From studies in Caridina multidentata, Crangon crangon, Atyephyra compresa, and various species from the genus Alpheus, early cleavage is known to vary from
holoblastic to incomplete (Brooks and Herrick, 1891; Weygoldt, 1961; Anderson, 1973; Klann and Scholtz, 2014).
Janolus fuscus followed the typical
holoblastic, spiral cleavage pattern conserved within annelids, molluscs, and nemerteans.
scaura: (1) transition from
holoblastic cleavage to superficial cleavage, (2) germdisc condensation, (3) germband formation and elongation, (4) germband flexure and limb bud formation, (5) limb bud elongation and segmentation, and (6) dorsal closure and reversal of cephalic direction.
The early
holoblastic cleavages are diagrammed in Fig.
Owenia collaris embryos undergo
holoblastic spiral cleavage to form a coeloblastula, which, although exceptionally hollow (again like some nemerteans), conforms to the ancestral pattern for annelids (Okada, 1970).
Early cleavage was radial and
holoblastic. The earliest embryos encountered in the gonad were wrinkled blastulae (Fig.
pentagona through the stages of
holoblastic radial cleavage, early blastula, wrinkled blastula, and gastrula was typical of development in lecithotrophic sea stars (Byrne, 1995).
Cleavage was equal, radial, complete (i.e.,
holoblastic), and rapid, dividing the embryo into a ball of cells (blastomeres).
Although microtubules have been correlated with cytoplasmic movements that follow fertilization in amphibians (4), ascidians (5), and annelids (6), these embryos do not form blastodisc caps and, unlike the squid, they undergo complete or
holoblastic cleavage.
After fertilization, early cleavage events were
holoblastic, progressing by furrow formation.