Gabbia Tryon, 1865

Ponder, Winston F., 2003, Monograph of the Australian Bithyniidae (Caenogastropoda: Rissooidea), Zootaxa 230 (1), pp. 1-126 : 9-13

Genus Gabbia Tryon, 1865

Gabbia Tryon, 1865: 220 . Type species: Gabbia australis Tryon, 1865 (= Bithynia vertiginosa Frauenfeld, 1862 herein) by monotypy.

Mysoria Godwin­Austen, 1919a: 211 , non Watson, 1893. Type species Bithynia costigera Küster , var curta Nevill, 1884 , by original designation, Bangalore, India.

Mysorella Godwin­Austen, 1919b: 431 , new name for Mysoria Godwin­Austen, 1919a .

Diagnosis

Shell ovate to conic, smooth or with axial and/or spiral sculpture, umbilicate to imperforate. Protoconch evenly coiled or with apex slightly tilted inwards; of about 1.3­1.5 whorls, smooth except for faint spiral striae or very fine spiral wrinkles, slightly tilted. Aperture ovate, with weak to moderate rim within perisotome (on which edge of retracted operculum rests). Outer lip prosocline, simple (lacks any sinus or outer varix).

Operculum calcified, oval, outer side flat to (usually) slightly concave, outer part concentric; nucleus eccentric, situated in middle to just below middle (relative to operculum located in aperture with shell upright). Muscle scar thick, convex, occupies most of inner surface, usually sculptured with pustules or concentric to irregular low ridges.

Radula taenioglossate, with large central teeth, cutting edge occupying about half width of tooth, each with several (1­6, usually fewer than 5) pairs of basal cusps, lateral edges extend beyond base, at about 50­70º. Lateral teeth with cutting edge about 0.3­0.7 length of lateral part of tooth, with near vertical inner edge and distinct basal excavation on inner side of prominent basal process; lateral process at about 50­70º to dorsal edge; inner marginal teeth larger than outer marginals, with many small, sharp cusps, outer marginal teeth with small, sharp cusps on distal end.

Alimentary canal similar to that of Bithynia , rectum straight, with elongately­oval, usually obliquely packed, faecal pellets.

Pallial genital ducts lie within pallial kidney. Testis large, seminal vesicle long and coiled. Prostate elongate oval, compressed in section. Penis on right side of head behind right tentacle; bifid, with accessory lobe shorter than, or about equal in length to, penial lobe. Accessory gland (in cephalic cavity) short to very long. Ovary with several discrete tubular lobes. Renal oviduct with about two tight coils. Glandular oviduct with anterior (pallial) capsule gland, with ventral channel, and posterior (usually mostly or entirely visceral) laterally compressed albumen gland; genital opening terminal. Bursa copulatrix opens anteriorly to ventral channel near oviduct opening and lies on inner side of capsule gland. Seminal receptacle small, lies in middle part of outer wall of albumen gland.

Distribution Asia, Australia.

Remarks

In most respects, the morphology of species of Gabbia is very similar to that described for B. tentaculata (see references above) but differs in the following characters: the shell is more conical in shape (rather than elongate­ovate); the apex of the protoconch is less strongly tilted inwards; the operculum has a moderately large, distinctly spiral nucleus in the centre of the operculum to just below the centre (as viewed in the aperture with the shell upright) (in a similar location but much smaller in B. tentaculata ); the apices of the gill filaments are usually on the right side of the gill (in the middle in Bithynia ); the bursa copulatrix lies on the inside of the capsule gland, not the outside and the small seminal receptacle is embedded in the middle part of the outer side of the albumen gland (not a large sac lying behind the albumen gland). This combination of characters, together with shared characters such as the simple outer lip (not sinuate as in Wattebledia Crosse, 1886 and lacking the varix present in species of Hydrobioides Nevill, 1884 ) also separate Gabbia from other bithyniid genera.

The radula of species of Gabbia differs from that of the type species of Bithynia only in the sides of the central teeth being at a slightly wider angle (about 70º rather than 50­ 60º) and the basal cusps of the central teeth are typically fewer and weaker. In most other respects the radulae are very similar, as are the opercula, head­foot, pallial cavity and most other anatomical details. However, there are some significant differences in the female genital system, as detailed above, although in other respects the details of the female system are very similar.

A detailed review of bithyniid genera is beyond the scope of this paper, although one is currently in preparation. Some names are based on species with similar shell morphology to the type species of Gabbia . These include the African Gabbiella Mandahl­Barth, 1968 (type species Bithynia stanleyi var humerosa Martens, 1879 from Lake Victoria, Africa) and Codiella Monterosato in Locard, 1894 (type species Turbo leachii Sheppard, 1823 , a taxon usually included in Bithynia but treated [probably correctly] as a genus by some authors, e.g., Beriozkina et al. 1995). These taxa are not yet known sufficiently well anatomically to differentiate them, but Gabbia is the senior name for taxa based on this type of shell morphology.

Wenz (1938) listed Digyrcidum Locard, 1882 , Neumayria Stefani, 1877 and Alocinma Annandale and Prashad, 1919 (as Allocima in error) as synonyms of Gabbia . None of these names have priority over Gabbia .

In Bithynia , Gabbia and several other bithyniid genera, the whole peristome has a rim within its edge which forms an opercular stop, keeping the operculum flush with the edge of the aperture when the snail is fully retracted.

Gabbia has been defined as “lacks umbilicus; peristome straight, lacking varix; base of peristome rounded. Operculum with large, paucispiral nucleus. Radula with 7­9 cusps on cutting edge, and 3­4 pairs of basal cusps” ( Brandt, 1974: 61). In introducing Gabbia, Tyron (1865: 220) gave the following diagnosis: “Shell like Amnicola Gould and Hald. Operculum paucispiral, calcareous.” In his remarks he noted that the operculum was “somewhat calcareous like Bith. tentaculata .” Smith (1887:236) stated that “the generic division Gabbia , proposed by Tryon for this species, appears to be altogether unnecessary. The character upon which he founded the group was a supposed peculiarity in the operculum which he describes as ‘paucispiral, calcareous’. His own figure and the shells before me show that the operculum is not paucispiral, but normally concentric, as in other species of Bithinia .” Smith concludes that Gabbia is a synonym of Bithynia . Despite this strong statement, the use of the name Gabbia has continued virtually unabated in the literature but has never been satisfactorily separated from Bithynia . For example the name is used by Thiele (1928, 1929) as a subgenus of Bithynia with the following diagnosis ( Thiele, 1929: 154) (as translated by Bieler and Mikkelsen, 1988: 224) “shell in most cases fairly low spired; last whorl large, bulging, smooth; umbilicus closed or chink­like; operculum with large spirally coiled median part.” Thiele (1928, 1929) recognised three “sections” of Gabbia ­ Gabbia s.s., as well as Parabithynia Pilsbry, 1928 and Emmericiopsis Thiele, 1928 . Pace (1973: 35) noted that Tryon's description of Gabbia “does not distinguish it from Bithynia (s.s.)”. Tryon himself (1883: 260) reduced Gabbia to a subgenus of Bithynia , noting that it was “possibly synonymous with Bithynia , from which it only differs slightly in its operculum.”

The status of Gabbia has been variously interpreted. It has been given generic status ( Tryon, 1865; Cotton, 1942; Iredale, 1943, 1944; Smith, 1992) or treated as a subgenus of Bithynia (or Bulimus ) ( Tryon, 1883; Thiele, 1929; Wenz, 1938; Starmühlner, 1976), while others ( Tate, 1882; Hedley, 1896; Smith, 1887; Pace, 1973) have treated it as a synonym of Bithynia . Gabbia has also been used for some SE Asian taxa, either as a genus (e.g. Habe, 1964; Benthem Jutting, 1963; Chung, 1984; Chitramvong & Upatham, 1989; Chitramvong, 1991, 1992) or subgenus of Bithynia ( Kuroda, 1941; Brandt, 1968, 1974).

Chung (1984) described the radula, operculum, mantle pigmentation and allozymes of Gabbia misella from Korea and Chitramvong (1991, 1992) described the morphology, including anatomy, of three species from Thailand and compared them with species in other bithyniid genera ( Bithynia, Hydrobioides and Wattebledia ).

Mysorella was defined by its broadly­ovate, umbilicate, shell which possesses strong spiral cords. The genus was originally diagnosed as having only a single pair of basal cusps on the central teeth ( Godwin­Austen, 1919a; Annandale, 1920) but Seshaiya (1930) and Starmühlner (1974) showed that additional small denticles are often present. There are 7­9 cusps on the cutting edge while the lateral teeth have the formula 3+1+3. Details of the anatomy of M. costigera have been provided by Seshaiya (1930). The radula is illustrated by Godwin­Austen (1919a, fig. 3), Thiele (1928, text fig. 4; 1929, fig. 127) and Seshaiya (1930, text fig. 10). The anatomy, radula and operculum of the type species and a species from Australia, which is very similar to the type species, are virtually indistinguishable from Gabbia . In addition, within the Australian Gabbia species are taxa ranging from smooth to strongly spirally lirate and the umbilicus also varies in width within the genus. For these reasons, Mysorella is tentatively treated as a synonym of Gabbia pending more detailed assessment of the Asian fauna (see also remarks under G. carinata n.sp.).

Uniform characters

Details given above that are uniform throughout the taxa described herein are usually not repeated in the descriptions.

Shell: Inner rim of peristome – present in all species to a greater or lesser extent (related to degree of thickening of peristome) and is not mentioned in the descriptions.

Operculum: All species have a similar, calcified operculum but this structure is illustrated for most taxa. Only a few details are given in the descriptions.

Radula: The tooth shape is generally very similar between species so these details are mostly not given in the description (although are available from the figures).

Head­foot: All species have a similar head­foot as outlined in the generic description. Only the pigmentation is given.