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In marine invertebrates there is a trade-off between fecundity and the amount of
energy that can be invested in each egg. Thus as a rule, a species produces either
many small eggs with planktotrophic development or fewer, large eggs with
lecithotrophic development (Thorson, 1950). Regarding asteroids, the presence of
small (less than 200 µm diameter) freely spawned eggs is considered indicative of
planktotrophic larval development, whereas large (greater than 700 µm) freely
spawned eggs indicate pelagic lecithotrophy.
The distribution of egg sizes in many asteroids is conspicuously bimodal.
Sewell & Young (1999) performed a re-examination of asteroids and echinoids egg
sizes and tested the prediction of bimodality in holothuroids and ophiuroids. Eggs
diameters in asteroid species range from 100 to 3500 µm, and the two modes are
found in the ranges of 100 to 150 µm and 700 to 1000 µm. All species known to have
planktotrophic larvae have small eggs, ranging from near 100 µm in several species
up to 230 µm in Astropecten scoparius Verrill (Emlet et al., 1987). Species with
pelagic lecithotrophic larvae have eggs from 300 µm in Astropecten latespinosus to
1460 µm in Pteraster tesselatus Sladen. Brooding species have eggs that range from
300 µm in Asterina scobinata Verrill to 3500 µm in Rhopiella Koehleri Fisher. The
ranges in egg diameter for planktotrophic and lecithotrophic species do not overlap,
but egg sizes overlap considerably between lecithotrophic and brooding species
(Emlet et al., 1987).
McEdward & Janies (1993) proposed a multifactor classification scheme for
patterns of development in asteroids. Developmental patterns were classified using
three completely independent characters, 1) the morphological nature of development
can be clearly described using the distinction between indirect and direct
development. In their scheme all indirect types have larvae and all direct types do not,
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