Araphura pygmothymos, 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 : 131-135

Araphura pygmothymos sp. nov.

Figures 87–89

Material examined. 1 (J58833), holotype, Central Bass Strait, 66 km S of Rodondo Island, Stn BSS 158 , 39º48.6'S 146º18.8'E, 82 m depth, sand with silt and mud, 13 November 1981 ; 1 (J58834), paratype, same data as holotype; 1 (J56692) , paratype, Central Bass Strait, 100 km SSE of Cape Liptrap, Victoria, Stn BSS 156 , 39º45.90'S 145º33.3'E, 74 m depth, muddy fine sand, 13 November 1981 ; 1 (J58835), paratype, Central Bass Strait, 38 km SW of Cape Paterson, Stn BSS 155 , 38º55.5'S 145º17.00'E, 70 m depth, fine sand, 12 November 1981 ; all coll. R.S. Wilson .

Description of female. Body ( Fig. 87A, B) slender, holotype 2 mm long, 9.7 times as long as wide. Cephalothorax subrectangular, narrowing anteriorly with slight triangular rostrum, 1.6 times as long as wide, twice as long as pereonite 1, naked, eyes absent. Pereonites all naked and rectangular; pereonites 1 and 5 subequal in length; pereonites 2 to 4 subequal, 1.2 times as long as pereonite 1; pereonite 6 shortest, 0.8 times as long as pereonite 5 (all pereonites respectively 1.3, 0.9, 0.9, 0.9, 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 subrectangular, as long as all pleonites together, 1.25 times as long as wide.

Antennule ( Fig. 88A) of four articles, proximal article nearly 2.6 times as long as wide, as long as distal three articles together, with single outer distal simple seta surrounded by four penicillate setae; second article longer than wide, 0.43 times as long as first article, with three outer distal penicillate setae; third article compact, 0.6 times as long as second article, naked; fourth article tapering, with six simple and one penicillate distal setae, and one aesthetasc.

Antenna ( Fig. 88B) of six articles, proximal article compact, fused to cephalothorax; second article 1.3 times as long as wide, with dorsodistal seta; third article as long as wide, 0.8 times as long as second article, with dorsodistal seta; fourth article longest, 4.5 times as long as wide, nearly three times as long as second article, with penicillate seta in proximal half and crown of one simple and four penicillate distal setae; fifth article half as long as second, with one distal simple seta; sixth article minute with four distal setae.

Labrum ( Fig. 88C) rounded, hood-shaped, setose. Left mandible ( Fig. 88D) with wide, spade-like crenulate pars incisiva and linguiform lacinia mobilis, right mandible ( Fig. 88E) with lanceolate pars incisiva and without lacinia mobilis; pars molaris of both mandibles tapering, with fine distal denticulations. Labium ( Fig. 88H) simple, outer distal corner with unarticulated setose palp-like projection. Maxillule ( Fig. 88F) with nine finely-denticulate distal spines. Maxilla ( Fig. 88G) simple, linguiform, naked. Maxilliped ( Fig. 88I) palp first article naked, second article with one outer and three distal inner setae, third article with two longer mesial and two shorter distal inner setae, fourth article with four longer and one shorter distal setae and one small subdistal outer seta; basis naked; endites distally naked, with outer-distal microtrichia and paired inner setae.

Cheliped ( Fig. 89A) with rounded, naked basis 1.5 times as long as wide, merus subtriangular with single ventral seta shorter than width of merus, and covering about half of ventral margin of carpus; carpus 1.7 times as long as wide, with two midventral setae, one dorsodistal seta; propodus 1.2 times as long as wide, with two ventral setae, outer face with curving ridge of rounded tubercles from mid proximal to dorsodistal, inner comb-row of two setae; fixed finger with three setae below cutting edge; dactylus with dorsal rounded tubercles in proximal half.

Pereopod 1 ( Fig. 89B) longer than others, coxa without apophysis, with seta; basis slender, 4.2 times as long as wide; ischium compact, with one ventrodistal seta; merus just shorter than carpus, ventrodistally with seta and longer distally-denticulate spine exceeding half length of carpus; carpus distally with ventral seta and single distally-denticulate spines dorsally and ventrally; propodus 1.5 times as long as carpus, with ventrodistal spine and dorsodistal spinous apophysis; dactylus with proximal seta, unguis 1.4 times as long as dactylus, both together 0.9 times as long as propodus. Pereopod 2 ( Fig. 89C) similar to pereopod 1, basis 3.5 times as long as wide with dorsal penicillate seta; merus longer than carpus; propodus 1.8 times as long as carpus and with ventral fields of microtrichia; dactylus and unguis together 0.8 times as long as propodus. Pereopod 3 ( Fig. 89D) similar to pereopod 2.

Pereopod 4 ( Fig. 89E) somewhat more compact, basis 3.25 times as long as wide; ischium with two ventrodistal setae; merus 0.7 times as long as carpus, with two ventrodistal spines; carpus with four ventrodistal spines; propodus just longer than carpus, with ventral fields of microtrichia, two ventrodistal spines and one dorsodistal spine; dactylus about twice as long as unguis, and with fields of microtrichia, dactylus and unguis not fused into a claw, the two together 1.2 times as long as propodus. Pereopod 5 ( Fig. 89F) as pereopod 4, but with ventral penicillate seta on basis, carpus with dorsodistal seta. Pereopod 6 ( Fig. 89G) as pereopod 5, but propodus with two ventral and three dorsal distal spines.

Pleopods ( Fig. 89H) all alike, with naked basis, endopod and exopod without setae on inner margin, outer margins with respectively 8 and 12 plumose setae.

Uropod ( Fig. 89I) basis naked, exopod 0.6 times as long as proximal endopod segment, with one mesial and two distal setae; endopod of two segments, distal segment 0.6 times as long as proximal segment, setose as figured.

Male. Unknown.

Etymology. From the Greek pygme – a fist, and thymos – a warty excrescence, referring to the tubercles on the chela (noun in apposition).

Remarks. The characteristics of the genus Araphura and its distinctions from the closely related genera Araphuroides Sieg, 1886 and Tanaella Norman & Stebbing, 1886 are discussed by Sieg (1986a) and Larsen et al. (2009) (but see below): the latter give a key to the genus Araphura , in which the present species keys out to A. parabrevimanus . That species, found at> 3200 m off Panama (the record from 720 m in the Subantarctic by Kudinova-Pasternak, 1975, is highly unlikely), is well figured by Lang (1968), from which the distinctions of the present shallow-water Antipodean species, although subtle, can be seen clearly.

In particular, in A. parabrevimanus the dorsal surfaces of the propodus and dactylus of the chela are smooth, ornamented with rows of microtrichia, while in A. pygmothymos sp. nov. these surfaces are highly tuberculate, the line of tubercles on the propodus extending across the dorsal outer face. Recently, Bird (2011) has described Araphura whakarakaia from New Zealand. Also a species with tubercles on the cheliped propodus and dactylus; as well as the different orientation of this tuberculation, A. pygmothymos differs from the New Zealand species in lacking a crenulate cheliped carpus, in its more elongate pleotelson, and in having stout spines on the merus of pereopods 1 to 3, inter alia. Other differences characterizing the present species are the more compact antennule peduncle articles, the lack of a pseudoarticulationline on the fourth article of the antenna, the stronger distal spines on the merus and carpus of the pereopods, and the less-elongate uropodal exopod-process.

Araphura pygmothymos was found in the Central Bass Strait at depths of 70 to 82 m on fine to muddy sands.