Antiplotanais actuarius, 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 : 166-170

Antiplotanais actuarius sp. nov.

Figures 111–113

Material examined. 1 (J58529), holotype, Western Bass Strait, 26 km SW of Cape Otway, Stn BSS 120 , 39º01.0'S 143º22.1'E, 84 m depth, medium sand, 31 January 1981; coll. M.F. Gomon ; 1 (J56616), paratype, Southern Port Phillip Bay, Stn PPBES 985 , 38º21.0'S 144º51.5'E, 9 m depth, sand, 09 December 1971; coll. G.C.B. Poore & S.F. Rainer.

Description of female. Body ( Fig. 111A, B) compact, holotype 1.7 mm long, 4.5 times as long as wide. Cephalothorax subrectangular, tapering towards anterior with slight triangular rostrum, as long as wide, longer than pereonites 1 to 3 together, naked, eyes absent. Pereonite 1 shortest, 0.2 times as long as cephalothorax; pereonites 2 to 5 progressively longer, pereonite 2 being 1.4 times as long as pereonite 1, pereonite 5 being twice as long as pereonite 1; pereonite 6 as long as pereonite 4 (all pereonites respectively 4.5, 3.3, 2.8, 2.5, 2.1 and 2.4 times as wide as long). Pleon with five free subequal pleonites bearing pleopods; each pleonite 3.7 times as wide as long. Pleotelson pentangular, one-third length of pleon and 1.6 times as wide as long, with four small dorso-distal setae.

Antennule ( Fig. 112A) of three articles, proximal article 1.9 times as long as wide, 2.4 times as long as distal two articles together, with row of five inner setae, outer margin with proximal and mid-length tufts penicillate setae, one simple seta at mid-length and two distally; second article nearly twice as wide as long, 0.6 times as long as third article, with single inner distal penicillate and longer simple setae and outer distal simple seta; third article tapering, 0.25 times as long as first article, with six simple and one penicillate distal setae.

Antenna ( Fig. 112B) of six articles, proximal article compact, naked; second article stout, as long as wide, with dorsodistal seta much shorter than article; third article shorter than wide, with fine dorsodistal seta; fourth article longest, nearly five times as long as wide, with one simple and three penicillate distal setae; fifth article 0.4 times as long as fourth with one distal seta; sixth article minute with five distal setae.

Labrum (not figured) rounded, hood-shaped, distally setose. Left mandible ( Fig. 112C) with subtriangular pars incisiva and linguiform, crenulate lacinia mobilis, right mandible ( Fig. 112D) without lacinia mobilis but with wider, rounded pars incisiva; pars molaris of both mandibles stout with few (two or three) large, pointed, tooth-like protrusions on distal margin. Labium ( Fig. 112G) simple, finely setose on outer and distal margins. Maxillule ( Fig. 112E) with eight distal spines, palp with two distal setae. Maxilla not recovered. Maxilliped palp ( Fig. 112F) first article naked, second article with one outer and three inner setae, at least one of these finely denticulate in distal half; third article with four inner setae in distal half of article, two of these finely denticulate in distal half; fourth article with five inner to distal setae, four of these finely denticulate in distal half, and one outer subdistal seta; basis with single, long seta exceeding distal margin of endites; endites distally with two setae and two distinct tubercles, and microtrichia. Epignath ( Fig. 112H) elongate, linguiform, naked.

Cheliped ( Fig.113A)withroundedbasisreachingpereonite 1 ventrally, 1.65 times as long as wide, with single dorsodistal seta; merus subtriangular with single ventral seta; carpus elongate, 2.5 times as long as wide, with three midventral setae very unequal in length, and row of six minute setae along dorsal margin; propodus slender, curved, 1.5 times as long as wide, fixed finger 0.7 times as long as palm, with two ventral setae, three setae on cutting edge; dactylus naked.

Pereopod 1 ( Fig. 110B) longer than others, coxal apophysis large (evident dorsally on whole animal, see Fig. 108A), triangular, pointed, with seta; basis curved, 4.6 times as long as wide, with three simple setae along dorsal margin; ischium compact, with short ventral seta; merus 0.4 times as long as basis, with one dorsal and one ventral simple distal setae; carpus as long as merus with three dorsal and two ventral simple distal setae; propodus 1.4 times as long as carpus, with three distal setae; short, naked dactylus half as long as slender unguis, both together 1.2 times as long as propodus. Pereopod 2 ( Fig. 113C), coxa similar to that of pereopod 1, basis 3.7 times as long as wide, with two setae on dorsal margin; ischium with single seta; merus 0.4 times as long as basis, ventrodistally with two simple setae; carpus 1.1 times as long as merus, with one dorsodistal seta, ventrodistally with two simple setae and field of microtrichia; propodus 1.6 times as long as carpus, with two dorsal subdistal setae, shorter ventral subdistal seta, and fields of microtrichia; short, stout dactylus with proximal seta longer than dactylus, slender unguis longer than dactylus, both together 0.4 times as long as propodus. Pereopod 3 compact ( Fig. 113D), similar to pereopod 2, basis with two simple setae on dorsal margin; ischium with single seta; merus ventrodistally with two simple setae and field of microtrichia; carpus ventrodistally with two simple setae and field of microtrichia; propodus with two dorsal subdistal setae, shorter ventral subdistal seta, and fields of microtrichia; short, stout dactylus with proximal seta longer than dactylus, slender unguis longer than dactylus.

Pereopod 4 ( Fig. 113E) basis stout, 2.2 times as long as wide, with two penicillate setae mid-ventrally; ischium with two ventrodistal setae; merus 1.1 times as long as carpus, with field of microtrichia across ventral and ventrolateral surfaces in distal two-thirds, and two small ventrodistal spines; carpus with robust distal molar spine, one dorsodistal blunt seta, and “prickly tubercles” ( sensu Błażewicz-Paszkowycz, 2007 ) surrounded by minute spines in ventrodistal half; propodus as long as carpus, with fields of microtrichia, mid-dorsal penicillate seta, simple dorsodistal seta, and two small ventrodistal spines; dactylus slender, with fields of microtrichia, three times as long as curved unguis, both together 0.9 times as long as propodus. Pereopod 5 (not figured) as pereopod 4. Pereopod 6 ( Fig. 113F) as pereopod 4, but basis with simple setae, propodus with three dorsodistal setae finely denticulate in their distal half.

Pleopods ( Fig. 113G) all alike, with naked basis, exopod shorter than endopod; endopod and exopod without setae on inner margin, outer margins with respectively 9 and 16 plumose setae, proximal seta on both rami separated from others.

Uropod ( Fig. 113H) biramous, basis naked; exopod half as long as endopod, with one fine proximal, one shorter and one longer distal setae; endopod with residual (atrophied) articulation line, with two penicillate setae just proximal to this line, one subdistal and four distal simple setae and two subdistal penicillate.

Male. Unknown.

Etymology. From the Latin actuarius – a shorthand writer, a pun referring to the shorter chela (“hand”) in proportion to the cheliped carpus in this species when compared with the other two described species of Antiplotanais .

Remarks. The genus Antiplotanais shares with the Typhlotanais greenwichensis -group (see above) the conspicuous coxal apophyses on the anterior pereopods, and prickly tubercles on the carpi of the posterior pereopods. It differs in the much more compact antennule and antenna, the proportionately shorter habitus (all less than 6 times as long as wide with all pereonites at least twice as wide as long), the relatively long pleonites, the presence of dorsal or dorsodistal setae on the pleotelson, the stouter dactyli on the posterior pereopods and the presence of distal lobes on the mandibular pars molaris.

There were two described species of Antiplotanais , A. coochimudlo Bamber, 2008 , from off Brisbane, Queensland, and A. lutze (Bamber, 2005) , from Esperance Bay, Western Australia. Antiplotanais actuarius sp. nov. differs from the other two particularly in the presence of dorsal setae on the bases of the anterior pereopods, in the cephalothorax being no longer than wide, and in the proportionately-shorter cheliped propodus (including the fixed-finger), being 0.64 times as long as the carpus compared with 0.85 times in A. coochimudlo and the same length in A. lutze . All three species are from sandy substrata in shallow waters off Australia.

Bamber (2008) remarked that the dactyli and ungues of the posterior pereopods appeared to be fused; it is evident from the present material that this is not the case. The posterior ungues are distinct but very short, and confirmed by re-examination of paratypic material of A. lutze , so evidently missed in the examination of the previous material of this genus of very small animals.

Antiplotanais actuarius was recorded only twice, from Port Phillip Bay and the Western Bass Strait at 9 and 24 m respectively, on sandy substrata.