Feel for the pen where the mantle comes to a point near the squid's head. The pen isn't a backbone - it's a tiny internal shell. Now turn the squid over so that the fins and pen are placed against the table. Look for the squid's siphon. The siphon is a fleshy tube near the squid's head.
Squids force water from the mantle out through the siphon to propel themselves through the water.
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