Nemertesia falcicula

Altuna, Álvaro, 2012, New records of bathyal Leptolida (Cnidaria: Hydrozoa: Leptothecata) from the Bay of Biscay and the northwestern Iberian Peninsula (northeastern Atlantic), Zootaxa 3565, pp. 1-17 : 11-13

Nemertesia falcicula ( Ramil & Vervoort, 1992a)

(fig. 5A–E, table 5)

Plumularia falcicula Ramil & Vervoort, 1992a: 180 , fig. 46a–h.— Bouillon et al. 2006: 369.

Nemertesia falcicula: Ansín Agís et al. 2001: 205 , fig. 80a–k.— Ramil & Vervoort, 2006: 136 (table 2).— Altuna, 2010: 24.

Material examined. ECOMARG 2009, 20.07.2009, Avilés Canyon System, station R1, 43 º43.75’N– 06º05.41’W, 500 m, two colonies, one with gonosome, and a fragment with one gonotheca. INDEMARES 2010, 0 8.08.2010, Galicia Bank, station DR01, 42º40.866’N – 11º36.645’W, 999 m, 17 colonies, 13 of them with gonosome. INDEMARES 2012, La Gaviera Canyon (Avilés Canyon System), station 01aROV7, 43 º52.569’N– 05º54.005’W, 660 m, 0 6.05.2012, six small colonies, two of them with gonothecae, on a stone with Phelliactis sp. collected with a ROV.

Description. Colonies up to 5.2 cm high and 3.6 cm wide, formed by a mass of intertwined hydrorhizae giving rise to a thick polysiphonic stem 5–6 mm high and 1.7 mm wide. Stem giving off polysiphonic branches distally that rise more or less at the same level. Branches ultimately forming small clusters of adjacent monosiphonic hydrocauli; clusters basally joined, with some accessory secondary tubules. Hydrorhiza and stem with numerous bithalamic nematothecae formed by a thin straight stalk, and a cup-shaped distal chamber. Hydrocauli up to 2.0 cm long, not ramified, not neatly segmented, sometimes divided into internodes by straight nodes. Internodes with one or two distal apophyses. If there is one, they occur alternatively left and right; if there are two, they are opposite. Each apophysis with a small mamelon on its upper side and one bithalamic nematotheca.

Hydrocladia short, originating from apophyses in alternate pairs basally, and opposite and decussate with at most in four longitudinal rows distally, alternate for the whole length, or even opposite basally and alternate distally. When opposite, 1–2 cauline bithalamic nematothecae, sometimes symmetric at same level of hydrocaulus, occurring between each pair of hydrocladia. Hydrocladia monomerous, formed by a short basal athecate internode with a single bithalamic nematotheca, and a succession of up to seven thecate internodes (normally five) (fig. 5C). Nodes always oblique excepting the first, which is almost straight. Thecate internodes long and delicate, each with one hydrotheca and four bithalamic nematothecae. Hydrothecae in the lower third of internode small, shallow, with adnate adcaulinar wall, wider than tall; rim even, sligthly tilted downwards. Hydrothecal aperture circular, perisarc thin. Nematothecae include one mesial inferior, two laterals almost at distal end of hydrotheca on short apophyses, and one mesial supracalycine.

Female gonothecae pedicellate inserting singly or in pairs on hydrocladial apophyses, strongly curved, with lateral circular aperture (fig. 5E).

Remarks. The structure of the colonies is characteristic, promptly identifying the species (fig. 5A). The numerous nematothecae at the bases of the colony and hydrorhiza are also a constant feature. Some monosiphonic Plumularia -like colonies that were not ramified, but had gonosome, were collected in station DR01.

The species belongs to Nemertesia Lamouroux, 1812 as suggested by Ansín Agís et al. (2001), instead of Plumularia Lamarck, 1815 as originally described by Ramil & Vervoort (1992a). Nevertheless, Plumularia -like stems are very common, more even so than those of the Nemertesia type, and sometimes only a few hydrocladia are arranged in decussate verticils in the whole colony. The same has been shown by Moura et al. (2012b), also in colonies of Nemertesia , with hydrocladia solely arranged in one plane.

The first basal athecate internode may be absent, and sometimes the thecate internodes have two supracalycine nematothecae instead of one. The nematothecae are deciduous, and may be completely lacking in some hydrocladia.

Distribution. Nemertesia falcicula was recorded previously only from a few stations in the Strait of Gibraltar and the Moroccan coast of the Alboran Sea ( Ramil & Vervoort 1992a, 480–580 m depth), and the Canary Islands ( Ansín Agís et al. 2001, 350– 1800 m depth).

The hydroid was collected from the Avilés Canyon System at 500–660 m depth, and from the Galicia Bank at 999 m depth, within the bathymetric range already known of this rarely-recorded bathyal hydroid. This species is new for the Bay of Biscay fauna, and the northernmost record of it thus far.