Ptychogastria Allman 1878

Genus Ptychogastria Allman, 1878

Pectyllis Haeckel, 1879: 265.

Pectanthis Haeckel, 1879: 267.

Pectyllis – Haeckel 1881a: 9; 1881b: 10.

Pectanthis – Haeckel 1881a: 17; 1881b: 19.

Crawling ptychogastriid medusae with swimming capabilities; with dome-shaped, marginally-“lobed” umbrella, and eight-lobed manubrium, giving rise to as many mesenterial partitions of the subumbrellar cavity; mouth quadrangular, with simple lips; eight radial canals; centripetal canals either present or absent; eight pairs of gonads conFned to the sides of the manubrial lobes; tentacles Fliform and adhesive, occurring simultaneously and arranged in clusters around the bell margin; velum broad; 16 free, ectoendodermal statocysts (2 per octant).

The diagnoses given by Bouillon & Boero (2000) and Bouillon et al. (2006) are broadened again, so as to include the shape of the umbrella, the presence/absence of centripetal canals, and the presence of a velum, as Allman (1878) and/or Mayer (1910) did earlier.

As underlined by Mayer, the «differences between the genera “ Pectyllis,” “ Pectis,” and “ Pectanthis,” as deFned by Haeckel, are so slight as to appear of speciFc rather than of generic value». Indeed, Haeckel (1879) distinguished Pectis (type species Pectis antarctica) from both Pectanthis (type species Pectanthis asteroides) and Pectyllis (type species Pectyllis arctica) through the presence of centripetal canals. In contrast, the tentacles were described as arranged in distinct groups in Pectanthis, and forming comparatively more contiguous groups in both Pectis and Pectyllis.

Similarly, Browne (1903) acknowledged earlier that “When Pectis antarctica and Pectanthis asteroides have been again examined it may be found that one genus with three species will be quite sufFcient”. However, it will be shown at the end of this paper that the former species does not belong to Ptychogastriidae, but to a different family of Trachymedusae, viz. Rhopalonematidae Russell, 1953.

1. Centripetal canals absent …………………………………………… P. asteroides (Haeckel, 1879)

– Centripetal canals present ……………………………………………………… P. polaris Allman, 1878