanaidacea) of Australia, Zootaxa 1836 (1), pp. 1-92 : 17-23

Sinelobus barretti n. sp.

( Figs 7–9 )

Material examined. Holotype. Male ( NMV J56135 ), 2.4 mm, Cradoc, Huon estuary, Tas (43° 07.135'S 147° 00.697'E), 0.3 m depth, macrophyte washings, Coll. Neville Barrett, 5 Nov 1996.

Paratype. One female ( NMV J56136 ), 2.3 mm, holotype location .

Other material. Three males, four females (two ovigerous), holotype location.

Diagnosis. With characters of genus. Antennule article 1 about 2.5 (female) and 3.5 (male) times as long as wide; left mandible with lacinia mobilis molar-like, broad and with undulating margin; right mandible with lacinia mobilis present as large bifurcated peg-like structure; cheliped propodus with anvil-shaped process on fixed finger that is wider than long and on males extends about half distance to dactylus articulation; dactylus length about twice basal width; pereopod coxa with two setae, lacking pronounced anterior bulge; uropod with four articles in mature animals.

Description. FEMALE

Body ( Fig. 7 ). Small, observed body length to 2.3 mm; preserved specimens with mottled pigmentation on dorsal surface, most prominent towards anterior of cephalothorax, near posterior margin of pereonites and pleonites, and on chelipeds.

Cephalothorax rounded and narrowing anteriorly in dorsal view, length similar to width and one quarter body length.

Pereon occupies about 53% of total length; pereonites with isolated setae along anterio-dorsal and lateral margins; pereonite 1 length about one-fifth width; pereonite 2 slightly longer than pereonite 1; pereonite 3 one and a half times length of pereonite 2; pereonites 4 and 5 similar, about 1.5 times length of pereonite 3; pereonite 6 about four-fifths length of pereonite 5.

Pleonites together one sixth as long as body; pleonites 1 and 2 similar, each with a prominent row of plumose setae extending transversely around lateral margin onto dorsal surface; pleonite 3 four-fifths length of pleonite 2; pleonite 4 two-thirds length of pleonite 3; pleonite 5 absent.

Pleotelson about length of pleonites 3 and 4 together; posterior margin with pair of short setae central between pair of long setae, two long setae plus shorter pappose seta adjacent to articulation with uropod, one long seta anterio-laterally.

Antennule ( Fig. 7 ). Article 1 about 2.5 times longer than wide, with three pappose setae two-fifths distance along margin, three simple setae and three pappose setae distally; article 2 two-fifths length of article 1, with four or five simple setae and two or three pappose setae distally; article 3 about three-quarters length of article 2, with two to four setae distally; article 4 greatly reduced and cap-shaped, with numerous long setae and two or three aesthetascs.

Antenna ( Fig. 7 ). Article 1 as long as wide, lacking setae; article 2 slightly longer than wide, about 1.5 times length of article 1, with two or three setae distally; article 3 half length of article 2, lacking setae; article 4 twice length of article 3, with single simple and pappose setae distally; article 5 slightly shorter than article 4, more than twice as long as wide, with several pappose and simple setae distally; article 6 reduced to small terminal cap with numerous long setae.

Mouthparts ( Fig. 8 ). Labrum carpeted distally by fine setae.

Left mandible with large digitate lacinia mobilis, pars incisiva broad and crenulated, pars molaris broad; right mandible with lacinia mobilis present as large bifurcated peg-like structure, pars incisiva smooth and acute, pars molaris broad.

Labium with inner and outer lobes covered by fine setae near distal margins; outer lobe rounded, with fine spines on lateral margin, lacking terminal process.

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

Maxilliped coxa and basis not joined medially; coxa with long proximo-medial seta and very fine spines on lateral margin; basis with a single long seta medio-distally; endite setose around distal margin, with small spiniform seta medial towards the distal margin and two large circumplumose setae and two simple setae distally; palp with four articles, first wider than long with distal seta and on outer margin and very fine lateral spines, article 2 slightly longer than article 1 with five long setae distally, article 3 similar in size to article 2 and fringed with about nine long setae along inner margin, article 4 similar in length to article 3 but half width, with a seta two-thirds distance along outer margin, two long terminal setae, and two adjacent rows of about four setae distally on inner margin.

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

Cheliped ( Fig. 7 ). Basis longer than wide with single seta near each of ventrodistal and dorsodistal corners; merus triangular with a seta two-thirds distance along ventral margin; carpus 1.5 times length of basis, longer than wide, with a seta distal on ventral margin and two dorso-distal setae; propodus similar in length to carpus, fixed finger flattened into anvil-shaped process that is wider than long and extends about two-thirds distance from large terminal spiniform seta to dactylus articulation, single seta midway along ventral margin, six simple setae near terminal seta along dorsal margin of fixed finger and group of three setae plus a lateral seta near articulation with dactylus; dactylus length about 2.5 times basal width, with row of five or six short setae along ventral margin, projecting ventral spinous process near unguis, unguis short and solid, about onefifth total length of dactylus, with slightly bifurcated tip.

Pereopod 1 ( Fig. 9 ). Coxa barely produced anteriorly with a single seta; basis length approximately four times width; merus about one-third length of basis; carpus slightly longer than merus; propodus 1.5 times length of merus, with two distal setae; unguis one-third length of dactylus.

Pereopods 2 and 3 ( Fig. 9 ). Similar; basis width one-third length; merus two-fifths length of basis, with short spiniform seta and long simple setae ventro-distally; carpus two-thirds length of merus, parallel series of two and three serrated spiniform setae along distal margin; propodus 1.5 times length of carpus; unguis nearly half length of dactylus.

Pereopods 4 and 5 ( Fig. 9 ). Similar; basis width almost half length; merus with a pair of large ventro-distal spiniform setae; carpus with adjacent rows of two and three serrated spiniform setae along distal margin; propodus length similar to merus, with seta near distal ventral margin and pappose seta plus two or three long simple setae near distal dorsal margin; unguis merged into claw-like dactylus, with comb-like lateral rows of about twelve flattened setae on the two sides.

Pereopod 6 ( Fig. 9 ). Carpus with parallel rows of two and three spiniform setae around distal margin; propodus with distal comb-like row of about six flattened denticulate setae and dorso-distal pair of long denticulate setae and pappose seta; dactylus with lateral comb-like rows of about twelve setae.

Pleopods 1–3 ( Fig. 9 ). Similar; basal article with six 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 along inner margin, large terminal circumplumose seta and numerous plumose setae along outer margin.

Uropod ( Fig. 9 ). Four articles, basal article length 1.5 times width, three long setae distally, article 2 twothirds length of basis and lacking setae, article 3 twice length of article 2 with two long simple setae and two pappose setae, article 4 two-thirds length of article 3 with five long simple setae and a pappose seta.

MALE. Similar to female, other than

Body ( Fig. 7 ). Cephalothorax pear-shaped, slightly longer than wide, with prominent concavity affecting anterior two-thirds of lateral margin.

Pereon about 48% of total length.

Pleonites together one seventh as long as body.

Antennule ( Fig. 7 ). Article 1 about 3.5 times longer than wide.

Antenna ( Fig. 7 ). All articles more elongate than in female, article 2 twice as long as article 1.

Cheliped ( Fig. 7 ). All articles proportionately wider than in female; basis length similar to width; propodus with anvil-shaped process on fixed finger that is wider than long and extends about half distance from large terminal spiniform seta to dactylus articulation; dactylus length about twice basal width.

Etymology. Named after Neville Barrett, collector of the type specimens, in recognition to his contribution to marine science and conservation in Tasmania.

Distribution. Cradoc, Huon estuary, Tasmania, 0–1 m depth.

Remarks. This species shares with the genera Sinelobus and Tanais a reduction of the pleon to four segments. It differs from Tanais and agrees with Sinelobus in possessing an anvil-shaped propodal fixed finger, relatively few antennule aesthetascs, antenna with six articles, maxillule palp with two long setae, and single plumose seta on endopod inner margin.

Sinelobus was regarded by Sieg (1980b) as monotypic, comprising a single cosmopolitan species Sinelobus stanfordi that encompassed five synonyms ( Tanais philetaerus Stebbing, 1904 , Tanais fluviatilis Giambiagi, 1923 , Tanais sylviae Mello-Leitao, 1941 , Tanais estuarius Pillai, 1954 and Tanais herminiae Mañé- Garzón, 1943); however, the expanded species diagnosis of Sieg (1980b) encompasses much variation in morphology, and the taxon has been detected worldwide in a large range of habitat types. It seems unlikely that a single species could possess a native distribution that extends from the hypersaline marine lagoon at the type locality of Clipperton in the eastern Pacific, to tropical Australian estuaries, a brackish Galapagos crater, South African marine sponge beds, and a lake at 400 m altitude on Saint Helena ( Gardiner 1975; Sieg 1980b). No known transport vector between these locations exists, as should be evident if a single species had invaded all these locations. Clearly, ‘ Sinelobus stanfordi’ warrants further investigation given the likelihood that it comprises a species complex.

Sinelobus barretti occurs at a much higher latitude other known Sinelobus taxa. It differs morphologically from descriptions of Sinelobus stanfordi in possessing a much shorter dactylus fixed finger on male, a transverse row of setae on pleonites 1 and 2 that barely extends onto the dorsal surface, paired spiniform setae located three-quarters distance along the medial margin of the maxilliped endite, and less elongate basal article of antennule (see Bird & Bamber 2000; Monod 1977; Shiino 1965; Sieg 1980b). Sinelobus barretti most closely approaches Sinelobus ‘stanfordi’ of Arcturus Lake, Galapagos, in form, but the male has a wider and more pear-shaped cephalothorax, and a cheliped with narrower propodus and much more elongate anvilshaped process on the fixed finger ( Gardiner 1975). Sinelobus barretti may also differ from congeners in possessing seven rather than eight large terminal spines on the maxillule endite. Seven spines only were observed on microscopic preparations of appendages, although a smaller eighth spine may possibly have been obscured.

Sinelobus barretti occurs abundantly amongst shoreline macrophytes at a single known location, where a salinity of 4 o /oo was measured. The species was collected during a broad-scale study of macrobenthos in 48 estuaries around Tasmania, but was misidentified in reporting as Sinelobus stanfordi ( Edgar et al. 1999a; Edgar et al. 1999b). During that study, S. barretti was found to possess a particularly unusual distribution for Tasmanian estuarine animals. All other species with more than 10 individuals collected (184 taxa in total) were either marine or possessed wide distributions with known presence at multiple other sites. Given its highly localised known distribution, against a background of extensive macrobenthic surveys of Tasmanian estuaries, and the scale of impacts within its home estuary through land clearance and human settlement ( Edgar et al. 1999a), this species appears to qualify as a threatened species under Tasmanian legislation and the IUCN Red List guidelines ( IUCN 2001). A threat assessment for this species should be undertaken.

Figures

FIGURE 7. Sinelobus barretti n. sp. Cradoc, 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 8. Sinelobus barretti n. sp. Cradoc, Tas. Labrum (L), left mandible (Mdl), right mandible (Mdr), labium (La), maxillule (Mx), maxilliped (Mxp), epignath (E). Scale units 0.1 mm.

FIGURE 9. Sinelobus barretti n. sp. Cradoc, Tas. Pereopods 1–6 (P1–P6), pleopod (Pl), uropod (U). Scale units 0.1 mm.