Leptochelia evansi, 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 : 12-15

Leptochelia evansi n. sp.

( Figs 6–7 )

Material examined. Holotype. Male ( NMV J62324 ), 3.2 mm, Seven Mile Beach, WA (29.17°S 114.89°E), 1 m depth, seagrass ( Amphibolis antarctica and A. griffithii ) washings, 3 March 1985.

Paratypes. 16 males ( NMV J62325 ), holotype location, June 1985 – June 1987.

Other material. 32 males ( NMV J62326 ), Cliff Head, WA (29.52°S 114.99°E), 1 m depth, seagrass ( Amphibolis antarctica ) washings, June 1985 – June 1987; six males ( NMV J62327 ), Little Armstrong Bay, Rottnest Island, WA (31.99°S 115.50°E), seagrass washings, 1 m depth, 21 Jan 1996.

Description. MALE. Body ( Fig. 6 ). Observed length 1.8–4.0 mm; body slender, about ten times longer than broad; cephalothorax frontal margin straight from eye to slight rostrum, lateral margin straight-sided for about one third distance from eye, then expanded in smooth convex curve to anterio-lateral corner of pereonite-1, length about 1.2 times width and approximately one-sixth body length; eyes pear-shaped, about one-fifth length of cephalothorax.

Pereon just over half total length; pereonite-1 length about one-quarter width; pereonites 2 and 3 similar, about 1.5 times length of pereonite-1, length about one-third width; pereonites 4 and 5 about 1.6 times length of pereonite-3, length about half width; pereonite-6 about 1.1 times length of pereonite-3, length about one-third width.

Pleonites 1–5 similar other than declining in width posteriorly with pleonite 5 four-fifths width of pleonite-1, together one-fifth as long as body.

Pleotelson about 1.2 times length of pleonite 5; posterior margin with paired long and small central setae, one or two simple setae and plumose seta posterio-laterally, one or two simple seta anterio-laterally and another near anterio-dorsal margin.

Antennule ( Fig. 6 ). Two-thirds length of body, article-1 about ten times longer than wide, with distal seta; article-2 about 44% of article-1; article-3 about 17% of article-2, articles 4-11 comprising flagellum that extends about one-quarter of total antennule length, each article with two or three aesthetascs distally; terminal article minute.

Antenna ( Fig. 6 ). Six articles, together about two-fifths as long as antennule; article-1 as long as wide, with single seta; article-2 about length of article-1 but narrower, with two or three setae; article-3 length 1.5 times length of article-2, with two distal setae; article-4 about two-thirds length of article-3, with three simple and two plumose setae; article-5 about 2.1 times length of article-4 but half width, with two or three long setae distally; article-6 reduced to small terminal cap, with about five setae, the longest extending about half length of antennule articles.

Mouthparts reduced and fused.

Cheliped ( Fig. 6 ). Length similar to length of body; basis large, one sixth length of carpus; merus triangular with two setae; carpus about half length of cheliped, seven times longer than wide, with about eight scattered setae; propodus similar in length and width to carpus, inner comb-like row of about 15 seta and separate longer seta near articulation with dactylus, fixed finger similar length to palm, smoothly curved as long projection with length about 15 times width, three setae on inner margin and two setae on outer margin, minute terminal spine; dactylus slightly longer than fixed finger but otherwise with matching proportions and with overlapping tip, inner margin smoothlycurved with row of about ten very short setae, unguis minute.

Pereopod-1 ( Fig. 7 ). Basis width one-sixth length, length 1.4 times length of merus and carpus together, with single seta about one-fifth distance along dorsal margin; ischium with one ventral seta; merus one-third length of basis with dorso-distal seta; carpus similar in length to merus with five distal setae; propodus slightly less than length of merus and carpus together, with four or five distal setae including spiniform seta; dactylus about threefifths length of propodus, unguis about 1.5 times length of dactylus.

Pereopods 2 and 3 ( Fig. 7 ). Similar; basis width about one-sixth length, length 1.6 times length of merus and carpus together, with seta about one-quarter distance along dorsal margin; ischium with two ventro-distal setae; merus one-quarter length of basis, with spiniform seta and simple seta distally; carpus slightly longer than merus, with two spiniform setae and simple seta near distal margin; propodus 1.3 times length of carpus, with spiniform seta and two simple setae near distal margin; dactylus and unguis together about half length of propodus, unguis about two-thirds length of dactylus.

Pereopods 4 and 5 ( Fig. 7 ). Similar; basis width about one-third length, length 1.3 times length of merus and carpus together, with two setae near ventral margin; ischium with 2 ventro-distal setae; merus two-fifths length of basis, with two spiniform setae distally; carpus slightly longer and about equal in width to merus, with four spiniform setae and one or two simple setae near distal margin; propodus 1.2 times length of carpus, with two spiniform setae ventro-distally and two simple setae dorso-distally; dactylus and unguis partially fused into claw, together just over half length of propodus, unguis about one-half length of dactylus.

Pereopod-6 ( Fig. 7 ). Similar to pereopod-5, other than with slightly wider basis with width about 2.7 times length; propodus with three simple setae dorso-distally.

Pleopods 1–5 ( Fig. 7 ). Similar; basal article with plumose seta, exopod with about 29 plumose setae on inner margin, no clear gap between proximal-most seta and others in series; endopod with about 21 plumose setae on inner margin, plumose seta midway on outer margin.

Uropod ( Fig. 7 ). Basal article length about 1.4 times width, with four distal setae; exopod with one small article, length about one-third of article-1 of endopod, with four long terminal setae that extend about halfway to end of endopod; endopod with six articles.

Etymology. This species is named in honour of David Evans, CSIRO senior technician, who assisted with field surveys at the type location.

Distribution. Rottnest Island to Dongara, WA.

Remarks. Leptochelia evansi n. sp. belongs to a well-defined group of Leptochelia with males possessing chelipeds that are long, slender and chelate—a group referred to by Lang (1973) as Leptochelia group 1, and by Bamber (2005) as Leptochelia minuta aggregate. This group includes L. erythraea (Kossman, 1880) , L. forresti (Stebbing, 1896) , L. longichelipes ( Lang, 1973) , L. longimana Shiino, 1963 , L. minuta Dana, 1849 , L. mirabilis Stebbing, 1905 and L. vimesi Bamber, 2005 . The smoothly curving fixed finger and dactylus of the male distinguish L. evansi from others in the group. Leptochelia forresti , L. longichelipes and L. longimana all possess a male cheliped with a fixed finger that has a turning point in convexity (apophysis) about one-third distance to end (see Shiino 1963; Lang 1973), rather than smoothly curved as in L. evansi . The chelipeds of Leptochelia mirabilis are about twice as long as the body ( Brown 1957), and both this species and L. minuta possess a protuberant process at the distal end of the inner margin of the fixed finger ( Larwood 1954). Leptochelia erythraea differs from L. evansi in inter alia having an antennule article-3 that is more than half (cf. about one-sixth) the length of article-2 ( Larwood 1954).

The only previously-known Australian species in this group, L. vimesi from Albany, Western Australia ( Bamber 2005), possesses prominent hyposphenia below pereonites 2–4. It also differs from L. evansi in possessing a longer antennule (three-quarters body length), cheliped dactylus with low apophysis on inner margin, and uropod with two-articled exopod and six-articled endopod in well-developed males.

Figures

FIGURE 6. Leptochelia evansi. Seven Mile Beach, WA. Male dorsal (holotype), antennule (A 1), antenna (A 2), cheliped (CH), pleotelson (Plt). Scale units: 1 mm for whole animal, 0.1 mm for appendages.

FIGURE 7. Leptochelia evansi. Seven Mile Beach, WA. Male. Pereopods 1 – 6 (P 1 – P 6), pleopod (Pl), uropod (U). Scale units 0.1 mm for full appendages.