Title: American malacological bulletin
Identifier: americanmal6719881990amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
ROLLER AND STICKLE: THAIS INTRACAPSULAR DEVELOPMENT 193 observed within 3.5-4 days after oviposition. Stomodaeal in- vagination, cephalic expansion, and formation of the shell field invagination (Fig. 11) occurred 5 days after deposition and followed the same pattern as described for Thais haemastoma floridana (D'Asaro, 1966). The early trochophore (Fig. 12) was characterized by a prominent stomodaeum, an apical tuft, the beginning of pro- totrochal and telotrochal ciliation, and the appearance of the larval kidneys. The late trochophore stage (Fig. 13) exhibited antero-posterior elongation, prominent larval kidneys, and well formed prototrochal, metatrochal, and telotrochal ciliation. The early veliger stage was characterized by the presence of the velar ciliation (Fig. 14). The dorsal margin of the shell gland was complete, and the protoconch covered the posterior region of the digestive gland's primordial cells. At this stage, the operculum was first evident (Fig. 15). By 8 days after cap- sule deposition, torsion, which results in a 180° rotation of the visceral mass, was complete. At this time, the apical ciliation and operculum were well developed, and the ventral foot and larval tentacles were first seen (Figs. 16-18). No nurse eggs, as described by Rivest (1983), were observed. The viscosity of the intracapsular contents declined over the course of the developmental period; however, the measured intracapsular osmolarity did not change during development. It is therefore possible that the intracapsular albumen is consumed by the embryos and replaced by sea water. CAPSULAR CONTENT CHANGES DURING DEVELOPMENT Capsule weight changes prior to hatching are il- lustrated in Table 2. During the intracapsular developmental period, the weight of the capsule contents significantly in- creased 63.0%; capsule wall weight decreased 43.4%; and the total capsule weight (contents and wall) decreased 18.4%. Total capsule ash significantly increased 37.8%, while total capsule calcium increased 24-fold over the encapsulated developmental period. Total capsule organic material significantly decreased 37.7%; however, other inorganic material (excluding calcium) showed a non-significant in- crease of 2.0%. HATCHING AND REARING OF VELIGERS Hatching of veligers (Figs. 17, 18) at 25°/00S and 25°C occurred between 12-13 days after capsule deposition. The shell length at hatching was 49.7 ± 8.3 /*m. Hatching was ac- complished through the dissolution of the capsule's oper- culum, possibly by mechanical means (St. Amant, 1938) or by chemical means (Sullivan and Bonar, 1984). Most (96-100%) embryos developed into normal appearing veligers and survived to hatching. In some capsules approximately 2-4% of the veligers were either dead or malformed at hatch- ing. Hatched veliger larvae survived up to 50-53 days when kept in laboratory cultures and fed a mixture of Isochrysis galbana and Monochrysis lutheri. Ninety percent of the hatched veligers survived 45-50 days in culture. The shell
Text Appearing After Image:
Fig. 11. Light micrograph showing stomodael invagination (S) and apical plate formation (Ap), immediately after gastrulation and prior to formation of trochophore (D, digestive system primordium; Sg, shell gland). Fig. 12. SEM of early trochophore stage (At, Apical tuft cilia- tion; Lk, larval kidney; Pt, prototrochal ciliation; S, stomodaeum; Tt, telotrochal ciliation). Fig. 13. SEM of late trochophore stage, show- ing formation of metatrochal ciliation (Lk, larval kidney; Mt, metatrochal ciliation; Pt, prototrochal ciliation; S, stomodaeum; Tt, telotrochal cilia- tion). Fig. 14. SEM of a dorsolateral view of early veliger larva (A, Apical ciliation; Lk, larval kidneys; P, protoconch; V, velum). Fig. 15. SEM illustrating a ventral view of an early veliger larva, illustrating shell operculum formation and prominent shell gland ciliation (Lk, larval kidneys; Op, shell operculum; P protoconch; Sg, shell gland; V, velum). Fig. 16. Light micrograph illustrating a midsaggital sec- tion (7 jtm) through a veliger (three days prior to hatching), showing further elongation of foot and operculum (F, foot; Op, shell operculum; P, protoconch; V, velum). length of the veligers after 37 days in culture was 122.4 ± 28.3 fim. No settlement/metamorphosis occurred, even though the larvae appeared healthy and fed on the algal species pro- vided (Fig. 18).

Note About Images