Embryogenesis and Larval Development of the Asteroid Patiriella regularis Viewed by Light and Scanning Electron Microscopy

Abstract

The sea star Patiriella regularis (Verrill, 1867) has indirect development through bipinnaria and brachiolaria larvae. Development of this species is typical of asteroids with planktotrophic larvae and takes 9-10 weeks. The embryos develop through a wrinkled blastula and hatch as early gastrulae. In contrast to most asteroids, a third enterocoel forms on the left side of the stomach of the bipinnaria. This structure gives rise to the left posterior coelom; its significance is discussed. We suggest that this coelom is homologous to the trunk coelom in enteropneust embryology. The surface features of the larvae were examined by scanning electron microscopy. Newly hatched gastrulae are covered by cilia, and the bipinnaria have bands of cilia that follow the contours of the larval processes. A previously undescribed plug-like structure positioned on the post-oral surface appears to function as a seal for the mouth. Brachiolaria larvae have three brachiolar arms and a centrally located adhesive disc. Each arm is covered by adhesive papillae. Raised epithelial cells that dot the surface of the papillae and adhesive disc may be batteries of secretory cells. The brachiolar arms have an extracellular coat that may serve as a protective cover for the adhesive surfaces. Competent brachiolaria swim along the substratum and exhibit searching behavior with flexure of the median brachium. They settle on the undersides of natural shell substrata and do not respond to a primary algal film. Shade appears to be an important factor in settlement and metamorphosis in P. regularis. Metamorphosis takes 5-6 days, and the post-larvae take up a free existence at a diameter of 450-500 {mu}m. The indirect development of P. regularis contrasts with the lecithotrophic and viviparous modes of development of other Patiriella species and provides the comparative basis to determine the ontogenic changes involved with evolution of direct development in the genus. The use of the divergent life histories of Patiriella as a model system for the study of evolutionary change in development is discussed.

Interactive Effects of Endogenous and Exogenous Nutrition on Larval Development for Crown-Of-Thorns Starfish

“…Maximum length, maximum width, posterior width, ciliated band length, and gut area were measured using ImageJ (Figure 1). At day 4, 8, and 16 after the start of feeding, all surviving larvae were categorized into the following developmental stages: (1) early bipinnaria-gut fully formed, preoral and anal lobes present, coelomic pouches below or close to mouth; (2) advanced bipinnaria-coelomic pouches fuse as axohydrocoel above the mouth, anterodorsal and posterolateral arms start to form; (3) early brachiolaria-brachiolar arms start to appear as stump-like projections from the anteroventral surface of the larvae, anterior extension of axohydrocoel, anterodorsal, posterolateral, and posterodorsal arms start to elongate, preoral arms start to form; (4) mid-late brachiolaria-brachiolar arms prominent, starfish rudiment developing in the posterior region of larvae, postoral arms form, and other larval arms more elongated; and (5) abnormal-stunted and deformed larvae [24,39,40]. surface of the larvae, anterior extension of axohydrocoel, anterodorsal, posterolateral, and posterodorsal arms start to elongate, preoral arms start to form; (4) mid-late brachiolaria-brachiolar arms prominent, starfish rudiment developing in the posterior region of larvae, postoral arms form, and other larval arms more elongated; and (5) abnormal-stunted and deformed larvae [24,39,40].…”

Application of a sandwich hybridisation assay for rapid detection of the Northern Pacific seastar, Asterias amurensis

“…Larvae of P. mortenseni were reared to bipinnaroid stage (8Á14 days) by M. Barker, Portabello Marine Laboratory, University of Otago, according to previously described protocols (Barker 1978;Byrne & Barker 1991). Adult tissue samples from the tube feet of A. amurensis (collected by M. de Salas, Hobart, Tasmania), C. muricata, P. regularis, P. mortenseni and Stichaster australis were collected and stored in RNALater TM .…”

Development and distribution of the peptidergic system in larval and adult Patiriella: Comparison of sea star bilateral and radial nervous systems

“…P. regularis has planktotrophic development through feeding larvae, a mode of development considered to represent the ancestral state for echinoderms (Strathmann, 1978;Byrne and Barker, 1991). As with many asteroids, P. regularis has two larval stages, the bipinnaria, followed by the brachiolaria (Fig.…”

“…The rudiment of the developing juvenile is located in the posterior region. During metamorphosis, the larval body degenerates as the young sea star develops (Byrne and Barker, 1991). Confocal microscopy of the larvae of P. regularis was used to determine the pattern of differentiation of the peptidergic system with respect to changes in larval anatomy, particularly the increasing complexity of the ciliated band system during the bipinnaria stage and morphogenesis of the attachment complex.…”