Two New Species of the Brazilian Millipede Genus Rhicnosthetus Hoffman, 2006 (Polydesmida: Chelodesmidae), Including a Key to Males

© 2021 Academia Sinica, Taiwan Open Access Two New Species of the Brazilian Millipede Genus Rhicnosthetus Hoffman, 2006 (Polydesmida: Chelodesmidae), Including a Key to Males Rodrigo Salvador Bouzan1,2,*, Luiz Felipe Moretti Iniesta1,2 , and Antonio Domingos Brescovit1 1Laboratório de Coleções Zoológicas, Instituto Butantan, Avenida Vital Brasil, 1500, 05503-090, São Paulo, Brasil. *Correspondence: E-mail: [email protected] (Bouzan) E-mail: [email protected].br (Brescovit) 2Pós-graduação em Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brasil. E-mail: [email protected] (Iniesta) Received 9 November 2019 / Accepted 18 February 2021 / Published 25 May 2021 Communicated by Benny K.K. Chan The genus Rhicnosthetus Hoffman, 2006 is revisited. Two new species from state of Mato Grosso, Brazil are described: Rhicnosthetus chagasi sp. nov. and Rhicnosthetus penabarbosai sp. nov. In addition, a new record for R. rondoni Hoffman, 2006, a key to males and a distribution map of all species are included. Key words: Neotropical, Diplopoda, Millipedes, Chelodesminae, Amazon rainforest. BACKGROUND Millipedes (class Diplopoda) are known by their low vagility and limited distribution, with taxa restricted in determined mountains, islands and patches of forest (Golovatch and Kime 2009; Enghoff 2015; Nguyen et al. 2019). Members of the class are distributed on all continents except for Antarctica and can be found, mainly, in all soil extracts, in litter and under logs and stones (Hopkin and Read 1992). Millipedes are also recognized by their important biological role as detritivores, feeding on decaying vegetable matter and mineral soils (Golovatch and Kime 2009; David 2015). The class has approximately 12,000 described species (Sierwald and Bond 2007), although it is estimated that this number may be as high as 80,000 species (Adis 2002). Currently, Diplopoda consists of 16 orders, 144 families and about 2,950 genera (Shelley 2003). Chelodesmidae is the second largest family in the class Diplopoda with almost 800 described species (Hoffman 1980). The family is divided into two subfamilies: Chelodesminae from the Neotropical region and Prepodesminae from Africa and Spain. Currently, 345 species are recognized in 19 tribes for Chelodesminae and only one tribe for Prepodesminae (Hoffman 1980; Enghoff et al. 2015). For the remaining species, no assignment to any tribal position has been proposed (Hoffman 1980; Bouzan et al. 2017). Among these taxa, the genus Rhicnosthetus (Fig. 1) was described by Hoffman (2006) to accommodate the species R. coriaceus (Schubart, 1947) described from the state of Mato Grosso, and R. rondoni Hoffman, 2006 described from the state of Rondônia, Brazil. According to Hoffman (2006), the genus is recognized by having a longitudinally striated podosterna (see discussion below), microgranular tergal texture, a prolonged gonapophysis and seminal groove running along a broad lobe on the acropodite. Based on recently collected material of Rhicnosthetus, the present study revisits the genus with a new record of R. rondoni, and the designation of a lectotype for R. coriaceus. The species Rhicnosthetus chagasi sp. nov. and R. penabarbosai sp. nov., from the state of Mato Grosso are also described. A key to males and a distribution map for all species of the genus are also provided. Citation: Bouzan RS, Iniesta LFM, Brescovit AD. 2021. Two new species of the Brazilian millipede genus Rhicnosthetus Hoffman, 2006 (Polydesmida: Chelodesmidae), including a key to males. Zool Stud 60:21. doi:10.6620/ZS.2021.60-21. Zoological Studies 60:21 (2021) doi:10.6620/ZS.2021.60-21 1 © 2021 Academia Sinica, Taiwan MATERIALS AND METHODS The material examined is deposited in the following institutions (curators in parentheses): CZUFMT, Universidade Federal do Mato Grosso, Cuiabá, Brazil (A. Chagas-Jr); IBSP, Instituto Butantan, São Paulo, Brazil (A. D. Brescovit); MNRJ, Museu Nacional do Rio de Janeiro, Rio de Janeiro (A. B. Kury); MZSP, Museu de Zoologia, Universidade de São Paulo, São Paulo, Brazil (R. Pinto da Rocha); VMNH, Virginia Museum of Natural History, Virginia, USA (K. Ivanov). Morphological drawings were made using a Leica MZ12 stereoscope with a camera lucida. Photographs were taken with a Leica DFC 500 digital camera mounted on a Leica MZ16A stereomicroscope. Extended focal range images were composed with Leica Application Suite version 2.5.0. Scanning electron micrographs were acquired from Instituto Butantan using a FEI Quanta 250 SEM with a digital SLR camera attached. All measurements are in millimeters, and are omitted after the first occurrence. For gonopod terminology we follow Pena-Barbosa et al. (2013), Koch (2015) for vulvae and Attems (1898) and Brölemann (1900) for other somatic characters. The geographical coordinates were obtained from the original literature (when provided). For the material examined without any information about geographic coordinates, we georeferenced using the central point of the municipality labeled. RESULTS TAXONOMY Order Polydesmida Pocock, 1887 Suborder Leptodesmidea Brölemann, 1916 Family Chelodesmidae Cook, 1895 Subfamily Chelodesminae Cook, 1895 Genus Rhicnosthetus Hoffman, 2006 Rhicnosthetus Hoffman, 2006: 43–55. Type species: Rhicnosthetus rondoni Hoffman, 2006, by original designation. Fig. 1. Live male specimen of Rhicnosthetus chagasi sp. nov., from Fazenda São Nicolau, Cotriguaçu, Mato Grosso, Brazil. Photographed by: Dr. Domingos de Jesus Rodrigues. page 2 of 14Zoological Studies 60:21 (2021) © 2021 Academia Sinica, Taiwan Diagnosis: Males of Rhicnosthetus differ from those of other chelodesmid genera by the combination of the following characters: microgranular tergal texture (Fig. 2a–b), seminal groove running along a broad lobe on the acropodite (Figs. 6e, 7a, c–d) (reduced in R. penabarbosai sp. nov.; Figs. 9e, 10a, c–d), small spine in the median region of the prefemoral process (Fig. 4a– b) (reduced in R. chagasi sp. nov.; Figs. 6d, 7a) and a hook-shaped acropodital process (Fig. 3a–b). Distribution: Known from the Brazilian states of Rondônia and Mato Grosso (Fig. 11). Composition: Four species, Rhicnosthetus rondoni, R. coriaceus, R. chagasi sp. nov. and R. penabarbosai sp. nov. Key to males of Rhicnosthetus 1. Prefemoral process reaching only half the size of the acropodite (Fig. 3a, c) .......................................... R. rondoni Hoffman, 2006 1’. Prefemoral process exceeding half the size of the acropodite (Fig. 4a) ............................................................................................... 2 2. Solenomere and acropodital process divided at the base of the acropodital region (Fig. 9e) .................. R. penabarbosai sp. nov. 2’. Solenomere and acropodital process not divided at the base of the acropodital region, divided apically (Fig. 7a, c) ........................ 3 3. Acropodital process longer than the solenomere (Fig. 7a–d) ........ ......................................................................... R. chagasi sp. nov. 3’. Acropodital process about same length as the solenomere (Fig. 4a–d) ............................................. R. coriaceus (Schubart, 1947) Rhicnosthetus rondoni Hoffman, 2006 (Figs. 3, 11) Rhicnosthetus rondoni Hoffman, 2006: 52, figs. 21–25 (Male holotype and three males paratypes from Nova Esperança (-8.727772°; -63.867630°), Porto Velho, Rondônia, Brazil, 6-8/XII/1983, P.E. Vanzolini coll., deposited in MZSP, not found; male paratype from Nova Brasília, Ji-Paraná (-10.886901°; -61.913764°), Rondônia, Brazil, 6-11/XI/1984, P.E. Vanzolini coll., deposited in VMNH, not examined). Material examined: BRAZIL. Mato Grosso: Aripuanã (-10.654524°; -59.915741°), Mata margem esquerda do rio Aripuanã, jusante do Salto de Fig. 2. Male of Rhicnosthetus chagasi sp. nov. (CZUFMT MYR 851). (a) Paranota, dorsal view; (b) Detail of the microgranular tergal texture; (c) sternite of body ring 9 in ventral view; (d) leg (7th leg pair) in lateral view. Scale bars: a, c = 1 mm; b = 300 µm; d = 2 mm. page 3 of 14Zoological Studies 60:21 (2021) © 2021 Academia Sinica, Taiwan Dardanelos, 2M, VII/2003, C. Strussmann coll. (CZUFMT-MYR 864). Diagnosis: Males of R. rondoni differ from all other species of the genus based on the combination of gonopodal characteristics: prefemoral process reaching half the size of the acropodite (Fig. 3c) and falciform acropodital process exceeding the size of the solenomere (Fig. 3b). Distribution: Known from the states of Mato Grosso and Rondônia, Brazil (Fig. 11). Rhicnosthetus coriaceus (Schubart, 1947) (Figs. 4–5, 11) Leptodesmus coriaceus Schubart, 1947: 11, figs. 10–11 (syntypes: 10 males, 10 females and 6 juveniles from Santa Terezinha, (-10.471803°; -50.515290°), formerly Barra do Tapirapé, Mato Grosso, Brazil, 23.XI.1939−15.III.1940, A. L. de Carvalho coll., deposited in MZSP and MNRJ). Only 2M and 2F deposited in MZSP, and 3M 2F deposited in MNRJ were examined (male lectotype, MNRJ 11812, and all remaining material as paralectotypes are here designated). Rhicnosthetus coriaceus: Hoffman, 2006: 55, figs. 26–27. Diagnosis: Males of R. coriaceus differ from all other species of the genus based on the combination of gonopodal characteristics: prefemoral process robust and reaching half the size of the acropodite (Fig. 4a) and acropodital process not exceeding the size of the solenomere (Fig. 4d). Descriptive notes on females: (Paralectotype, MNRJ 11625). Pair of legs on body ring 3 with the coxae possessing a small process. Posterior margin of the vulvae aperture smooth, without projections (Fig. 8b). Vulvae rounded shaped in ventral view (Fig. 5a) and elliptical shaped in lateral view (Fig. 5b). Apical region with the intermediate membrane elevated (Fig. 5d) and medial region with a small aperture (Fig. 5c), ventral view. Total length: 55.41. Total width: 8.35. Posterior margin of the vulvae aperture: 1.59 width. Vulvae: length 0.75, width 0.50. External valve: length Fig. 3. Rhicnosthetus rondoni (CZUFMT MYR 864), left gonopod. (a) mesal view; (b) detail of the acropodite and prefemoral process, mesal view; (c) ectal view; (d) detail of the acropodite and prefemoral process, ectal view. Scale bars: a, c–d = 500 µm; b = 400 µm. Abbreviations: AP, acropodital process; PfP, prefemoral process; S, solenomere; SG, seminal groove; SP, spiniform process. page 4 of 14Zoological Studies 60:21 (2021) © 2021 Academia Sinica, Taiwan 0.62, width 0.32. Internal valve: length 0.48, width 0.24. Operculum: length 0.28, width 0.42. External valve (EV, Fig. 5a, 5d) bigger; with long and scattered setae in comparison of the internal valve (IV, Fig. 5a, 5d). Operculum large and densely covered by setae (OP, Fig. 5a–b). Distribution: Known only from the state of Mato Grosso, Brazil (Fig. 11). Rhicnosthetus chagasi sp. nov. (Figs. 1–2, 6–8, 11) urn:lsid:zoobank.org:act:861C83D6-EBD8-445D-B56D3FCCF84BFE47 Material examined: Male holotype and female paratype from Chácara dos Idosos, Cotriguaçu (-9.901695°; -58.570062°), Mato Grosso, Brazil, deposited in IBSP 7782 and IBSP 7783, respectively. Non-types: BRAZIL. Mato Grosso: Cotriguaçu (-9.901695°; -58.570062°), Chácara dos Idosos, no data and collector, Mato Grosso, Brazil, 2M and 1F (CZUFMT MYR 851); Fazenda São Nicolau, 13.XII.2009, L. D. Battirola coll., 4M and 3F (IBSP 5366). Etymology: The specific epithet is a patronym in honor of Dr. Amazonas Chagas Júnior, for his friendship and several contributions to our knowledge of Myriapods in Brazil. Diagnosis: Males of R. chagasi sp. nov. differ from all other species of the genus based on the combination of gonopodal characteristics: prefemoral process slender and reaching half the size of the acropodite (Fig. 6d) and a falciform acropodital process exceeding the size of the solenomere (Fig. 6f). Description: Male (Holotype, IBSP 7782). Coloration in life: head reddish brown. Antennae with yellow and brown antennomeres. Body dark brown, with the paranota tip yellow (Fig. 1); (long-preserved in 70% ethanol): Head ocher with the apex brown. Antennae Fig. 4. Rhicnosthetus coriaceus (MNRJ 11625), left gonopod. (a) mesal view; (b) detail of the acropodite and prefemoral process, mesal view; (c) ectal view; (d) detail of the acropodite and prefemoral process, ectal view. Scale bars: a–c = 500 µm; d = 400 µm. Abbreviations: AP, acropodital process; PfP, prefemoral process; S, solenomere; SG, seminal groove; SP, spiniform process. page 5 of 14Zoological Studies 60:21 (2021) © 2021 Academia Sinica, Taiwan yellowish. Body light brown and paranota tip yellowish (Fig. 6a–c). Body rings: cuticle with microgranular texture (Fig. 2b); paranota rectangular with posterior edges slightly produced (Fig. 2a); ozopore centralposteriorly situated on paranota (Fig. 2a). Stigma oval. Sternites with podosterna rough (= longitudinally striated – Hoffman, 2006) (Fig. 2c). Sternite of body ring 4 with a pair of small rounded projections appressed against each other. Sternite of all the body rings with two pairs of small rounded projections (Fig. 2c). Pair of legs on body ring 3 with coxae possessing a rectangular-shaped gonapophysis. Gonopod aperture on seventh body ring oval, posterior edge without any modifications. Legs yellowish, without modifications, with scattered thin setae (Fig. 2d). Telson with the same color as the body. Total length: 54.60. Total width: 8.04. Collum, length, 1.88, width, 6.81. Antennomere lengths (1 > 7): 0.65; 1.39; 1.38; 1.43; 1.29; 1.37 0.35. Podomeres lengths (1 > 7): 0.66; 0.95; 2.38; 0.77; 0.84; 1.47; 0.45. Gonopod aperture, length 0.94, width 1.81 Telson, length 1.57. Gonopod: length 2.11, width 1.72. Coxae: length 0.74, width 1.00. Telopodite: length 2.11, width 0.80. Gonopods (Figs. 6d–f, 7a–d): coxae equivalent to about half the length of the telopodite and prominently rounded in ectal view (Figs. 6f, 7c). Coxae with two setae on the distal dorsal side. Presence of small spiniform process hidden by the coxa in mesal view (SP; Fig. 6d). Cannula: hook-shaped. Prefemoral region long, 1/2 length of telopodite. Prefemoral process long and slim, with the apical region curved and reaching half the length of the acropodite (PfP; Figs. 6d, 7a). Prefemoral process with a reduced small spine in the medial region of the process. Acropodite elongated and robust; composed of a large and concave lobe on dorsal side conducting the seminal groove along its edge (SG; Fig. 6d, f); and distal and falciform acropodital process (AP; Fig. 6d, f). Solenomere and acropodital process Fig. 5. Rhicnosthetus coriaceus (MNRJ 11625), left vulva. (a) ventral view; (b) latero-ventral view; (c) detail of the medial region, ventral view; (d) detail of the apex, ventral view. Scale bars: a = 300 µm; b = 400 µm; c–d = 100 µm. Abbreviations: EV, external valve; Op, operculum; IV, internal valve. page 6 of 14Zoological Studies 60:21 (2021) © 2021 Academia Sinica, Taiwan close to the apical region of the acropodite (Fig. 6d–f). Female (Paratype, IBSP 7783). Body as in male. Pair of legs on body ring 3 with the coxae possessing a small, blunt process (Fig. 8a). Posterior margin of the vulvae aperture smooth, without projections (Fig. 8b). Vulvae rounded shaped in ventral view (Fig. 8c) and elliptical shaped in lateral view (Fig. 8d). Apical region with a large aperture (Fig. 8f) and medial region with Fig. 6. Rhicnosthetus chagasi sp. nov. (holotype, IBSP 7782), dorsal view of anterior (a), midbody (b) and posterior (c) body rings. Scale bars = 2 mm. Left gonopod. (d), mesal view; (e), ventral view; (f), ectal view. Scale bars: 1 mm. Abbreviations: AP, acropodital process; PfP, prefemoral process; SG, seminal groove; SP, spiniform process. page 7 of 14 Zoological Studies 60:21 (2021) © 2021 Academia Sinica, Taiwan a small aperture (Fig. 8e), ventral view. Total length: 54.72. Total width: 7.78. Posterior margin of the vulvae aperture: 1.73 width. Vulvae: length 0.77, width 0.573. External valve: length 0.51, width 0.24. Internal valve: length 0.54, width 0.18. Operculum: length 0.24, width 0.38. External valve (EV, Fig. 8c–d) with long and scattered setae in comparison of the internal valve (IV, Fig. 8c–d). Operculum large and densely covered by long setae; small setae restricted in the centro-apical part (OP, Fig. 8c–d). Distribution: The species is known from the region of Cotriguaçu, state of Mato Grosso, Brazil (Fig. 11). Rhicnosthetus penabarbosai sp. nov. (Figs. 9–11) urn:lsid:zoobank.org:act:D500C918-01ED-40FF-97644937B79B1A7F Material examined: Male holotype and male paratype from Chapada dos Parecis (-14.339394°; - 56.39202°), Diamantina, Mato Grosso, Brazil, XI.1993, D. Novaes & R. Pardini coll., deposited in IBSP 7784 and IBSP 7785, respectively. Etymology: The specific epithet is a patronym in honor of Dr. João Paulo P. Pena Barbosa, for his outstanding contributions to our knowledge concerning the Chelodesmidae, and for his friendship and advice over the years. Diagnosis: Males of R. penabarbosai sp. nov. differ from all other species of the genus by having the prefemoral process as long as the acropodite (Figs. 9d– f, 10a–d) and by having the solenomere and acropodital process divided at the base of the acropodital region (Fig. 9e). Description: Male (Holotype, IBSP 7784). Coloration (long-preserved in 70% ethanol): Head ocher. Antennae yellowish ocher. Body ocher and paranota tip yellowish – not uniform throughout the Fig. 7. Rhicnosthetus chagasi sp. nov. (CZUFMT MYR 851), left gonopod. (a) mesal view; (b) detail of the acropodite, mesal view; (c) ectal view; (d) detail of the acropodite and prefemoral process, ectal view. Scale bars: a–c = 500 µm; d = 400 µm. Abbreviations: AP, acropodital process; PfP, prefemoral process; S, solenomere; SG, seminal groove; SP, spiniform process. page 8 of 14Zoological Studies 60:21 (2021) © 2021 Academia Sinica, Taiwan body, probably due to ethanol depigmentation (Fig. 9a–c). Body rings: cuticle with microgranular texture; paranota rectangular with posterior edges slightly produced (Fig. 9b); ozopore central-posteriorly situated on paranota. Stigma oval. Sternites with podosterna smooth. Sternite of body ring 4 with a pair of small rounded projections appressed against each other. Sternite of all the body rings with two pairs of small Fig. 8. Rhicnosthetus chagasi sp. nov. (CZUFMT MYR 851), female. (a) Legs of body ring 3, lateral view; (b) posterior margin of the vulvae aperture; (c) ventral view; (d) lateral view; (e) detail of the medial region, ventral view; (f) detail of the apex, ventral view. Scale bars: a = 1 mm; b = 500 µm; c–d = 400 µm; e–f = 100 µm. Abbreviations: EV, external valve; Op, operculum; IV, internal valve. page 9 of 14Zoological Studies 60:21 (2021)