Selaginopsis trilateralis Fraser, 1936a

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: 44

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Selaginopsis trilateralis Fraser, 1936a


Selaginopsis trilateralis Fraser, 1936a 

Selaginopsis trilateralis Fraser, 1936a: 504  , fig. 3.

Pericladium trilateralis  .— Cairns et al., 2002: 25.

Syntype. BCPM 976-00574-001: Canada, British Columbia, Houston Stewart Channel , 22 July 1935, 27  – 33 m, labelled "type"; 60% IPA.

Lectotype, by present designation. BCPM 976-00574-001: Canada, British Columbia, Queen Charlotte Islands (=Haida Gwaii), Houston Stewart Channel, near Rose Harbour, 30 fm (55 m), 22 July 1935, one colony, 16 mm high, in fairly good condition, without gonothecae, labelled “ type ”; 60% IPA.

Type locality. Canada, British Columbia: Queen Charlotte Islands (= Haida Gwaii), Houston Stewart Channel near Rose Harbour , 55 m ( Fraser 1936a). 

Current status. Valid, as Pericladium trilaterale ( Fraser, 1936a)  .

Remarks. Fraser (1936a) did not designate a name-bearing type of his Selaginopsis trilateralis  . It was originally described by him as “A rigid colony, 18 mm high…”, suggesting an account of one specimen. A single colony of the species from one of the two original type localities (western end of Houston Stewart Channel, Haida Gwaii, British Columbia), labelled as the “ type ”, exists in the Fraser Hydroid Collection at the RBCM ( BCPM 976-00574-001). That specimen is approximately the same size recorded by Fraser (16 mm vs. 18 mm high). However, as noted above, the species was reported by Fraser (1936a) to have been found at a second location, “…in the western portion of the channel (Houston Stewart Channel), 15- 18 f. (25- 30 m.).” No type material is known to exist from that location, but we have avoided assuming that none exists ( ICZN Recommendation 73F). Instead of concluding that the existing type specimen is the holotype by monotypy, we have designated it as the lectotype. Other specimens in the Fraser collection ( BCPM 976-00575-001: off Frederick Island, 29 July 1936, 25 m, dry; BCPM 976-00575-002: Frederick Island, slide) are not part of the type series. Those hydroids were collected after the original description of the species was published by Fraser (1936a), and at a different location (Frederick Island, Haida Gwaii) than the type locality. Fraser’s original figure of the species is somewhat misleading in that the proximal branch is illustrated with only two instead of three rows of hydrothecae. All branches in the lectotype colony have three hydrothecal rows.

This species is listed as Thuiaria trilateralis  in WoRMS. Unlike in the genus Thuiaria Fleming, 1828  , the hydrothecal rim of the species is marked by two low, rounded cusps ( Fraser 1936a) rather than being circular or sinuous. It is assigned here to Pericladium Allman, 1876  in having hydrothecae arranged in more than two longitudinal rows, and in having hydrothecal margins with two marginal cusps. The spelling of the specific name, as Pericladium trilateralis in Cairns et al. (2002)  , is corrected here to P. trilaterale  .


British Columbia Provincial Museum


Empresa Pernambucana de Pesquisa Agropecu�ria, IPA


Royal British Columbia Museum














Selaginopsis trilateralis Fraser, 1936a

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

Selaginopsis trilateralis

Fraser, 1936a : 504

Pericladium trilateralis

Cairns et al., 2002 : 25