Obelia irregularis Fraser, 1943a,

Calder, Dale R. & Choong, Henry H. C., 2018, Names of hydroids (Cnidaria, Hydrozoa) established by Charles McLean Fraser (1872 - 1946), excluding those from Allan Hancock Expeditions, Zootaxa 4487 (1), pp. 1-83: 69-70

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Obelia irregularis Fraser, 1943a


Obelia irregularis Fraser, 1943a 

Obelia irregularis Fraser, 1943a: 77  , pl. 16, fig. 3.

Holotype. MCZ-IZ 9013: St Kitts and Nevis, off St Kitts, 17°19’27”N, 62°50’30”W, USCSS Blake, 250 fm (457 m), 14 January 1879, two fragments of a colony, ca. 3 cm high, in poor condition, coll. A. Agassiz, labelled “ type ”; 70% ethanol.GoogleMaps 

Type locality. St. Kitts and Nevis: off St Kitts , 17°19’27”N, 62°50’30”W, 250 fm (457 m) ( Fraser 1943a).GoogleMaps 

Current status. Valid.

Remarks. Obelia irregularis  was described by Fraser (1943a) in a collection sent on loan to him from the MCZ. As with other species in that collection, no name-bearing types were designated for it. The species is not represented in the Fraser Hydroid Collection at the RBCM, and the only known type material of O. irregularis  is that returned by Fraser to the MCZ (MCZ-IZ 9013). The count number (“1”) accompanying the type ( MCZ –IZ 9013), and Fraser’s (1943a) description (“Colony 3 cm. in height…”), indicate that the species was described from a single hydroid. Although two fragments were found in the type collection examined at the MCZ, they are considered parts of the same colony. The specimen is therefore taken to be the holotype by monotypy ( ICZN Art. 73.1.2). Another hydroid recorded as O. irregularis  at the MCZ (MCZ-CNID 77), from Grand Manan, New Brunswick, Canada, is not part of the type series. That identification is dubious given the much different environmental conditions of the collection locality.

In his account of O. irregularis, Fraser (1943a)  observed and briefly described hydrothecae and gonothecae. The holotype examined here is now in poor condition, and neither of these structures could be distinguished with certainty.

Obelia irregularis  is listed as a valid species in WoRMS, a conclusion that seems justified at present given the location, depth, and distinctive morphology of the hydroid as described by Fraser (1943a). In particular, the hydrothecal rim was said to have “…10 regularly rounded teeth [cusps], the division between them extending deep into the hydrothecal wall.” Hydrothecal pedicels are wavy but not noticeably annulated. While gonothecae were described by Fraser, the character of the gonophores remains unknown. Uncertainty therefore exists about the generic assignment of the species.


Museum of Comparative Zoology


Royal British Columbia Museum














Obelia irregularis Fraser, 1943a

Calder, Dale R. & Choong, Henry H. C. 2018

Obelia irregularis Fraser, 1943a : 77

Fraser, 1943a : 77