An old empty shell of Megastraea undosa, wedged under a rock and covered in the pink coralline algaLithothamnion, which has cemented it to the substrate.
One of the largest gastropod shells found on the Southern California coast, this species varies between 40 mm and 145 mm. The shell lacks an umbilicus, and has a turbinate-conical shape. Like other shells of the family turbinidae it is composed of a thick inner nacreous layer, covered by a thinner porcellanous layer. In this species both are covered by a dark brown shaggy periostracum in life. The periphery of the shell forms a twisted ridge at the outer edge of each whorl. Each whorl also has regular, coarsely sculpted rows of fine knobs and folds. The base is marked with several spiral cords concentric to the arcuated columella which has a pearly groove. The unusual operculum has four strong ridges on its outer side decorated with hard shelly bristles that radiate in a curvilinear fashion from its pointed edge.[4][5]
Habitat
This large snail inhabits rocky shores in shallow waters, generally protected areas below the low tide level.
^Astraea undosa - Properties - The Taxonomicon Archived 18 January 2010 at the Wayback Machine
^W.H. Dall, Thesaurus conchyliorum, or, Monographs of genera of shells, v. 5 (1887)
^Rogers, Julia Ellen (1907), The shell book
W.H. Dall (1910) New Species of West American Shells; The Nautilus v. 23, 1910
External links
Wikimedia Commons has media related to Megastraea undosa.
"Lithopoma undosum". Gastropods.com. Retrieved 9 November 2011.
Alf A. & Kreipl K. (2011) The family Turbinidae. Subfamilies Turbininae Rafinesque, 1815 and Prisogasterinae Hickman & McLean, 1990. In: G.T. Poppe & K. Groh (eds), A Conchological Iconography. Hackenheim: Conchbooks. pp. 1–82, pls 104–245.
Williams, S.T. (2007). Origins and diversification of Indo-West Pacific marine fauna: evolutionary history and biogeography of turban shells (Gastropoda, Turbinidae). Biological Journal of the Linnean Society, 2007, 92, 573–592.
Proo, Sag del, Larval and early juvenile development of the wavy turban snail, Megastraea undosa (Wood, 1828) (Gastropoda : Turbinidae); The Veliger 46 (4), 2003