periostracum


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periostracum

[‚per·ē′äs·trə·kəm]
(invertebrate zoology)
A protective layer of chitin covering the outer portion of the shell in many mollusks, especially fresh-water forms.
References in periodicals archive ?
Though much of this material is clearly old, some specimens were of fresh appearance and retained the periostracum, indicating that the species is probably still extant at the site, even though we found no live specimens during our survey.
The shell of Haliotis discus hannai Ino is polycrystalline composites of calcium carbonate and proteins and glycoproteins and consists of the periostracum, prismatic and nacreous layers with calcite in the outer prismatic layer and aragonite in the inner nacreous layer.
69) well-preserved, up to 15 mm in length but more commonly less than 10 mm, dextral, relatively thick; spire acute-conical, bearing up to 7 whorls, sutures deeply impressed; growth lines inconspicuous, worn; aperture tear-shaped (Harmen & Berg 1971); subfossils lack periostracum.
1F); (5) polychaetes do not have an external organic tube lining similar to the periostracum of mollusks and the external organic cuticle of bryozoans (Nishi 1993; Vinn et al.
The valves, which rarely exceed 7 cm in length, have three sections: a periostracum, a prismatic layer, and a nacre layer (Leon et al.
Fresh shells were categorized as having the hinge ligament unbroken or the periostracum largely intact.
Internal growth annuli were defined as areas of discontinuity of the prismatic layer that extended from the nacreous layer to the periostracum (Fig.
This process results in a stratification of material such that lighter larval somatic tissue and periostracum overlay heavier larval shell.
To remove the periostracum, the valve was soaked in sodium hypochlorite solution overnight and then shucked with a scrubbing brush.
corrugata has a stronger corrugated periostracum and is proportionally higher than the preceding species.