Tridentata orthogonalis ( Gibbons & Ryland, 1989 ) Calder & Faucci, 2021

Calder, Dale R. & Faucci, Anuschka, 2021, Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands, Zootaxa 5085 (1), pp. 1-73 : 33-35

Tridentata orthogonalis ( Gibbons & Ryland, 1989) , comb. nov.

Fig. 10c

Sertularia orthogonalis Gibbons & Ryland, 1989: 423 , fig. 38A–D.

Type locality. Fiji: Viti Levu, Pacific Harbor, Ndeumba Island, Ndeumba fringing reef ( Gibbons & Ryland 1989, as Sertularia orthogonalis ).

Voucher material. Laysan Island , 18.ix.2002, one colony, 6 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5439 .— Laysan Island , on Halimeda sp. and unattached, 17.ix.2002, four colonies or colony fragments, 6–14 mm high, with gonothecae, coll. A. Faucci, ROMIZ B5440 .

Remarks. Tridentata orthogonalis ( Gibbons & Ryland, 1989) , comb. nov., originally described from Fiji, is a morphologically striking but little-known species. To date, the only other published records of it are those Coles et al. (2003, as Sertularella orthogonalis ) from American Samoa and Hewitt & Campbell (2010, as Sertularia orthogonalis ) from Australia.

Gibbons & Ryland (1989) noted the general resemblance of their hydroid to Sertularia tongensis Stechow, 1919b from Tonga. They distinguished it from that species in that each hydrotheca has an abcauline intrathecal ridge and three distinct intrathecal cusps. Colonies from Laysan Island conform well with the original account of S. orthogonalis and have been identified as such here. Based on characters of both the trophosome and gonosome of the species, it has been transferred in this work from Sertularia Linnaeus, 1758 to Tridentata Stechow, 1920 .

As for S. tongensis , it somewhat resembles S. borneensis Billard, 1925a , and was considered a questionable synonym of that species by Schuchert (2003). In turn, S. borneensis was considered conspecific with Tridentata maldivensis ( Borradaile, 1905) by Calder (2010), although it now seems better to maintain them as separate species until their gonosomes can be compared and their genetic affinities determined. Galea (2010) assigned the replacement name Sertularia ephemera to S. tongensis , considering it referable to the same genus as Sertularella tongensis Stechow, 1919b , a different species. However, the latter hydroid is now assigned to Bicaularia Song, Lyu, Ruthensteiner, Wang & Gravili, 2019 , and homonymy between Sertularella tongensis (= Bicaularia tongensis ) and Sertularia tongensis (= Tridentata tongensis ) no longer exists.

This report extends the known distribution of T. orthogonalis to the central North Pacific Ocean.

Reported Distribution. Hawaiian archipelago. First record.

Elsewhere. Fiji ( Gibbons & Ryland 1989, as Sertularia orthogonalis ); American Samoa ( Coles et al. 2003, as Sertularella orthogonalis ); Australia ( Hewitt & Campbell 2010, as Sertularia orthogonalis ).

Figures

FIGURE 10. Sertulariidae and Symplectoscyphidae. a, Tridentata loculosa (Bale, 1852), part of hydrocaulus with two hydrothecal pairs, Midway Atoll, ROMIZ B5434. Scale equals 0.2 mm. b, Tridentata loculosa (Bale, 1852), gonotheca, Midway Atoll, ROMIZ B5434. Scale equals 0.2 mm. c, Tridentata orthogonalis (Gibbons & Ryland, 1989), part of hydrocaulus with two hydrothecal pairs, Laysan Island, ROMIZ B5440. Scale equals 0.2 mm. d, Tridentata rugosissima (Thornely, 1904), part of hydrocaulus with one hydrothecal pair, Laysan Island, ROMIZ B5489. Scale equals 0.1 mm. e, Tridentata turbinata (Lamouroux, 1816), part of hydrocaulus with two hydrothecal pairs, Pearl & Hermes Atoll, ROMIZ B5444. Scale equals 0.1 mm. f, Tridentata turbinata (Lamouroux, 1816), gonotheca, Pearl & Hermes Atoll, ROMIZ B5444. Scale equals 0.2 mm. g, Bicaularia tongensis (Stechow, 1919b), part of hydrocaulus with two hydrothecae, Midway Atoll, ROMIZ B5445. Scale equals 0.1 mm.