Once the extending pharyngeal basket has joined the stomach and started to produce its first stigmata, the stereotypical body plan of the zooid
is completed, thus becoming a first-generation bud on which new budlets start to appear (day 9; Fig.
Botryllid colonies, like all colonial ascidians, consist of individual feeding and reproductive units called zooids
that are encased in a common outer covering, the tunic.
Botryllus schlosseri is a cosmopolitan colonial ascidian that undergoes cyclical generation changes, or takeovers, during which adult zooids
are resorbed and replaced by their buds.
Coloniality and inducible polymorphism: the interaction of zooid
and colony level control.
Colonies are composed of numerous asexually produced zooids
organized into systems (typically 7-10 zooids/system), with up to 100 systems comprising a colony.
These crystals are incorporated into the zooid
walls as spheres, which may coalesce and develop into threads (Ryland, 1976) and eventually many other ultrastructural forms (see, e.g., Sandberg, 1977).
Hosts carrying a single zooid
were transferred to glass Petri dishes (147 mm in diameter) filled with 150 mL of < 0.45 [micro]m 15 psu water, enriched with varying amounts of Cerophyl [R] to reach different bacterial concentrations.
These juveniles were both at the single zooid
stage while 98% of the juveniles in the controls had progressed to the two-zooid stage.
Other studies have confirmed higher concentrations of bryostatins on larvae (~10 X), as well as in zooids
with ovicells (~3 X) compared to zooids
with no ovicells (Lopanik et al., 2004, 2006).
However, the relationships among these components of variance in zooid
morphology have not been evaluated in detail.
For consistency with methods used in quantitative genetics, within-colony zooid
data were treated as replicate measurements, and colony means were used to calculate phenotypic variance-covariance matrices, P (Cheetham et al.
Both an oocyte and testis developed on the abdomen of the zooid