Leptochelia gadgeti Edgar, 2012, n. sp.

Leptochelia gadgeti n. sp.

(Figs 8–9)

Material examined. Holotype. Male (NMV J62314), 3.1 mm, Cliff Head, WA (29.52°S 114.99°E), 1 m depth, seagrass (Amphibolis antarctica) washings, 5 January1986.

Paratypes. Two males (NMV J62315), holotype location, June 1985 – June 1987.

Other material. Ten males (NMV J62316), Seven Mile Beach, WA (29.17°S 114.89°E), 1 m depth, seagrass (Amphibolis antarctica and A. griffithii) washings, June 1985 – June 1987. Two males (NMV J62317) Little Armstrong Bay, Rottnest Island, WA (31.99°S 115.50°E), seagrass washings, 1 m depth, 21 Jan 1996.

Description. MALE. Body (Fig. 8). Observed length 1.9–3.2 mm; body slender, about ten times longer than broad; cephalothorax frontal margin produced into rostrum, lateral margin with concavities where basis and merus of cheliped adjoin, length about 1.5 times width and approximately one-fifth body length; eyes relatively small, pear-shaped, about one-sixth length of cephalothorax.

Pereon just over two-thirds total length; pereonite-1 length similar to width; pereonites 2 and 3 similar, about 1.6 times length of pereonite-1, length about 1.2 times width, waist-like concavity in posterior lateral margin; pereonite-4 and 5 similar, about 1.4 times length of pereonite-3, length about 1.5 times width, waist-like concavity in posterior lateral margin; pereonite-6 half length and similar width to pereonite-5.

Pleonites 1–5 similar, together one-eighth as long as body and slightly wider.

Pleotelson length similar to pleonite 5; posterior margin with small paired central setae, one or two simple lateral setae.

Antennule (Fig. 8). Length two-third length of body, article-1 about 20 times longer than wide, with distal seta; article-2 about 45% of article-1, length about 12 times width; article-3 length about one-tenth of article-2, with three distal aesthetascs; articles 4–10 comprising flagellum that extends about one-quarter of total antennule length, each article with two or three aesthetascs distally; terminal article minute.

Antenna (Fig. 8). Six articles, together about one-tenth as long as antennule; article-1 as long as wide, lacking setae; article-2 slightly longer than article-1, with two spiniform setae and small simple seta distally; article-3 length similar to article-1, with distal spiniform seta; article-4 about three times longer than article-3, with three long simple and two plumose setae distally; article-5 about two-fifths length of article-4, with two long setae distally; article-6 reduced to small terminal cap, with about four setae, the longest extending about half length of antennule articles.

Mouthparts reduced and fused.

Cheliped (Fig. 8). Length about 1.2 times length of body; basis length 1.6 times width; merus triangular with two setae; carpus slightly less than half total length of cheliped, 15 times longer than wide; propodus similar in length and slightly narrower than carpus, inner comb-like row of about 12 setae near articulation with dactylus with outer setae in series over twice length of other setae, fixed finger about 30% total propodus length, with large trapezoidal protuberance that extends about two-thirds length of fixed finger and is centred midway along inner margin, five distal setae, minute terminal spine; dactylus slightly longer than fixed finger, inner margin evenly-curved with row of about eight very short setae, unguis minute.

Pereopod-1 (Fig. 9). Basis width one-sixth length, length 1.2 times length of merus and carpus together, with two setae about one-third distance along dorsal margin; ischium with one small ventral seta; merus about half length of basis; carpus three-fifths length of merus with three or four distal setae; propodus four-fifths length of merus and carpus together, with about four distal setae including spiniform seta; dactylus and unguis together about three-quarters length of propodus, unguis about two-thirds length of dactylus.

Pereopods 2 and 3 (Fig. 9). Similar; basis width about one-sixth length, length 1.6 times length of merus and carpus together, with three setae about one-third distance along dorsal margin; ischium with two small ventro-distal setae; merus two-fifths length of basis, with spiniform seta distally; carpus two-thirds length of merus, with spiniform seta and two or three simple setae near distal margin; propodus twice length of carpus, with spiniform seta and simple seta five-sixths distance to distal margin; dactylus and unguis together about two-thirds length of propodus, unguis about half length of dactylus.

Pereopods 4 and 5 (Fig. 9). Similar; basis width about one-third length, length 1.4 times length of merus and carpus together, with two seta near ventral margin; ischium with 2 ventro-distal setae; merus two-fifths length of basis, with two spiniform setae distally; carpus similar in length and width to merus, with four spiniform setae and one or two simple setae near distal margin; propodus twice 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 just over half length of dactylus.

Pereopod-6 (Fig. 9). Similar to pereopod-5, other than with slightly shorter propodus, length about 1.5 times carpus and 1.2 times dactylus; propodus with four simple setae dorso-distally.

Pleopods 1–5 (Fig. 9). Similar; basal article with plumose seta, exopod with about 20 plumose setae on inner margin, gap between proximal-most seta and others in series; endopod with about 15 plumose setae on inner margin, plumose seta midway along outer margin.

Uropod (Fig. 8). Basal article length similar to width, with about four distal setae; exopod with long article, length about equal to length of endopod articles 1 and 2 together, with two long terminal setae that extend to end of endopod; endopod with five articles.

Etymology. The specific name alludes to similarity between the long chelipeds and the extendable prosthetic arms of the animated character Inspector Gadget.

Distribution. Rottnest Island to Dongara, WA.

Remarks. Male Leptochelia gadgeti n. sp. can be distinguished from all other known leptocheliid species in possessing a large flat process on the inner margin of the cheliped fixed finger. The small pleon and the waist-like constrictions between pleon articles immediately distinguish this tanaidacean from other known Australian species of Leptochelia without dissection.