These snails are popularly known as "bubble snails", and their shells as "bubble shells", because the shell of some of the species is very inflated indeed, almost spherical in shape, and is also very thin and light.
According to some experts, Bulla is currently the only recent genus in the familyBullidae, which in turn is the only member of the superfamilyBulloidea. The family also includes the extinct genus †AcrocolpusCossmann, 1895.
All Bulla species have large, ovate, external shells, which are large enough to accommodate the whole snail when retracted. All species have rather similarly shaped shells, which have a deep, narrow umbilicus at the apex. No operculum is seen.
The smooth shell of Bulla spp. is ovate and expanded, with a deep, sunken involute top. Since little difference exists between the shells and in the morphology of the radular teeth, some uncertainty remains about the exact taxonomy of the species in Bulla.
Anatomy of the soft parts
The gizzard of Bulla is rather different from that of other herbivorous groups. It has three large, corneous crushing plates and ancillary corneous spines, instead of just grinding plates. These crawling snails show prominent, frilled, or lobed parapodia.
These snails are mostly nocturnal and can be found on shallow, sandy coasts grazing among sea grasses, feeding primarily on green algae. They bury themselves in mud when the tide is out.
Predators
In the coastal lagoons and bays of California, the colorful Navanax inermis is a well-known predator of sea slugs, especially Bulla gouldiana, which it envelopes whole.
Taxonomy
This family seems to have evolved separately in an early stage of the evolutionary history of the opisthobranchs. For a fuller treatment of the whole group see Cephalaspidea.
Bulla, Haminoea, and Smaragdinella form the well-defined monophyletic group Bulloidea, according to the 1996 phylogenetic analysis of Paula M. Mikkelsen,[2] but according to Dr. Bill Rudman and others, differences in the alimentary canal and reproductive system still put Haminoea and Smaragdinella into the separate superfamily Haminoeidea.
Historically, since the 18th century and even in the 20th century, the genus name Bulla has been used for a great number of bubble-shelled species that belonged to the order Cephalapsidea. From the mid-20th century, authors began to restrict species to the genus Bulla in its current meaning. Misidentifications were still numerous through high levels of intraspecific variability in the shell, radula, and male genital systems. The monograph by Malaquias & Reid (2008) has offered a systematic revision of this genus and has brought order in this genus [3]
Distribution: on sandy sublittoral bottoms of warmer seas, tropical Indo-Pacific, Pakistan, Sri Lanka, Philippines
Length: 60mm (largest shell of the Cephalaspidea)
Description: This is the common bulla in tropical Indo-Pacific; globose, inflated, moderately solid body whorl. The white aperture is as long as the rest of the shell. The rounded outer lip is extended posteriorly beyond the apex. The columella in a reversed 'S'-shape, smooth and thinly callous. It is cream-colored with blotches of dark purple-brown.
Distribution: Northwest America, California to Ecuador
Length: 30–64mm
Description: semitransparent head, mantle, and foot are yellowish-brown with mottled pale-bluish dots; reddish to brown involute (= sunken) apex; the aperture is wide anteriorly, narrow posteriorly; their egg mass is yellow to orange tangled string of jelly, containing oval capsules. Each one contains up to 25 eggs, which develop into veliger larvae.
Distribution: Brazil, North Carolina to Florida, Bahamas, Caribbean.
Length: 25mm
Description: thin, rotund, oval shell with a smooth, glazed surface; pale color with brown spots; involute (= sunken) apex; large body whorl; long aperture, wide anteriorly; white columella.
Description: the shell looks like the one of Bulla ampula, but is smaller and more cylindrical. Its color is cream, with clouding of brown or gray in two to four spiral bands, generally spotted with squarish chocolate dots, bordered to the right by white spots.
Bulla quoyii Gray in Dieffenbach, 1843 brown bubble shell
Distribution: Southern Australia, northern New Zealand
Length: 44mm-60mm
Description: The calcified shell has a gray-brown color, with blotches of various shades of brown; the snail has a bright honey-golden color. The hind extremities of the headshield have evolved into tentacles, directing the water over Hancock's organ. The egg-mass is a jelly-like sphere, with the eggs in a spiral string. After the breeding period, there occurs a mass mortality of the animals, just like the sea hares.
Description: The shell is thin, delicate and rather narrow. The body whorl is oval and convex. The smooth elongated aperture narrows posteriorly, but is wide anteriorly. The columellar callus is rather small; The thin outer lip is incurved and extends a little beyond the apex; The color is brown-gray, with darker, smudged dots and dashes, spread unevenly over the surface. The surface is smooth, with some spiral grooves at the posterior end and at the apical umbilicus. There is no operculum. The foot is well developed. There are no parapodia (fleshy winglike outgrowths). The broadened head has no tentacles. The gills and the osphradium are inside the mantle cavity. The radula has three laterals on each side of the central tooth.
In addition to the above, several names in Bulla apply to the species Akera bullata, including Bulla akera (Gmelin, J.F., 1791), Bulla norwegica (Bruguière, J.G., 1789), Bulla canaliculata (Olivi, 1792), Bulla resiliens (Donovan, E., 1801), Bulla fragilis (Lamarck, J.B.P.A. de, 1822), Bulla hanleyi (Adams A. in Sowerby G.B. II, 1850/1855), Bulla elastica (Sandri & Danilo, 1856), Bulla farrani (Norman, 1890), Bulla globosa (Cantraine, F.J., 1840)[5][6]
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