Bathytanais parageios, Błażewicz-Paszkowycz & Bamber, 2012

Błażewicz-Paszkowycz, M. & Bamber, R. N., 2012, The Shallow-water Tanaidacea (Arthropoda: Malacostraca: Peracarida) of the Bass Strait, Victoria, Australia (other than the Tanaidae), Memoirs of Museum Victoria 69, pp. 1-235 : 102-107

Bathytanais parageios sp. nov.

Figures 68–70

Bathytanais fragilis Larsen & Heard, 2001 partim (shallow-water specimens only).

Material examined. 1 (J58584), holotype, MAFRI-H28 GI, Long Island Hastings , 38º19'S 145º14'E, 17 m depth, 4 March 1997 ; 6 (J66538), paratypes, MAFRI-H27 G4, Crib Point , 38º21'S 145º14'E, 12 m depth, 4 March 1997 ; 4 (J66579), paratypes, MAFRI-H28 GI, Long Island Hastings , 38º19'S 145º14'E, 17 m depth, 4 March 1997 ; all coll. DPI Victoria, Smith McIntyre grab. 1 (J56781) , paratype, WBES stn 1723, Western Port , 38º17.07'S 145º14.86'E, 14 m depth, sand, 22 November 1973, coll. Marine Studies group, Smith McIntyre grab. 3

(J51621), paratypes, VC-34-C1, 38º32.42'S 146º29.68'E, 40 m depth, fine mud, 11 May 1998, coll. N Coleman, Smith McIntyre grab. 22 specimens (incl. 1 brooding), MSL-EG 70, 37º53.39'S 148º15.40'E, 43 m, coarse sand, 4 June 1991, coll. N Coleman, Smith McIntyre grab (cited as paratypes of B. fragilis under a different registration no. in Larsen & Heard, 2001). 1 (J58465) , paratype (dissected and figured), CR 81-T-1 stn 155, 38º55.5'S 145º17.0'E, 70 m depth, fine sand, 12 November 1981, coll. R. S. Wilson, Smith McIntyre grab. 1 (J55908) , paratype, CPBS 31 N/3, Crib Point , 38º20.94'S 145º13.62'E, 15 m depth, fine sand and mud, 29 March 1965, coll. Marine Studies group, Smith McIntyre grab. 2 (J56676) , paratype, CPBS 31 N/4, same data as previous. 3 (J23557) , paratypes, MSL-EG 58, Eastern Bass Strait , 37º51.19'S 148º38.53'E, 51 m depth, mud and shell, 29 September 1990, coll. Marine Studies group, Smith McIntyre grab, RV Sarda . 1 (J17283) and 1 (J17281) , paratypes, MSL-EG 16, Eastern Bass Strait , 38º04'S 148º25.7'E, 28 m depth, sand and shell, 12 August 1989, coll. G Parry, Smith McIntyre grab, RV Sarda .

Description of female. Body ( Fig. 68) elongate, holotype 3.8 mm long, eight times as long as wide. Cephalothorax subrectangular, as long as wide, shorter than pereonites 1 and 2 together, with rounded triangular rostrum, naked; eyes present, pigmented. Pereonites cylindrical; pereonite 1 shortest, half length of cephalothorax; pereonite 2 longer, 0.75 times as long as cephalothorax; pereonite 3 longest, as long as cephalothorax; pereonites 4 and 5 subequal, longer than pereonite 2, pereonite 6 just shorter than pereonite 2 (all pereonites respectively 1.9, 1.1, 0.8, 1.0, 0.9 and 1.1 times as wide as long). Pleon of five free subequal pleonites bearing pleopods plus pleotelson, the whole shorter than pereonites 5 and 6 together; pleonites 5 times as wide as long; each pleonite with one plumose, articulating lateral seta on each side. Pleotelson semicircular, short, 1.6 times as long as pleonite 5, twice as wide as long, distally with two posterolateral simple setae on each side.

Antennule ( Fig. 69A) of four articles, proximal article twice as long as wide, naked; second article as long as wide, about one-third length of first, distally with two simple and three penicillate setae; third article two-thirds length of second with two simple distal setae; fourth article slender, as long as second article, with five setulose distal setae, longest three longer than cephalothorax and antennule together, but without aesthetasc (possibly a generic character: G Bird, pers. comm.).

Antenna ( Fig. 69B) of six articles, proximal article compact, naked; second article dorsally with slight flange-like expansion bearing single simple distal seta, ventral margin with three distal setae and laminar apophysis (flange) exceeding distal edge of third peduncle article, distally rounded, not transparent, with long mid-distal seta; third article just shorter than wide, half as long as second article, expanded mid-dorsally with mid-distal spine; fourth article half as long as second, distally with one simple seta, two penicillate setae and long dorsal setulose seta 3.5 times as long as article; fifth article half as long as fourth with two long setulose distal setae; sixth article minute with two long setulose distal setae.

Labrum ( Fig. 69C) apically rounded, setose. Left mandible ( Fig. 69D) with wide, curved, crenulate lacinia mobilis, right mandible ( Fig. 69E) without lacinia mobilis; pars incisiva bilobate, pars molaris robust, distally flat with marginal rugosity extended as short, rounded “teeth” ventrally. Labium ( Fig. 47G) rounded, finely setose with microtrichia on inner face, outer margins finely denticulate. Maxillule ( Fig. 69F) with seven distal spines and sparse outer setules, palp slender with two distal setae. Maxilla ( Fig. 69F) oval, naked. Maxilliped ( Fig. 69H) with single inner spine on basis reaching distal margin of second palp article; palp first article naked, second article with two simple setae and shorter denticulate seta on inner margin, outer margin with one simple seta; third article with three denticulate setae on inner margin; fourth article with five submarginal simple ventral setae, four distal denticulate setae and one mid-dorsal denticulate seta; endites ( Fig. 69 H') characteristic of genus, wider than maxilliped bases, with denticulate outer corner, two elongate ovate spines and single inner slender spine. Epignath ( Fig. 69I) slender, curved, distally setose.

Cheliped ( Fig. 70A) basis 1.8 times as long as wide, naked; merus with one mid-ventral seta; carpus 1.6 times as long as wide, ventral margin convex with two mid-ventral setae, dorsally with proximal and distal simple setae; propodus longer than wide, distally with comb of five shorter setae on inner face and three longer setulose setae, fixed finger short with lamellate apophyses on cutting edge, one longer and one shorter ventral setae, one longer and two shorter simple setae distally below cutting edge; dactylus with outer margin smooth and bearing one setulose seta.

Pereopod 1 ( Fig. 70B) longer than others, coxa simple with seta; basis slender, arcuate, 4.4 times as long as wide with three dorsal setae in proximal half; ischium compact with single seta; merus just over half length of basis, with ventrodistal seta; carpus 0.6 times as long as merus with one ventrodistal and two dorsodistal setae; propodus as long as merus, with two distal setae; dactylus curved, half as long as propodus, unguis slender, twice as long as dactylus. Pereopod 2 ( Fig. 70C) more compact, basis 4 times as long as wide; merus 0.8 times as long as basis, with two ventrodistal setae; carpus 1.3 times as long as merus, with slight dorsal expansion and single dorsal and ventral distal setae; propodus twice as long as carpus, with two distal setae; dactylus with long dorsoproximal seta, one-third length of propodus and half length of slender, curved unguis. Pereopod 3 ( Fig. 70D) similar to pereopod 2, but dactylus without dorsal seta.

Pereopod 4 ( Fig. 70E) coxa not evident; basis stouter, 2.3 times as long as wide, with three simple dorsal setae and two ventrodistal penicillate setae; ischium with two ventrodistal setae; merus half as long as carpus, each with ventrodistal microtrichia and rugosity and molar spines, carpus with dorsodistal seta; propodus as long as carpus, with mid-dorsal penicillate seta, dorsodistal spine exceeding claw, inner and outer ventrodistal molar spines; dactylus and claw fused into unguis, curved, bearing microtrichia, half as long as propodus. Pereopod 5 (not figured) as pereopod 4 but without dorsal penicillate seta on propodus. Pereopod 6 ( Fig. 70F) similar to pereopod 4, but basis without penicillate setae, merus with triangular dorsodistal spine, propodus with three distal serrate spines adjacent to unguis.

Pleopods ( Fig. 70G) all alike, with naked basis; endopod shorter than exopod, with single inner-subdistal plumose seta, exopod without setae on inner margin; outer margins of endopod and exopod with 16 and 23 plumose setae respectively, on both rami proximal seta on outer margin separated from remaining setae.

Uropod ( Fig. 70H) basis with one outer simple seta. Rami slender, exopod of one segment exceeding proximal segment of endopod, with one mesial and two distal simple setae, endopod of two segments, proximal segment with two penicillate and one simple distal setae, distal segment with two penicillate and five simple distal setae.

Male. Unknown.

Etymology. From the Greek parageios – pertaining to shallow water.

Remarks. Bathytanais parageios sp. nov. is close in morphology and locality to B. fragilis , but there are consistent differences. B. fragilis is characterized, inter alia, by the expansion on the second peduncle article of the antenna being transparent (confirmed in the examination of the types, see above), and somewhat wider proximally than distally, with two medial setae and no dorsal seta on the article; in the present species, this article has a slight dorsal expansion with a seta, and the ventral expansion is of uniform width throughout, with three medial setae, and quite opaque. The second peduncle article is also subtly different, that of B. fragilis having a forward-pointing spine-like apophysis bearing a seta, while that of B. parageios has a stout spine. Further, the third article of the antennule of B. fragilis has a seta some five times as long as the fourth antennular article, this seta being less than twice as long in B. parageios .

While these differences are sufficiently subtle to suggest variability with depth in one species, other notable differences are found in the uropod segmentation, B. fragilis having a one-segmented endopod some three times as long as wide, while that of B. parageios is two-segmented, and conspicuously more slender (as is the exopod) at five times as long as wide. Further differences are found in the spination of the posterior pereopods (especially pereopod 6), the setation of the maxilliped basis and endite, the proportionately shorter second and third articles of the antennular peduncle, the proportionately shorter fifth article of the peduncle of the antenna (half as long as the fourth in B. parageios , subequal in length in B. fragilis ), and the more numerous plumose setae on the rami of the pleopods, and the more gracile posterior pereopods in B. parageios . No variation between these morphologies was observed within the material examined.

These two taxa are thus considered sibling species, close in morphology but showing a number of distinctions, and separated by depth and habitat ( B. parageios on shallower sandy sediments, B. fragilis on deeper muds), this nichespecificity presumably having lead to allopatric speciation. Their antennal morphology distinguishes them entirely from all other described Bathytanais species.

Bathytanais parageios was collected from throughout the Bass Strait, from depths between 12 and 70 m, mainly on sandy substrata.