The five-lobed hydrocoel
grows around the larval esophagus and fuses with itself to form the ring canal and radial canals of the water vascular system.
Rudiment diameter was measured as the contact between ectodermal invagination and hydrocoel during the early stages of contact; at later stages rudiment diameter included the enveloping ectoderm.
Concentration of larval food affected the timing of development of the echinus rudiment from the earliest stages of rudiment formation: the invagination of ectoderm overlying the hydrocoel. Developmental plasticity in response to larval nutrition was easily detected,
Of these, all metamorphosed with a set of five primary podia growing from the left hydrocoel and between one and three pedicellariae, one on the dorsal surface associated with the base of the dorsal arch spicule, and two posterior on the left side--one at the base of the posterodorsal arm rod and one at the base of the pastoral arm rod (Fig.
In euechinoids, the vestibule is formed from an invagination of the larval epidermis that comes into contact with the left hydrocoel. In those species without an invagination, the structures developed on the larval epidermis, resulting in an apparently simpler metamorphosis compared to the eversion of the vestibule in euechinoids.
All of these authors attribute these unusual larvae to development of the hydrocoel
. For larvae with situs inversus, the right hydrocoel
enlarged instead of the left to produce the rudiment that becomes the juvenile oral surface.
Competent brachiolariae display a slight leftward flexion that coincides with appearance of the five hydrocoel
lobes in the rudiment on the left hand side of the larva (Figs.
The left posterior coelomic pouch is divided into a hydrocoel and somatocoel, and the former expands forward, gradually, along the stomach and esophagus, producing a 5-lobed hydrocoel (Fig.
Table 1 Chronology of development of Ophiodaphne formata (26 [degrees]C) Time after fertilization Stage 2 h 2-cell stage 2.5 h 4-cell stage 3 h 8-cell stage 3.5 h 16-cell stage 5 h Morula 6.2 h Blastula with blastocoel 9 h Hatching 21 h Gastrula, 140 [micro]m long and 120 [micro]m wide 1.5 d 2-armed ophiopluteus 2.5 d 4-armed ophiopluteus 4.5 d 6-armed ophiopluteus 6.5 d 8-armed ophiopluteus with posterior coelom 13.5 d Hydrocoel formation 15.5 d Left hydrocoel 5-lobed 18.5 d Rudiments of adult skeleton appear as spicules 20.5 d Metamorphic climax begins, larval arm degenerates rapidly 21.5 d Completion of metamorphosis with absorption of larval arms Acknowledgments
cordatus is condensed (no larval morphogenesis) and presents a shift in the relative timing (heterochrony) of the appearance of the major features (archenteron, coelom + vestibule, hydrocoel
), if compared to the typical echinoid development (archenteron, larval skeleton, larval gut, coelom, hydrocoel
Four lobes of the hydrocoel appear at the base of the preoral lobe on the future oral surface.
On the left side the anterior coelom gives rise to the hydrocoel [ILLUSTRATION FOR FIGURES 3D-F OMITTED].