Macrolabrum sarda, 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 : 78-83

Macrolabrum sarda sp. nov.

Figures 51–54

Material examined. 1 (J57788), holotype, Stn SA63 , Flinders Island, South Australia, “The Hotspot” reef, 5 n miles W of N end of Flinders Island , 33º40.30'S 134º22.00'E, 17 m depth, 19 April 1995, SCUBA, coll. G.C.B. Poore; 1, 1 (J56372), paratypes, same sample as Holotype; 1 (J56373), paratype, Stn SA59 , Flinders Island , South Australia, bay on NW coast of Flinders Island , 33º41.42'S 134º28.30'E, 3 m depth, 23 November 1981, hand dredge, coll. G.C.B. Poore; 1 (J56366), paratype, Stn BSS180 , Central Bass Strait , 8 km south of South East Point , Wilsons Promontory, Victoria, 39º12.9'S 146º27.3'E, 65 m depth, 18 November 1981, medium sand, coll. R. S. Wilson.

Description of female. Body ( Fig. 51A) typical of a pagurapseudid, small, holotype about 3.5 mm long. Cephalothorax ( Fig. 51A, B) subrectangular, slightly narrower anteriorly, almost as long as wide, with denticulate rostrum; paired plumose setae behind ocular lobe, lateral margins with six hooked spine-like apophyses and seven plumose setae. Eyelobes distinct, eyes present as group of black-pigmented ocelli. Epistome conspicuous, exceeding anterior margin of carapace, visible dorsally. Pereonite 1 with undulating anterior and posterior margins, 0.4 times as long as cephalothorax and 2.8 times as wide as long, laterally with seven or eight plumose setae on each side; pereonite 2 similar to but just longer than pereonite 1, twice as wide as long, laterally with two plumose setae on each side; pereonites 3 to 6 naked. Pleon 0.4 times as long as whole body, with five free subequal pleonites, each pleonite nearly as long as pereonite 6 and slightly wider than long; pleonites 1 and 2 only bearing pleopods. Pleotelson subrectangular, about twice as long as last pleonite, 1.5 times as long as wide, with three lateral setae on each side.

Antennule ( Fig. 52A) proximal peduncle article 3.5 times as long as wide, inner margin with four proximal spine-like apophyses accompanied by simple setae, further simple setae in distal half, outer margin with proximal penicillate setae, distal simple setae and distal spine; second peduncle article 0.5 times as long as first, inner spine-like apophysis at mid-length, both margins with single mid-length plumose seta and tuft of distal plumose setae; third article 0.85 times as long as second, with short inner and outer plumose setae; fourth article one-third length of third. Main flagellum of four segments including minute distal segment, first, second and third segments with 3, 2 and 1 aesthetascs respectively; accessory flagellum of three segments, first segment short, second segment longest and distally exceeding distal edge of first segment of main flagellum, third segment minute.

Antenna ( Fig. 52B) with two basal articles fused into wide proximal peduncle article bearing complex denticulation along inner margin, one plumose and one simple inner setae; third article one-third length of fused proximal articles, as long as wide with inner distal spine-like apophysis and outer distal spine and adjacent simple seta; fourth peduncle article twice as long as third with inner distal spine-like apophysis and outer distal penicillate seta; fifth article 2.5 times as long as third with distal crown of penicillate setae and long outer simple seta. Flagellum of two unequal segments, distal segment with three distal setae.

Labrum (not figured) bilobed rounded, sparsely setose, epistome large, exceeding rostrum. Left mandible ( Fig. 52C) with heavily denticulate outer margin, quadricuspid pars incisiva, tricuspid lacinia mobilis, setiferous lobe with four distally denticulate setae, pars molaris round, blunt, crushing face with marginal crenulations; palp of three articles, proximal article with inner distal crenulations and long, plumose inner seta, second article longest, 1.7 times as long as proximal article, inner margin with five plumose and two simple marginal setae, and 23 shorter simple setae essentially in two rows; third article half as long as second, with six progressively-longer inner setae and two outer setulose subdistal setae. Right mandible ( Fig. 52D) as left but without lacinia mobilis. Labium ( Fig. 52G) with hook-like denticulation on outer margin, palp elongate, setose, with two distal setae. Maxillule ( Fig. 52E) inner endite with four distally-denticulate distal setae and outer apophysis below setose margin, outer endite with 9 distal spines, outer margin setose; palp of two articles with indistinct articulation, distally with six setae each minutely denticulate in its distal half. Maxilla ( Fig.52F) outer margin setulose, outer lobe of moveable endite with two subdistal and five distal simple setae, inner lobe with seven simple setae and one plumose seta; fixed endite outer lobe with fpur simple, three trifurcate and one bilaterally denticulate distal spines, inner lobe with one longer distally denticulate seta and rostral row of 16 setae. Maxilliped ( Fig. 52H) basis with two inner and three distal setae and small outer setulose apophysis; proximal palp article with denticulate inner and outer margins, and one inner and one outer plumose setae; second article with denticulate inner and outer margins, outer margin with one distal and three marginal plumose setae, inner margin with two distal plumose setae and two more in proximal half, and sparse simple setae; third article with five simple and four finely-denticulate inner marginal setae; distal article with six finely-denticulate inner-marginal and distal setae, paired outer subdistal plumose setae; endite ( Fig. 52 H') with finely setose outer margin, distally with two plumose setae and five bi- or trifurcate spines progressively smaller towards inner margin, and two subdistal plumose setae; three coupling-hooks. Epignath ( Fig. 52I) large, oval, distal spine coarsely setose.

Chelipeds showing dimorphism. Right cheliped ( Fig. 53B) with compact basis 1.3 times as long as wide, with three dorsal setae on slight apophysis, mid-ventral finely-denticulate spine, two ventrodistal finely-denticulate spines and ventrodistal plumose seta; exopodite absent. Merus subtriangular with pronounced distal triangular extension, five simple and three plumose ventral setae. Carpus elongate, 2.3 times as long as wide, dorsally with sparse fine setae and mid-dorsal hook-like apophysis, ventrally with denticulate margin in distal half, four simple and one plumose marginal setae. Propodus robust, 1.35 times as long as wide, with three ventral and one dorsoproximal short setae; fixed finger wide, blunt, distally rounded, claw nor evident, with row of crenulations distally and tuft of three proximal setae on cutting edge, two ventral setae; moveable finger stout, strongly curved, cutting edge with rounded crenulations. Left chela (not figured) more slender, fixed finger pointed with distal claw.

Pereopod 1 ( Fig. 54A) longest pereopod, coxa with triangular apophysis bearing two plumose setae; basis stout, 2.3 times as long as wide, with mid-proximal spine, dorsal margin expanded, expansion incomplete distally, bearing 19 plumose setae interspersed with eleven triangular spinules, ventral margin with three proximal simple setae, three central plumose setae and one distal plumose seta; exopodite present ( Fig. 54 A'), large, second article with two dorsal setules, distal article with 18 plumose setae. Ischium as long as wide, with naked dorsal margin, three plumose ventral setae. Merus 0.8 times as long as basis, dorsally with two plumose and one simple distal setae, ventrally with 10 marginal plumose setae, 17 submarginal denticulate setae in two rows. Carpus short, half length of merus, ventrally with three spines and subdistal simple setae, and with two mid dorsal simple setae and dorsodistal tuft of three simple setae and one spine. Propodus 1.7 times as long as carpus, with four ventral spines in distal half and sparse distal setae. Dactylus stout, curved, 0.8 times as long as propodus, with three ventral and one dorsal setae, unguis slender, sharp, 0.3 times as long as dactylus.

Pereopods 2 to 6 similar to each other, each about one-half to one-third as long as pereopod 1. Pereopod 2 ( Fig. 54B) coxa with simple seta; basis stout, 1.9 times as long as wide, dorsally with plumose proximal seta and four simple and one penicillate setae in distal half, ventrally with two distal plumose setae; ischium with paired ventrodistal setae. Merus, carpus and propodus bearing “sucker-like” spines, generally in three ventral rows, and sparse plumose setae as figured. Merus 1.5 times as long as basis; carpus 0.7 times as long as merus; propodus 0.75 times as long as carpus; dactylus and unguis not fused, with minute inner seta, together 0.8 times as long as propodus; adjacent distal propodal, spine simple but with inner distal fine denticulation. Pereopod 3 ( Fig. 54C) with only plumose setae on basis, three ventrodistal plumose setae on ischium, dorsal penicillate seta on propodus. Pereopod 4 ( Fig. 54D) slightly more compact, basis 1.5 times as long as wide; fewer sucker-like spines on merus; carpus just longer than merus; propodus short, 0.3 times as long as carpus, with two denticulate distal spines; dactylus plus unguis 1.5 times as long as propodus. Pereopod 5 ( Fig. 54E) as pereopod 4 but with more plumose setae on basis and ischium. Pereopod 6 ( Fig. 54F) carpus twice as long as merus, only one sucker-like spine on merus.

Pleopods ( Fig. 53A) only present on pleonites 1 and 2, biramous, reduced; basis with single dorsal and no ventral plumose seta, and suggestion of proximal articulation; exopod with six outer and distal plumose setae, endopod almost circular, with eight marginal plumose setae.

Uropod ( Fig. 54G) biramous, basis outer margin with two plumose and one penicillate setae, inner margin with one subdistal simple seta; endopod longer than basis, of three segments increasing in length, first and second segments each with inner distal simple seta, third segment with three stout distal setae each with fine serrations in distal half and one penicillate seta; exopod of one segment, subequal in length to proximal two endopod segments together, with three distal setae each with fine serrations in distal half.

Male. Closely similar to female, chelipeds not significantly sexually-dimorphic.

Etymology. The SV Sarda was one of the vessels used on the Bass Strait Survey between 1979 and 1984 (noun in apposition).

Remarks. The only other species of Macrolabrum to show minute distal segments on both flagella of the antennule are M. aenigmaticus , M. boeri and M. abrucei , but these have only two segments in the accessory flagellum; further, M. aenigmaticus has no pleopod basis setae and only two uropod endopod segments, while the other two have only one uropod exopod segment, and M. boeri has six ventral setae on the pleopod basis.

In fact, the only other species of the Pagurapseudinae to have a three-segmented accessory flagellum on the antennule is Pagurapseudes victoriae (see above), and then only in rare, larger individuals, while the complex setation of the basis and merus of pereopod 1 and of the second mandible palp article are unique to Macrolabrum sarda sp. nov..

Macrolabrum sarda sp. nov. was recorded from the Central Bass Strait, at 65 m on medium sand, as well as from South Australia at 3 to 17 m depth.