File:American malacological bulletin (1986) (18157440321).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (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:
HOAGLAND: ENCAPSULATION IN CALYPTRAEIDAE 177
Text Appearing After Image:
Fig. 4. Diagramatic ventral view of Crepidula sp. S = snout; Ne = neck lappets; G = gill; Pp = propodium; F = main part of foot; Me = mantle edge; Fp = food pouch; Os = osphradium. When laid, the egg mass is attached to the propodium or the substratum beneath it, and fills the area between the propodium and neck lappets, obscuring the gill. gland that determines final capsule shape. Neither he nor I could detect such a gland in Crepidula or Calyptraea. Rather, the propodium seems to massage the egg packet, making the membrane of uniform thickness. The final triangular or heart-shape is mechanically the simplest possible for a stalked, non-rigid sac (Fig. 5). This shape is the same throughout the family Calyptraeidae and also occurs in the Hipponicidae. In using Hipponix grayanus Menke of Costa Rica as an out-group for anatomical comparisons, I observed a ma- jor anatomical difference despite similarity in final egg cap- sule shape. There is a short, cupped structure on the dorsal side of the propodium to which the egg sacs are attached. This structure participates in capsule shaping and may be a foot capsule gland as sought by Werner for Crepidula. Histological studies are required before conclusions can be drawn. BROODING AND RELEASE OF THE LARVAE OR JUVENILES All species of Calyptraeidae and Hipponicidae so far examined deposit a cluster of stalked egg sacs containing one to several eggs per sac. The sac is composed of a thin membrane; the stalk is an extrusion of the membrane. The membrane appears to be double in the upper portion of the stalk. When originally deposited, the walls of the sac are flac- cid and stick together. They often adhere along the midline of the sac, forcing the eggs into an arc or even two clusters within the sac. As the eggs develop, the sac becomes full and swollen. The embryos are crowded within the sac, which also contains a small amount of fluid and some cell debris and fragments of disintegrating embryos. The embryos turn about within the fluid. The proportion of embryos that do not develop varies with species. In Crepidula fornicata, it is about 10%, in C. convexa it is 23%, based on 100 broods per species examined over 3 years at Woods Hole, Massachusetts. At release, the egg sacs split open along a cleavage line vertical along the stalk axis. There is no exit pore. All young within a capsule are necessarily released at the same time. The female raises and lowers the shell at the release of her brood, and in C. fornicata at least, sometimes uses the radula to pull the egg sacs free of her mantle cavity. When released, the young are either veligers, pediveligers, or crawl-

Note About Images