Metagathotanais Bird & Holdich
Creators: name: Larsen, Kim
name: Bird, Graham
name: Ota, Mayumi
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Tanaidacea
Agathotanaidae
Metagathotanais

description: Genus Metagathotanais Bird & Holdich
Type species: Metagathotanais insulcatus Bird & Holdich
Diagnosis, female: (modified after Bird & Holdich 1988) cephalothorax shorter than pereonites 1 and 2 together. Pereonite-6, pleonites and pleotelson fused or partly fused. Antennule four-articled, with or without minute terminal cap-like article. Antenna six-articled, article-2 with dorsal seta. Mandible molar reduced, lacinia mobilis of left mandible small and spiniform or reduced. Maxillule endite with eight to ten terminal spiniform setae. Maxilliped bases and endites together oval or heart-shaped. Epignath without terminal spiniform seta. Cheliped sclerites (‘pseudocoxa’) fused ventromedially, not protruding below ventrum of cephalothorax. Uropod basis and endopod fused and without exopod.
Male. Generally as the female but the pleon fusion is either be incomplete or absent. Mouthparts functional. Reduced pleopods present,
Metagathotanais furcilla n. sp. Larsen & Bird Figs 1–3
Material examined. Holotype: non-ovigerous female (Reg. # ZMH K-43312)), ANDEEP II, sample # DZMB-HH 10445, station 137, 63°44.98’S, 47°75’W, 4976 m, 14 March 2002, EBS-supra. Paratypes (Reg. # ZMH K-43313): one fragmented non-ovigerous female, one preparatory male (dissected), and one non-ovigerous female (dried out), ANDEEP II, sample # DZMB-HH 10444, same locality and date as holotype, EBS-epi.
Diagnosis. Pereonite-6, pleonites and pleotelson incompletely fused in both genders. Antennule with minute terminal cap-like article. Antenna article-2 with one short dorsomedial and one longer dorsodistal setae; article-3 naked. Lacinia mobilis of left mandible reduced. Maxillule endite with ten terminal spiniform setae. Maxilliped basis with one outer seta; endites naked. Pereopods 1–3 merus and carpus with short spiniform setae. Pereopods 1–6 propodus with two to four dorsodistal spines. Uropod long (marginally shorter than pleotelson)
Etymology. Name derived from the Latin for ‘fork’, (in diminutive) as a noun, alluding to the diagnostic dorsodistal spines on the propodus of the pereopods.
Description. Non-ovigerous female (holotype, not dissected).
Body (Fig. 1 A). Heavily calcified, 8.5 times as long as wide. Cephalothorax with clear lateral shield, naked; lateral margins almost straight in dorsal view; longer than wide, shorter than pereonites 1 and 2 combined. Pereonites with weak lateral shoulders; pereonite 1 wider than long; pereonites 2–5 longer than wide, subequal; pereonite 6 square or marginally longer than wide. Pleon short (including pleotelson 0.15 times as long as total body length); all pleonites subequal and incompletely fused with pereonite-6, with each others and with pleotelson. Pleotelson longer than three last pleonites combined, acorn-shaped, apex rounded, with paired setae, and covered by dorsal plate.
Description. Preparatory male (paratype).
Body (Fig. 3 A, B). As non-ovigerous female except: Pleon short (including pleotelson 0.17 times as long as total body length).
Antennule (Fig. 1 B). Shorter than cephalothorax. Article-1 1.7 times as long as rest of antennule combined, with two simple and three setulose subdistal setae. Article-2 less than one-third as long as article-1, with one long simple and one setulated subdistal setae. Article-3 less than half as long as article-2, with dorsodistal process giving rise to two simple setae, one simple distal seta on ventral margin. Article-4 with one simple distal seta. Terminal cap-like article minute and partly fused to article-4, with at least two (broken) setae.
Antenna (Fig. 1 C). Shorter than antennule article-1. Article-1 naked. Article-2 with one subdistal seta and several setules. Article-3 longer than article-2, apparently naked but with dorsodistal process. Article-4 longer than combined length of other antenna articles, with one setulated distal seta. Article-5 as long as article-3, tapering and apparently naked. Article-6 minute, with one subdistal and three long simple distal setae.
Mouthparts. Labrum (Fig. 1 D) narrower than clypeus, distal edge setulose. Mandibles (Fig. 1 E, F) with no trace of functional molars although a non-chitinised process is present on right mandible. Right mandible (Fig. 1 E) incisor without denticles. Left mandible (Fig. 1 F) lacinia mobilis reduced to inner denticle completely fused with incisor, incisor blunt. Labium (Fig. 1 G) with small setulose outer process. Maxillule (Fig. 1 H) endite with ten spiniform distal setae and subdistal setules. Palp with two relatively short terminal setae. Maxilla (Fig. 1 I) ovoid, featureless. Maxilliped (Fig. 1 J) basis with one short seta on outer medial margin near palp insertion. Endites without setae but with blunt denticle. Palp article-1 naked, articles 2 and 3 with three pinnate setae on inner margin, article-4 only half as wide and long as article-3, with one simple outer and four pinnate inner setae. Epignath (Fig. 1 K) as long as maxillule palp, featureless.
Cheliped (Fig. 1 L). Basis naked, incompletely fused to sclerite, less than twice as long as merus. Merus with one medial seta. Carpus marginally longer than propodus including fixed finger, with one medioventral seta and one dorsodistal and one dorsomedial small setae. Propodus with one long rigid inner seta behind dactylus insertion. Fixed finger with one ventral seta and three setae on inner margin, inner margin with prominent distal carina. Dactylus as long as fixed finger, naked.
Pereopod-1 (Fig. 2 A). Coxa rounded, naked. Basis as long as combined length of carpus and propodus, naked. Ischium with one simple seta. Merus 0.7 times as long as carpus, widening distally, with one small spiniform ventrodistal seta. Carpus less than half as long as basis, with one dorsodistal and two ventrodistal small spiniform setae. Propodus longer than carpus, with one ventrodistal simple and one spiniform setae and two dorsodistal spines and scales. Dactylus and unguis combined shorter than propodus. Unguis longer than dactylus, with dorsodistal acute process.
Pereopods 2–3 (Fig. 2 B,C). As pereopod-1 except propodus with one spiniform seta only.
Pereopods 4–5 (Fig. 2 D,E). Coxa naked, partly fused to body. Basis longer than combined length of carpus and propodus, with one setulated ventromedial seta. Ischium with one seta. Merus shorter than carpus, widening distally, with two ventrodistal bayonet setae. Carpus less than half as long as basis, with one bone-shaped and three distal bayonet setae. Propodus marginally longer than carpus, with three bayonet setae and three dorsodistal spines. Dactylus and unguis subequal, together longer than propodus, not fused.
Pereopod-6 (Fig. 2 F). As pereopod-4 except: propodus with four bayonet setae and four dorsodistal spines. Pleopods (Fig. 3 C). All pairs similar, heavily calcified and immobile but not fused, without setae.
Uropod (Fig. 1 M). Marginally shorter than pleotelson. Basal article fused to uniarticulate endopod, with one medial and two distal setae.
Remarks. Metagathotanais furcilla n. sp. can be separated from the other two known species, M. insulcatus and M. loerzae Guerrero-Kommritz by the incomplete fusion of the pleonites and the dorsodistal spines of the propodi of pereopods 4–6; additionally, the short spiniform setae on the merus and carpus of pereopods 1–3 appear to be unique in this species.
description: Published as part of Larsen, Kim, Bird, Graham & Ota, Mayumi, 2013, The ANDEEP Tanaidacea (Crustacea: Peracarida) revisited I: the family Agathotanaidae Lang, with description of four new species, pp. 424-444 in Zootaxa 3630 (3) on pages 426-430, DOI: 10.11646/zootaxa.3630.3.2, http://zenodo.org/record/216501