Leptochelia billambi, 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 : 107-113

Leptochelia billambi sp. nov.

Figures 71–74

Material examined. 1 (J58472), holotype, 1 (J58474), allotype, 162

(J58473), paratypes, sample Stn CPBS 000/4, 38º21.17'S 145º13.15'E, 2 m depth, sandy mud, 6 April 1965, coll. MSG, Smith McIntyre grab .

Portland Exotic Species survey material: 31 (J66139) at 3 m depth, 9 (J66142) at 0.5 m depth, 16 specimens (J66139) at 7 m depth, paratypes, MAFRI-P17 SCR, Portland No. 6 berth, 38º21'S 147º37'E, 3 May 1996 . 2 (J66126) at 7 m depth, 4 (J66123) at 3 m depth, paratypes, MAFRI-P16 SCR, Portland No. 2 berth, 38º20'S 147º37'E, 3 May 1996 . 1 (J66094) at 3 m depth, paratypes, MAFRI-P15 SCR, Portland SL Pattersons Berth, 38º21'S 147º37'E, 2 May 1996 . 3 (J66156) at 3 m depth, 2 (J66158) at 0.5 m depth, paratypes, MAFRI-P18 SCR, Portland No. 1 berth, 38º21'S 147º37'E, 4 May 1996 . 1 (J66386), paratype, MAFRI-M47 -G47, Port of Melbourne , 37º50'S 144º53'E, 14 m depth, 7 December 1999 .

Other material examined. A further 521 idiotypic individuals from the Bass Strait, Western Port and Port Philip Bay , many without registration numbers, and including 303 (9 brooding), 3 and 38 juveniles. Numerous further specimens exist in the collections of Museum Victoria .

Description of female. Body ( Fig. 71A, B) slender, holotype 2.4 mm long, 6.4 times as long as wide. Cephalothorax subrectangular, tapering towards anterior, 1.4 times as long as wide, longer than pereonites 1 and 2 together, with slight rostrum, eyelobes rounded, eyes present and black, single setae at posterior of eyelobes and mid-laterally. Pereonites 1 and 6 subequal and shortest, pereonites 2 to 5 subequal, progressively longer, pereonite 5 longest and 1.4 times as long as pereonite 1 (all pereonites respectively 1.9, 1.7, 1.5, 1.5, 1.4 and 1.9 times as wide as long). Pleon with five free subequal pleonites bearing pleopods; each pleonite about 5.6 times as wide as long, with 2 or 3 lateral setae. Pleotelson pentangular, as long as last two pleonites together, twice as wide as long, with one anterolateral and posterolateral seta on each side and two distal setae.

Antennule ( Fig. 72A) of three longer and one minute distal articles, proximal article 4 times as long as wide, 1.6 times as long as distal three articles together, with proximal, mesial and distal inner groups of penicillate setae, inner and outer simple mesial setae and one long inner distal seta longer than second article; second article twice as long as wide, one-third as long as first article, distal seta just longer than article; third article just shorter than second, with one distal seta; fourth article minute, with three distal setae and one aesthetasc.

Antenna ( Fig. 72B) of six articles, proximal article compact, with fine distal seta; second article as long as wide, with single inner distal and dorsodistal slender spines; third article just longer than wide, with dorsodistal slender spine; fourth article longest, 3.2 times as long as wide and twice as long as third, with mid-length seta reaching two-thirds of length to distal margin, and distal tufts of penicillate and simple setae; fifth article 0.6 times as long as fourth; sixth article minute, with four simple and one penicillate distal setae.

Labrum ( Fig. 72C) hood-shaped, setose, typical of genus. Left mandible ( Fig. 72D) with crenulate lacinia mobilis wider than distal end of mandible, distal crenulation on pars incisiva, pars molaris with strong rugosity; right mandible ( Fig. 72E) similar but without lacinia mobilis, pars incisiva distally bifurcate. Labium ( Fig. 72G) wide, bilobed, distally finely setose, without palp. Maxillule ( Fig. 72F) with ten distal spines and setose margins, rows of setules on inner distal face; palp distinct, with two distal setae. Maxilliped ( Fig. 72H) palp first article naked, second article with finely setose inner margin, and with one outer, one ventral and three inner setae, distal-most inner seta not reaching distal margin of third palp article; third article with nine inner marginal and one distal submarginal finely denticulate setae; fourth article with nine inner/distal finely denticulate setae and one outer subdistal seta; basis with five long setae extending to third palp article; endites distally with fine outer setules and three robust spatulate spines, inner spine shorter than others.

Cheliped ( Fig. 73A) with rounded, comparatively slender basis 2.3 times as long as wide; merus triangular with three ungrouped ventral setae; carpus twice as long as wide, with two midventral setae and two shorter marginal dorsal setae; propodus slightly longer than wide, with inner distal comb of seven setae and longer seta at base of dactylus; fixed finger with four ventral and three inner setae, cutting edge crenulate; dactylus naked.

Pereopod 1 ( Fig. 73B) longer than other pereopods, coxa with seta; basis slender, 4.4 times as long as wide, with single dorsoproximal simple and penicillate setae; ischium compact with one ventral seta; merus as long as carpus, with one dorsodistal and two ventrodistal setae; carpus with two ventrodistal setae, one medial distal seta and three dorsodistal setae, longest of which is half length of propodus; propodus 1.8 times as long as carpus, with three setae on subdistal dorsal mound and one subdistal ventral seta; dactylus slender, extending into shorter slender unguis 0.7 times as long as dactylus, the two together as long as propodus. Pereopod 2 ( Fig. 73C) more compact than pereopod 1; coxa with longer seta; basis 3.1 times as long as wide; ischium with 2 setae; merus as long as carpus and 1.5 times as long as wide, with strong ventrodistal spine and ventral rows of microtrichia; carpus with single dorsodistal and ventrodistal setae and two ventrodistal spines, and ventral rows of microtrichia; propodus 1.6 times as long as carpus, with three distal setae and ventral rows of microtrichia; dactylus and short unguis curved, together 0.7 times as long as propodus. Pereopod 3 ( Fig. 73D) similar to pereopod 2, but carpus shorter than merus and with two dorsodistal setae.

Pereopod 4 ( Fig. 73E) basis stout, 2.23 times as long as wide with two ventroproximal penicillate setae; ischium with two ventrodistal setae; merus with paired ventrodistal spines and ventral rows of microtrichia; carpus just shorter than merus, with outer, ventral and inner distal spines each with fine subdistal setules, and ventral rows of microtrichia; propodus 1.2 times as long as carpus, with two ventrodistal spines, five dorsodistal setae mostly as long as dactylus, and ventral rows of microtrichia; dactylus and distinct unguis curved, 0.6 times as long as propodus. Pereopod 5 ( Fig. 73F) as pereopod 4, but carpus with additional simple distal seta, propodus as long as carpus. Pereopod 6 ( Fig. 73G) as pereopod 5, but propodus with seven finely denticulate and one simple distal setae.

Pleopods ( Fig. 73H) all alike, typical for the genus but basis naked, endopod with single inner plumose seta and proximal outer seta separated from remainder.

Uropod ( Fig. 73I) biramous, basis naked; exopod of one segment, 0.8 times as long as proximal endopod segment, outer distal seta longer than inner distal seta; endopod of five segments, distal segments slender.

Description of male. Larger than female (allotype length 4.2 mm), body ( Fig. 71C) more compact, cephalon as long as pereonites 2 to 4 together, with large eyelobes bearing large black eyes; pereonite 1 shortest, pereonites 2, 3 and 6 subequal, twice as long as pereonite 1, pereonite 4 longest, three times as long as pereonite 1, pereonite 5 just shorter than pereonite 4. Five free pleonites, subequal in length, each as long as pereonite 1, pleotelson as long as pleonites 5 and 6 together.

Antennule ( Fig. 74A) elongate, first peduncle article 6.4 times as long as wide, curved, with single dorsodistal penicillate and simple setae; second article 0.43 times as long as first with single ventral and dorsal distal simple setae; third article half as long as second and twice as long as wide with single ventral and dorsal distal simple setae; flagellum of 9 segments, segments 1 to 7 bearing proximal row of 6 or 7 aesthetascs, segment 8 naked, segment 9 minute, distally with six simple and one penicillate setae.

Antenna ( Fig. 74B) proximal article compact; second article as long as wide, with single ventrodistal seta; third article longer than second, twice as long as wide, with single simple dorsodistal seta; fourth article 3.3 times as long as third, with incipient secondary articulation at mid-length bearing single simple and penicillate setae, distally ventral pairs of penicillate and simple setae, and stronger dorsal seta reaching half length of fifth article; fifth article 0.9 times as long as fourth with two longer and one shorter distal setae; sixth article minute, with four simple distal setae.

Mouthparts ( Fig. 74D) atrophied, naked maxilliped and maxillule palp with two distal setae distinguishable.

Cheliped ( Fig. 74C) larger and more slender than that of female; basis 1.7 times as long as wide; merus short, with two ventral setae; carpus three times as long as wide, with three midventral setae and four dorsal marginal setae; propodus 1.4 times as long as wide, fixed finger 1.25 times as long as palm, with six ventral setae, three setae adjacent to cutting edge, two inner tooth-like apophyses on cutting edge; dactylus slender, curved, with proximal seta and row of 13 setae along cutting edge.

Pereopods ( Fig. 74E to J) similar to but more slender than those of female, merus shorter than carpus on pereopods 1 to 3; on pereopods 4 to 6 propodus much longer than carpus, distal carpal spines more elongate than those of female, microtrichia restricted to dactylus, dactylus proportionately longer than in female.

Pleopods ( Fig. 74K) with longer setae than on those of female. Uropod ( Fig. 74L) basis with inner distal row of setae; exopod two-segmented, longer than proximal endopod segment; endopod of five segments, more heavily setose than that of female.

Etymology. Named after William Lamb, 2nd Viscount Melbourne, after whom the city of Melbourne was named in 1837 (the original Melbourne being a village in Derbyshire, England).

Remarks. Bamber (2008) gave an identification key to the species of the Leptocheliidae then known from Australian waters, through which the present species would key out to Leptochelia opteros Bamber, 2008 , the commonest species in Moreton Bay, Queensland: it is indeed close to that species, and shares with it a distal seta on the proximal article of the antenna; however, L. billambi sp. nov. is a larger species, its cheliped and antennule are more elongate than those of L. opteros , the fixed finger of the chela has 4, not 3, ventral setae, the chela comb-row has more setae, and the maxilliped basis has 5 distal setae (4 in L. opteros ). The male appears generally as a larger version of that of L. opteros , but that male is characterized by having a dorsodistal flange on the basis of pereopod 6, absent in the present species. Finally, L. billambi was recorded on sandy mud substrata, while L. opteros lives amongst sublittoral algae and epifaunal communities. The incipient secondary articulation of the fourth antennal peduncle article in the male is so far unique to this species in the Leptocheliidae .

A range of morphometric and meristic characters in females has been analyzed for some 22 taxa attributable to the Leptochelia savignyi (Krøyer, 1842) -complex (see Bamber, 2008; Bamber, 2010), with which the present species has been compared. The only other species which has the proximal article of the antennule approaching as slender as 4 times as long as wide is L. savignyi sensu stricto, ranging from 3.5 to 3.8 times as long as wide ( Bamber, 2010), while in the figure of L. savignyi sensu Sars (1886) from the Mediterranean this article is 4 times as long as wide. However, that species has only 4 maxilliped-basis setae (five in L. billambi ) and a proportionately shorter cheliped basis and carpus in the adult, while the distal seta on article 2 of the antennule is not longer than the article itself (longer in L. billambi ), the uropod exopod is only just longer than half of the proximal endopodsegment length (0.8 times as long in L. billambi ), and the dactylus plus unguis of pereopod 1 are shorter than the propodus (equal in length in L. billambi ); further, the male of L. savignyi sensu stricto also has a dorsodistal flange on the basis of pereopod 6 ( Bamber, 2010), unlike that of L. billambi . Other than the present species, there are only four described species which have the distal seta on article 2 of the antennule as long as or longer than the article itself ( L. itoi Ishimaru 1985 , L. daggi Bamber, 2005 , L. opteros Bamber, 2008 and L. guduroo Bamber, 2008 ), but all of these have the first peduncle article of the antennule less than three times as long as wide.

Leptochelia billambi was recorded commonly at between 0 and 14 m depth in Port Phillip Bay and Western Port , Victoria .