Asolene meta ( Ihering, 1915 )

Schilithz, Aline G., Barbosa, Kevin P., Cowie, Robert H., Mota, Ester M., Barbosa, Helene S. & Thiengo, and Silvana C., 2025, Redescription of Asolene meta (Caenogastropoda: Ampullariidae) from the São Francisco basin, Brazil, Zoologia (e 24034) 42, pp. 1-15 : 4-9

Asolene meta ( Ihering, 1915)

Figs 3–10

Ampullaria meta Ihering, 1915: 12 , figs 6, 7.

Pomacea meta ( Ihering, 1915) , Cowie and Thiengo 2003: 69. Pomacea meta ( Ihering, 1915) , Simone 2006: 55, fig. 2.

Asolene meta ( Ihering, 1915) , Schilithz et al. 2013: 288.

Holotype: MNRJ 12861 ( Fig. 3A).

Type locality: Barra, Bahia State, Brazil ( Ihering 1915).

Description. Shell: Shell globose, thick, yellowish to brown with dark brown spiral bands variable in number and thickness, when present ( Fig. 3). Ranging in size from 23 to 32 mm in adult shell height and 26 to 35 mm in adult shell width. Periostracum thick and yellowish. Shell comprising three to four rounded whorls, increasing rapidly in size. Spire low, with ratio of spire height to overall shell height ranging from 0.05 to 0.15; apex usually eroded. Body whorl rounded, ranging in height from 22 to 29 mm. Umbilicus deep and wide. Aperture oval, ranging in size from 10 to 23 mm in height and from 12 to 17 mm in width; inside of shell lip usually white.

Operculum: Operculum corneous with concentric nucleus, thick, less flexible than that of Pomacea canaliculata (Lamarck, 1822) , dark brown, tightly sealing aperture ( Fig. 4); ranging in size from 14 to 20 mm in height and from 10 to 13 mm in width.

Radula: Radula taenioglossate, 3 to 6 mm long, 1 to 2 mm wide, with a mean of 32 rows ( Fig. 5A–B). Rachidian rectangular with a concave base and lateral edges and apex convex, one prominent, sharply pointed, triangular central cusp, bounded by three to four minors sharply pointed, triangular denticles on each side ( Fig. 5C). Lateral teeth with a long base, with four triangulate sharply pointed cusps, one major and three minor ( Fig. 5D). Marginal teeth elongated with two sharply pointed cusps, one major and one minor ( Fig. 5E).

Reno-pericardial system: Pericardium small, bounding base of mantle cavity at left. Auricle oval anterodorsal to ventricle, with thin walls; two veins, the branchial-pulmonary efferent vein and the efferent renal vein; connected to ventricle through atrioventricular valve. Ventricle quadrangular, larger than the auricle and denser; connected to bulbous aorta, which splits forming the anterior and posterior aortae. Ampulla voluminous, oval elongated, extending along floor of pericardial cavity ( Fig. 6B). Siphon approximately half the size compared to Pomacea species, formed by two folds, the left end connects to the right end, thus forming an extendable cylindrical tube ( Fig. 6B). Osphradium ( Fig. 6A, C) anterior to lung and posterior to siphon, elongate oval, stalked, with bipectinate ridges on its anterior portion, following a single central crest with longitudinal ridges. Kidney formed by two interconnected chambers, anterior and posterior ( Fig. 6D), communicating via small aperture at anterior left of posterior chamber. Anterior chamber located at mantle roof below ctenidium, dense, wider than long, with rounded borders, smaller than posterior chamber; excretory tissue forming two unequal sets of lamellae occupying entire lumen, regularly arranged transversely on both sides of anterior afferent renal vein; posterior set of lamellae overhanging broad nephropore. Nephridial gland absent. Posterior chamber located superficially on visceral mass, above sets of loops of intestine, elongate, larger and thinner than anterior chamber; internal lamellae spaced irregularly along two branches of two major veins, the renal afferent vein and posterior renal efferent vein; posterior afferent renal vein longer than the anterior afferent renal vein, following the central region of the posterior chamber with numerous branches along its length; efferent renal vein along left of posterior afferent renal vein, subdivided into numerous branches.

Reproductive system (male): Testis voluminous, cream colored, occupying the anterior three whorls of the spire, surrounding digestive gland; thin vas deferens emerging ventrally from testis, continuing along ventral midline of whorl, until entering the rounded seminal vesicle at base of mantle cavity; seminal vesicle separated from the prostate by a small constriction; prostate cylindrical and compact, following along the rectum on the right side of the mantle cavity; anterior end of prostate crossing over rectum, connecting to rounded, muscular penis bulb; wall of penis bulb thinning anteriorly, forming thin-walled penis pouch at right of penis bulb, containing the coiled, whip-like penis when retracted; penis pouch opening to medial channel on the dorsal surface of penis sheath, allowing passage of penis during copulation ( Fig. 7A). Penis long and cylindrical with the diameter gradually decreasing from the base to the apex, formed by a simple epithelium with cubic cells and an extensive layer of muscular fibers; spermatic channel closed ( Fig. 7B–D). Penis sheath curved to the right, broad-based with width decreasing gradually from base to apex; medial channel at ventral surface of penis sheath, formed by two folds, the left overlapping the right one, starting at base of penis sheath and extending to almost the apical gland; penis sheath with two accessory glands on ventral surface—one apical and one basal—and one gland on dorsal surface; apical gland with rugose surface formed by tall, prismatic epithelium cells, occupying distal one quarter of penis sheath ventral surface ( Fig. 7E, F); internal basal gland, smooth and rounded, at right side of penis sheath near medial channel; basal dorsal gland occupying proximal third of sheath base ( Fig. 7G), formed by conjunctive tissue consisting of rounded to oval cells, numerous ducts and a central duct, surrounded by acini, single pore opening externally ( Fig. 7H).

Reproductive system (female): Ovary arborescent occupying similar position to the testis in males, formed by numerous diverticula embedded in the digestive gland; diverticula connected to one another, forming three to four branches that merge into the thin visceral oviduct, extending through the floor of mantle cavity, connecting to seminal receptacle. Pallial oviduct dominating floor of mantle cavity, comprising muscular, oval elongated seminal receptacle, two blind diverticula of albumen gland and spiral lamellae of capsule gland, embedded within a mass of parenchymal tissue, peach colored in live specimens ( Fig. 8A–D); copulatory bursa lacking; seminal receptacle lies transversely to pallial oviduct, exposed at the surface of parenchymal mass, with highly convoluted lumen bearing orientated sperm ( Fig. 8D); posterior end of seminal receptacle abruptly turning to left into a thin channel; albumen gland flattened forming two concave diverticula extending around periphery, one diverticulum anterodorsally at left and the other posteriorly at right, forming a U-shaped curve to connect to capsule gland; capsule gland completing three revolutions coiling counterclockwise, doubling back and completing four clockwise revolutions, with three of these emerging from parenchymal tissue, to connect with elongate, voluminous vagina; vagina narrowing anteriorly, communicating to mantle cavity via small opening adjacent to rectum ( Fig. 8A).

Eggs: Eggs non calcareous, rounded, unpigmented, becoming more translucent before hatching, allowing visualization of juveniles inside eggs; laid under water, on submerged vegetation embedded in gelatinous mass ( Fig. 9); one clutch of 72 eggs was recovered in the laboratory; eggs 3.5 to 4.0 mm in diameter; 44 juveniles hatched approximately nine days after clutch was laid.

Biogeography: Asolene meta is native to northeast Brazil, in the Rio São Francisco Basin , from west of Bahia to Pernambuco. We expect that its range may extend southwest of Bahia ( Fig. 1 ) .

Phylogenetic analysis: The topologies of the ML and BI trees are almost identical. We choose to show the ML tree, on which the BPP values are included for those clades recovered in both phylogenies ( Fig. 10). The COI gene was sequenced from four individuals from the type locality of A. meta , which were identical and for this reason, we chose to use one of them for this study. The complete matrix included 18 sequences from eight species and lengths from 573 to 657 bp including missing data. Both phylogenetic trees recovered A. meta in a well-resolved and strongly supported clade of other Asolene species ( Fig. 10). However, in the BI phylogeny a single specific sister species to A. meta was not recovered, while in the ML tree a clade of A. platae and A. pulchella with low support was recovered as sister to A. meta , with low node support for the three-species clade. The complete alignment contained 120 parsimoniously informative sites, including 51 between A. meta and A. platae-pulchella , 31 between A. meta and A. spixii , and 39 between A. spixii and A. platae-pulchella . This entire Asolene clade was sister to Felipponea iheringi (Pilsbry, 1933) . The mean K2P interspecific distance between A. meta and A. spixii was 5.38 ± 0.29% (5.18–5.88%) and 7.02 ± 0.51% (6.12–7.93%) between A. meta and A. platae-pulchella . We detected through the DeSigNate analysis 15 binary and 1 asymmetric molecular character between A. meta and A. platae-pulchella / A. spixii ( Table 2).

Figures

Figure 1. Distribution of Asolene meta, with Brazil inset. Shaded area: range determined from sample site data; dashed line: range inferred based on habitat similarities. 1: Barra (Bahia); 2: Juazeiro (Bahia); 3: Casa Nova (Bahia); 4: Propriá (Sergipe); 5: Penedo (Alagoas).