Antennella gracilis Allman, 1877

Calder, Dale R., 2013, Some shallow-water hydroids (Cnidaria: Hydrozoa) from the central east coast of Florida, USA, Zootaxa 3648 (1), pp. 1-72 : 38-41

Antennella gracilis Allman, 1877

Fig. 11a , 12

Antennella gracilis Allman, 1877: 38 , pl. 22, figs. 6, 7.

Antennella secundaria .— Schuchert 1997: 14, fig. 4d, e [part]. Type locality. USA: Florida, off Carysfort Reef ( Allman 1877: 38).

Voucher material. Off St. Lucie Inlet, 27°11.8’N, 79°57.3’W, 87 m, 04.x.1986, Johnson-Sea-Link, J028/JSL 2132, submersible lockout, one colony, up to 2.3 cm high, without gonophores, coll. R. Roesch, ROMIZ B1090 .

Remarks. Antennella gracilis Allman, 1877 , originally described from the southeast coast of Florida, has been regarded in several contemporary works (e.g., Cornelius 1995b; Calder 1997; Schuchert 1997; Cairns et al. 2002; Ansín Agís et al. 2001; Vervoort & Watson 2003) as coterminous with A. secundaria ( Gmelin, 1791) , a Mediterranean species with a supposed worldwide distribution. The two appear much alike. However, Schuchert (1997: 15–18) recently discovered that the voucher material listed above (ROMIZ B1090), while identified as and resembling A. secundaria , differed from European and Indian Ocean material of that species in both cnidome and in morphology of lateral nematothecae. Large nematocysts were elongate and nearly cylindrical, and thought to be macrobasic mastigophores (19–23 µm x 5.5–6.5 µm), rather than elongate-oval microbasic mastigophores (10.5– 13.5 µm x 4.0–5.0 µm). As for lateral nematothecae, the upper chamber was conical and emarginated rather than conical with innerside significantly lowered, while the cavity of the lower chamber was marked by perisarcal ridges rather than appearing smooth. Schuchert noted that the examined material from Florida might belong to a different species, a suggestion taken here to be correct. Rather than assigning it to a new species, however, the material is referred to a resurrected A. gracilis , partly on morphological grounds (it corresponds in most respects with the description by Allman 1877) and partly on zoogeographic grounds (the collection site is within two degrees of latitude of the type locality of the species off the southeast coast of Florida).

The type of Antennella gracilis (MCZ, no catalog number) was examined earlier by both Calder (1997) and Schuchert (1997). It appears to have been dry at some time in the past, and has also been combined in the same bottle with specimens of Monostaechas quadridens McCrady, 1859 . While the material is in unsatisfactory condition, a small axillary nematotheca is present contrary to the report of Fraser (1944: 315), who indicated that it was of normal size and situated some distance from the hydrotheca. Fraser was misled by an imperfect illustration of the species by Allman (1877).

Three kinds of nematocysts, namely seed-shaped heteronemes, microbasic mastigophores, and what are believed to be merotrichous isorhizas (but considered macrobasic mastigophores by Schuchert 1997), were observed in material examined here ( Fig. 12 ).

Due to the brief description and imprecise illustration of Antennella gracilis by Allman (1877), as well as its subsequent confusion with A. secundaria , the distribution of this species is uncertain.

Reported distribution. Atlantic coast of Florida. Off Carysfort Reef ( Allman 1877).—Off St. Lucie Inlet ( Schuchert 1997, as Antennella secundaria ).

Western Atlantic. North Carolina ( Nutting 1900) to the Caribbean Sea ( Vervoort 1968; Bandel & Wedler 1987), including Bermuda ( Calder 1997, as Antennella secundaria ) and the Gulf of Mexico ( Calder & Cairns 2009, as A. secundaria ).

Elsewhere. Records from the Indian Ocean ( Thornely 1904), western Pacific ( Stechow 1913; Hargitt 1924), and eastern Pacific ( Fraser 1948) need verification.

Figures

FIGURE 11. a, Antennella gracilis: part of hydrocaulus with two hydrothecae, ROMIZ B1090, scale equals 0.25 mm. b, Antennella incerta: front view of hydrotheca, showing laterally-displaced axillar nematotheca, ROMIZ B3973, scale equals 0.25 mm. c, Antennella incerta: hydrocaulus with three hydrothecae, ROMIZ B3973, scale equals 0.25 mm. d, Halopteris alternata: part of hydrocaulus with a hydrocladium and two hydrothecae, ROMIZ B3974, scale equals 0.20 mm. e, Halopteris alternata: part of hydrocladium with two hydrothecae, ROMIZ B3974, scale equals 0.20 mm. f, Halopteris carinata: part of hydrocladium with two hydrothecae, ROMIZ B1128, scale equals 0.20 mm. g, Halopteris carinata: male gonotheca, ROMIZ B1128, scale equals 0.25 mm. h, Halopteris carinata: female gonotheca with two nematothecae, ROMIZ B1128, scale equals 0.25 mm.

FIGURE 12. Antennella gracilis, nematocysts, ROMIZ B1090. a, seed-shaped heteroneme, from tentacle; b, microbasic mastigophore, from tentacle; c, merotrichous isorhiza, from nematophore; d, discharged merotrichous isorhiza; e, part of thread of merotrichous isorhiza, showing mid-portion of thread with spines.