Pennate vs Centric
Definition
The two morphological groups of diatoms. Pennate diatoms are elongate with bilateral symmetry (Naviculaceae, Pinnularia, Cymbella). Centric diatoms are circular with radial symmetry (Cyclotella, Aulacoseira). Freshwater bodies are dominated by pennate forms.
- Pennate symmetry
- Bilateral, elongate outline
- Centric symmetry
- Radial, circular outline
- Pennate examples
- Naviculaceae, Pinnularia, Cymbella
- Centric examples
- Cyclotella, Aulacoseira
- Freshwater bias
- Pennate forms dominate freshwater assemblages
Common questions
Why does the pennate versus centric split matter in a diatom drowning case?+
Because the two groups favour different water types, the mix recovered from lung tissue or bone marrow can support or contradict a claimed drowning location, independent of species-level identification.
Can a marine or brackish scene still yield pennate diatoms?+
Yes, pennate forms occur in marine and brackish water too, just less dominantly than in freshwater. The examiner interprets the ratio and the specific taxa present rather than pennate presence alone.
Does the pennate-centric distinction help date a death?+
Not directly. It is primarily a habitat indicator used alongside diatom counts and species composition to assess drowning location and medium, not a timing tool.
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