Ascidiacea 565 



the ideal habitat for ascidians is one in which there is a considerable 

 natural flow of clear water, yet not sufficient water movement, such as 

 wave action, to dislodge the animal. This habitat will vary according 

 to the size of the animal and its relative area of attachment. 



Compound ascidians as a rule tend toward a two-dimensional state 

 with a maximum area of attachment and minimum thickness. Such 

 forms may be found in profusion on the under surface of rocks and 

 stones in the lower intertidal and upper littoral zones; a few species may 

 be attached to algae and eel grass in the same region. Solitary ascidians 

 are usually larger and possess a relatively smaller area of attachment. 

 Their size and water requirements alone may prohibit their attachment 

 to such surfaces as are occupied by the majority of compound forms, and 

 they are more typically to be found attached to the sides and upper 

 surfaces of rocks, large stones, wharf piles, and the under surface of 

 ships and floats, etc., though very rarely above and often much below 

 the low-tide level. Mud and sand flats at some depth are typical habitats 

 of some species of Molgula and Polycarpa, although they may become 

 attached to rock surfaces in very sheltered positions. 



The principal methods of capture are thus three- fold: turning over 

 boulders at low-tide level, often necessitating the use of a crow-bar; 

 scraping piles, rocks, and ship-bottoms with long-handled net-scrapers; 

 and dredging. 



BREEDING SEASONS 



The breeding season for ascidians of both the Pacific and the Atlantic 

 coasts, including the West Indian fauna typical of the Gulf of Mexico, 

 seems to be summer. Certain forms, namely the various species of 

 Ascidia and probably Molgula and Ciona have no definite season; in- 

 dividuals above a certain size are sexually mature and may breed 

 throughout the year, although the lower temperatures of winter retard 

 the rate of egg production. Most compound ascidians are actively bud- 

 ding during the winter and the individual zooids do not attain sexual 

 maturity until early summer. Some solitary forms such as Styela and 

 probably most species of the families Styelidae and Pyuridae have a 

 breeding season limited to summer months. With the exception of 

 Styela partita, and the polystyelids Boltenia echinata little is known con- 

 cerning the members of these two families from this point of view. 



