setchellii is unusual in that it is comprised of a single cell.
The siphonous construction of the alga means it is an elongate cell
with no cell wall divisions that is coiled around itself. This construction
is rather obvious under the microscope. The elongate internal structures
of Codium are known as utricles and are drawn schematically
1: Schematic drawing of C. setchellii utricles (note rounded
(After Scagel 1967)
utricles of C. setchellii have a rounded tip. Utricles in this
species are heavily branched; the shape is usually cylindrical, but
may be narrowly clavate (Abbott and Hollenberg
1976). The utricle may be between 65 and 90 micrometers in diameter
and typically 0.65 to 1.0 millimeters long. Utricle walls up to 16 micrometers
thick; the walls are lamellate at the apex and lack internal sculpturing.
Figure 2: Lateral view of siphonous utricles of C.
Figure 3: View down onto surface of utricles
with Codium fragile
cellular structure is similar to the related Codium fragile,
but slight differences in the utricle can be used to differentiate these
congeners. Utricles in C. fragile have a thorn-like projection
which is absent in C. setchellii. The tips of the utricle are
smooth in C. setchellii, thus there is a clear morphological
difference at the utricle tip.