ABSTRACT
Sea urchins feed on algae by scraping with their teeth on hard surfaces of rocks. Each tooth is supported by connective tissue that fixes it so firmly to the dental slide of the jaw that it cannot be moved. On the other hand oral abrasion and aboral renewal cause a slow shift of the tooth along the dental slide. The tooth support has to be soft to allow this shift whereas it has to be stiff during feeding. On the base of morphological findings it was proposed that the tooth support consists of catch connective tissue with mutable mechanical properties under nervous control. We present the first biomechanical study on the tooth support of echinoids. A single jaw of Diadema setosum was fixed to a trough containing artificial sea water (ASW) or experimental solutions. The length of the tooth support was 9 –14 mm. A weight of 30 g was applied to the tip of the tooth and its displacement was recorded. Immediately after application of the weight the tooth moved quickly. After a few minutes the movement decelerated to a rate of 2 — 20 µm/hour and remained constant for several hours. Finally the movement accelerated again and the tooth was pulled out of the jaw. The tooth moved for 0.4–1.2 mm in 17 to 42 hours until failure of the tooth support. When we applied 10−4 — 10−3 M acetylcholine in ASW, the velocity of the tooth movement slowed down by 60%, i.e., the connective tissue became stiff. After washing with ASW the velocity accelerated again. ASW containing 100mM K+ had a similar stiffening effect. We conclude that the tooth support can change its stiffness under nervous control and thus this connective tissue is a catch connective tissue.
