title used in an account of west-coast marine invertebrates entitled A Snail's Odyssey
  Reproduction
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Metamorphosis

 

Reproductive events include metamorphosis considered in this section, and
COPULATION & LARVAL DEVELOPMENT
LARVAL BIOLOGY
SETTLEMENT CUES & TIMES
SELECTION OF SUBSTRATUM
ATTACHMENT DURING & AFTER SETTLEMENT
SETTLEMENT COUPLED WITH OCEANIC PROCESSES, and
POST-RECRUITMENT EFFECTS ON COMMUNITY STRUCTURE, considered in other sections.

 
Research study 1
 

Information on metamorphosis of Megabalanus californicus is provided by a researcher from the University of Vienna working at Scripps Institution of Oceanography, California. At 20oC in the laboratory, settlement by the cyprid larva is followed about 17h later by the first moult in which the photograph of barnacle Megabalanus californicus Kevin Leebivalved carapace is shed. The body at this time is divided into 2 halves, the posterior one representing the future barnacle body; the anterior one, representing a temporary stalk or peduncle (see 1st photo below). The moult takes only about 8min and involves a 90o rotation to bring the cyprid into an upright orientation. The new juvenile stretches and contracts to separate the carapace, which in a few moments drifts away. By this time the juvenile is supported on its peduncle and its motility is limited (see 2nd photo below). Over the next few hours primordial plates and several rows of cuticular hairs appear. The thorax now begins to rhythmically pump. By about 4h post-moult the peduncle flattens and becomes the base of the barnacle, the body shape becomes conical, and the juvenile is now sessile (see 3rd photo below). At about 6h post-moult the the rostrum, laterals, carina, and carinolateral plates grow in height and begin to calcify and become differentiated. The opercular plates (tergal and scutal) that protect the opening to the mantle cavity begin to calcify (see 4th photo below). By this time the cirri have differentiated and are beating continuously. At about 12h post-moult the base is fully cemented to the substratum. Gusenbauer 2003 Master Degree Univ Vienna, Austria 37pp. Photograph of adults courtesy Kevin Lee, Fullerton, California diverkevin.

NOTE the exact function of these hairs is uncertain. However, by their orientation towards and touching the substratum during post-moult body movements, the present author believes they may act to support the body to maintain its orientation during critical early cementation

Megabalanus californicus 1X

 
drawing of cyprid larva of barnacle Megabalanus californicus photograph of newly metamorphosed juvenile barnacle Megabalanus californicus photograph of newly metamorphosed juvenile barnacle Megabalanus californicus photograph of newly metamorphosed juvenile barnacle Megabalanus californicus
Settling cyprid larva about to cast off its bivalved carapace Newly metamorphosed juvenile showing mantle tissue, cyprid cement, & hairs 5h post-moult showing primordial tergal & scutal plates of the forming operculum
6h post-moult juvenile showing flattened, conical shape & 4 rows of cuticular hairs
 
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