Macrorhynchia clarkei ( Nutting, 1900 )

Calder, Dale R., 2013, Some shallow-water hydroids (Cnidaria: Hydrozoa) from the central east coast of Florida, USA, Zootaxa 3648 (1), pp. 1-72 : 51

Macrorhynchia clarkei ( Nutting, 1900)

Fig. 14g, h

Lytocarpus clarkei Nutting, 1900: 124 , pl. 32, figs. 5–7.

Macrorhynchia robusta .— Humann, 1992: 75, top photograph.— Humann & DeLoach, 2002: 75, top photograph [not Macrorhynchia robusta ( Fewkes, 1881) ].

Type locality. Bahamas: off Little Cat Island (Little San Salvador Island) , on a submerged bank connecting it and Eleuthera ( Nutting 1900). Syntype material, comprising three slides, is in the National Museum of Natural History, Smithsonian Institution ( USNM 18698 ) .

Voucher material. West Palm Beach, on reef seaward of the Breakers Hotel, 45 feet (13.7 m), January 1991, SCUBA, fragments of one colony, c. 15 cm high, with phylactogonia forming pseudocorbulae, but without gonophores, coll. P. Humann, ROMIZ B1129.

Remarks. The coenosarc of Macrorhynchia clarkei Nutting, 1900 contains numerous “black pigment cells,” as noted in the original description of the species, and colonies appear almost black macroscopically. The common name “black bush hydroid” is appropriate for this hydroid.

In a previous work ( Calder 1997: 65) I considered it likely that Macrorhynchia clarkei was conspecific with M. grandis ( Clarke, 1879) . The same opinion had been expressed earlier by Bogle (1975: 297). The two are held distinct here given apparent differences between them in both morphology and bathymetric distribution. For example, median inferior nematothecae extend beyond hydrothecal margins in M. grandis but not in M. clarkei . As for their type localities, M. grandis came from bathyal depths (339 fathoms = 620 m) in the Straits of Florida (24°08’N, 82°51’W) while M. clarkei was from much shallower waters (5-24 m) in the Bahamas. Although additional records of the two have extended their reported depth ranges, M. clarkei still appears to be a species more typical of shallow waters and M. grandis one of deeper regions. There is also no mention of the black pigment granules in M. grandis that are so conspicuous in M. clarkei . For the same reasons given above, M. clarkei is considered distinct from M. ramosa ( Fewkes, 1881) , originally described from St. Vincent in the Caribbean. Illustrations of type material portraying some characters of these three similar species are provided elsewhere ( Calder 1997: Fig. 20 a–c). Macrorhynchia allmani ( Nutting, 1900) from the warm western Atlantic also resembles M. clarkei but has been distinguished by having more widely spaced hydrocladia, longer hydrocladial internodes, deeper hydrothecae, and shorter median inferior nematothecae ( Calder, 1997). It also has two internal ridges per hydrocladial internode rather than one, with one beneath the intrathecal ridge and another beneath the lateral nematothecae. Nevertheless, as noted by Bogle (1975), careful study of the various nominal species assigned to Macrorhynchia Kirchenpauer 1872 is needed to sort out the taxonomy of this difficult group. Some recent authors ( Ansín Agís et al. 2001; Vervoort 2006) have recognized Nematophorus Clarke, 1879 as a genus distinct from Macrorhynchia , having a pseudocorbula instead of single phylactogonia, and have assigned M. clarkei to it.

Records of this species from Bermuda ( Bennitt 1922, as Lytocarpus clarkei ; Calder 1986, as Macrorhynchia clarkei ) are misidentifications of Macrorhynchia allmani Nutting, 1900 (see Calder 1997). Conversely, the hydroid from Florida illustrated by Humann (1992: 75) and Humann & DeLoach (2002: 75) and identified as Macrorhynchia robusta ( Fewkes, 1881) is referable to M. clarkei . That misidentification is entirely due to an error on my part, and was based on the voucher material above. The colony in their photograph is the same one examined here. Hydrothecal cusps are much more deeply cut in M. robusta than in M. clarkei .

Reported distribution. Atlantic coast of Florida. West Palm Beach ( Humann 1992; Humann & DeLoach 2002).

Western Atlantic. Florida and the Bahamas to the Caribbean Sea in the western Atlantic ( Vervoort 1968, as Lytocarpus clarkei ; Galea 2010).

Elsewhere. Cape Verde Islands ( Vervoort 1959, as L. clarkei ; Ansín Agís et al. 2001, as Nematophorus clarkei ; Vervoort 2006, as N. clarkei ).

Figures

FIGURE 14. a, Aglaophenia dubia: part of a hydrocladium with two hydrothecae, ROMIZ B1125, scale equals 0.10 mm. b, Aglaophenia latecarinata: part of a hydrocladium with two hydrothecae, ROMIZ B1086, scale equals 0.10 mm. c, Aglaophenia rhynchocarpa: part of a hydrocladium with two hydrothecae, ROMIZ B1083, scale equals 0.10 mm. d, Aglaophenia trifida: part of a hydrocladium with three hydrothecae, ROMIZ B1086, scale equals 0.10 mm. e, Gymnangium speciosum: part of a hydrocladium with three hydrothecae, ROMIZ B1131, scale equals 0.20 mm. f, Macrorhynchia allmani: part of a hydrocladium with two hydrothecae, ROMIZ B3982, scale equals 0.10 mm. g, Macrorhynchia clarkei: part of a hydrocladium with two hydrothecae, ROMIZ B1129, scale equals 0.10 mm. h, Macrorhynchia clarkei: a single phylactogonium from a pseudocorbula, ROMIZ B1129, scale equals 0.25 mm. i, Macrorhynchia philippina: part of a hydrocladium with three hydrothecae, ROMIZ B1092. Scale equals 0.10 mm.