Meeting Abstract
Hagfish are marine chordates that, despite lacking jaws, are able to feed on large, tough carcasses with the protraction and forceful retraction of a toothplate. In this study, the function of feeding apparatus muscles in Pacific hagfish Eptatretus stoutii was compared to that of previously studied Atlantic hagfish Myxine glutinosa. In this study, we observed the effects of stimulating each of the four major feeding apparatus muscles (deep protractor, sphincter, perpendicular, and retractor). Superficial muscles were first stimulated, in situ, as the apparatus was exposed in euthanized animals by a ventral incision. The head and apparatus were then excised in order to access deeper musculature. Each muscle group was stimulated tetanically (80V, 60Hz, 1ms duration). Trials involving five animals were filmed at 120 frames per second and analyzed with ImageJ. Results show that stimulating only the medial heads of the deep protractor muscle resulted in toothplate protraction, while individual stimulations of the perpendicular, sphincter, and retractor muscles induced toothplate retraction. This is similar to what had been previously determined in M. glutinosa using electromyography. In both species, the toothplate was shown to protract because of active contraction of the deep protractor muscle causing the cylindrical feeding apparatus to decrease in length and increase in diameter. In E. stoutii, differences in strain were found between in situ and excised feeding apparatuses. Transverse strain, or normalized change in width, was greater in situ by .05 while longitudinal strain, or normalized change in length, was greater for excised muscles by .03. Over all, total strain was approximately equal. This suggests that the loose connections to the body wall still constrain muscle displacement.
