Metacirolana helenae, Paiva & Souza–Filho, 2023

Paiva, Ricardo J. C. & Souza – Filho, Jesser F., 2023, Two new species of Metacirolana Kussakin, 1979 (Isopoda: Cirolanidae) from Brazilian waters, Journal of Natural History 57 (1 - 4), pp. 142-158 : 143-147

Metacirolana helenae sp. nov.

( Figures 1–5 )

Material examined

Holotype. Male, 1.6 mm (dissected and drawn), REVIZEE III #72, 02.117°S, 38.384°W 6 August 1998, 100.3 m, dredge, NOc Antares coll., MOUFPE 14958 .

Paratypes. 3 males, 1 females, REVIZEE I, #113, 03.200°S, 37.667°W, 8 September 1995, 98.5 m, N . Oc . Antares coll ., MOUFPE 14845 . 2 male, 1 female, REVIZEE III #72, 2.117°S, 38.384°W, 8 June 1998, 100.3 m, dredge, NOc Antares coll ., MOUFPE 14840 . 23 males, 13 females, 2 mancae, REVIZEE IV, #109, 1.733°S, 37.100°W, 11 October 2000, 47 m, dredge, NOc Antares coll ., MOUFPE 14847 .

Type locality. Brazil, oceanic banks of the North Chain , REVIZEE III #72 (02.117°S, 38.384°W) .

Etymology. Named in honour of Helena Pessoa Fidelis, beloved older daughter of the second author.

Diagnosis. Body about 2.5 × longer than wide, male pereion 1.8 × longer than pleon and female pereion 2.8 × length of pleon. Antenna 1 reaching pereonite 1 in the female and pereonite 2 in the male; peduncle article 1 shorter than article 2; article 2 with a tuft of five long setae in the posterodistal angle. Antenna 2 reaching pereonite 4 in the female and pereonite 6 in the male. Frontal lamina triangular, with very narrow basis widening distally. Pleonite 5 posterior margin broadly trilobate. Pleopod 2 male appendix almost straight with rounded tip, exceeding the apex of the endopod. Pleopods 3–5 with biarticulate exopod; endopod subequal to the exopod. Uropod exopod with a medial U-shaped excavation ending in an acute process. Pleotelson apex rounded and serrated without plumose setae.

Description. Based on holotype male (1.6 mm) MOUFPE 14958. Body smooth, 2.3 × longer than wide; pereion 1.8 × longer than pleon. Head interocular and submarginal grooves absent. Pereonite 1 without grooves or ventral carina. Pleonite 1 partially hidden by pereonite 7. Pleonite 2 to 5 with a subacute posterolateral margin. Pleonite 5 bearing three weakly developed longitudinal processes.

Antenna 1 peduncle article 2 with a tuft of five long plumose setae on posterodistal angle, one very long and reaching more than half of the flagellum; flagellum longer than peduncle; article 1 shortened, 1/4 of the length of article 2; article 2 elongated, being longer than peduncle article 3. Antenna 2 peduncle article 4 with two plumose setae; article 5 longer than previous articles. Mandible with 3-dentate incisor process; palp article 2 longer than article 1 (2.3 ×), article 3 falcate with setae along inner margin. Maxilla 1 endopod with three robust and plumose setae, exopod with seven robust setae. Maxilla 2 medial plate with four simple setae; lateral plate with three simple setae. Maxilliped inner plate with three distal setae; palp article 2 larger and wider than articles 3 and 4 together.

Pereopod 1 basis narrow, distally enlarged, anterior margin not produced; ischium triangular; merus anterior margin slightly produced over carpus, anterodistal angle without setae, posterior margin with four robust setae; carpus short and triangular, with two simple setae; propodus 1.5 × longer than wide, palm slightly curved, with three blunt processes, first two bearing one robust pectinate seta, distal one bearing a simple robust seta near to dactylus insertion; dactylus long with seven subdistal setae. Pereopod 2 basis narrow; ischium triangular, anterior margin not produced; merus anterodistal margin with three simple setae; carpus short, with three simple setae in the posterodistal angle; propodus 2 × longer than broad, palm slightly curved, two marginal blunt processes, bearing one robust pectinate seta, with a simple robust seta near the dactylus insertion; dactylus long with a subdistal seta. Pereopod 3 similar to pereopod 2. Pareopods 4–7 slender, similar in form. Pereopod 7 longer than the others; basis 3 × longer than wide; ischium, merus, carpus and propodus with few robust setae.

Penile papilla absent. Pleopod 1 peduncle with three robust setae and a plumose seta on inner margin. Pleopod 2 peduncle with four plumose setae on inner margin; appendix masculine straight with rounded tip, exceeding the apex of endopod. Pleopod 3 peduncle with three robust setae and one plumose seta on inner margin; exopod biarticulate; endopod subequal to exopod. Uropod peduncle with strongly produced and subacute distal angle bearing 2 long setae; endopod wide, 1.3 × longer than exopod, with subacute distal margin; exopod lanceolate, with acute distal margin. Pleotelson subtriangular, wider than long, without grooves or dorsal carinae, distal margin serrate and broadly rounded.

Female (sexually dimorphic characters only)

Body 2.6 × longer than wide, pereion 2.8 × length of pleon. Antenna 1 reaching pereonite 1; antenna 2 reaching pereonite 4.

Distribution. Brazil, Ceará, Rio Grande do Norte and Pernambuco, oceanic banks of the North Chain, depth of 47– 100 m.

Remarks. Metacirolana helenae sp. nov. belongs to the Metacirolana ̍ serrata group̾ by virtue of its ̍smooth body surfaces, lack of dorsal carinae and abundant chromatophores̾. Within this group, the new species is most similar to M. agaricicola Kensley, 1984 , from Belize, in the general shape of the body and in having the posterior margin of pleonite 5 broadly trilobate. However, the new species can be differentiated from M. agaricicola by the following characters (characters of M. agaricicola in parentheses): male antenna 1 with callynophore (vs lacking callynophore), female antenna 2 reaching pereonite 4 (vs peronite 2); endopod of uropod with a medial U-shaped excavation ending in an acute process on outer margin (vs lacking excavation); pleotelson distally convex (vs triangular). Additionally, Müller (1991) pointed out that M. agaricicola has few denticles on the posterior margins of female pereonites 4–7 and pleonites 1–5, which were missed on the original description. These denticles are absent in M. helenae sp. nov.

Metacirolana helenae sp. nov. can also be easily differentiated from M. riobaldoi , also known from Brazilian waters, in lacking denticles on the posterodorsal margin of the pereion and pleon segments. A comparison of morphological characters among the Metacirolana serrata group recorded from the Atlantic Ocean is given in Table 2 .

Figures

Figure 1. Metacirolana helenae sp. nov. Holotype, male, 1.6 mm, 2.117°S, 38.384°W, MOUFPE 14958. Paratype female, 2.1 mm, 3.200°S, 37.667°W, MOUFPE 14845. Scale bars = 0.1 mm. Hb, habitus; f, female; m, male.

Figure 2. Metacirolana helenae sp. nov. Holotype, male, 1.6 mm, 2.117°S, 38.384°W, MOUFPE 14958. Scale bars = 0.1 mm. A, antenna; C, clypeus; LF, frontal lamina; Md, mandible; Mx, maxilla; Mxp, maxilliped.

Figure 3. Metacirolana helenae sp. nov. Holotype, male, 1.6 mm, 2.117°S, 38.384°W, MOUFPE 14958. Scale bars = 0.1 mm. P, pereopod.

Figure 4. Metacirolana helenae sp. nov. Holotype, male, 1.6 mm, 2.117°S, 38.384°W, MOUFPE 14958. Scale bars = 0.1 mm. P, pereopod.

Figure 5. Metacirolana helenae sp. nov. Holotype, male, 1.6 mm, 2.117°S, 38.384°W, MOUFPE 14958. Scale bars = 0.1 mm. Pl, pleopod; Ur, uropod.