BIOL 321 Lecture Notes - Lecture 19: Siphuncle, Nautiloid, Ammonoidea
18 Nov 2016
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Document Summary
Lifestyle & body plan: active, pelagic, predatory (largest, fastest and smartest cephalopods, molluscan characteristics. Shell-secreting mantle (dorsal epithelium) but shell reduced or lost in most extant cephalopods: distinctive characteristics. Septate shell- divided into chambers by internal septa that are filled with gas for buoyancy. Prehensile appendages (arms and/or tentacles)- surrounding the mouth. Funnel- an exhalent siphon for water flowing through the mantle cavity. Taxonomic overview: three subclasses (one extinct) Nautiloidea- was the first cephalopod group to evolve. Most are extinct but there are a few species alive (~6 species). Ammonoidea- went extinct around the time of the dinosaurs. Nautilus squids, etc: primitive cephalopod characteristics. About 100 tentacles with no suckers that are used for prey capture. Shell is subdivided into chambers called septa that have perforations for passage of siphuncle. Siphuncle tissue withdraws all of the water from the chambers and fill it with gas. Water moves into tissue of siphuncle then is carried out and excreted.
