This section is divided into topics of patterns of development, considered here, and MATE SELECTION & COPULATION, DISPERSAL, and GENETICS, considered elsewhere.

Of the several littorine species common on west-coast shores, 2 species Littorina scutulata and L. plena release planktonic egg capsules and 2 species L. sitkana and L. subrotundata lay benthic egg masses that hatch to crawl-away juveniles.  Buckland-Nicks et al. 1973 Can J Zool 51: 359; Behrens Yamada 1989 Mar Biol 103: 403.

The 2 sympatric and highly similar species Littorina scutulata and L. plena have similar developmental patterns, but somewhat different capsule morphologies.  Actually, 2 types of capsule are produced by each species with one of the types being common to both species.  Littorina scutulata’s unique capsule has rims of unequal diameter, while L. plena’s unique capsule has rims of equal diameter.  The common capsule, produced by some females of each species, has only one rim and encloses about 5 eggs (range 2-11).  Littorina plena’s unique capsule is larger than the other types and has a mean of 19 eggs (range 6-47).  A large female L. plena produces about 1500 eggs in a season.  Murray 1979 Veliger 21: 469; Mastro et al. 1982 Veliger 24: 239; Hohenlohe 2002 Invert Biol 121: 25. Drawings are taken from the last reference cited.

Studies at Bodega Marine Laboratory, California show that despite occupying markedly different heights on the shore, local littorinids Littorina keenae (= supratidal), L. scutulata (= high intertidal), and L. plena (= high intertidal) spawn during roughly the same period Mar-Sept/Oct. Chow 1987 J Exp Mar Biol Ecol 110: 69.

In the Barkley Sound area of British Columbia herbivorous snails Lacuna vincta deposit eggs in winter/ spring and these hatch to planktotrophic veligers 2-4wk later.  Free-living planktonic life lasts for 7-9wk and settlement is mainly to the canopy fronds of large kelps Nereocystis luetkeana and Macrocystis integrifolia.  A large settlement occurs in April/May and a smaller one in summer/autumn.  After a brief period on the kelp the juveniles migrate down the stalks to the under-canopy area and into the intertidal zone.  Martel & Chia 1991 Mar Biol 110: 237. Photograph of Lacuna vincta courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

Planktotrophic species such as Littorina scutulata, L. plena, and L. keenae, actually have a “mixed” development where the early developmental stages are contained within complex pelagic capsules, each in their own egg envelope (see photo of L. scutulata on Left). The larvae emerge from their envelopes, then break free of the capsule and begin swimming and feeding in the plankton. 

A question with respect to species such as Littorina sitkana that have benthic, encapsulated development is the means by which the intracapsular albumen is consumed.  A survey of several species collected around Charleston, Oregon and Monterey, California including L. scutulata, L. plena, L. keenae,and L. sitkana shows that the velar cilia are much longer in the first 3 planktonic-developing species than in the last benthic-developing species (see graph on Right). This makes sense because after the planktotrophic species hatch the velum is used for locomotion and for collecting phytoplankton food.  Its retention and use by non-planktonic encapsulated species such as L. sitkana is less clear, but possibilities include rotating the larva to enhance oxygen diffusion, feeding on nurse eggs, or stirring the intracapsular albumen-containing fluids to enhance consumption.  In the confined, more viscous environment of L. sitkana’s egg capsule, short cilia may be more effective than long cilia.  Through use of fluorescent labeled bovine-serum albumen and of ferritin, the author describes an additional function for the velum, that is, taking up protein by the larva endocytotically in its cilitated cells as well as in cells of the foot tissue.  Thus, retention of a relatively large-sized velum in L. stikana, although smaller than in planktotrophic species, may be favoured because of its role in uptake of intracapsular proteins. Moran 1999 Biol Bull 196: 229.

NOTE an iron-containing serum protein in vertebrates, representing one of the chief forms in which iron is stored.  Uptake of bovine-serum albumen is monitored with a fluorescencce microscope.  Ferritin is an electron-dense protein and can be identified in tissues using transmission electron microscopy

A female Littorina scutulata encloses 2-4 eggs within capsules during Mar-Oct and releases them into the plankton.  Studies at Friday Harbor Laboratories, WA show that a female of 8mm shell length may produce 1000 eggs in a season, while one of 10mm may produce 10,000 eggs (see graph on Left).  In laboratory culture, the eggs hatch to veliger larvae within 7-9d and the larvae swim freely for several weeks before settling and metamorphosing at about 28d post-hatching (see graph on Right).  The study is the first to document metamorphosis of Littorina in the laboratory.  Life span of the adult is about 7yr.  Hohenlohe 2002 Invert Biol 121: 25.

NOTE the larvae are fed on mixed rations of microalgae Isochrysis galbana and Rhodomonas lens, at 12-14^oC. Four rations are tested, but only the one yielding best growth and metamorphosis is shown here: 10⁵cells ^. ml^-1