A comparative analysis of the locomotory systems of medusoid Cnidaria

Kurzfassung

Auf der Grundlage einer funktionell-morphologischen Analyse des lokomotorischen Systems bei Hydro- und Scyphomedusen wurde der Versuch unternommen, den Mechanismus ihrer Schwimmbewegungen allgemein zu charakterisieren. An Vertretern von insgesamt 42 Gattungen wurden der Bau und die funktionelle Variabilität des Schirmes, der Mesogloea, der Fibrillen der Mesogloea, der kontraktilen Elemente der Muskulatur und des Velums bzw. des Velariums untersucht und verglichen sowie eine Klassifizierung der Medusen nach der Struktur der Mesogloea und der Art der Fortbewegung vorgenommen.

Summary

1. The locomotory systems of forty-two genera of hydro- and scyphomedusae, representing nine orders, were surveyed, to serve as a basis for generalizations about medusan locomotion. The more pertinent of these have been discussed. The comparisons are based on previous studies ofPolyorchis montereyensis andCyanea capillata (Gladfelter 1972a, b).

2. The bell ranges from broad and flat to long, narrow and pointed; the mesoglea ranges from soft to rigid. Radial mesogleal fibers are distributed in the regions of the bell deformed during contraction, and are most densely arrayed along joint apices. A variety of “joint systems” is present, from none or temporary creases, to permanent exumbrellar creases, to elaborate systems in most Anthomedusae and Scyphomedusae: a classification of mesogleal skeletons was erected.

3. The contractile elements of the swimming muscle vary from widely spaced cord-like elements in weak swimmers to tightly packed ribbon-like processes with aligned striations in small strong swimmers, to thick cord-like elements in closely spaced, highly convoluted array arranged on larger mesogleal folds. Radial swimming muscles are present in flat forms.

4. The velum (Hydromedusae) or its analog, the velarium (Cubomedusae) is important in forms with strongly arched bells, where it functions as a nozzle during straight swimming and turning. It is less important in broader bells, which, however, can turn in a smaller radius than tall forms.