Do Sharks Have Placoid Scales in Their Anatomy?

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Discussion Overview

The discussion centers around the presence and characteristics of placoid scales in sharks, specifically within the context of chondrichthyes anatomy. Participants explore the visibility, tactile properties, and implications of these scales in both living and preserved specimens.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant notes the absence of visible placoid scales in their examination of a shark specimen, questioning their location in chondrichthyes anatomy.
  • Another participant suggests that scales typically grow from the dermal layer and wonders if there are rules predicting their absence as a dermal cover.
  • Several participants describe the tactile experience of shark skin, emphasizing that the denticles (placoid scales) are small and can be felt rather than seen, with one participant mentioning their sharpness and potential to cause abrasions.
  • It is mentioned that the placoid scales are oriented toward the tail and are described as tiny, with one participant recommending the use of a magnifier to observe them closely.
  • A participant shares an interesting cultural note about the use of shark skin in Japan for making food graters due to its rough texture.

Areas of Agreement / Disagreement

Participants express varying observations regarding the visibility and tactile nature of placoid scales, with no consensus on their anatomical presence or visibility in specimens. The discussion remains unresolved regarding the specifics of their anatomy.

Contextual Notes

Some limitations include the potential for individual variation in shark specimens, the conditions under which they are examined (living vs. preserved), and the reliance on tactile rather than visual identification of placoid scales.

gracy
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Where placoid scale is present in chondrichthyes ,?i looked on specimen of shark fish ,but did not find any placoid scale neither in external anatomy nor in internal anatomy ."
 
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Generally scales grow from the dermal layer, I suppose.

I don't know if there is a similar rule that helps predict where it is absent as a dermal cover.
 
Shark skin feels like sandpaper. The denticles (placoid scales) are pretty small, but you can feel them.
You have to "pet" the shark moving your hand from the tail toward the head. Be careful, it will clobber your skin.
They are very sharp, and they have an extremely hard (vitrodentine) layer on the outside, with a fine point.

Swimmers who have encountered harmless sharks have sometimes gotten what looks like road rash - a big abrasion - from rubbing the shark the wrong way, so to speak. Pat your specimen and see. Carefully... sharks make terrible cuddle pets.
 
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jim mcnamara said:
Shark skin feels like sandpaper. The denticles (placoid scales) are pretty small, but you can feel them.
You have to "pet" the shark moving your hand from the tail toward the head. Be careful, it will clobber your skin.
They are very sharp, and they have an extremely hard (vitrodentine) layer on the outside, with a fine point.

Swimmers who have encountered harmless sharks have sometimes gotten what looks like road rash - a big abrasion - from rubbing the shark the wrong way, so to speak. Pat your specimen and see. Carefully... sharks make terrible cuddle pets.
oh you mean as placoid scale are really small we can not see them and can only feel.
 
They are tiny little prickly points "aimed" toward the tail. In science terms retrorse projections. They are felt by touching only from 3 feet away. Too small to see. Try: Get a magnifier (like 10x or more) and get up close and personal with the shark specimen. Like inches away. The specimen is preserved (not alive), right? I hope so.
 
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The Japanese make food graters from shark skin, it's that rough and durable.
 

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