Ischnomesus wilsoni, 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 : 270-274

Ischnomesus wilsoni sp. nov.

( Figures 12–15 )

Material examined: Holotype: 1 adult female, 15 mm (dissected and drawn, mouthparts and pereopod 1 on two slides), ( MOUFPE 15535 ), station Ext 3 Lead 2 #1, R1, 2– 5 cm, campaign EXT3 LEAD2 , Espírito Santo Basin, 19°54’31.1”S, 39°36’56.8”W, 750 m depth, September 2007.

Paratypes: 1 adult female, ( MOUFPE 15536 ), station Atex #7, R3, 2– 5 cm, campaign ATEX, Espírito Santo Basin, 19°54’41.8’’S, 39° 36’75.62’’W, 830 m depth, 18 October 2006 . 1 manca, ( MOUFPE 15540 ), station Ext 3 Lead 2 #3, 2– 5 cm, campaign EXT3 LEAD2 , Espírito Santo Basin, 19°54’36.98”S, 39°36’54.8”W, 750 m depth, September 2007 . 1 adult female, ( MOUFPE 15541 ), station Ext 3 Lead 2 #4, R2, 0–2 cm, campaign EXT3 LEAD2 , Espírito Santo Basin, 19°54’36.6”S, 39°36’59.3’’W, 750 m depth, September 2007 . 1 manca, ( MNRJ 20854 ), station OP I#50A, 2–5 cm, Campos Basin , 22°03’69.4”S, 39°52’40.2”W, 1050 m depth, 20 November 2002 . 1 manca ( MNRJ 20856 ), station OP I #79, 2– 5 cm, Campos Basin , 22°20’67.1”S, 40°00’58.5”W, 775 m depth, 20 November 2002 .

Etymology. The species is named for Dr. George (Buz) Wilson from the Saugatuck Natural History Laboratory, Saugatuck Michigan in recognition of his contribution to the knowledge of Asellota Isopoda .

Diagnosis. Head dorsal surface with 2 short pedestal setae. Maxilliped epipod with numerous simple setae on external border. Pereonite I with 1 pair of antero- and posterolateral pedestal spine. Pereonites I–III with 1 pair of dorsal pedestal spines. Pereonites I–III with 1 lateral pedestal spine, last with pedestal spine length 3.0 pereonite II length. Pereonite IV with 3 pairs of dorsal pedestal spines and 1 anterolateral spine in each side; 3 lateral long pedestal spines. Pereonite V length 3.0 width, with 4 pairs of dorsal pedestal spines; 5 lateral long pedestal spines. Pereonite VI with 1 pair of lateral pedestal spines. Pereonites VI–VII with 1 pair of dorsal and dorsolateral pedestal spines. Pleotelson axial ridge with 1 pair of anterolateral pedestal spine and 2 pairs of dorsal pedestal spines. Lateral fields with 2 pairs of pedestal spines. Two pairs of lateral pedestal spines on pleotelson, 1 pair of posterolateral pedestal spines and 1 pair of posterior pedestal spines on pleotelson. One pair of tubercles in posterodorsal margin.

Description (based on female holotype, MOUFPE 15.535). Dorsal cuticle covered with coarse projections. Head length 0.9 width, dorsal surface with 2 pedestal setae. Delicate suture visible between head and pereonite I.

Antennula ( Fig. 13 C) with 6 articles. Article 1 squat and globular, with 4 lateral simple setae; article 2 longer than others, length 4 article 1 length, with 6 lateral simple setae and 5 ventromedial simple setae; article 3 elongate and tubular, 1.2 longer than 4–6 together, with 4 dorso- and ventromedial simple setae; 4 distal simple setae; article 4 with 4 distal setae; article 5 with 1 distal seta; article 6 with 3 distal setae.

Antenna ( Fig. 13 B) article 1 with 4 distal robust setae, 5 distal simple setae and 1 lateral; article 2 with 3 almost lateral setae, 3 distal robust setae and 7 distal simple setae; article 3 with 11 simple setae. Flagellum missing.

Mandible ( Fig. 14 E, F) with outer anterior margin setulated, incisor with 5 blunt teeth. Spine row of 4 serrated spines and 7 simple; lacinia mobilis of left mandible with 4 blunt teeth and incisor with 5 blunt teeth, spine row of 8 serrated spines. Molar with smooth grinding surface; posterior spine row present.

Maxillula ( Fig. 14 B) exopod with 10 large serrated spine-like apical setae; lateral margin with several fine cuticular hairs; distal margin of endopod with 1 stout serrated seta distomedially, 2 lateral setae, 1 each of side, 1 short robust (next to stout serrated seta) and 1 long; lateral and distal margin with numerous cuticular hairs.

Maxilla ( Fig. 14 C) basis with rows of short setae, outer lobe with 4 apical setulated spine-like setae, 4 simple setae and 1 setulated; lateral margin with several cuticular hairs; median lobe with 3 apical setulated robust setae and some fine cuticular hairs; inner lobe almost more than twice as broad as median or outer lobes, with 12 apical setulated setae, distal margin bearing 4 stout serrated setae distomedially, lateral margin with 2 setulated prominent setae, several fine cuticular hairs and surface of with cuticular comb rows

Maxilliped ( Fig. 14 A) basis broader than palp, with 13 long simple setae along basis; endite shorter than palp. Palp positioned in distal second of basis, articles 4–5 narrower than articles 1–3, all with numerous long simple setae, except 1, just 2 long simple setae in distal angles. Endite with 4 retinacula, 4 distal fan setae, 3 plumose setae and 7 simple setae; in distal angle robust sinuous (right side) seta with accessory seta and next long sinuous seta with long projections. Epipod with numerous simple setae on external border and 3 more central.

Pereon ornamented. Pereonite I with 1 pair of large antero and posterolateral pedestal spine subequal, length 2.5 width; in middle of pereonite, 1 pair of dorsal pedestal spines and 2 short tubercles in middle of spines.

Pereonite II with one pair of lateral pedestal spines; 1 pair of pedestal spines in middle of pereonite; one pair of short tubercles on posterior margin. Pereonite III with one pair of lateral pedestal spines; 1 pair of pedestal spine in middle of pereonite. Pereonite IV with 4 dorsal pairs of spines, second pair is dorsolateral; 3 long lateral pedestal spines on all length. Pereonite V with 4 pairs of dorsal pedestal spines, plus only one, close to posterior margin and 1 pair of dorso-posterolateral; with 5 long lateral pedestal spine on all length. Pereonite VI with 1 pair of lateral pedestal spines. Pereonites VI–VII with 1 pair of dorsal and dorsolateral pedestal spines. Pereonite VII with an intumescence with 2 short tubercles in middle.

Pereopod I ( Fig. 13 A) basis length 4 width, ischium length 2.4 width, 8 dorsal simple setae and 1 ventral; merus width 1.2 length, with 4 dorsodistal long setae, 1 ventral, 2 ventrodistal simple setae and 2 large simple spine-like seta; carpus length approximately 2.0 width, slightly tapering distally, ventral margin with 8 spine-like robust setae with accessory seta and 3 long simple spine-like seta, 6 dorsal simple setae with different size; propodus length approximately 3.2 width with 6 ventral simple setae, 6 spine-like robust setae with accessory seta, 1 long simple seta, 2 laterodistal and 12 dorsal simple setae with different size; dactylus with 1 dorsal and 7 lateral simple setae.

Pereopod V basis length 7.2 width with 3 dorsal simple setae. Ischium length 8.6 width with 2 setae, 1 medial and other distal. Merus length 3.6 width with 1 distal robust seta with accessory seta. Carpus length 14 width with 3 dorsal simple setae and 2 ventral. Propodus length 8.7 width with 2 dorsal and 3 ventral. Dactylus length 6.6 width, smooth.

Pleonite 1 with 1 pair of short dorsal tubercles.

Pleotelson axial ridge with 1 pair of anterolateral pedestal spine and 2 pairs of dorsal pedestal spines. Lateral fields with 2 pairs of spines. Two pairs of lateral pedestal spines on pleotelson, 1 pair of posterolateral pedestal spines and 1 pairs of posterior pedestal spines on pleotelson. One pair of tubercles in posterodorsal margin. Uropods uniramous and biarticulate.

Mancas ( Fig. 15 ). The present material included two mancas in different stages ( Fig.15 ), letter A is the manca in stage 1 or 2 (3.9 mm, MOUFPE 15.540), to affirm is necessary examined more specimens, because both stages have the legs absents, and C in stage 3 (5.2 mm, MNRJ 20856), pereopod VII is present but is rudimentary. The second pair of dorsolateral pedestal setae on pereonite V is absent. The specimen A illustrated in figure 15 is in poor condition. The pleotelson is shriveled, so one could not see if the ornamentation varied in this stage.

The mancas lack dorsolateral pedestal spines on pereonite IV. The spines are not calcified like in adult and they are longer in pereonites IV–VI and on pleotelson. The pattern of ornamentation is the same. The uropods were presents in mancas. Uropods uniramous and biarticulate.

Remarks. This species has ornamentation through all the body. Two species bear several projections on their body surface, in a pattern more or less similar to those observed in Ischnomesus wilsoni sp. nov.: I. antarcticus Schultz, 1979 and I. spaercki Wolff, 1956 . It is similar to I. antarcticus Schultz, 1979 , due to antero- and posterolateral spines on the pereonite I, in the same position, but they are more robust in I. antarcticus . All the species have lateral spines in pereonites II–VI, being anterolateral in pereonite IV and posterolateral in pereonite V. Ischnomesus wilsoni sp. nov. has fewer spines than I. antarcticus and I. spaercki . In all these species, the pleotelson is longer than wide, but this proportion is more visible in Ischnomesus wilsoni sp. nov. and I. antarcticus .

Bathymetric range. 750–1050 m depth.

Distribution. Espírito Santo Basin and Campos Basin.

Figures

FIGURE 12. Ischnomesus wilsoni sp. nov. holotype female, 15 mm, EXT 3 LEAD 2, (MOUFPE 15.535). A, habitus; B, lateral view; C, ventral view. Scale = 1 mm.

FIGURE 13. Ischnomesus wilsoni sp. nov. holotype female, 15 mm, EXT 3 LEAD 2, (MOUFPE 15.535). A, pereopod 1; B, antenna in different views; C, antennula. Scale = 0.1 mm.

FIGURE 14. Ischnomesus wilsoni sp. nov. holotype female, 15 mm, EXT 3 LEAD 2, (MOUFPE 15.535). A, maxilliped; B, maxillula; C, maxilla; D, paragnaths; E, right mandible; F, left mandible. Scale = 0.1 mm.

FIGURE 15. Ischnomesus wilsoni sp. nov. paratypes. Two mancas, A, manca female stage 1 or 2 female; B, ventral view, EXT 3 LEAD 2, (MOUFPE 15.540); C, manca female, stage 3; D, ventral view, Campos Basin, (MNRJ 20856).