Tridentata marginata ( Kirchenpauer, 1864 )

Calder, Dale R., 2013, Some shallow-water hydroids (Cnidaria: Hydrozoa) from the central east coast of Florida, USA, Zootaxa 3648 (1), pp. 1-72 : 31-33

Tridentata marginata ( Kirchenpauer, 1864)

Fig. 9e, f

Dynamena marginata Kirchenpauer, 1864: 13 , figs. 8a–c.

Tridentata marginata . — Jones, 2002: 218.

Type locality. “Mare pacificum,” on Sargassum ( Kirchenpauer 1864) .

Voucher material. Bethel Shoal off Vero Beach , 27°42.6’N, 80°06.8’W, 24 m, 18.ii.1976, Johnson-Sea-Link, JSL 328, diver lockout, two plumes, up to 4 cm high, without gonothecae, coll. S. Nelson, ROMIZ B1095 .— Fort Pierce, Fort Pierce Inlet State Park , 27°28’29.5”N, 80°17’25.8”W, on stranded Sargassum sp. , 14.vii.2012, 28° C, 35‰, collected manually, one colony, 1.5 cm high, with gonophores, coll. D.R. Calder, ROMIZ B3969 .

Remarks. Tridentata marginata ( Kirchenpauer, 1864) and Desmoscyphus inflatus Versluys, 1899 (also known as Sertularia inflata and Tridentata inflata ) are held to be conspecific here. The hydroid is common in shallowwaters of the southeastern United States on both benthic substrates and floating Sargassum . It is one of the few species of sertulariid hydroids known to liberate a free medusoid ( Migotto 1998).

Hydrothecae of Tridentata marginata resemble those of T. turbinata ( Lamouroux, 1816) , including the presence of a horseshoe-shaped ridge of perisarc on the internal surface of the abcauline wall below the orifice. The species differs from T. turbinata in having alternately branched instead of unbranched colonies. Although very young colonies of T. marginata may be unbranched as in T. turbinata , they can be distinguished from that species in having much smaller hydrothecae (e.g., diameter at base 75–98 µm vs. 121–149 µm).

This species has often been assigned to Sertularia Linnaeus, 1758 instead of Tridentata Stechow, 1920 . Major differences separate the two genera, apparent from a comparison of Sertularia argentea Linnaeus, 1758 , type species of Sertularia , and Sertularia perpusilla Stechow, 1919 , type species of Tridentata . Evidence of their distinctive morphological differences, briefly noted earlier ( Calder 1991a: 104) has also been supported by molecular data ( Moura et al. 2011). Although it may be polyphyletic as presently constituted, recognition of the genus Tridentata is, once again, upheld here. As for T. marginata , it was shown by Moura et al. to be very close genetically to T. perpusilla , type species of that genus.

Reported distribution. Atlantic coast of Florida. Biscayne Bay ( Jones 2002).

Western Atlantic. North Carolina ( Fraser 1944, as Sertularia inflata ) to Brazil (Oliveira et al. submitted, as S. marginata ), including Bermuda ( Calder 1991a), the Gulf of Mexico ( Calder & Cairns 2009), and the Caribbean Sea ( Galea 2008, as S. marginata ). The species is carried north of Cape Hatteras to New England on pelagic Sargassum in the Gulf Stream ( Hargitt 1908, as S. versluysi Nutting, 1904 ).

Elsewhere. Circumglobal in tropical and warm-temperate waters ( Migotto 1998, as S. marginata ; Vervoort & Watson 2003, as S. marginata ).

Figures

FIGURE 9. a, Sertularella unituba: part of hydrocaulus with two hydrothecae, ROMIZ B1099, scale equals 0.25 mm. b, Sertularella unituba: gonotheca, ROMIZ B1099, scale equals 0.25 mm. c, Tridentata distans: part of hydrocaulus with four hydrothecal pairs, ROMIZ B3968, scale equals 0.20 mm. d, Tridentata loculosa: part of hydrocaulus with two hydrothecal pairs, ROMIZ B1078, scale equals 0.20 mm. e, Tridentata marginata: part of hydrocaulus with two hydrothecal pairs, ROMIZ B3969, scale equals 0.35 mm.; f, Tridentata marginata: gonotheca, ROMIZ B3969, scale equals 0.25 mm. g, Tridentata turbinata: part of hydrocaulus with two hydrothecal pairs, ROMIZ B3970, scale equals 0.25 mm. h, Hincksella brevitheca: part of hydrocladium with hydrothecae, ROMIZ B1079, scale equals 0.25 mm. i, Synthecium tubithecum: part of hydrocladium with two hydrothecal pairs, ROMIZ B1074, scale equals 0.25 mm.