Clathrozoella drygalskii ( Vanhöffen, 1910 ), Vanhoffen, 1910

ÁLVARO L. PEÑA CANTERO, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa, Zootaxa 4293 (1), pp. 1-65 : 13-14

Clathrozoella drygalskii ( Vanhöffen, 1910)

( Table 3)

Clathrozoella drygalskii —Peña Cantero et al., 2003: 284–286, figs 1, 5A, 6A; Peña Cantero, 2014a: 1715.

Material examined. Stn 14, one stem, ca. 65 mm high (NIWA 117475); Stn 17, one colony, ca. 32 mm high, on stone (MNCN 2.03/529); Stn 107, a basally truncated stem, ca. 21 mm high (NIWA 117476).

Description. Stems up to 65 mm high. Branching sparse (65 mm high stem with four short primary branches, first one giving rise to secondary branch). Many sand grains on skeleton. Pseudohydrothecae curved, each associated with up to four other pseudohydrothecae. No cementing perisarc among pseudohydrothecae. Polyp with distal whorl of eight to ten filiform tentacles. One or two gonophores; when two present, one of them more developed.

Cnidome consisting of four categories of nematocysts: microbasic mastigophores, microbasic euryteles (the most abundant), haplonemes and desmonemes ( Table 3).

Remarks. There is no clear pattern in the arrangement of the pseudohydrothecae in the material studied. For example, in the material from Stn 17 the pseudohydrothecae are approximately alternate at the basal part of the stems, forming two longitudinal rows. However, they are curved to the same side, forming two planes separated by an obtuse angle. More distally, there are verticils of three or four pseudohydrothecae, roughly forming three or four longitudinal rows. In other parts, the pseudohydrothecae are more irregularly distributed, but can be found all around the stem.

I assigned the present material to C. drygalskii , with which it has closer similarities, including shape and size of pseudohydrothecae, size of nematocysts and pattern of pseudohydrothecal disposition. According to Vervoort & Watson (1996), the pseudohydrothecae are either approximately alternate in position (then forming a double row), or less distinctly alternate and forming three or four rows.

Although Peña Cantero et al. (2003) indicated that each pseudohydrotheca is associated with two others, in the present material they are associated with up to four. Nevertheless, it should be pointed out that this situation could also be present in material previously assigned to C. drygalskii where the pseudohydrothecae are less distinctly alternately arranged, also forming three or four rows [as in the material examined by Vervoort & Watson (1996)]. In the few parts of the present material where the pseudohydrothecae are alternately arranged, each pseudohydrotheca is associated with two others.

In contrast with previous descriptions of the species, in the material I studied there are many sand grains on the skeleton. Vervoort & Watson (1996) indicated that the exterior of the colonies is slightly encrusted with grains of sand and diatoms.

Ecology and distribution. Deep-water species ( Peña Cantero 2014a) collected at depths from 385 ( Vanhöffen 1910) to 1169 m ( Vervoort & Watson 1996); present material between 400 and 451 m. It seems to grow on hard substrata (Peña Cantero et al. 2003), having been reported on pebbles ( Vanhöffen 1910), debris ( Peña Cantero 2014a) and stones (present material). Gonophores in February (present material).

Clathrozoella drygalskii is known from the southern part of the Pacific Ocean (Peña Cantero et al. 2003). Outside Antarctic waters, it has been reported off New Zealand and southeastern Australia ( Vervoort & Watson 1996). In the Antarctic region, it is known from the Davis Sea ( Vanhöffen 1910) and off Queen Mary Coast ( Peña Cantero 2014a). Present material is the first record from the Ross Sea, from off Cape Adare and off Possession Islands .