Leucon (Alytoleucon) rhuanae Brito & Serejo 2023, sp. nov.
Creators: name: Brito, Ayrton Do Ramo
name: Serejo, Cristiana Silveira
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Cumacea
Leuconidae
Leucon
Leucon rhuanae

description: Leucon (Alytoleucon) rhuanae sp. nov.
(Fig. 1C, 2, 3 and 4)
Material examined. Holotype: Male, 5.1 mm, #SANSED3 P03- R1 (0–2), MNRJ 30608.
Paratypes: male, 4.1 mm, #HAB3 E10, MNRJ 28925 (dissected, lost inthe fire); male, 4.4 mm, #SANSED1 C10- R1 (0–2), MNRJ 30597 (dissected); male, 2.1 mm, #SANSED1 B09- R2 (0–2), MNRJ 30595; 2 females, 4.8–2.3, male, 2 mm, #SANSED1 B10- R2 (0–2), MNRJ 30596; male, 3.5 mm, #SANSED1 C11- R1 (0–2), MNRJ 30598; female, 2 mm, #SANSED2 D09- R2 (0–2), MNRJ 30599; female, 3.5 mm, #SANSED1 D11- R1 (0–2), MNRJ 30600; 2 females, 4.5– 3.6 mm, #SANSED2 E11- R2 (0–2), MNRJ 30601; male, 3.6 mm, #SANSED3 F09- R3 (0–2), MNRJ 30602; female, notmeasured (carapace), #SANSED3 F10- R1 (0–2), MNRJ 30603; male, 2 mm, #SANSED4 G09- R1 (0–2), MNRJ 30604; female, 4.8 mm, #SANSED2 P02- R1 (0–2), MNRJ 30606 *; 3 females, 5– 2 mm, male, 2.1 mm #SANSED3 P03- R3 (0–2), MNRJ 30609; female, 2.2 mm, #SANSED7 P05- R2 (0–2), MNRJ 30610; male, 4.5 mm, #SANSED3 P07- R2 (0–2), MNRJ 30611; female, 4.9 mm, #SANSED2 P11- R1 (0–2), MNRJ 30612; female, 3.1 mm, #SANSED7 A10- R1 (0–2), MRNJ 30613; 2 female, 3– 2.5 mm, male, 3.6 mm, #SANSED7 A10- R2 (0–2), MRNJ 30614; female, 3.8 mm, #SANSED7 A10- R3 (0–2), MNRJ 30615; male, 1.8 mm, #SANSED7 B09- R3 (0–2), MNRJ 30616; female, notmeasured (broken), #SANSED7 D10- R2 (0–2), MNRJ 30617; female, 4.1 mm, #SANSED7 D11- R3 (0–2), MNRJ 30618; female, 2 mm, #SANSED7 E09- R2 (0–2), MNRJ 30619; female, 2.4 mm, #SANSED7 E09- R3 (0–2), MNRJ 30620; male, 2.4 mm, #SANSED7 E10- R3 (0–2), MNRJ 30621; male, 4.9 mm, #SANSED8 F09- R1 (0–2), MNRJ 30622; female, 2.6 mm, #SANSED8 F09- R3 (0–2), MNRJ 30623; female, 2 mm, #SANSED8 F10- R3 (0–2), MNRJ 30624; male, 2.5 mm, female, 1.7 mm, #SANSED7 P03- R3 (0–2), MNRJ 30625; female, 3.8 mm, #SANSED7 P05- R3 (0–2), MNRJ 30626; female, 4 mm, #SANSED8 P10- R1 (0–2), MNRJ 30627; male, 2.6 mm, #SANSED8 P10- R3 (0–2), MNRJ 30628; male, 4.5 mm, #SANSED8 P11- R2 (0–2), MNRJ 30629.
Additional material (lost in the fire): male, 3.6 mm, 7 females, 4.3– 1.8 mm, #HAB3 D10, MNRJ 28924; males, 3.9 mm, #HAB3 E10, MNRJ 28925; female, 4.6 mm, #HAB3 G10, MNRJ 28926; male, 4.2 mm, #HAB3 I10, MNRJ 28927; female, 3 mm, #HAB4 B11, MNRJ 28928; male, 3.7 mm, female, 4.1 mm, #HAB8 D10, MNRJ 28930; female, 4.9 mm, #HAB10 B11, MNRJ 28931; 2 females, 4.1– 2.3 mm, #HAB10 H10, MNRJ 28929; female, 4 mm, # AMB4 B08, MNRJ 28910; female, notmeasured, # AMB4 F07, MNRJ 28911; 2 females, 3.1– 1.9 mm, # AMB4 F08, MNRJ 28912; female, 1.9 mm, # AMB5 A08, MNRJ 28913; 2 females, 3.7(broken) and 2.5 mm, # AMB5 C08, MNRJ 28914; 2 females, 4.1 and 4.6 mm, # AMB5 D08, MNRJ 28915; 3 female, 4.3– 1.8 mm, # AMB5 E08, MNRJ 28916; male 2.3 mm, female 4.1 mm, # AMB6 CAN7, MNRJ 28917; female, 4.3 mm, # AMB11 B08, MNRJ 28918; female, 2.5 mm, # AMB11 D08, MNRJ 28919; female, 2.5 mm, # AMB11 E08, MNRJ 28920; female, 3.4 mm, male, 2 mm, # AMB11 E09, MNRJ 28921; female, 4.7 mm, # AMB11 F06, MNRJ 28922; 3 females, 4.5– 2.5 mm, # AMB12 G08, MNRJ 28923.
Development. Females: mature longer than 4 mm, preparatory between 3.6–4 mm, immature between 2.6–3.6 mm, manca shorter than 2.6 mm. Males: mature longer than 4.9 mm, preparatory between 4.1–4.9 mm, second immature between 2.6–4.1 mm, first immature between 2.1–2.6 mm (estimated), manca shorter than 2.1 mm (specimen MNRJ 30628 with first immature ready for molt).
Type locality. Santos Basin, RJ/SP, Brazil, 24°53’25”S – 43°52’19”W; 1731 m.
Distribution. Brazil: Santos Basin (SC, PR, SP, RJ), Campos Basin (RJ), Espírito Santo Basin (ES); 1021–2501 m.
Etymology. The name rhuanae is in honour of Rhuana Butruce da Silva.
Diagnosis. Pseudorostrum short, 0.2–0.27 times carapace length. Serrations dorsally on carapace interrupted for a small gap before posterior end. Pereopod 1 basis 0.7 times length of remaining articles together. Pereopod 2 basis about as long as remaining articles. Pereopod 3 ischium with plumose and simple setae. Mature males with penial lobes. Uropodal peduncles with 2 setae on dorsal surface. Uropodal exopod longer than endopod. Uropodal endopod article 1 more than 3 times longer than article 2 (excluding terminal seta).
Description: Holotype, mature male, MNRJ 30608.
Mature male, 5.1 mm. Carapace 1.5 times pereon length including pseudorostrum, with dorsal serrations interrupted for a small gap before end of carapace; pseudorostrum acute, about 0.2 times carapace length (measured from frontal lobe to posterior margin); antennal notch absent; anteroventral corner rounded. Pereonite 5 with pair of small tube-like penial lobes. Pleon 0.5 times total body length, with 2 pairs of pleopods (Fig. 1C and 2).
Antenna 1, main flagellum of 4 articles; accessory flagellum of 1 article as long as main flagellum article 1 (Fig. 3 fl).
Antenna 2, with brush of setae on articles 4 and 5 outer margin (seen through carapace), flagellum reaching the end of pleon (Fig. 1C).
Paratype. Preparatory male, 4.1 mm, MNRJ 28925 (lost inthe fire).
Preparatory male, 4.1 mm. Antenna 1, slightly geniculate between articles 1 and 2; article 1, 1.5 times length of article 2, naked; article 2 shorter than article 3, with simple and plumose setae on distal inner face; article 3 with distal simple setae; main flagellum of 3 articles, article 3 with 3 simple setae and 2 aesthetascs; accessory flagellum of 1 article, shorter than ½ main flagellum article 1 (Fig. 3 a 1).
Mandibles, basis truncate, incisor with 2 distal simple setae, lacinia mobilis with 3 cusps (Fig. 3 md).
Maxilla 1 with 2 endites, palp with one bristle (Fig. 3 mx1).
Maxilla 2 with 3 endites; broad endite with row of distal plumose setae; narrow endites with simple setae (Fig. 3 mx2).
Maxilliped 1, basis with long plumose seta; ischium absent; carpus with plumose setae at outer distal corner and numerous simple setae on inner margin; propodus with 2 long plumose setae and numerous plumose setae on inner margin; dactylus with strong terminal and 2 subterminal simple setae (Fig. 3 mxlp1).
Maxilliped 2, basis about 0.8 times length of remaining articles together, with plumose seta at inner distal corner; merus with tiny setae; carpus about 10 plumose setae along inner margin; propodus with 2 long plumose seta on outer margin and 2 plumose setae on inner margin; dactylus with strong terminal seta and 2 subterminal simple setae (Fig. 3 mxlp 2).
Maxilliped 3, basis0.8 timeslengthof remainingarticlestogether,withplumosesetaeoninnermargin, distolateral corner with 3 long plumose setae; ischium with tiny simple setae on inner margin; merus with long plumose setae on outer margin; carpus with plumose setae on inner margin and small simple seta at outer corner; dactylus with strong terminal seta and 2 subterminal simple setae; exopod, flagellum with 5 articles (Fig. 3 mxlp3).
Pereopod 1, basis 0.7 times length of remaining articles together with plumose setae on inner face, plumose setae on inner margin, row of 5 teeth on outer face and cuspidate seta at inner distal corner; ischium with simple setae and tooth at inner distal corner; merus, carpus and propodus with simple setae; dactylus with long terminal simple setae, 3 pairs of subterminal simple setae and most proximal one single; exopod with teeth on inner face, flagellum with 6 articles (Fig. 4 p 1).
Pereopod 2, basis 1.1 times length of remaining articles together with simple and plumose setae; ischium quite short with plumose setae; merus with plumose setae; carpus with 2 cuspidate setae on outer distal corner; propodus naked; dactylus with 9 long setae; exopod with teeth on inner face, flagellum with 5 articles (Fig. 4 p 2).
Pereopod 3, basis 1.9 times length of remaining articles together with plumose setae; ischium with plumose setae; merus, carpus and propodus with simple annulate setae; dactylus small with long simple setae; exopod with teeth on inner face, flagellum with 6 articles (Fig. 4 p 3).
Pereopod 4, basis and ischium with plumose setae, basis 1.5 times length of remaining articles together; merus, propodus and carpus with simple and annulate setae; dactylus small with long simple seta; exopod flagellum with 5 articles (Fig. 4 p4).
Pereopod 5, basis 1.3 times length of remaining articles together with plumose setae; ischium with plumose setae; merus, carpus and propodus with simple annulate setae; dactylus small with simple long seta (Fig. 4 p 5).
Pleopods, 2 pairs. Rami with 4 short setae (Fig. 4 pl1).
Uropod, peduncle longer than pleonite 6 with 4 simple setae on inner margin, 2 dorsal long simple setae; endopod 2-articulate, article 1,>3 times article 2 length (excluding terminal seta), with 9 cuspidate setae on inner margin, article 2 distal seta fused to article, 3 cuspidate setae on inner margin; exopod longer than endopod with 4 plumose distal setae and 5 plumose setae on inner margin (Fig. 4 u).
Variations. Calcification varies between specimens collected in summer and winter, with summer specimens usually less calcified, which the dorsal serration on carapace is difficult to see through a light microscope (Fig. 3 h).
Preparatory male has carapace with antennal notch U-like (V-like in females), antero-ventral corner acute. Pleonite 5, penial lobes absent (Fig. 3 h).
Immature and manca stages present frontal lobe higher and more rounded than preparatory and mature stages. Uropods rami seems to be more subequal in length in youngest stages.
Remarks. Leucon (Alytoleucon) rhuanae sp. nov. is similar to L. (A) pallidus Sars, 1865 in dorsal serration of the carapace, which is interrupted by a short gap near its posterior end, the pereopod 1 basis being longer than half of the remaining articles together, and the uropodal exopod being longer than the endopod. However, they differ in several aspects. Leucon (A) rhuanae sp. nov. presents pseudorostrum measuring about 0.2 to 0.27 times carapace length (versus about 0.27 to 0.35 times carapace length), male pereopod 3 ischium with simple setae (versus modified lanceolate setae), uropodal endopod article 1 at least 3 times longer than article 2 (versus 2 times longer than article 2) (Sars 1900; Bishop 1982b). Leucon (A) rhuanae sp. nov. has 2 long dorsal setae on the uropodal peduncle, one distally and one in the middle, whereas the presence of these setae in L. (A) pallidus is not clear inthe illustration of Sars (1900).
Leucon (A) rhuanae sp. nov. is also similar to L. (A) turgidulus Bishop, 1982 in pereopod 2 basis about as long as remaining articles together, uropodal exopod longer than endopod, uropodal endopod article 1 more than 3 times longer than article 2 (excluding terminal seta) and uropodal peduncle with 2 long dorsal setae. However, L. (A) rhuanae sp. nov. differs from L. (A) turgidulus in a shorter pseudorostrum measuring about 0.2 to 0.27 times carapace length (versus 0.3 times of carapace length), dorsal serration of carapace that is interrupted for a short gap near its posterior end (versus dorsal serration continuous), and pereopod 1 basis longer than half of remaining articles together (versus basis shorter than half of remaining articles together) (Bishop 1982b).
description: Published as part of Brito, Ayrton Do Ramo & Serejo, Cristiana Silveira, 2023, Leuconidae Sars, 1878 (Crustacea: Cumacea) from the southwestern Atlantic, filling the distribution gap along the Brazilian coast, pp. 101-134 in Zootaxa 5383 (2) on pages 107-112, DOI: 10.11646/zootaxa.5383.2.1, http://zenodo.org/record/10350586