The Atlantic bubble shell, Bulla striata, is a member of the Family
Bullidae, the true bubble shells. The shell is thin and usually delicate,
smooth, oval and inflated with an umbilicate (depressed) spire. The
aperture is longer then the shell and is rounded at both ends, narrow
posteriorly and wde anteriorly. The lip is thin and slightly constricted
centrally. No operculum is present. The foot is well developed and the
foot and mantle are slightly translucent. When the foot and mantle are
extended, the animal completely envelops the shell, but it also can retract
completely into it. There are no parapodia (fleshy winglike outgrowths).
The head is broadened and lacks tentacles. The small eyes occur on the
dorsal surface of the cephalic shield. (Abbot 1974, Abbot and Morris 1995,
Baily-Matthews Shell Museum undated).
Color is variable, pale reddish gray to brown-gray, mottled with darker
smudged purplish brown dots. The aperature and the smooth, thin columellar
callus is white (Abbot 1974, Abbot and Morris 1995, Oliver and Nicholls
Tucker (1974) remarks that the type striata specimen comes form the
Mediterranean, and that the Caribbean form is sometimes designated as the
subspecies Bulla striata umbilicata. The author also notes that
specimens identified as Bulla amygdale are probably a smooth form of
Bubble shells belong to the gastropod suborder Cephalaspidea, the
headshield slugs, and to the order Opisthobranchia which also contains the
sea hares, saccoglossans, nudibranchs, and others. The flattened cephalic
shield possessed by members of the suborder is used for burrowing (Rupert
and Fox 1988).
Potentially Misidentified Species
Bulla striata is relatively easily distinguished from co-occurring
cephalaspideans by its size and shape. The solitary paper bubble,
Haminoea solitaria, is smaller than B. striata (1.3 cm versus
2 cm) and has a spiral-grooved, fragile white shell. The channeled barrel
bubble, Acteocina canaliculata, is very small (lass than 5 mm), and
the shell is more strongly spired than that of B. striata (Rupert
and Fox 1988).
HABITAT AND DISTRIBUTION
Bulla striata is widely distributed throughout the shallow tropics
and subtropics on both sides of the Atlantic, including the Mediterranean,
Morocco, Canaries, the Azores, and Florida.
Bulla striata occurs in soft sediment habitats throughout the IRL
system (Mikkelsen et al. 1995, De Maintenon and Mikkelsen 2001, NBI
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Rupert and Fox (1988) indicate that Bulla striata typically reach a shell length of around 2 cm.
Reproduction in Bulla striata involves copulation with internal
fertilization between hermaphroditic individuals. Fertilized eggs are
deposited as an external egg mass which individuals may attach to seagrass
The egg masses are long, irregularly coiled, gelatinous cylindrical cords.
Egg capsules of specimens from the Western Mediterranean are ovoid and
around 160 µm in length and each usually contains a single embryo.
Uncleaved eggs average around 80 µm in diameter (Murillo and Templado
Histological studies conducted by De Maintenon and Mikkelsen (2001) reveal
that B. striata is a true simultaneous hermaphrodite, with male and
female reproductive systems maturing at the same time. This is believed to
be atypical for opisthobranchs, most of which are protandric (functionally
male first) hermaphrodites (Gosliner 1994).
Larval development is planktotrophic. Murillo and Templado (1998) report
that veligers from the Western Mediterranean hatch 4-5 days after egg
deposition. The authors reared planktonic larvae for up to 10 days but
animals did not achieve metamorphosis. By day 10 the larval shell of the
veligers attained a length of around 115 µm and the surface of the shell
Temperature tolerance experiments conducted by Murray and Wingard (2006)
indicate Bulla striata is tolerant across a broad range of
temperatures. Under both normal and hypersaline conditions, individuals
survived and reproduced during extended (175-plus days) exposures to
temperatures reaching 17.5 °C and 31 °C. Under hyposaline
conditions, survival remained high but no reproduction occurred.
Ross et al. (2000) calculated salinity tolerance indices for 32 mollusc
species. The authors ranked Bulla striata as a "marine species",
i.e., rather than as a "marine species with a tolerance for low salinity".
Murray and Wingard (2006), however, demonstrated that B. striata was
capable of surviving (although apparently not reproducing) during prolonged
exposure to salinities as low as 16 ppt.
Although many bullid gastropods are herbivores, Bulla striata is
reportedly a predatory species that feeds principally on molluscs
(Baily-Matthews Shell Museum undated).
No information is available.
Although bubble shells are vulnerable to certain predators, specific
information regarding the predators of Bulla striata is lacking.
The California predatory cepalaspid Navanax inermis is known to feed
on Bulla gouldiana (Rudman 2003).
Bulla striata is a burrowing species found in unconsolidated sand
and mud substrata. They are common residents of estuarine flats and
seagrass beds (De Maintenon and Mikkelsen 2001). As a whole, the members
of order Cephalaspidea are species that are adapted for life on or in sandy
bottoms. Cimino et al. (2004) suggest that the order retains the most
ancestral characters found among the opisthobranchs.
The empty shells of dead B. striata are often an important resource
for hermit crabs (Turra and Pereira Leite 2001).
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Pacific Coasts of North America. Second Edition. Van Nostrand Reinhold
Company, New York. 663 p.
Abbot RT and PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and
the West Indies. Peterson Field Guides. Houghton Mifflin Company, NY. 350
Baily-Matthews Shell Museum. Undated. Bulla striata species profile.
Available online [http://www.shellmuseum.org/Sanibel/shells_bulla.html].
Cimino G, Fontana A, Cutignano A, and M Gavagnin. 2004. Biosynthesis in
opisthobranch molluscs: General outline in the light of recent use of
stable isotopes. Phytochem Rev 3:285-307.
Gosliner TM. 1994. Gastropoda: Opisthobranchia. Pp 253-255 in: Harrison FW
and AJ Kohn (eds.). Microscopic Anatomy of Invertebrates, Volume 5.
Mollusca I. Wiley-Liss, NY.
de Maintenon M and PM Mikkelsen. 2001. Late reproductive system development
in two cephalaspideans (Gastropoda, Opisthobranchia): Bulla striata
Bruguiere, 1792, and Actocina atrata Mikkelsen and Mikkelsen, 1984.
The Veliger 44:237-260.
Mikkelsen PM, Mikkelsen PS, and DJ Karlen. 1995. Molluscan biodiversity in
the Indian River Lagoon, Florida. Bulletin of Marine Science 57:94-127.
Murillo, L and J Templado. 1998. Spawn and development of Bulla
striata (Opisthobranchia, Cephalaspidea) from the western
Mediterranean. Iberus 16:11-19.
Murray JB and GL Wingard. 2006. Salinity and temperature tolerance
experiments on selected Florida Bay mollusks. US Geological Survey Open
File Report 2006-1026. Us Department of Interior/US Geological Survey. 59
NOAA National Benthic Inventory (NBI). Undated. Bulla striata collection
information. Available online.
Oliver APH and J Nicholls. 2004. Guide to Seashells of the World. Firefly
Books, NY. 320 p.
Rudman WB. 2004. Navanax inermis, Cooper 1863. Species profile from
Sea Slug Forum. Australian Museum, Sydney. Available online.
Ross MS, Meeder JF, Sah JP, Ruiz PL and GJ Telesnicki. 2000. The Southeast
Saline Everglades Revisited: 50 Years of Coastal Vegetation. Journal of
Vegetation Science 11:101-112.
Rupert EE and RS Fox. 1988. Seashore Animals of the Southeast. A Guide to
Common Shallow-Water Invertebrates of the Southeastern Atlantic Coast.
University of South Carolina Press. 429 p.
Turra A and FP Pereira Leite. 2001. Shell utilization patterns of a
tropical rocky intertidal hermit crab assemblage: I. The case of Grande
Beach. Journal of Crustacean Biology 21: 393-406.