Ischnomesus longiseta, Souza-Filho, 2017

Souza-Filho, Jesser F., 2017, Three new species of the genus Ischnomesus (Isopoda: Asellota: Ischnomesidae) from Brazilian deep sea, Zootaxa 4312 (2), pp. 259-276 : 265-269

Ischnomesus longiseta sp. nov.

( Figures 6–9 )

Material examined: Holotype: 1 adult female, 2.5 mm, (MOUFPE 15568), station Atex #3, R3, 0–2 cm, campaign ATEX, Espírito Santo basin, 19°54.5’00”S, 39°36.9’00”W, 800 m depth, October 2006.

Paratypes: 1 adult male, 3 mm (dissected and drawn, pleopods on one slide), ( MOUFPE 15569 ), station Atex #11, R1, 0–2 cm, campaign ATEX, Espírito Santo basin 19°53.7’00”S, 39°36.2’00”W, 798 m depth, October 2006 . 1 adult female (dissected and drawn, mouthparts on one slide), ( MOUFPE 15656 ) station LEAD TEG #4 , R2, 0–2 cm, campaign LEAD TEG, Espírito Santo Basin, 19°48’26”S, 39°30’38”W, September 2008 . 1 adult female, ( MOUFPE 15570 ), station Ext 3 LEAD2 #4, R2, 2– 5 cm, campaign EXT3 LEAD2 , Espírito Santo Basin, 19°54’29.28”S, 39°37’13.18”W, 750 m depth, September 2007 . 1 adult female, ( MOUFPE 15571 ) station Atex #12, R1, 0–2 cm, campaign ATEX, Espírito Santo Basin, 19°53’00”S, 39°35’00”W, 793 m depth, October 2006 . 1 adult male, ( MOUFPE 15572 ) station Ext 3, lead2 #2, R2, campaign EXT3 LEAD2 , Espírito Santo Basin, 19°54’36.64”S, 39°36’59.28”W, 750 m depth, September 2007 . 1 adult female, ( MOUFPE 15573 ) station FPSO P- 34 #12, R2, 0–2 cm, campaign FPSO P-34 , Espírito Santo Basin, 21°10’12.4”S, 40°01’13”W, isobath 1000 m depth, August 2007 . 1 adult female, ( MOUFPE 15655 ) station 3 loc Bia #3, R2, 0–2 cm, campaign 3 Loc Bia , 19°53’25.6”S, 39°36’44”W, 650 m depth, July 2007 . 1 adult female, ( MOUFPE 15657 ) station ATEX #10 , R1, 0– 2 cm, campaign ATEX, Espírito Santo Basin, 19°54.4’00”S, 39°37’00”W, 820 m depth, October 2006 .

Additional material examined (Different location of the holotype): 2 adults females, (UFS-CRU-0176), station BN4R1, 0–2 cm, campaign Marseal, Alagoas-Sergipe Basin, 10°32'07.1"S 36°05'11.5"W, 400 m, March 2013. 2 adults females, (UFS-CRU-0177), station FN4R2, 0–2 cm, campaign Marseal, Alagoas-Sergipe Basin, 11°11'20.4"S 36°52'16.8"W, 400 m, October 2013. 1 adult female, (UFS-CRU-0178), station HN4R1, 0–2 cm, campaign Marseal, Alagoas-Sergipe Basin, 11°37'31.2"S, 37°13'16.7"W, 400 m, October 2013. 1 adult female, (UFS-CRU-0181), station BN4R2, 2– 5 cm, campaign Marseal, Alagoas-Sergipe Basin, 10°32'06.9"S 36°05'11.7"W, 400 m, March 2013. 1 adult female, (UFS-CRU-0182), station FN4R1, 0–2 cm, campaign Marseal, Alagoas-Sergipe Basin, 11°11'20.6"S, 36°52'16.4"W, 400 m, October 2013. 1 adult female, (UFS-CRU-0183), station BN4R3, 0–2 cm, campaign Marseal, Alagoas-Sergipe Basin, 10°32'05.8"S 36°05'10.4"W, 400 m, October 2013.

Etymology. New Latin, from longus = long plus seta = hair, this names is in reference to the long setae present on the dorsal surface of the body.

Diagnosis. Head dorsal surface with some simple setae. Pereonites without spines, but covered with long simple setae. Pereonite V length 2.7 width. Uropods uniramous, biarticulate.

Description (based on female holotype, MOUFPE 15.568). Body more or less flattened and elongated, dorsal cuticle covered with long setae. Tegument extremely decalcified. Head 1.2 wider than long, dorsal surface without spines, but with some simple setae.

Antennula ( Fig. 8 B) with 6 articles. Article 1 squat and globular, with 1 seta on anterior margin; article 2 length 4.6 article 1 length, 2 ventromedial long setae and 2 distal setae; article 3 length 1.6 article 4 length, 1 lateral seta, 1 ventromedial and 1 distal seta; article 4 with 1 distal seta; articles 5 and 6 subequal and shorter than others; articles 5 smooth. Article 6 with 3 terminal setae.

Antenna ( Fig. 8 A) article 2 with 2 setae; article 3 length 2 width, with 4 setae; article 4 small with 2 setae. Flagellum missing.

Mandible ( Fig. 9 B) with smooth outer margin, incisor with 4 blunt teeth; spine row of 4 serrated spines; lacinia mobilis of left mandible with 4 blunt teeth. Molar with smooth grinding surface; spine row on posterior margin present.

Maxilulla ( Fig. 9 E) exopod with 10 large spine-like apical setae; lateral margin with several fine cuticular hairs; distal margin of endopod with 4 large setae, being the last largest, lateral margin with some fine cuticular hairs.

Maxilla ( Fig. 9 D) basis with some rows of short setae, outer lobe with 3 apical spine-like setae and some fine setae and rows of short setae on lateral margin; median lobe with 4 apical spine-like setae; inner lobe almost more than twice as broad as median or outer lobes, with 6 simple apical setae, distal margin bearing 2 stout serrated setae distomedially; 2 setulated prominent setae; some fine cuticular hairs and surface with some cuticular comb rows.

Maxilliped ( Fig. 9 A) palp consisting of 5 articles, decreasing in length and width distally; basis broader than palp, with 2 simple setae. Article 1 of the palp with 2 laterodistal simple setae, one of each side, being the outer about 3x longer than the internal; article 2 with 1 laterodistal simple seta, bigger than others of this articles, 1 medial distal and 2 laterodistal inner, with some simple setae extremely thin; article 3 with 1 laterodistal simple seta, 2 medial distal simple setae and 2 laterodistal inner simple setae; article 4 with 3 laterodistal inner simple setae, one more medial; article 5 with 3 distal simple setae.

Pereopod I ( Fig. 8 C) basis length 6.3 width, smooth; ischium length 3 width, smooth; merus width 2.0 length, with 2 lateral long setae; carpus length approximately 3.8 width, ventral margin with 6 simple setae and 2 dorsal long simple setae; propodus length approximately 4.5 width with 1 ventral simple seta, 1 dorsal long setae and 1 anterior long simple seta; Dactylus length 4.5 width with 1 lateral simple seta and 1 anterolateral simple seta. Pereopods II-VII damaged.

Pleotelson with axial ridge and 5 lateral simple setae on lateral fields.

Uropods uniramous, biarticulate.

Description (based on adult male paratype, 3 mm, ATEX, MOUFPE 15.569) Body elongated; dorsal cuticle covered with several long setae. Head wider 0.8 than long. Pereonite V length 4.0 width, 3.4 total body length.

Pleopod I ( Fig.10 A) not fused. Length 10 width and distal margin with 1 simple seta. Pleopod II ( Fig. 10 B) stylet not extending to distal margin of protopod. Protopod distal margin 8 simple setae. Pleopod III ( Fig. 10 C) exopod length almost than endopod length, apex with 1 long plumose seta extending to distal margin of the endopod. Lateral margin fringed with fine setae. Pleopod IV ( Fig. 10 D) setae absent.

Remarks. Ischnomesus longiseta sp. nov. can be easily distinguished from the other species of Ischnomesus by its body covered with long setae. Ischnomesus longiseta sp. nov. resembles I. vinogradovi in having pereonites, pleonite and pleotelson without spines or tubercles, and pleotelson almost rounded. The Ischnomesus longiseta sp. nov. have the pereonites I–IV broader than I. vinogradovi .

Bathymetric range. 400–1000 m depth.

Distribution. Alagoas-Sergipe Basin and Espírito Santo Basin.

Figures

FIGURE 6. Ischnomesus longiseta sp. nov., holotype adult female, 2.5 mm, ATEX, (MOUFPE 15.568). A, habitus; B, lateral view; C, ventral view. Scale = 1 mm.

FIGURE 7. Ischnomesus longiseta sp. nov., male paratype adult, 3 mm, ATEX, (MOUFPE 15.569). A, habitus; B, lateral view; C, ventral view. Scale = 1 mm.

FIGURE 8. Ischnomesus longiseta sp. nov. male paratype adult, 3 mm, ATEX, (MOUFPE 15.569). A, antenna; B, antennula; C, pereopod 1. Scale A and B = 0.1 mm; scale C = 1 mm.

FIGURE 9. Ischnomesus longiseta sp. nov., paratype adult female, LEAD TEG, (MOUFPE 15.656). A, maxilliped; B, mandibles; C, paragnaths; D, maxilla; E, maxillula. Scale = 0.1 mm.

FIGURE 10. Ischnomesus longiseta sp. nov., male paratype adult, 3 mm, ATEX, (MOUFPE 15.569). A, pleopod 1; B, pleopod 2; C, pleopod 3; D, pleopod 4. Scale = 0.1 mm.