Fig. 2

Muscular morphology of the feeding apparatus of three different morphotypes of I. alpestris: (a) the late-larval morphotype (LLM), (b) the mid-metamorphic morphotype (MMM), (c) the post-metamorphic morphotype (PMM). Muscles: (bhe) branchiohyoideus externus, (cm) ceratomandibularis, (gh) geniohyoid, (lh) levator hyoideus, (rc) rectus cervicis and (sr1) subarcualis rectus 1. Ligaments: (hml) hyomandibular ligament and (hql) hyoquadrate ligament. The directional effect of each muscle on the movement of the tip of the hyobranchial apparatus (i.e., the basibranchial) is encoded by the arrows, protractors (blue and dashed), retractors (purple and solid), and elevators (orange and dotted). Note that there is no direct hyobranchial elevator in the PMM. Depression of the hyobranchial system is achieved by a combination of rectus cervicis activity and the ligamentous and muscular suspension of the hyobranchial skeleton to the skull. Please note that the course of the ligaments was obtained from other morphological descriptions [33, 35, 48] and could not be verified in this study