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Species Name: 
Bursatella leachii de Blainville, 1817

Common Name(s):
Ragged Sea Hare

Synonymy:
Many authors consider the circumtropical species Bursatella leachii to be comprised of as many as eight distinct subspecies.

Species Description:
Bursatella leachii, the ragged sea hare, is a medium- to large-sized benthic opisthobranch mollusc within the Order Anaspide, the sea hares. The body is variably colored, grayish-green to white-tan with dark brown blotches and spots, compact and rounded, with distinct head and neck regions evident. The body is also covered with numerous long, branching fleshy papillae that give the animal its ragged appearance. The gill is covered by a pair of fleshy parapodia. Two long, retractile olfactory tentacles called rhinophores occur on the head, and also two fleshy enrolled oral tentacles occur at each side of the mouth. Adults completely lack a shell (Voss 1980, Kaplan 1988, Rupert and Fox 1988).

Potentially Misidentified Species:
Although Bursatella is a monophyletic genus containing only B. leachii, a wide range of color and morphological variations has prompted come authors to suggest that the global distribution comprises several distinct subspecies (Eales and Engel 1935, Bebbington 1969). If this convention is followed, the subspecies occurring in Florida is Bursatella leachii pleii Rang, 1828.

Sea hares of the genus Aplysia co-occur with B. leachii throughout much of its range. Bursatella and Aplysia are easily distinguished from one another, as Aplysia are larger, lack the frilled, ragged appearance of Bursatella and possess large swimming flaps that are absent in B. leachii.

II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
Bursatella leachii is a circumtropical species found nearly worldwide in warm temperate to tropical marine environments (Rudman 1998). Kruczynski and Porter (1969) list North Carolina as the northern limit of the species on the US east coast.

IRL Distribution:
Bursatella leachii can be found throughout the IRL system, although much of the time it apparently persists at relatively low population densities (see below).

III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
Adult ragged sea hares are capable of attaining lengths of 25 cm, although 7.5-10 cm is more typical of Florida populations (Voss 1980, Kaplan 1988).

Published field and laboratory information is lacking, but the experience of aquarists suggests that the maximum life expectancy of this and other species of sea hares is just over one year (van Horn 2005).

Abundance:
Although Bursatella leachii is spatially and temporally highly sporadic in occurrence, it is periodically encountered at high densities in the environment (Rudloe 1971, Lowe and Turner 1976). Localized populations of B. leachii have been reported at densities of 660 individuals per square meter. Such irruptive population outbreaks are probably attributable to vagaries of the environment and the relative rarity of situations in which environmental conditions are near-optimal. Population explosions most likely occur when larval supply is good, dietary resources are abundant, and tides, currents, and weather conditions are favorable (Rudman undated).

Just as mass-settlement events are a common aspect of the life history, so too are mass mortality events. Hundreds to thousands of dead and dying animals are sometimes encountered washed ashore, and storms, tides, and extreme high temperatures often serve as exacerbating factors.

Reproduction:
As with most sea hares, Bursatella leachii is a cross-fertilizing simultaneous hermaphrodite (Kaplan 1988). Fertilization is internal, with one individual transferring sperm via an eversible penis located on the right side of the head to the dorsally located gonopore (genital opening) of a second individual (Van Horn 2005). Thus inseminated, individuals lay large, tangled, spaghetti-like benthic egg masses that are usually orange, yellow, green, or brown in color. The string-like egg masses are comprised of numerous separate capsules, each of which contains 1-20 eggs that are approximately 87 µm in diameter (Paige 1988).

Ragged sea hares attain sexual maturity at 2-3 months of age (Paige 1988). At least in some parts of its range, the species appears to undergo continuous recruitment with no well-defined reproductive season (Clarke 2004).

Embryology:
The larval biology of Bursatella leachii had previously been poorly studied, largely due to lack of success at rearing specimens in the laboratory (Henry 1952, Bebbington 1969). More recently, research findings by Paige (1988) have provided more detail on larval and postlarval development. This work is summarized here.

Under laboratory culture conditions at 25°C, animals hatch out as planktotrophic larvae approximately a week after egg masses have been laid. Newly hatched veligers lack eyes and possess a pair of sensory statocysts at the base of the foot. Individuals are negatively geotropic and they maintain themselves in the water column by swimming using a well-developed velum.

Growth of the planktonic larvae after hatching is rapid. Veligers attain maximum size approximately 15 days after hatching, and metamorphic competency is reached at 19 days posthatch. Paige (1988) notes that this is the shortest known larval duration for aplysiids possessing planktonic larvae.

Competent B. leachii metamorphose to take up a juvenile existence on the species of cyanobacteria that they will utilize as food, such as Microcoleus lyngbyaceus (now Lyngbya majuscula). Individuals that are competent to metamorphose are capable of delaying settlement for as much as 2.5 months until a suitable settlement substratum (i.e., blue-green algae from the Family Oscillatoriaceae) is encountered.

Upon settlement, an individual will attach to the substratum via mucus threads and retract into the shell to metamorphose. The process takes 1-2 days. Within a day of metamorphosis, postlarvae are seen crawling across the substratum ingesting food with a radula that is already well developed.

Postlarval growth is rapid. The shell stops growing when individuals reach 2.5-3 mm length, and between 15-20 days post-settlement the vestigial shell is discarded. By this time, the juvenile begins to resemble the adult in appearance, including the presence of rudiments along the body that will become the fleshy papillae. At this time, the juvenile also has the ability to discharge a small cloud of ink if irritated (Paige 1988).