Megaspira adenticulata, Daniel & Ovando & Santos, 2022

Daniel, Victor R., Ovando, Ximena M. C. & Santos, Sonia B., 2022, A new species of Megaspira (Stylommatophora: Megaspiridae) from Ilha Grande, Southeast Brazil, Zoologia (e 21022) 39, pp. 1-11 : 4-8

Megaspira adenticulata sp. nov.

Figs 13–35

http://zoobank.org/ 08B4C9CF-8909-474B-9C3E-798A197DA331

Diagnosis. Shell with 16 whorls and 27 mm in height, on average. Aperture with no lamella folded on inner lip of smooth aperture. Columella sculpture with a rough texture over entire surface.

Description. Cephalo-pedal mass brownish in all its extension, especially close to cephalic portion, and presence of several ridges along body ( Figs 13, 14 ). Thin, cylindrical tentacles, with central axis of dark gray. Foot with gradual tapering in its posterior portion, no external gland in the posterior terminal part of the foot. Sole almost entire, groove not deep in its median portion.

Shell. Oblong (in juvenile specimens) or conical-elongated (in adults) ( Figs 15–18 ), shell height from 18.2 to 32.8 mm with 16 convex whorls on average ( Table 2 ). Spire high with moderate growth, spiral angle with 15.8° on average ( Table 2 ). Aperture oval, with apertural height and length almost similar on average ( Table 2 ; Figs 15, 16 ), with lower lip slightly enlarged; lamella folded on inner lip of aperture, absence of parietal teeth; peristome with reflected edges, mainly on the columellar lip side ( Fig. 16 ). Umbilicus closed covered by peristome reflection. Protoconch smooth, without sculpture, with 2.5 to 2.75 whorls ( Figs 19, 20 ). Third whorl, with faint incomplete radial lines ( Fig. 20 ). Teleoconch sculpture with numerous oblique ribs, well marked, arranged close to each other ( Fig. 21 ). Columellar axis microsculpture with a rough texture along its entire length surface, without internal columellar lamellae ( Figs 22–24 ).

Jaw. Shaped like horseshoe, with rectangular curved central plate; lateral plates of smaller size, overlapped each other on both sides of jaw ( Fig. 25 ). Lateral plate surfaces with fine, parallel lines, evident on the outer margin without forming true sculpture ( Fig. 25 ).

Radula formula: 20 + 18 + 1 + 18 + 20 and 18 + 16 + 1 + 16 + 18 (M + L + R + L + M), being: M: Marginal, L: Lateral, and R: Rachidian. Rachidian tooth symmetric, tricuspid with mesocone well developed, triangular blunt end, trapezoidal basal plate; ecto- and endocone smaller than mesocone, without accessory cusps ( Figs 26, 27 ). Lateral teeth, asymmetric, bicuspid, with larger and conical mesocone; ectocone smaller than mesocone, triangular, rounded end; basal plate rectangular ( Figs 25, 26 ). Marginal teeth bicuspid, with oblique insertion, basal plate reduced to small square-shaped plate, mesocone elongated, ectocone triangular, smaller than mesocone ( Fig. 28 ).

Pallial system. Kidney elongated, triangular, thin, about ¼ of pallial cavity in length, between pericardial cavity and rectum. Pericardial cavity located on left side of kidney ( Figs 29–31 ); pulmonary vein visible in median and distal region of mantle roof ( Figs 30, 31 ). Slender vessels on both sides of main pulmonary vein (close to distal portion of pallial system).

Reproductive system. Ovotestis with five or six branches of enlarged digitiform acini, each branch with 12 to 15 acini simple or bifurcated ( Fig. 32 ). Hermaphrodite duct tubular, contorted, with same diameter along its extension ( Fig. 33 ). Albumen gland elongated, irregularly shaped, translucent, formed by small irregular acini ( Figs 32, 34 ). Oviduct cylindrical, elongated, accompanying shape of spire ( Figs 33, 34 ). Penial complex tubular, long and slender, with three regions differentiated (proximal phallus, median epiphallus and distal flagellum), proportions of those regions 4: 1: 1 length respectively, each delimited by well-defined narrowing ( Figs 32, 34, 35 ). Prostate with numerous digitiform acini over oviduct surface. Genital diverticle in club shaped, between crossing penial complex and female system ( Fig. 35 ). Genital atrium short, cylindrical, with insertion of bursa copulatrix (also called the copulation pouch), six times length of genital flagellum, bursa sac slightly elongated in its terminal portion ( Fig. 35 ).

Type locality. Brazil: state of Rio de Janeiro, municipality of Angra dos Reis, Ilha Grande, Jararaca trail, 23.17950° S, 44.20421°W .

Type material. Holotype. Shell and soft parts preserved in alcohol. Original label; Daniel VR, Ovando XMC, Santos SB, Souza ST, Lacerda LEM leg. “ Col. Mol. UERJ 11395 -A” . Paratypes: Eleven. Collected with Holotype. Col. Mol. UERJ 11395 -B; One. Collected with Holotype. MNRJ 23.760 .

Additional material examined. BRAZIL, Ilha Grande , 1 shell, Jararaca trail; 23.17950° S, 44.20421° W; 22 Mar. 1997; Santos SB et al. leg.; Col. Mol. UERJ 695 • 1 shell Same locality; 20 Sep. 1995; Queiroz V leg.; Col. Mol. UERJ 697 • 2 shells, Same locality; 15 Aug. 1996; Queiroz V leg.; Col. Mol. UERJ 701 • 1 (1 shell), Same locality; 15 Aug. 1996; Queiroz V leg.; Col. Mol. UERJ 1076 • 4 (2 shells, 2 specimens preserved in ethanol), Same locality; 29 Aug. 2002, Santos SB et al. leg.; Col. Mol. UERJ 1742 • 2 (1 shell, 1 specimen preserved in ethanol), Same locality; 09 Jan. 2002, Santos SB et al. leg.; Col. Mol. UERJ 1749 • 4 shells, Same locality; 09 Jan. 2002, Santos SB et al. leg.; Col. Mol. UERJ 1771 • 7 shells, Same locality; 13 Apr. 2002; Santos SB et al. leg.; Col. Mol. UERJ 1794 • 6 (3 shells, 3 specimens preserved in ethanol), Same locality; 20 Oct. 2000; Santos SB et al. leg.; Col. Mol. UERJ 2076 • 4 shells, Same locality; 07 Jan. 2001; Santos SB Ribeiro F leg.; Col. Mol. UERJ 2135 • 10 (6 shells, 4 specimens preserved in ethanol), Same locality; 21 Apr. 2001; Santos SB et al. leg.; Col. Mol. UERJ 2167 • 4 shells, Same locality; 27 Oct. 2001, Santos SB et al. leg.; Col. Mol. UERJ 2228 • 2 (1 shell, 1 specimen preserved in ethanol), Same locality; 31 Jul. 2001; Monteiro SP leg; Col. Mol. UERJ 2239 • 2 shells, Same locality; 13 Apr. 2003; Santos SB leg.; Col. Mol. UERJ 2957 • 3 (2 shells, 1 specimen preserved in ethanol) Same locality; 25 Jan. 2005; Miyahira IC leg.; Col. Mol. UERJ 6677 • 13 (5 shells, 8 specimens preserved in ethanol), Same locality; 25 Oct. 2015; Daniel VR, Ovando XMC, Santos SB, Souza ST, Lacerda LE leg.; Col. Mol. UERJ 11395 .

Etymology. The epithet “ adenticulata ”, meaning without teeth, refers to the absence of parietal teeth in the shell aperture. The presence of a parietal tooth is considered a diagnostic character for other species of Megaspira .

Habitat and distribution. The species was found under leaf litter, especially near rocks and in shallow soil. Only known from the type locality.

Comparison with other species. Megaspira adenticulata sp. nov. have an aperture without lamella parietal. This structure is present in the other species of Megaspira . Also, the columellar sculpture in M. adenticulata sp. nov. shows a rough texture and not inner lamellas, characteristic of Megaspira iheringi Pilsbry, 1925 , M. pilsbryi and M. elatior robusta . In M. iheringi and M. elatior robusta have three small lamellae that rise 3 ½ whorls inward ( Pilsbry 1904, 1925). The shell in M. adenticulata sp. nov. has 16 whorls on average and 27 mm in height whereas M. iheringi have 14 whorls and 28 mm. In Megaspira elatior robusta the shell is 16.7 mm in height and has 39 whorls ( Table 1 ). The shell does not have light brown spots, as observed by Pilsbry (1925) in Megaspira iheringi and M. elatior .

Figures

Figures 13–18. Living specimen of Megaspira adenticulata sp. nov. and shell morphology in different views: (13, 14) specimen showing the pigmentation of the cephalopedal mass; (15–18) apertural, dorsal and lateral views of the shell. Scale bars: 1 mm. Photos: Regiana Salgado de Mello.

Figures 19–28. Megaspira adenticulata sp. nov.: (19–21) shell of young specimen in SEM showing the absence of apertural lamellae and detail of the microsculpture of the teleoconch: (22–24) detail of microsculptura of columela in SEM showing small papillae on the entire surface; (25) jaw; (26–28) detail of radula showing the rachidian, lateral and marginal tooth. Scale bars: 19, 20, 22 = 1 mm; 21, 24 = 200 µm; 24, 26, 28 = 20 µm; 25 = 100 µm; 27 = 10 µm.

Figures 29–31. Megaspira adenticulata sp. nov.: detail of proximal, median and distal portions of pallial system. (A) Anus, (MB) Mantle border, (Ki) kidney, (MV) Mantle vessels, (Pe) Pericardium, (PV) Pulmonar vein, (Pn) Pneumostome, (R) Rectum, (Ur) Ureter). Scale bars: 20–24 = 1 mm.

Figures 32–35. General view of reproductive system dissected out of Megaspira adenticulata sp. nov.: (32, 34) dorsal and ventral views of reproductive; (33) detail of ovotestis; (35) detail of distal portion of reproductive system showing the genital atrium and genital diverticle. (Ov) Ovoteste, (HD) Hermaphrodite Duct), (AG) Albumen gland, (BC) Bursa copulatrix, (BD) Bursa duct, (DV) Deferens vas, (Ep) epiphallus, (Ph) proximal phallum, (GA) Genital atrium, (Fl) Flagellum, (Ov) Ovotestis, (Pr) Prostate, (U: uterus), (BD) Bursa duct, (GD) Genital diverticle, (Ph) Proximal phallum, (GA) Genital atrium, (U) Ureter). Scale bars: 32–35 = 1 mm.