Botryllus schlosseri
Scientific Name:-
Botryllus schlosseriCommon Name:-
Golden star tunicate, Star squirt
Malayalam Name:-
Category:-
Sponges
Status:-
Photo courtesy: http://nas.er.usgs.gov/,
http://www.animalbase.uni-goettingen.de/,
http://www.arkive.org/,
http://www.microscopy-uk.org/
Description:-
Botryllus schlosseri is a colonial sea squirt that typically forms flat sheets 3-4 mm thick and up to 10 cm across. Colonies that overgrow narrow-bladed seaweeds may appear lobate, and colonies growing in stalked, fleshy lobes have been reported in southern Australia. Botryllus schlosseri grows on a variety of surfaces, include docks, boat hulls, buoys, ropes, pilings and the undersides of rocks, and on mussels, solitary sea squirts, seaweeds and eelgrass (Zostera marina), and they often do well in polluted waters.
Each colony consists of many small individuals called zooids, that are arranged in circular, oval or star-shaped clusters called systems, within a clear, firm, fleshy matrix. Each zooid pumps water through its body, filtering out food particles. As described below, all the zooids in a system discharge their filtered water into a common space within the matrix, from which it exits the colony.
A single system is 5-10 mm in diameter, and may have up to about 20 zooids. The zooids themselves are about 2-5 mm long and oval to tear-drop shaped, with the narrower end pointing toward the center of the system. The zooids can be orange, yellow, red, white, gray-green, purple, dark gray or black, or certain combinations of these colors, though all zooids within a colony are the same color. Networks of transparent blood vessels running through the matrix have numerous dead ends that are visible as small pigmented blobs embedded in the clear matrix between the systems and around the edges of the colony.
The following details can be seen with a microscope and some dissection. At the top of each zooid there is a small opening, called the oral aperture, with 16 small tentacles around the inside of the opening. Water enters through this opening into a sac that occupies much of the zooid's interior. The sac is pierced with holes, called stigmata, that are arranged in 8-12 (usually 9-10) horizontal rows. As water passes through the stigmata, the zooid captures food particles on a sheet of mucous that is then ingested, and absorbs oxygen from the water. The water leaves the zooid through a gaping opening, called the atrial aperture, into a central common space that receives water from all the zooids in a system, and then exits the colony though a central pore.
Colonies typically mature after 1-2 months, and reproduce in spring and early summer. Temperatures of at least 11°C and salinities of at least 25 ppt are needed for reproduction. During its reproductive period, which lasts up to 10 weeks, a colony can produce up to 8,000 eggs. The eggs are retained within the colony where they develop into tadpole-shaped larvae with 8 finger-like buds, called ampullae, on the head end. When released from the colony a larva spends less than a day in the water column before attaching head-down onto a firm surface. The settled larva metamorphoses into a zooid, which buds off others to the sides to form a colony. Colonies in Monterey Bay can grow up to 1,400 zooids in 10 weeks. Colonies that develop from larvae that settle in the spring live for about 3 months and those that develop from fall settlers live for about 8 months, though colonies kept in the laboratory have survived for up to 7 years (Chadwick-Furman & Weissman 1995). Botryllus schlosseri's temperature and salinity limits are interrelated, but high mortality has been reported below 3°C and 16 ppt and above 44 ppt.
Crabs, snails and flatworms have been observed feeding on Botryllus schlosseri. Botryllus schlosseri can overgrow other attached, filter-feeding organisms and compete with them for food. It is a nuisance fouler on boat hulls and equipment, and can overgrow and compete with cultured oysters and mussels and increase processing costs for these shellfish.
Its range has spread over the last 100 years to a nearly worldwide extent. Ranging in the western Atlantic Ocean from the Bay of Fundy to North Carolina, this is "the most common colonial tunicate in North America."
The colony can regrow and reproduce from fragments. Larvae remain in the water column for less than 36 hrs before settling on a hard substrate to grow into juvenile tunicate colonies.
This tunicate species can withstand estuarine habitats with low salinities (18 ppt or less).
Botryllus schlosseri may fuse with kin to form chimaeras which vary their life histories depending on environmental conditions.
All sea-squirts filter suspended particles from the water. They maintain a current that passes through their body by beating tiny hair-like structures known as 'cilia'; the water enters through an opening called the 'inhalant siphon', and passes through the pharynx, where plankton and detritus become trapped in mucus and are passed to the stomach. The water then passes out through a second opening called the 'exhalent siphon'. In the star ascidian, the exhalent siphons of all the members of the colony open into a shared chamber, known as the cloaca, water then passes out of a shared exhalent siphon at the centre of the colony.
In the star ascidian, the zooids are hermaphroditic; after fertilisation, eggs are retained until the tadpole larvae have formed. The larvae are then released through the exhalent siphon, and live in the water column for about 36 hours, before settling and forming new colonies. Asexual reproduction can also take place through budding. Colonies may live for up to one and a half years. Star ascidians are predated upon by cowries (members of the genus Trivia), which are gastropod molluscs; cowries also lay their eggs into holes made in the star-ascidian test.
Synonyms:-
: Alcyonium borlasii Turton, 1807; Alcyonium schlosseri Pallas, 1766; Aplidium verrucosum Dalyell, 1839; Botryllus aurolineatus Giard, 1872; Botryllus badium Alder & Hancock, 1912; Botryllus badius Alder & Hancock, 1912 ;Botryllus bivittatus Milne-Edwards, 1841 ;Botryllus calendula Giard, 1872; Botryllus calyculatus Alder & Hancock, 1907; Botryllus castaneus Alder & Hancock, 1848; Botryllus gemmeus Savigny, 1816; Botryllus gouldii Verrill, 1871; Botryllus marionis Giard, 1872; Botryllus miniatus Alder & Hancock, 1912; Botryllus minutus Savigny, 1816; Botryllus morio Giard, 1872; Botryllus polycyclus Savigny, 1816; Botryllus pruinosus Giard, 1872; Botryllus rubens Alder & Hancock, 1848; Botryllus rubigo Giard, 1872; Botryllus smaragdus Milne-Edwards, 1841; Botryllus stellatus Gaertner, 1774; Botryllus violaceus Milne-Edwards, 1841; Botryllus violatinctus Hartmeyer, 1909; Botryllus virescens Alder & Hancock, 1848; Polycyclus renieri Salfi, 1931