Meromonakantha mauri, Segadilha & Serejo & Błażewicz, 2019

Segadilha, Juliana Lopes, Serejo, Cristiana Silveira & Błażewicz, Magdalena, 2019, New species of Typhlotanaidae (Crustacea, Tanaidacea) from the Brazilian coast genera Hamatipeda, Meromonakantha and Paratyphlotanais, with description of Targaryenella gen. nov., Zootaxa 4661 (2), pp. 309-342 : 319-325

Meromonakantha mauri sp. nov. Segadilha & Błażewicz

LSID urn:lsid:zoobank.org:act:F69A5FC6-B56F-4DCF-9915-9B795AFFA6B5

( Figs. 4–6 )

Material examined. Holotype: female non-ovigerous, length 1.2 mm ( MNRJ 28871 ) Sta P 27 #1 R2.

Paratypes: one female non-ovigerous, length 1.4 mm ( MNRJ 27376 ) dissected, Sta #44; one manca ( MNRJ 20593 ) Sta #50A; one female ( MNRJ 28872 ) Sta #44; one female ( MNRJ 28873 ) Sta P 27 #3 R2; one female ( MNRJ 28874 ) Sta P 27 #7 R2 .

Diagnosis. Cephalothorax as long as broad; maxilliped endites each with one gustatory cusp; pereopods 1–3 propodus with slender dorsodistal spine; pereopod-1 propodus with dorsal and ventral spines; pereopods 2–3 carpus ventral spines almost reaching half length of propodus; pereopods 2–3 carpus and propodus with dorsal and ventral spines; uropod exopod one-articled, 0.8 times as long as endopod; endopod two-articled, articles semifused, 7.3 times L:W.

Etymology. Named in honour of MSc. Fábio Mauro (Museu Nacional/UFRJ) in recognition of his solicitude and help to the first author since the beginning of her studies with Tanaidacea .

Description of female. Paratype dissected, length 1.4 mm ( MNRJ 27376). Body ( Figs. 4A ) about 6.5 times L: W. Cephalothorax rounded, about as long as broad, wider than pereonites, twice as long as pereonite-1, naked; eyes absent.

Pereonites 1–6: pereonite-1 trapezoidal and pereonites 2–6 hexagonal wider than long, with setae on lateral margins; 2.2, 2.7, 2.9, 2.1, 1.5, 1.1 times L:W, respectively; pereonite-1 trapezoidal, narrower distally; pereonites 2–6 hexagonal.

Pleon ( Fig. 4A ) 0.2 TBL, with five subequal pleonites, together about half length of cephalothorax, all with long setae on lateral margins. Pleotelson rectangular, 0.6 times L:W, with a pair of setae distally.

Antennule ( Fig. 4B ) stout, shorter than cephalothorax (0.6 times L:W), with three articles; article-1 0.6 TL, about 1.8 times L:W, with two simple and six penicillate medial setae, and simple and two penicillate setae distally; article-2 0.7 times L:W, 0.2 times as long as article-1, with simple and penicillate distal setae; article-3 slender, about 3.7 times L:W, 2.2 times as long as article-2, with five simple setae and with apical spur.

Antenna ( Fig. 4C ) of six articles, article-1 broken during dissection; article-2 long, 1.7 times L:W, with distal seta reaching distal margin of article-3; article-3 0.7 times L:W, half as long as article-2, with distal seta; article-4 about four times L:W, 3.6 times as long as article-3, with simple and two penicillate setae distally; article-5 3.2 times L:W, half as long as article-4, with distal seta broken; article-6 minute with setae broken.

Mandibles ( Fig. 4 D–E) with molar broad with rounded tubercles on distal margin. Left mandible ( Fig. 4D ) incisor with five teeth, lacinia mobilis well developed, with two lobes; right mandible broken during dissection, only molar recovered ( Fig. 4E ). Maxillule ( Fig. 4F ) endite with eight terminal spines; palp not recovered. Maxil- liped ( Fig. 4G ) basis with simple seta almost reaching distal margin of endites; each endite with one seta and one gustatory cusp on distal margin and microtrichia in outer corner; palp with four articles; article-1 triangular, naked; article-2 with at least two simple inner setae and one minute outer seta; article-3 with at least three simple inner setae; article-4 with at least three serrate inner setae and one subdistal outer seta. Labrum, labium, maxilla and epignath not recovered.

Cheliped ( Fig. 4H ) basis 1.5 times L:W, with posterior lobe partly occluded by the lower part of the cephalo- thorax, and with dorsodistal seta; merus triangular, with ventral seta; carpus stout, 1.2 times L:W, with two ventral and two dorsal setae (distal and subproximal); propodus longer than carpus, about twice L:W, with two setae near dactylus insertion (inner and outer); fixed finger with two ventral setae; cutting edge with two subdistal small teeth and three setae; dactylus slightly longer than fixed finger, with one minute dorsal seta.

Pereopod-1 ( Fig. 5A ) walking type; slender, longer than others; coxa with seta; basis elongate, more than ten times L:W, naked; ischium with ventral seta; merus 1.8 times L:W, with ventrodistal minute seta; carpus about twice L:W, with dorsodistal seta; propodus four times L:W, 0.8 times as long as merus and carpus combined, with dorsodistal and ventrodistal spine; dactylus 0.6 times as long as unguis; dactylus and unguis combined about as long as propodus.

Pereopod-2 ( Fig. 5B ) walking type; coxa with seta; basis almost six times L:W, naked; ischium with ventral seta; merus twice L:W, with ventrodistal seta and slender spine; carpus 2.2 times L:W, with dorsodistal slender spine and two ventrodistal spines (one long, almost reaching half length of propodus); propodus 4.5 times L:W, about as long as merus and carpus combined, with one dorsodistal slender spine and ventrodistal spines and fine setae distally; dactylus 0.6 times as long as unguis, with seta reaching dactylus distal margin; dactylus and unguis combined 0.7 times as long as propodus.

Pereopod-3 ( Fig. 5C ) similar to pereopod-2, except, basis 6.5 times L:W; carpus ventrodistal spine shorter; propodus about four times L:W.

Pereopod-4 ( Fig. 5D ) walking type; coxa absent; basis 3.4 times L:W, naked; ischium with two ventral setae; merus 1.7 times L:W, with two circumplumose distoventral spines; carpus 1.7 times L:W, with dorsodistal seta, one large serrate distal spine and two circumplumose spines distoventrally; propodus 4.7 times L:W, with dorsodistal seta as long as dactylus and two distoventral spines; dactylus about twice as long as unguis, semifused with unguis; dactylus and unguis combined half as long as propodus.

Pereopod-5 ( Fig. 5E ) similar to pereopod-4, except, basis four times L:W; propodus 4.4 times L:W.

Pereopod-6 ( Fig. 5F ) similar to pereopod-4, except, basis 3.6 times L:W; merus 2.2 times L:W; propodus about three times L:W, with three dorsodistal setae shorter than unguis ( Fig. 5G ); dactylus 1.7 times as long as unguis.

Pleopod ( Fig. 5H ). All pleopods similar; basal article naked; exopod with five plumose setae on outer margin and with one plumose seta on inner margin; endopod with ten plumose setae on outer margin; gap between proximal seta and the other setae in both rami.

Uropod ( Fig. 5I ) 1.5 times as long as pleotelson; basis 1.4 times L:W, naked; exopod one-articled, about 6.5 times L:W, 0.8 times as long as endopod, with simple medial seta, one stout and one simple setae distally; endopod two-articled, articles semifused, 7.3 times L:W; article-1 with three penicillate setae, article-2 with four long simple and three penicillate setae distally.

Distribution. This species is known from break of the continental shelf and slope off southeast Brazil ( Fig. 6 ), where it occurs at mainly in sand, with only one station in mud bottom, at depths ranging from 535 to 1050 m.

Remarks. Meromonakantha mauri sp. nov. is a typical member of the genus Meromonakantha by the presence of its body habitus with hexagonal pereonites 2–5, cephalothorax wider than the pereonites and stout antennule article-1 (twice L:W; Table 3 ). Meromonakantha mauri is different from all other members of the genus by: presence of slender and long ventral spine on the carpus of pereopod-2 that reaches almost half length of the propodus, presence of a slender dorsodistal spine on the propodus of pereopods 2–3, and a one-articled uropod exopod.

Within the genus, only M. irregularis and the new species have maxilliped endites with one gustatory cusp; both can be distinguished by: (1) body slender, more than six times L:W (about five times in M. irregularis ); (2) antennule article-3 stouter, 3.7 times L:W (4.4 times in M. irregularis ); (3) pereopod-1 merus with ventral seta (instead of spine); (4) pereopods 2–3 merus with ventral spines; and (5) pereopods 2–3 carpus dorsal spines.

Meromonakantha mauri resembles M. macrocephala from the North Atlantic ( Iceland) in habitus, however differs from it by: (1) antennule article-3 slender, about four times L:W (about twice in M. macrocephala ); (2) antenna article-4 slender, four times L:W (about three times in M. macrocephala ); and (3) pereopod-1 propodus with ventral spine.

The new species is distinct from M. natatoris in having: (1) body stouter; (2) antennule article-2 wider than long ( M. natatoris have the article longer than wide); (3) antennule article-3 stouter, less than four times L:W (almost six times in M. natatoris ); (4) antenna articles 2–3 setae shorter than half length of article-4; (5) cheliped carpus stouter, almost once L:W (twice in M. natatoris ); and (6) pereopod-1 propodus with dorsal and ventral spines.

Meromonakantha mauri is different from M. nutae in having (1) body stouter; (2) pereopod-1 propodus with ventral spine; (3) pereopods 2–3 merus with ventral spines; and (4) pereopods 2–3 carpus and propodus with dorsal and ventral spines.

The poor description of M. setosa from the NW Pacific and inaccessible type material make any detailed com- parison of the species impossible.

Figures

FIGURE 4. Meromonakantha mauri sp. nov. Paratype, female dissected, MNRJ 27376. A. Dorsal view, Scale = 1 mm. C. Antennule, D. antenna. E. left mandible, F. right mandible molar, G. maxillule, H. maxilliped, I. cheliped. Scale = 0.1 mm.

FIGURE 5. Meromonakantha mauri sp. nov. Paratype, female dissected, MNRJ 27376. A–F. Pereopods 1–6, G. pleopod, H. uropod. Scale = 0.1 mm.

FIGURE 6. Geographic distribution of Meromonakantha mauri sp. nov., along the southeastern Brazilian coast. Red point: type-locality (holotype); yellow points: paratypes.