Meromonakantha anarsios, 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 : 183-187

Meromonakantha anarsios sp. nov.

Figures 123–125

Material examined. 1 (J62058), holotype; 1 (J62059), paratype, Stn BSS 36 (CR 79-K-1), Eastern Bass Strait, 82 km ENE of North Point, Flinders Island, 293 m, 28 March 1979, 39º27.7'S 148º41.4'E, 293 m depth, coarse sand, 28 March 1979, coll. G.C.B. Poore.

Description of female. Body ( Fig. 123A, B) slender, holotype 1.4 mm long, 7.5 times as long as wide. Cephalothorax subrectangular, narrowing anteriorly (conical) with slight triangular rostrum, 1.2 times as long as wide, twice as long as pereonite 1, naked, eyes absent. Pereonites all naked and rectangular; pereonites 1 and 6 subequal in length; pereonites 2 and 3 subequal, 1.3 times as long as pereonite 1; pereonites 4 and 5 subequal, 1.5 times as long as pereonite 1 (all pereonites respectively 1.6, 1.2, 1.1, 1.0, 1.0 and 1.3 times as wide as long). Pleon of five free subequal pleonites bearing pleopods plus pleotelson; each pleonite 4.2 times as wide as long. Pleotelson subpentangular, as long as last two pleonites together, 1.75 times as wide as long.

Antennule ( Fig. 124A) of three articles, proximal article three times as long as wide, 1.7 times as long as distal two articles together, outer margin with three pairs of penicillate setae, one central and one distal simple setae each as long as distal two articles together; second article longer than wide, 0.25 times as long as first article, with two distal simple setae; third article tapering, 1.4 times as long as second article, with five simple and one penicillate distal setae.

Antenna ( Fig. 124B) of six articles, proximal article compact, fused to cephalothorax; second article just longer than wide, with dorsodistal seta; third article as long as wide and as long as second article, with strong dorsodistal seta; fourth article longest, four times as long as wide, 3.6 times as long as third article, with three simple and two penicillate distal setae; fifth article 1.5 times as long as third, with one distal simple seta; sixth article minute with four distal setae.

Labrum and left mandible not recovered. Right mandible ( Fig. 124C) with wide, spade-like pars incisiva bearing upper and lower marginal rounded “teeth” and submarginal denticulations; pars molaris stout, blunt, with rounded distal tubercles. Labium ( Fig. 124F) simple, outer distal corner with unarticulated setulose projection. Maxillule ( Fig. 124D) with eight distal spines and small seta. Maxilla ( Fig. 124E) simple, linguiform, naked. Maxilliped ( Fig. 124G) palp first article naked, second article with one outer and three distal inner setae, one of inner setae finely plumose; third article with three longer and one shorter distal inner setae, fourth article elongate, with four distal setae and one subdistal outer seta; basis naked; endites distally naked, with outer-distal microtrichia and paired inner setae. Epignath ( Fig. 124H) elongate, ribbon-like, distally pointed.

Cheliped ( Fig. 124I) sclerite dorsally inserted, basis not reaching anterior of pereonite 1 ventrally, 1.6 times as long as wide with outer dorsodistal seta; merus subtriangular with single ventral seta, and covering about half of ventral margin ofcarpus;carpus1.9 timesaslongaswide, withtwomidventral setae, one dorsodistal seta; propodus elongate, 1.5 times as long as wide, with two ventral setae, inner comb-row of three setae; fixed finger slender, two-thirds as long as palm, with three setae below cutting edge; dactylus with proximal seta.

Pereopod 1 ( Fig. 125A) coxa without apophysis; basis slender, 3.8 times as long as wide, with two dorsal penicillate setae in proximal half; ischium compact, with one ventrodistal seta; merus 0.7 times as long as carpus, ventrodistally with two slender spines; carpus distally with slender spines dorsally, mesially and ventrally; propodus slightly curved, 1.3 times as long as carpus, with ventral subdistal seta; dactylus naked, unguis 1.4 times as long as dactylus, both together 1.2 times as long as propodus. Pereopod 2 ( Fig. 125B), similar to pereopod 1, basis with mid-dorsal simple seta but no penicillate setae; carpus with additional distal seta; propodus straight, 1.9 times as long as carpus; dactylus and unguis together 0.9 times as long as propodus. Pereopod 3 ( Fig. 125C) similar to pereopod 2, basis naked.

Pereopod 4 ( Fig. 125D) somewhat more compact, basis three times as long as wide with two penicillate setae; ischium with two ventrodistal setae; merus as long as carpus, with two stout ventrodistal spines; carpus with four curved distal spines and dorsodistal seta; propodus 1.2 times as long as carpus, with two curved ventrodistal spines and one dorsodistal seta; dactylus with fine ventral denticulation, about twice as long as unguis, the two together as long as propodus. Pereopod 5 ( Fig. 125E) as pereopod 4, but without penicillate seta on basis, propodus with dorsodistal spine-like apophysis but no seta. Pereopod 6 ( Fig. 125F) as pereopod 5, but propodus with three dorsodistal setae.

Pleopods ( Fig. 125G) all alike, with naked basis, endopod and exopod elongate, linguiform, without setae on inner or outer margins, exopod wider and slightly longer than endopod, each respectively with seven and three distal plumose setae.

Uropod ( Fig. 125H) basis naked, twice as long as wide; exopod of two subequal segments, just longer than proximal endopod segment; endopod of two subequal segments, setose as figured.

Male. Unknown.

Etymology. From the Greek anarsios – strange, incongruous, as this species diverges on a number of characters from the current diagnosis for the genus (see below).

Remarks. With the long seta on the third article of the antenna, the simple setation/spination of the pereopods (lacking fields of microtrichia or prickly-tubercles), the conformation of the cephalothorax, of the mandibular molar process and of the uropods, inter alia, the present species accords with Meromonakantha rather than any other typhlotanaid genus. It diverges from the diagnosis given by Błażewicz-Paszkowycz (2007) in that neither the cephalothorax nor the pleon are wider than the pereon, and the dactyli and ungues of the posterior pereopods are not “semi-fused”.

Although, as pointed out by Błażewicz-Paszkowycz (2007), the genus is in need of revision once sufficient material of a number of its less-well described species becomes available, Meromonakantha anarsios sp. nov. is also distinguished from all of the other species in having relatively long curved spines on the posterior pereopods, a more slender proximal article to the antennule, and the pereonites mostly parallel-sided.

While these differences may be considered sufficient to distinguish Meromonakantha anarsios as a separate genus, we choose at present to maintain its affiliation with other members of Meromonakantha rather than erect a monotypic genus.