Akanthinotanais Sieg

Larsen, Kim, Nagaoka, Ryoko & Froufe, Elsa, 2012, Tanaidacea (Crustacea) from Macaronesia III. The shallow-water Tanaidomorpha from the Cape Verde archipelago, Zootaxa 3498, pp. 24-44 : 38-42

Subgenus Akanthinotanais Sieg

Diagnosis (modified after McLelland 2008). Antennule setae not bifurcate. Eye-lobes present, most often with visual elements. Maxillule endite terminating with eight to nine spiniform setae.

Type species. Pseudotanais (Akanthinotanais) gerlachi Sieg

Pseudotanais (Akanthinotanais) breviaquas , n. sp. Larsen Figures 9–10

Material examined. Holotype ovigerous female, 1.9 mm (Reg # MMF 42312). Mindelo marina, St. Vicente, 0.5 m depth, hard bottom algae. Paratypes (Reg # MMF 42313): one non-ovigerous female (dissected), five females, two mancae, same locality.

Diagnosis. Eyes with visual elements. Antenna article 2 and 3 with spiniform dorsodistal setae; article 4 and 5 with long robust distal setae. Maxilliped endites with vestigial division. Cheliped carpus with dorsodistal angular process. Pereopod 1 carpus setae of unequal lengths. Pereopods 2–4 ischium with one small simple seta and one robust seta. Pereopods 2–3 propodal terminal spiniform setae shorter than dactylus/unguis combined. Pereopods 4–6 carpus with one bone-shaped and three spiniform setae no longer than half the length of propodus. Uropod endo- and exopod biarticulate and almost of equal length.

Etymology. From the Latinization of ‘shallow-water’. The name refers to the shallow-water habitat of this species.

Description. Body from ovigerous female holotype, appendages from non-ovigerous dissected paratype.

Body ( Figs. 9 A) 6.5 times as long as broad. Cephalothorax longer than pereonites 1–3, narrowing anteriorly, with indistinct eye-lobes bearing visual elements. Pereonites, all pereonites with seta at pereopod attachment. pereonite 1 reduced to being only slightly longer than pereopod width. Pereonites 1 and 4–6 with pair of dorsolateral setae. Pereonite 1–3 and 6 shorter than wide. Pereopod 4 and 5 longer than wide. Pleon about one–third of total body length. All pleonites with pair of dorso-medial setae, all bearing pleopods. Pleotelson longer than pleonites 3–5 combined, apex ventrally bent, with pair of apical setae.

Antennule ( Fig. 9 B) longer than cephalothorax. Article 1 longer than half of total length, four times as long as broad, with six small setulated medial and one long (longer than half of article 1) simple medial setae, dorsally with one long (longer than half of article 1) and one small simple and four setulated distal setae. Article 2 less than twice as long as broad, shorter than article 3, with one long (longer than half of article 1), simple distal seta. Article 3 less than half as long as article 1, six times as long as broad, with three simple, three long (longer than half of article 1), one setulated distal setae, and one aesthetasc. No modifications on setal apex observed.

Antenna ( Fig. 9 C) marginally shorter than antennule. Article 1 marginally longer than wide, shorter than article 2, naked. Article 2 about as long as article 3, with short dorsodistal robust seta. Article 3 less than half as long as article 4, with short dorsodistal robust seta. Article 4 as long as article 1–3 combined, with one long robust, two simple, and four setulated distal setae. Article 5 about half as long as article 3, with one simple distal seta. Article 6 minute, with four simple setae.

Mouthparts. Labrum ( Fig. 9 D) only proceeding shortly from clypeus, naked. Mandibles ( Figs. 9 E,F) molar tapering and ending in one pronounced spine. Left mandible ( Fig. 9 E) lacinia mobilis well developed with outer crenulations; incisor with inner process and only one denticle. Right mandible ( Fig. 9 F), lacinia mobilis not articulated from mandibular body, gently curved, incisor with outer crenulations. Labium ( Fig. 9 G), lobes naked, gently curved and featureless. Maxillule ( Fig. 9 H) endite with eight spiniform setae, palp uniarticulate but with sharp decrease in width midlenght and two relatively short terminal setae. Maxilla ( Fig. 9 I) ovoid and featureless. Maxilliped ( Fig. 9 J) bases completely fused, with long seta near palp insertion. Endites almost completely fused, with one short inner seta and, small spinules on disto-lateral margins. Palp article 1 naked; article 2 with one simple, one long (longer than article 2–4 combined) setae and two setules, without outer seta; article 3 with three inner setae; article 4 with four inner setae. Epignath ( Fig. 9 K) tapering distally, naked.

Cheliped ( Fig. 10 A) sclerite well developed. Basis as long as carpus, with one dorsodistal seta. Merus ovoid, with one ventral seta. Carpus less than twice as long as broad, with two unequally length ventral setae, one relatively long dorsodistal seta arising from a right angle process and one small spiniform dorsoproximal seta arising from a grove. Propodus longer than carpus, with one small seta between dactylus and fixed finger. Chela forcipate. Fixed finger with one ventroproximal seta and three inner setae. Dactylus as long as, but narrower than, fixed finger, with distal denticles and small proximal simple seta.

Pereopod 1 ( Fig. 10 B) coxa fused to lateral shield but with seta near basis attachment. Basis longer than three succeeding articles combined, with small dorsoproximal seta. Ischium with small seta. Merus shorter than carpus, extending dorsodistally, naked. Carpus about three-quarters as long as propodus, with small ventrodistal and dorsodistal setae. Propodus more than half as long as basis, with ventro-subdistal seta apparently without dorsodistal spine. Dactylus and unguis combined marginally shorter than propodus. Unguis longer than dactylus.

Pereopod 2 ( Fig. 10 C) Basis longer than three succeeding articles combined, naked. Ischium with two ventrodistal setae, one of which is robust, almost spiniform. Merus shorter but wider than carpus, not extending dorsodistally, with two small ventrodistal setae, one of which is spiniform. Carpus longer than three-quarters as long as propodus, with one simple dorsodistal, and two unequally length ventrodistal spiniform setae. Propodus more than half as long as basis, with dorsodistal spine and with ventrodistal seta. Dactylus and unguis combined two-thirds as long as propodus. Unguis longer than dactylus.

Pereopod 3 ( Fig. 10 D) as pereopod 2 except: basis small dorsoproximal simple seta and ventromedial setulated seta. Carpus with two ventrodistal spiniform and one dorsodistal bone-shaped setae. Dactylus broken.

Pereopod 4 ( Fig. 10 E) Basis wider than on pereopod 1–3, with two dorsoproximal setulated setae. Ischium with two small ventrodistal setae, one of which is robust. Merus shorter than carpus, with two ventrodistal spiniform setae. Carpus marginally shorter than propodus, with one short and two longer serrated distal spiniform, and one bone-shaped dorsodistal setae. Propodus half as long as basis, with one long dorsodistal and two shorter ventrodistal spiniform setae. Dactylus incompletely fused with unguis to form claw, less than half as long as propodus.

Pereopod 5 ( Fig. 10 F) as pereopod 4 except: ischium setae not robust. Propodus with dorsomedial setulated, dorsodistal spiniform, and only one ventrodistal spiniform setae.

Pereopod 6 ( Fig. 10 G) as pereopod 4 except: basis with only one dorsoproximal setulose seta. Propodus with one long and one short dorsodistal and two shorter ventro-subdistal spiniform setae.

Pleopods ( Fig. 9 L) all similar, basis article naked. Endopod shorter and narrower than exopod, with five plumose setae (the innermost shorter than others). Exopod with 13 plumose setae. No gap between proximal setae.

Uropods ( Fig. 9 M) As long as pleotelson. Basal article naked, almost square. Endopod with two subequal length articles. Article 1 with one distal simple seta and two setulated distal setae; article 2 with one long subdistal, two long distal, and three small distal setae. Exopod with two subequal length articles, slightly shorter and narrower than those of endopod. Article 1 with one distal simple seta, distal article with two long simple setae.

Remarks. The new species can easily be separated from the other species of the subgenus by the antenna article 4 and 5 long spiniform seta and additionally by the specific characters given in Table 1).

Species Characters

P. (A.) siegi Kudinova-Pasternak Long pleopod setae. Lack of denticles on the cheliped fixed finger/dactylus.

Pereopods 2–4 with one short and one spiniform ischial setae. Much shorter uropods.

P. (A.) makrothrix Dojiri & Sieg (only Longer pereonite 2. Pereonites 1,2 & 4–6 with dorsal setae. Maxilliped endites

rudimentarily described) incompletely fused. Pereopod 6 with two spiniform meral setae.

P. (A.) longipes Hansen Presence of maxilliped endite setae. Much wider cheliped propodus. Pereopods 2–4 with one short and one spiniform ischial setae. Presence on pereopod 4–6 carpus of only three spiniform setae.

P. (A.) scrappi Bamber Presence of setae on pereopod 1. Pereopod 6 with double number of propodal spiniform setae. Many more pleopodal exopod plumose setae.

P. (A.) guillei Shiino Eyes with visual pigmentation. Lack of paired setae on pereonite 2 and 3. Shorter

uropods.

P. (A.) similis Sieg Pereopods 2–4 with one short and one spiniform ischial setae. Pereopod 4–6 with the

claw-shaped dactylus/unguis. Biarticulated uropods.

P. (A.) mortenseni Sieg Cheliped carpus with dorsodistal process, much wider propodus. Pereopod 4–6 with

claw-shaped dactylus/unguis. Longer uropodal exopod.

P. (A.) gaussi Vanhöffen Pereopods 2–4 with one short and one spiniform ischial setae. Many more pereopod

plumose setae.

P. (A.) gerlachi Sieg Cheliped carpus with dorsodistal process.

P. (A.) malayensis Sieg Many more pleopod plumose setae. Longer uropodal exopod.

This subgenus has representatives in both deep (P. A. gaussi Vanhöffen, P. A. longipes Hansen, P. (A.) makrothrix Dojiri & Sieg , P. (A.) siegi Kudinova-Pasternak ) and shallow water ( P. (A.) gerlachi Sieg , P. (A.) guillei Shiino , P. (A.) malayensis Sieg , P. (A.) mortenseni Sieg , P. (A.) scrappi Bamber , P. (A.) similis Sieg ).

The subgenus Akanthinotanais is currently being raised to full genus level as well as family level (McLelland in press). We concur with this systematic change and have thus not made comparisons with other species of Pseudotanais from other subgenera.

While there are several reports of tanaidaceans with tantulocaridean parasites ( Greve 1965, Boxshall & Lincoln 1987, Grygier & Sieg 1990, Larsen 2005), there is only one record of parasitic copepods on tanaidaceans ( Bamber & Boxhall 2006). This is a record of a genus from the family Nicothoidae which, among other things, is characterized by its parasitic shape (a greatly reduced body and no appendages on the infectious stage). The species described above was found with a, potentially parasitic, harpacticoid copepod loosely attached to pereopod 2. As the copepod was fully developed with a complete array of appendages, we cannot say whether this copepod represents a pre-infectious form or was simply attached by some sampling artefact.

Figures

FIGURE 9. Pseudotanais (Akanthinotanais) breviaquas n. sp., female. A holotype, lateral view scale bar 1.0 mm. B – M paratype, Scale bars 0.1 mm. B, antennule. C, antenna. D, labrum. E, left mandible. F, right mandible. G, labium. H, maxillule. I, maxilla. J, maxilliped. K, epignath. L, pleopod. M, Uropod.

FIGURE 10. Pseudotanais (Akanthinotanais) breviaquas n. sp. A, cheliped. B, pereopod 1. C, pereopod 2. D, pereopod 3. E, Pereopod 4. F, pereopod 5. G, pereopod 6. Scales bars 0.5 mm.