. Bulletin of the British Museum (Natural History). 490 EVOLUTIONARY TRENDS IN CAPITATE HYDROIDS AND MEDUSAE The ancestral Codonid can be envisaged as having a deep bell-shaped umbrella with nematocysts, either scattered over the exumbrella, or arranged in perradial tracks (Text-fig. 40). The stomach would be tubular with a simple circular mouth and the gonad would completely encircle the stomach. Four radial canals, a ring canal and four perradial tentacles complete the picture of the ancestral codonid and few would disagree with this interpretation. To this, I would add that the tentacles we
. Bulletin of the British Museum (Natural History). 490 EVOLUTIONARY TRENDS IN CAPITATE HYDROIDS AND MEDUSAE The ancestral Codonid can be envisaged as having a deep bell-shaped umbrella with nematocysts, either scattered over the exumbrella, or arranged in perradial tracks (Text-fig. 40). The stomach would be tubular with a simple circular mouth and the gonad would completely encircle the stomach. Four radial canals, a ring canal and four perradial tentacles complete the picture of the ancestral codonid and few would disagree with this interpretation. To this, I would add that the tentacles were probably monUiform and it is possible that budding of daughter. Fig. 40. Diagrammatic representation of an ancestral Codonid medusa with ring gonad, exumbrellar nematocyst tracks and four perradial tentacles with moniUform arrangement of nematocyst batteries. medusae from the stomach would take place before maturation of the gonads. Medusae of the genus Sarsia are recognized as departing but little from the generally accepted idea of a simple codonid but two features require comment. The more usual arrangement of nematocysts on the exumbrella is the scattered one, but there are some nematocyst tracks in various forms, Ectopleura (Text-fig. 41) and Hybocodon (Text-fig. 42) in the Tubulariidae, Neoturris in the Pandeidae, and special tracks in Zanclea and various " pteronemids " and Proboscidactyla stellata (Limnomedusae) ;' all are widely divergent forms and and this may imply the persistence of an ancestral character (see p. 504). ' The type of nematocyst track found in Zanclea is also found in the Chrysomitra medusae of the Chondropiiora which are believed to have a Capitate ancestry (Totton, 1954 • P'eard, 1955).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural Histor
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