Diatom
Definition
A microscopic alga with a silica cell wall (frustule) bearing species-specific surface ornamentation. Diatoms are abundant in freshwater, marine, and brackish environments. Their frustules survive acid digestion, making them recoverable from bone and soft tissue for drowning location analysis.
- Type
- Microscopic alga with silica cell wall
- Structure
- Frustule with species-specific ornamentation
- Habitat
- Freshwater, marine, and brackish water
- Forensic use
- Drowning location and site analysis
Common questions
Why do diatoms survive acid digestion of tissue while other cells don't?+
The frustule is made of silica, a mineral resistant to the strong acids used to digest organic tissue in the laboratory, so diatoms remain intact and countable even after soft tissue and most cellular material has been dissolved away.
How does diatom analysis help distinguish drowning from post-mortem immersion?+
Diatoms found in internal organs such as bone marrow or lung tissue suggest the person was alive and breathing when water entered, since circulation is needed to carry diatoms past the lungs, whereas diatoms only on skin or clothing are also consistent with a body placed in water after death.
Related terms
- 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...
- 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...
- 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...
- Frustule
- The silica cell wall of a diatom, composed of two overlapping valves (epitheca and hypotheca). Frustules are taxonomically distinctive, chemically resistant to...
- 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...
- Plant Macrofossil
- A plant fragment large enough to be seen with the naked eye or low magnification: leaves, seeds, bark pieces, root fragments. Macrofossils...
- Pollen Assemblage
- The full complement of pollen and spore types recovered together from a sample, characterised by species identity and relative abundance. Assemblages are...
- Secondary Transfer
- The movement of a glass fragment from a primary surface (which contacted the broken glass) to a secondary surface (which contacted the...
- Sexine and Nexine
- The two layers of the pollen exine (outer wall). Sexine is the sculptured outer layer (spines, ridges, reticulum), nexine is the smoother...
- Wood Anatomy
- The microscopic cellular structure of wood, including vessel arrangement, ray type, fibre dimensions, and parenchyma distribution. These features are species-specific and form...
Explained in these topics
- Botanical Evidence: An Overview
- Pollens and Diatoms in Forensic InvestigationMicroscopic eukaryotic algae of class Bacillariophyceae with a silica (SiO2) cell wall called the frustule. Each frustule has two valves, the epitheca (upper)...