Moulted shells are found at Burntcoat Head. Ovalipes ocellatus
Class: Malacostraca Order: Decapoda Family: Portunidae Genus: Ovalipes
Distribution Crabs in the genus ovalipes In Canada there are disjunct populations in the Gulf of St. are distributed worldwide. Lawrence and the Northumberland Strait. The Northumberland This specific species, Strait is a tidal water body between Prince Edward Island and Ovalipes ocellatus, known as the coast of eastern New Brunswick and northern Nova Scotia. the lady crab, occurs along In Nova Scotia they occur in several other coastal areas the eastern seaboard of including the Bay of Fundy and Minas Basin. Most populations North America, from occur south of Cape Cod, Massachusetts and continue south Canada south to Florida. along the Atlantic coast. They converge with two other species of Ovalipes; O. stephenson and O. floridanus.
Habitat They live in shallow coastal It is most often found in sandy substrates in quite shallow water, waters and off shore areas including mud banks sand bars. It may occur in surf zones with sandy bottoms. where there is strong wave action and constantly shifting sands.
Food The lady crab feeds on live or decaying marine organisms such It is both a predator and a as fish, crabs, or clams. When fish or worms pass by, it comes scavenger. out of the sand and grabs the animal with its claws.
Reproduction Courtship takes place The testes or ovaries are situated dorsally in the thorax. Testes between these crabs with open externally in the male near the basal segment of the last the male following and then pair of legs while the ovaries in the female open externally on holding on to a female. the ventral surface of thoracic segment 6 (covered by the folded When this is acceptable to abdomen) The sperm cells produced by the male are housed in her, mating occurs. During cases called spermatophores. During copulation these are mating the male clasps the transferred to the female and stored in her sperm receptacle female from behind and (spermatheca). Eggs released from her ovaries become fertilized. they remain together for a These are carried around in her abdomen for a period of time as period of time. This can be they develop. They are tiny and number in the thousands. They for several hours. form a gelatinous mass held in her abdominal flap.
Development There are two main stages of larval development, first as zoea The female releases her and later as megalops. Zoea are extremely small and are eggs from her abdominal shrimplike in appearance. They go through several moults, each flap into the water. She time becoming slightly larger and adding more limb buds. They moves her abdomen rapidly continue growing to the second stage - megalops. As from side to side. This they moult during this second larval stage all the basic movement causes the eggs parts of an adult crab become obvious. When larval to break open and the development is complete further development leads larvae emerge. These tiny to the immature and then mature adult form. New "zoea" larvae now adapt to little crabs will continue to moult through life until a a new planktonic lifestyle. maximum size is reached of 10 centimetres. Moulted shell
The carapace of this crab has projections known as Characteristics frontal teeth between the eye sockets. There are This is a very attractive crab 3 of these. There are 5 on each side behind the eyes with beautiful patterns on known as marginal teeth. The number of these its shell (both male and along the carapace help to distinguish this crab female). These are reddish from other similar-looking crabs. It has compound purple spots covering its eyes on the tips of stalks. The tail of this crab is body and claws. In the tucked underneath the body and lies against the water and under direct abdomen. The tail of the female lady crab is shaped sunlight, the colouring like a rounded triangle, while the tail of the male is appears iridescent. pointed and narrow.
Adaptations They have adapted to strong wave action and The genus Ovalipes belongs constantly shifting sands by burrowing just to a group of crabs known beneath the sand surface. As waves toss the as “the swimming crabs”. sand around, the crab quickly shifts position The last pair of legs are and digs back under the surface. The eyes, modified into paddles and on stalks, can remain just above the surface are adapted for swimming. allowing the crab to remain hidden from The claws are sharp and predators as well as being an effective hunter. powerful with jagged teeth. The lady crab will dart out of its hiding place The disruptive colouration using its powerful paddles to swim after its provides good camouflage prey, grabbing the animal with its claws. when out in the open water. They are considered to be an aggressive crab.
Status/Threats Predators include fish, shore birds, and They are preyed upon by a lobsters. They also include other crabs. variety of animals as larvae, Lady crabs prey on and are prey of a as juveniles and as adults. variety of molluscs and other crustaceans.
Sightings in Nova Scotia
They occur on many coastal Empty shell moults or carapaces are often areas including the Bay of found along shorelines. Living adults are Fundy and Minas Basin. well camouflaged but can be observed.