Frustule
Definition
The silica cell wall of a diatom, composed of two overlapping valves (epitheca and hypotheca). Frustules are taxonomically distinctive, chemically resistant to degradation, and are the diagnostic element recovered by the diatom test. Their persistence in bone marrow is the basis of the vital-reaction inference.
- Composition
- Silica cell wall
- Structure
- Two overlapping valves, epitheca and hypotheca
- Diagnostic value
- Surface patterning is species-specific
- Chemical resistance
- Survives concentrated nitric and sulfuric acid digestion
Common questions
What exactly is a frustule?+
A frustule is the rigid cell wall of a diatom made of silica. It consists of two overlapping parts that fit together like a Petri dish, an upper half called the epitheca and a lower half called the hypotheca. The frustule's detailed surface patterns are distinctive to each diatom species.
Why do forensic scientists care about frustules?+
Frustules survive the acid digestion used in the diatom test to recover diatoms from bone marrow in drowning cases. This chemical resistance is the entire reason the test works. The frustule also persists after death and decomposition, making it recoverable as evidence long after soft tissues are gone.
How are frustules used in drowning investigations?+
Forensic scientists dissolve soft tissue from bone marrow using strong acids like nitric and sulfuric acid. The frustule survives this digestion intact. Finding diatoms with intact frustules in the bone marrow is the vital reaction that supports a drowning diagnosis.
Related terms
- Diatom Test
- A laboratory test for ante-mortem submersion in which bone marrow (from sealed femur diaphysis) is acid-digested and the diatom species identified in...
- Acetolysis
- Erdtman's 1934 extraction method. The sample is treated with a 9:1 mixture of acetic anhydride and concentrated sulphuric acid, which dissolves cellulose...
- Aperture
- An opening in the pollen wall through which the pollen tube emerges. Classified by shape into pores (porate), furrows (colpate) and combined...
- Assemblage
- The full community of diatom taxa present in a sample. The relative frequencies and absolute counts of species in an assemblage reflect...
- Diatom
- A microscopic alga with a silica cell wall (frustule) bearing species-specific surface ornamentation. Diatoms are abundant in freshwater, marine, and brackish environments....
- Diatom Test for Drowning
- Acid digestion of bone marrow (femur or sternum) followed by microscopic examination for diatoms. Diatoms in marrow indicate that water was aspirated...
- Dry Drowning
- Drowning in which laryngospasm seals the glottis, preventing water entry into the lungs. The victim asphyxiates without pulmonary aspiration. Autopsy shows non-specific...
- eDNA Meta-Barcoding
- Environmental DNA analysis using PCR amplification of a target gene region from a complex environmental sample (water, soil), followed by high-throughput sequencing...
- Epitheca and Hypotheca
- The two halves of the frustule. The epitheca (larger) fits over the hypotheca (smaller) like a lid over a box. During cell...
- Forensic Palynology
- The application of pollen and spore analysis to legal investigations. A forensic palynologist identifies the species composition of pollen assemblages from crime-scene...
- matK
- Maturase K gene, located in the chloroplast trnK intron. The second CBOL-approved plant barcode marker, with an approximately 870 bp diagnostic amplicon....
- Pennate vs Centric
- The two morphological groups of diatoms. Pennate diatoms are elongate with bilateral symmetry (Naviculaceae, Pinnularia, Cymbella). Centric diatoms are circular with radial...
Explained in these topics
- Diatom Biology and TaxonomyThe two-part silica cell wall of a diatom, consisting of an upper half (epitheca) and a lower half (hypotheca) that fit together like a Petri dish. Its intrica...
- Drowning: Wet, Dry, Diatom Test and Vitreous MarkersThe rigid siliceous cell wall of a diatom, which survives strong acid digestion and post-mortem decomposition intact, making it recoverable from bone marrow sp...
- Plant DNA, the Paloverde-Seed Case and the Diatom Test in DrowningThe silica cell wall of a diatom, composed of two overlapping valves (epitheca and hypotheca). Frustules are taxonomically distinctive, chemically resistant to...
- Pollens and Diatoms in Forensic InvestigationThe silica cell wall of a diatom. Resists acid digestion (concentrated HNO3 + H2SO4) used to dissolve soft tissue, which is why the test works at all.