Obeliscus agassizi Pilsbry, 1906

D'Ávila, Sthefane, Simone, Luiz Ricardo L., Oliveira, Luiz Fernando Cappa de, Charles, Laurent & Maestrati, Philippe, 2020, Rediscovery of Obeliscus agassizi Pilsbry, 1906 (Gastropoda, Subulinidae, Obeliscinae), annotated checklist of species of Obeliscus Beck, 1837 and first description of the anatomy for the genus, Zoosystema 42 (12), pp. 159-172 : 162

Obeliscus agassizi Pilsbry, 1906

Obeliscus agassizi Pilsbry, 1906: 249 , pl. 36, fig. 76. — Clench & Turner 1962: 7. — Salgado & Coelho 2003: 155. — Simone 2006: 187, fig. 686.

TYPES. — Lectotype. ANSP 59334 • Paralectotypes. ANSP 465075 ; FMNH 140941 .

TYPE LOCALITY. — Brazil (collected by J. G. Anthony, during the Agassiz expedition), no specific locality.

OTHER LOCALITIES. — Brazil, Alagoas and Pernambuco states, Biological Reserve of Pedra Talhada (present study).

MATERIAL EXAMINED. — Brazil • Pedra Talhada Biological Reserve, municipalities of Quebrangulo Alagoas state and Lagoa do Ouro , Pernambuco state; MZUSP 133507 • MZUSP 133635.

HABITAT. — In leaf-litter.

MORPHOLOGICAL DESCRIPTION

Shell ( Fig. 1 A-H)

Shell turriform-conic, minutely perforate, not decollated, dextral, tapering; periostracum thin, yellowish, opaque in fully developed individuals, glossy in young individuals. Columella nearly straight, slightly concave ( Fig. 1C ). Embryonic whorls smooth, shining ( Fig. 1A ). Protoconch with c. 3 whorls. Boundary between protoconch and teleoconch well defined. Last whorls plicate below suture, nearly smooth elsewhere ( Fig. 1B ). Spire of c. 12 whorls, convex, very regularly increasing ( Fig. 2A ). Sutures well marked, a little inclined ( Fig. 1B, E ). Teleoconch of c. 10 whorls, smooth, except for growth lines ( Fig. 2D ). Aperture somewhat oblique, ovate ( Fig. 1C ); inner lip simple, outer lip thin.

Head-foot ( Figs 1 D-F; 2B, C)

Head protruded. Head-foot almost transparent in living animals, color pale cream, with fine tessellation ( Figs 1 D-F, 2B). Foot broad, sole oval, edges rounded in fixed animals. Genital opening visible as a rounded area, without tessellation in fixed animals, and as a small fissure near head in living animals ( Fig. 2B ).

Mantle organs ( Fig. 2C )

Mantle edge simple, thick. Rectum narrow, walls thick, running along right edge of pulmonary cavity. Ureter running parallel to rectum, both structures covered by fine membrane. Pulmonary cavity very long and narrow, occupying the two last whorls. Kidney and pericardium restricted to middle and left sides, occupying c. 1/20 of pallial roof. Pulmonary vein running along entire pallial cavity, oblique in anterior 1/5, running along left edge in remaining regions.

Circulatory and excretory systems ( Fig. 2C )

Pericardium located at columellar margin of posterior end of pallial cavity, c. 1/3 of the kidney length. Auricle small, triangular, located in middle length of kidney left margin. Ventricle near same size of auricle. Kidney occupying c. 1/5 of pulmonary cavity length, located along middle and left regions of transition pallial cavity and visceral mass. Kidney rather bilobed, with smaller lobe just anterior to auricle. Pulmonary vein running along columellar margin of pallial cavity, straight in posterior 4/5 portion of the mantle, curved in anterior 1/5 portion, converging to pneumostome region along with renal tube and rectum.

Visceral mass ( Figs 2C, E )

Digestive gland brownish, located along inferior region of seventh visceral whorl, covering part of stomach at sixth whorl and filling entire visceral whorls posterior to stomach, including nepionic whorls ( Fig. 2E ). Rectum visible at eighth visceral whorl.

Genital system ( Figs 3 A-F)

Gonad located at the sixth visceral whorl, covered by the digestive gland ( Fig. 3E : go). Albumen gland elongated, sheltering spermoduct under its columellar face. Carrefour lying at tran- sition between spermoviduct and albumen gland ( Fig. 3B ). Seminal receptacle as wide sinuous tube, lying at superior half of albumen gland ( Fig. 3B : sr). Spermoviduct long, occupying first three shell whorls, running along columellar muscle ( Fig. 3A, E ). Autospermoduct situated at columellar face of spermoviduct ( Fig. 3A : at). Allospermoviduct situated at the opposite face, visible as a separated duct until reach the freeoviduct ( Fig. 3A, E : al). Prostate with well defined acini, occupying columellar surface of spermoviduct ( Fig. 3A, E : pt). Bursa copulatrix about as wide as its duct ( Fig. 3E : bc), lying in transition between spermoviduct and free oviduct; length c. 1/2 of that of spermovioduct. Free oviduct c. 1/2 length of bursa copulatrix duct. Vagina c. 1/2 free oviduct length. Atrial retractor muscle well developed. Vas deferens with greater diameter at level of free oviduct, adhered to free oviduct wall at its more convoluted and thicker portion through fine muscle bundles. Vas deferens meeting gland with unidentified function after leaving prostate, running along entire free oviduct; vas deferens convoluted in median portion of free oviduct, showing greater diameter until basis of free oviduct, joining to penis. Penis long, club-shaped ( Fig. 3A, C : pe). At the meeting point with the penial complex, the vas deferens forms a discrete bursa which lies on the phallus wall. Penial complex passing under right ommatophore and under esophagus. Penial retractor muscle ( Fig. 3D : pm) originated in diaphragm region close to columellar muscle, inserted terminally in the epiphallus.

Figures

FIG. 1. — Obeliscus agassizi Pilsbry, 1906 shell and living specimen: A, SEM of apex in profile; B, same, middle region of teleoconch; C, same, last whorl, frontal view, asterisk showing epiphragm; D-F, living crawling specimen, shell length c. 6 mm; G, detail of suture of protoconch, SEM; H, detail of epiphragm insertion on body whorl. Scale bars: A-C, 1 mm; G, 0.15 mm; H, 0.1 mm.

FIG. 2. — Obeliscus agassizi Pilsbry, 1906 anatomical drawings: A, outline of adult shell, part of read-foot also shown; B, soft parts last whorls, specimen just extracted from shell; C, whole specimen view, pallial cavity extracted and extended to right; D, detail of shell first whorls showing delicate sculpture; E, detail of visceral mass. Abbreviations: see Material and methods. Scale bars: 2 mm.

FIG. 3. — Obeliscus agassizi Pilsbry, 1906 anatomical drawings: A, outline of adult shell, part of read-foot also shown; B, soft parts last whorls, specimen just extracted from shell; C, whole specimen view, pallial cavity extracted and extended to right; D, detail of shell first whorls showing delicate sculpture; E, detail of visceral mass. Abbreviations: see Material and methods. Scale bars: 2 mm.