Monotheca flexuosa ( Bale, 1894 )

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 : 37

Monotheca flexuosa ( Bale, 1894)

Fig. 11a

Plumularia flexuosa Bale, 1894: 115 , pl. 5 figs 6–10.

Monotheca flexuosa .— Calder, 2020: 225, fig. 7d–f.

Type locality. Australia: Victoria, “mouth of Snowy River and Cape Lefebvre ” ( Bale 1894, as Plumularia flexuosa ) .

Voucher material. Kure Atoll, on algae, 26.ix.2002, one colony, 2.5 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5447.

Remarks. Originally described from Australia, Monotheca flexuosa ( Bale, 1894) was recently reported in the central North Pacific from the main Hawaiian Islands of Oahu and Maui ( Calder 2020). While its overall distribution is still uncertain, Watson (2011a) suspected that the species might be cosmopolitan.

In having slender colonies and cup-shaped hydrothecae with essentially straight margins, M. flexuosa resembles M. margaretta Nutting, 1900 , the type species of Monotheca Nutting, 1900 . Unlike in M. margaretta , however, its stems are more flexuous, lateral nematothecae appear sessile rather than pedicellate, and hydrothecae lack a median adaxial notch. Another similar species is M. pulchella ( Bale, 1881) , but its stem is robust with stronger perisarcal ridges, and hydrocladia arise midway along much shorter cauline internodes ( Bale 1894; Watson 2011a). As for M. obliqua ( Johnston, 1847) , its margin is more sinuous, and female gonothecae appear to be smooth ( Cornelius 1995b) rather than transversally ridged, as in M. margaretta ( Calder 1997) , or smooth to faintly undulated, as in M. flexuosa ( Watson 2011a) .

Evidence for recognition of Monotheca as distinct from Plumularia Lamarck, 1816 has been made elsewhere on the basis of both morphology ( Calder 1997) and genetics ( Moura et al. 2018). Species currently assigned to the genus are small and often epiphytic, although M. obliqua , M. flexuosa , M. margaretta , and M. bergstadi Gil & Ramil, 2021 are or appear to be substrate generalists ( Watson 2011a; Gravili et al. 2015; Calder 2019; Gil & Ramil, 2021).

Reported Distribution. Hawaiian archipelago. Oahu: Palea Point, just outside Hanauma Bay, 8 m ( Calder 2020). — Maui: Kanaio, 12 m ( Calder 2020).

Elsewhere. Australia ( Watson 2011a); Japan ( Hirohito 1974, as Monotheca flexiosa ); New Zealand ( Vervoort & Watson 2003, as M. pulchella );? South Africa ( Stechow 1925; Millard 1975, as M. pulchella );?Strait of Gibraltar ( Medel & Vervoort 1995, as M. pulchella );?Vema Seamount ( Millard 1966b, as M. pulchella ).

Figures

FIGURE 11. Plumulariidae. a, Monotheca flexuosa (Bale, 1894), part of hydrocaulus with two hydrocladia, each with a hydrotheca, Kure Atoll, ROMIZ B5447. Scale equals 0.1 mm. b, Monotheca gibbosa, sp. nov., holotype, part of hydrocaulus with hydrocladia and three hydrothecae, Laysan Island, ROMIZ B5448. Scale equals 0.1 mm. c, Monotheca gibbosa, sp. nov., holotype, part of hydrocaulus, and a hydrocladium with one hydrotheca, Laysan Island, ROMIZ B5448. Scale equals 0.05 mm. d, Plumularia floridana (Nutting 1900), part of hydrocaulus with bases of two hydrocladia, one with two hydrothecae, Gardner Pinnacles, ROMIZ B5449. Scale equals 0.1 mm. e, Plumularia strictocarpa Pictet, 1893, part of hydrocaulus with bases of two hydrocladia, one with two hydrothecae, Kure Atoll, ROMIZ B5453. Scale equals 0.1 mm. f, Plumularia strictocarpa Pictet, 1893, part of hydrorhiza, and proximal end of hydrocaulus with a gonotheca, Kure Atoll, ROMIZ B5453. Scale equals 0.2 mm.