Tridentata distans ( Lamouroux, 1816 )

Calder, Dale R., 2013, Some shallow-water hydroids (Cnidaria: Hydrozoa) from the central east coast of Florida, USA, Zootaxa 3648 (1), pp. 1-72 : 30-31

Tridentata distans ( Lamouroux, 1816)

Fig. 9c

Dynamena distans Lamouroux, 1816: 180 , pl. 5, figs. 1a, B.

Sertularia stookeyi .— Fraser, 1943: 93.

Sertularia gracilis .— Jones, 2002: 215.

Type locality. Atlantic Ocean, on Fucus natans (= Sargassum natans ) and other flotsam ( Lamouroux 1816: 180).

Voucher material. Fort Pierce Inlet , north jetty, north side, 27°28’24.1”N, 80°17’21.2”W, intertidal zone, on stem of Thyroscyphus ramosus , 14.vii.2012, 28° C, 35‰, collected manually, one colony, 5 mm high, without gonothecae, coll. D.R. Calder, ROMIZ B3968 .

Remarks. Billard (1906) noted that the original description of Tridentata distans by Lamouroux (1816, as Dynamena distans ) was inadequate, and he justifiably described illustrations of the species in that initial account as “gross.” Nevertheless, he was able to confirm the identity of the species after examining Lamouroux’s type at l’Institut Botanique de Caen. That identification, upheld in a subsequent review of Lamouroux’s types ( Billard 1909), is the foundation of the current concept of the species.

Recently, the possible existence of cryptic species in T. distans has been raised on the basis of molecular studies ( Moura et al. 2011, as Sertularia distans ). Moreover, the generic affinity of the species needs clarification. Moura et al. showed that the species was genetically closer to Sertularia operculata Linnaeus, 1958 , type species of Amphisbetia L. Agassiz, 1862 , than to Sertularia perpusilla Stechow, 1919 , type species of Tridentata Stechow, 1920 . Differences in morphology support such a possibility. For example, gonothecal walls in T. distans are ovate and smooth rather than barrel-shaped with transverse ribs as in S. perpusilla .

Tridentata distans is a eurytopic hydroid with a wide latitudinal range, occurring from temperate regions to the tropics. In the southeastern United States it is frequent both inshore ( Calder 1983, as Sertularia distans ) and on hard bottoms of the continental shelf ( Wenner 1984, as S. distans ). Live colonies were found in estuaries of South Carolina at salinities of 20–34‰ (Calder 1976, as S. stookeyi Nutting, 1904 ) and temperatures of 8–32° C ( Calder 1990, as S. distans ). It is also a component of the pelagic Sargassum fauna (e.g., Lamouroux 1816, as Dynamena distans ; Fraser 1944, as S. stookeyi ; Calder 1991a).

This species is noteworthy for the minuteness of its hydrothecae.

Reported distribution. Atlantic coast of Florida. Between Biscayne and Duck Keys ( Fraser 1943, as Sertularia stookeyi ); Biscayne Bay ( Jones 2002, as S. gracilis Hassall, 1848 ).

Western Atlantic. Massachusetts ( Fraser 1912a, as S. stookeyi ) to Brazil (Oliveira et al. submitted, as S. distans ), including Bermuda ( Calder 1991a), the Gulf of Mexico ( Calder & Cairns 2009), and the Caribbean Sea ( Fraser 1943, as S. stookeyi ).

Elsewhere. Circumglobal in tropical, subtropical, and temperate waters ( Vervoort & Watson 2003, as S. distans ).

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.