Parakonarus robertsoni, Edgar, Graham J., 2012

Edgar, Graham J., 2012, New Leptocheliidae (Crustacea: Tanaidacea: Tanaidomorpha) from Australian seagrass and macro-algal habitats, and a redescription of the poorly-known Leptochelia ignota from Sydney Harbour, Zootaxa 3276, pp. 1-37 : 26-34

Parakonarus robertsoni n. sp.

( Figs 14–18 )

Holotype. Male ( NMV J62321 ), 3.1 mm, Seven Mile Beach, WA (29.17°S 114.89°E), low water mark, turf macroalgal washings, 4 June 1985.

Paratypes. One male and one female ( NMV J62322 ), holotype location, June 1985 – June 1987.

Other material. One male, ( NMV J62323 ) Bickley Point, Rottnest Island, WA (32.00°S 115.56°E), seagrass washings, 0.5 m depth, 10 Jan 1991.

Description. FEMALE. Body ( Fig. 14 ). Observed length 3.7 mm; body about six times longer than broad; cephalothorax frontal margin with slight rostrum, lateral margin with very slight concavity anteriorly and convex posteriorly, length about 1.3 times width, approximately one-fifth body length; front margin of second thoracomere demarcated by slight indentation in dorsal profile and weak calcification, and dorsal midline of second thoracomere also weakly calcified, which is apparent as an obvious line in preserved specimens; eyes relatively small, extending triangularly forward, about one-sixth length of cephalothorax.

Pereon about 0.6 times total length; pereonite-1 length about one-quarter width; pereonites 2 and 3 similar, about twice length of pereonite-1, length about two-fifths width; pereonites 4 and 5 similar, about 1.8 times length of pereonite-3, length about 1.2 times width; pereonite-6 about 1.3 times length of pereonite-3, length about 1.6 times width.

Pleonites 1–5 similar, other than with pleonite 5 five-sixths width and 1.5 times length of pleonite 4, together one-fifth as long as body.

Pleotelson similar in length to pleonite 5; posterior margin with one pair of long central setae, a simple seta and plumose seta dorso-distally, a simple seta on each lateral margin.

Antennule ( Fig. 14 ). One-sixth length of body, article-1 length just over twice width, with numerous setae as figured; article-2 about one-quarter length of article-1, with two distal setae; article-3 length about 1.3 times length of article-2, with three or four distal setae; article-4 minute, with three or four distal setae.

Antenna ( Fig. 14 ). Six articles, together four-fifths length of antennule; article-1 as long as wide, lacking setae; article-2 slightly wider than long, with distal seta, finely setulated in part; article-3 three-quarters length of article- 2, length two-thirds width, with two distal setae; article-4 three-times length of article-3, three times as long as wide, with six to eight setae; article-5 one-third length of article-4, with two or three setae; article-6 minute, with about five terminal setae.

Mouthparts (Fig. 15). Labrum rounded, setulose.

Left mandible with large crenulated lacinia mobilis, pars incisiva acute with bifurcated tip, pars molaris broad with slight crenulations; right mandible similar but with broader pars incisiva.

Labium with inner and outer lobes finely setulose.

Maxillule endite setulose, with ten large terminal spiniform setae, each with length about 20% of total endite length; palp with two long terminal setae.

Maxilliped palp article-1 lacking setae; article-2 with one outer and four inner setae; article-3 with row of about eight pinnate setae; article-4 with row of four or five setae on distal inner margin, two longer distal setae, and medial seta; basis with four long setae extending to base of palp article-3; endites distally with three distal spines (one spatulate) and two spiniform setae as coupling hooks

Cheliped ( Fig. 14 ). About one-quarter length of body when extended; basis length 1.5 width with single dorsodistal protuberance with seta; merus triangular with about eleven setae near ventral margin; carpus extends distally as a ventral cuff over the base of the propodus, similar in length to basis, length 1.5 times width, with five or six setae near ventral margin; propodus slightly shorter than carpus, length 1.5 times width, inner comb-like row of three setae near articulation with dactylus, fixed finger slightly shorter than palm and set along the same axis, with terminal spine, single seta on ventral margin, three setae on inner margin of fixed finger; dactylus ventral margin smoothly-curved, unguis short and solid, extending about one-third length of dactylus.

Pereopod-1 ( Fig. 16 ). Basis width one-third length, length slightly less than length of merus and carpus together, with single long seta about one-quarter distance along dorsal margin; ischium with one ventral seta; merus half length of basis with one seta near ventral margin; carpus 1.2 times length of merus with three distal setae; propodus about 1.2 times length of carpus, with three distal simple setae and plumose seta; dactylus long and slen- der, dactylus and unguis together 1.2 times length of propodus, unguis about 1.5 times length of dactylus.

Pereopods 2 and 3 ( Fig. 16 ). Similar; basis length just over twice width, 1.5 times length of merus and carpus together, with two or three setae about one-third distance along dorsal margin; ischium with distal seta; merus onequarter length of basis, with rudimentary spiniform seta and simple seta distally; carpus with similar length to merus, two rudimentary spiniform setae near distal margin; propodus 1.5 times length of carpus, with rudimentary spiniform seta, row of very small setae, and two long simple setae near distal margin; dactylus and unguis together about two-thirds length of propodus, unguis about equal in length to dactylus.

Pereopods 4 and 5 ( Fig.16 ). Similar; basis width about three-fifths length, length 1.3 times length of merus and carpus together, with two or three plumose setae about one-third distance along margin; ischium with two ventro-distal setae; merus one-third length of basis, with two ventro-distal tubercles that extend into setae; carpus similar in length and width to merus, with three small spiniform setae and one simple seta near distal margin; propodus similar in length to carpus, with two small spiniform seta ventro-distally and four long simple setae dorso-distally, the longest longer than dactylus; dactylus and unguis fused into claw, together about two-third length of propodus, unguis about one-quarter length of propodus.

Pereopod-6 ( Fig. 16 ). Similar to pereopods 4 and 5, other than propodus with five long setae dorso-distally

Pleopods 1–5 ( Fig. 16 ). Similar; basal article with plumose seta, exopod with about 25 plumose setae on inner margin; endopod with about 19 plumose setae on inner margin, plumose seta midway on outer margin.

FIGURE 15. Parakonarus robertsoni . Seven Mile Beach, WA. Female. Labrum (L), left mandible (Md l), right mandible (Md r), labium (La), maxillule (Mx), maxilliped (Mxp). Scale units 0.1 mm for full mouthparts.

Uropod ( Fig. 16 ). Long and slender, extending a similar distance to distance from third pleonite to rear of pleotelson; basal article length about 1.2 times width, lacking distal setae; exopod with one article, about 1.4 times length to article-1 of endopod, with two long terminal setae, the longest extending to article-5 of endopod; endopod with six articles.

MALE. Body ( Fig. 17 ). Observed length 2.7–4.0 mm; body robust, about five times longer than broad; cephalothorax frontal margin with rostrum, lateral margin with concavity behind eye, then expanded in smooth convex curve to anterio-lateral corner of pereonite 1, length about 1.2 times width, slightly less than one-quarter body length; eyes large, pear-shaped, about one-quarter length of cephalothorax.

Pereon length half total body length; pereonites 1–3 similar, length about one-quarter width; pereonites 4 and 5 similar, about twice length of pereonite-3, length about two-fifths width; pereonite-6 about 1.2 times length of pereonite-3, length one-third width.

Pleonites 1–5 similar, length one-fifths width, together one-quarter of total body length.

Pleotelson with similar length to pleonite 5 and three-quarters width; posterior margin with a pair of long central setae, a long plumose seta and small simple seta dorso-distally.

Antennule ( Fig. 17 ). Two-fifths length of body, article-1 about three times longer than wide, with numerous small setae as illustrated; article-2 about two-fifths length of article-1, with several distal setae; article-3 about onethird length of article-2, expanded dorsally to cover part of first article of flagellum, with long dorso-distal seta; articles 4–14 comprising flagellum with length about two-thirds total antennule length, each article with numerous aesthetascs, terminal article minute.

Antenna ( Fig. 17 ). Six articles, together about half as long as antennule; article-1 as long as wide, lacking setae; article-2 about length of article-1, with three setae; article-3 three-quarters length of article-2 and similar width, with one distal seta; article-4 just over twice length of article-3, with about five simple and about five plumose setae; article-5 1.6 times length of article-4 and two-thirds width, with three long setae distally; article-6 reduced to small terminal cap, with four long setae, the longest extending about 0.8 total length of antennule.

Mouthparts reduced and fused.

Cheliped ( Fig. 17 ). About half length of body when extended; basis length 1.5 width; merus triangular with about eleven setae near ventral margin; carpus similar in length to basis, length 1.3 times width, with four setae on ventral margin, eight or nine small dorsal setae; propodus similar length and two-thirds width to carpus, ventral margin almost straight, inner comb-like row of about 17 setae extend obliquely nearly full distance across palm, fixed finger triangular, about one-sixth total length of propodus, with terminal spine, two setae on ventral margin, about six simple setae on inner margin; dactylus elongate, opposed to full length of propodus, length just over four times length of propodus fixed finger, width about one-sixth length, ventral margin with smooth sinusoidal curve, row of about seven very short setae, unguis short and solid, extending about one-tenth total length of dactylus.

Pereopod-1 ( Fig. 18 ). Basis width one-quarter length, length 0.8 times length of merus and carpus together, with simple seta about one-fifth distance along dorsal margin; ischium with two small ventral setae; merus onethird length of basis with ventro-distal seta; carpus twice length of merus with spiniform and three simple setae distally; propodus slightly longer than carpus, with two spiniform and a simple seta distally; dactylus long and slender, dactylus and unguis together about 88% of length of propodus, unguis equal in length to dactylus.

Pereopods 2 and 3 ( Fig. 18 ). Similar; basis width about one-quarter length, length 1.4 times length of merus and carpus together, with seta about one-quarter distance along dorsal margin; ischium with two ventro-distal setae; merus one-third length of basis, with spiniform seta and simple seta distally; carpus length 1.3 times merus, with three spiniform setae and about three simple setae near distal margin; propodus 1.5 times length of carpus, with two spiniform setae and simple seta distally; dactylus and unguis together about half length of propodus, unguis equal in length to dactylus.

Pereopods 4–6 ( Fig. 18 ). Similar; basis width about one-third length, length 1.4 times length of merus and carpus together, with seta midway ventrally and a plumose seta about one-third distance along dorsal margin; ischium with 2 ventro-distal setae; merus one-third length of basis, with two spiniform setae distally; carpus slightly longer and about equal in width to merus, with four spiniform setae and simple seta near distal margin; propodus 1.5 times length of carpus, with two spiniform seta ventro-distally and about three setae dorso-distally; dactylus and unguis partially fused into claw, together about three-fifths length of propodus, unguis about one-third length of dactylus.

Pleopods 1–5 ( Fig. 18 ). Similar; basal article with plumose seta, exopod with about 25 plumose setae on inner margin, distinct gap between proximal seta and others in series; endopod with about 16 plumose setae on inner margin, plumose seta midway on outer margin.

Uropod. Similar to female other than with more and longer setae.

Etymology. This species is named in honour of Alistar Robertson for initiating investigations of seagrass epifauna that led to this study.

Distribution. Rottnest Island to Dongara, WA.

Remarks. Bird (2011) noted a number of major character differences that distinguished species in the genera Konarus and Parakonarus from Pseudoleptochelia , including, for females, stout antennules, a lack of spine-like processes on antenna articles 2–3, a dense group of setae on the ventral cheliped merus, a cheliped carpal cuff, similar meral setation on pereopods 4–6, and elongate propodus on male cheliped. He recognised a single Parakonarus species ( Parakonarus kopure ) and two species of Konarus ( Konarus crassicornis and Konarus cheirus ). Features that differentiate female Parakonarus from Konarus include pereonites 1–3 together shorter rather than about equal to total length of pereonites 4–6, greater number of spiniform setae on pereopods (e.g. carpus of pereopods 4 and 5 with three small spiniform setae rather than two), and uropod exopod with one rather than two articles.

Parakonarus robertsoni n. sp. has close affinities with P. kopure . For females, P. robertsoni differs from P. kopure in antenna article-3 possessing two rather than one distal setae, maxilliped basis possessing four rather than five distal setae, and uropod endopod possessing six rather than five articles; for males, the antennule flagellum is longer (11 rather than 7 or 8 articles), and, most notably, the cheliped propodus is four times rather than twice the length of the opposed fixed finger.

Female P. robertsoni is also close to southwestern Australian Leptochelia fairgo Bamber, 2005 , differing in subtle features only—about eleven rather than five ventral setae on the cheliped merus, wider cheliped carpus, and a longer, more slender uropod with relatively shorter exopod. Bird (2011) also noted the close relationship between P. k o p u re and L. fairgo , remarking that L. fairgo “shares certain characters with Parakonarus , such as stout antennules, thin setae on antenna articles 2–3, a dense setal group on the cheliped merus, a cheliped carpal cuff, similar meral setae on pereopods 4–6 and a subchelate male cheliped with an inferior carpal process.” These features are shared with P. robertsoni . The original description of L. fairgo makes no mention of an obvious demarcation of the second thoracomere, as is present in both P. robertsoni and P. kopure , although inspection of type specimens indicates that this demarcation is also present in L. fairgo (Andrew Hosie, Western Australian Museum, pers. comm.). Given the close relationships between these three taxa, L. fairgo is transferred to the genus Parakonarus as Parakonarus fairgo n. comb.

Male P. robertsoni differ from P. fairgo in the form of the cheliped carpus, the distal margin being relatively straight rather than produced into a pronounced apophysis. Antenna article- 5 in male P. robertsoni is also considerably more elongate than in L. fairgo , and the cheliped merus possesses many more setae. This latter feature, plus similar slender uropods, and co-occurrence in the same samples, unify the male and female specimens described here.

In addition to collections at the temperate type location near Albany, WA ( Bamber 2005), P. fairgo has been recorded at subtropical Moreton Bay, Queensland ( Bamber 2008). Notably, however, female specimens from Moreton Bay attributed to P. f a i rg o possessed more setae on the cheliped merus than specimens collected at Albany, no males were examined, and the collection locations are widely-separated geographically (~ 4,000 km coastal distance) and biophysically (~6o water temperature difference); consequently, it seems likely that the Moreton Bay taxon represents a sibling species rather than being conspecific. If this supposition is correct, then at least four Parakonarus species exist— P. fairgo , P. robertsoni , P. k o p u re and the undescribed Moreton Bay species.

Another Australian leptocheliid species, Pseudoleptochelia straddi Bamber 2008 , could potentially belong to Parakonarus , given the elongate dactylus of the male cheliped that align this species more closely with Parakonarus and Konarus than with other Pseudoleptochelia , and 11-articled antennule flagellum. No female P. straddi are known. However, P. straddi is immediately distinguishable from known Parakonarus species because of the presence of a large rounded apophysis on the ventral margin of the cheliped propodus, and may in fact comprise the male corresponding with females attributed to Konarus cheiris at Moreton Bay ( Bird 2011, Bamber pers. comm.).

The habitat preference of P. robertsoni appears distinct from other known Australian Parakonarus taxa but is similar to that of P. kopure in New Zealand. Parakonarus robertsoni is only known from algae and seagrasses in the shallow sublittoral fringe around low water mark (<1 m depth), whereas P. fairgo appears restricted to sandy substrata, in water depths of 23–40 m in W. A. and in 3–10 in Moreton Bay ( Bamber 2008).

Figures

FIGURE 14. Parakonarus robertsoni. Seven Mile Beach, WA. Female lateral, antennule (A 1), antenna (A 2), cheliped (CH), pleotelson (Plt). Scale units 0.1 mm.

FIGURE 16. Parakonarus robertsoni. Seven Mile Beach, WA. Female. Pereopods 1 – 6 (P 1 – P 6), pleopod (Pl). Scale units 0.1 mm for full appendages.

FIGURE 17. Parakonarus robertsoni. Seven Mile Beach, WA. Male dorsal (holotype), antennule (A 1), antenna (A 2), cheliped (CH), pleotelson (Plt). Scale units 0.1 mm.

FIGURE 18. Parakonarus robertsoni. Seven Mile Beach, WA. Male. Pereopods 1 – 6 (P 1 – P 6), pleopod (Pl), uropod (U). Scale units 0.1 mm for full appendages.