Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa Author ÁLVARO L. PEÑA CANTERO text Zootaxa 2017 2017-07-14 4293 1 1 65 journal article 32747 10.11646/zootaxa.4293.1.1 dc2674e2-e260-4b6e-ad3a-731d610bccc5 1175-5326 828475 6FF96B5C-1F80-47ED-9962-19603DCBF550 Monocoryne antarctica sp. nov. ( Figs 3 A, 4; Table 2 ) Material examined. Stn 126, one polyp, c. 13 mm long (holotype, NIWA 115613). Description. 13-mm-long polyp ( Fig. 3 A). Basal 9 mm devoid of tentacles, enveloped by thin perisarc. Basal 3 mm provided with anchoring filaments. Capitate tentacles, usually in groups of three, one of them usually more developed. Gonophores absent. Cnidome consisting of stenoteles in two size groups ( Fig. 4 A–B), desmonemes ( Fig. 4 A, D), fusiform microbasic mastigophores? ( Fig. 4 B, D) and an unidentified, relatively large, tear-shaped type ( Fig. 4 C). Measurements (in µm). Cnidome : larger stenoteles [range 33– 36 x 30 –33, mean 34.8±1.0 x 31.6±0.8 (n=10); ratio, range 1.0–1.2, mean 1.1±0.1 (n=10)], smaller stenoteles [range 19– 21 x 15–16 , mean 19.9±0.7 x 15.6±0.4 (n=10); ratio, range 1.2–1.4, mean 1.3±0.1 (n=10)], desmonemes [range 20–22 x 13.5–17, mean 20.8±0.7 x 14.6±0.9 (n=10); ratio, range 1.3–1.5, mean 1.4±0.1 (n=10)], microbasic mastigophores? [range 27– 30 x 13–15 , mean 28.6±1.0 x 13.6±0.7 (n=10); ratio, range 1.9–2.3, mean 2.1±0.1 (n=10)], unidentified type [range 43– 48 x 20–25 , mean 45.6±1.7 x 22.4±1.6 (n=12); ratio, range 1.9–2.2, mean 2.0±0.1 (n=12)]. Remarks. Notwithstanding the absence of gonophores, Monocoryne antarctica sp. nov. is recognizable by the cnidome (cf. Table 2 ). Only Monocoryne bracteata ( Fraser, 1943 ) also has two size categories of stenoteles ( Schuchert et al. 2016 ), although in Fraser’s species they are smaller, particularly the larger ones. The unidentified type of nematocysts in M. antarctica sp. nov. could correspond to the microbasic euryteles observed in Monocoryne gigantea ( Bonnevie, 1899 ) and Monocoryne colonialis Brinckmann-Voss & Lindner, 2008 , but if so they are larger in M. antarctica sp. nov. (cf. Table 2 ). FIGURE 3. Monocoryne antarctica sp. nov. : A, general view of polyp (holotype). Staurotheca gracilis sp. nov. : B, colony general appearance (holotype). C, Symplectoscyphus densus sp. nov. : C, colony general appearance (holotype). Scale bar: 5 mm. TABLE 2. Comparative morphometric data (in µm) of the cnidome of the known species of Monocoryne [(1) from Schuchert et al . (2016), (2) Brinckmann-Voss & Lindner (2008), (3) Stepanjants et al . (2003), (4) Millard (1975); (a) as Monocoryne bracteata ; (b) microbasic heteronemes; (c) undetermined heteronemes; (d) unidentified type].

Monocoryne bracteata (1)	Monocoryne colonialis (2)	Monocoryne colonialis (3)(a)	Monocoryne gigantea (3)
Larger stenoteles	10.5–13 x 14–15	-	-	-
Smaller stenoteles	8–9 x 11.5–13	15–21 x 11–15	15–25 x 12–21	14–18 x 12–21
Desmonemes	5–6.5 x 7–9	10–12 x 7–9	11.5–12.5 x 8–9	10 x 8
Microbasic mastigophores	5–6.5 x 13.5–18b	22–31 x 8–12	21–37 x 7–14	19–24 x 8–11
Microbasic euryteles	-	Not observed	35.0–37.0 x 12.0–12.5	22.5–25.0 x 12.0–12.5
continued.

Monocoryne minor (4) Monocoryne sp.(3) Monocoryne antarcticum sp. nov.

Larger stenoteles	-	-	33-36 x 30-33
Smaller stenoteles	15.3-18.0 x 13.0-15.3	10.0–17.0 x 4.0–14.0	19–21 x 15–16
Desmonemes	9.0–13.5 x 6.3–10.8	7.0–10.0 x 5.5–7.0	20–22 x 13.5–17
Microbasic mastigophores	16.2–18.9 x 6.3–7.6c	15.0–18.0 x 5.0–8.0(?)	27–30 x 13–15
Microbasic euryteles	-	-	43–48 x 20–25d

FIGURE 4. Cnidome of Monocoryne antarctica sp. nov. : A, larger stenotele (arrow) and three desmonemes; B, smaller stenotele (arrow) and three microbasic mastigophores?; C, unidentified type (arrow); D, several desmonemes and one microbasic mastigophore? (arrow). Scale bar: 10 µm. Apart from the differences in the cnidome, there are geographical reasons to consider M. antarctica sp. nov. a different species. Monocoryne colonialis and M. bracteata are known from the North Pacific, M. gigantea from the North Atlantic and Monocoryne minor Millard, 1966 from South Africa . Only a species of Monocoryne , described as Monocoryne sp. by Stepanjants (1979) , had been reported from Antarctic waters. Monocoryne antarctica sp. nov. can be distinguished from Stepanjants’ material by the cnidome, as only one category of stenoteles was described by her, microbasic euryteles or equivalent were not described, and the remaining shared nematocysts are distinctly larger in M. antarctica sp. nov. This species also differs from the other geographically close species, M. minor from South Africa , by the presence of only three categories of nematocysts, and their distinctly smaller size, in Millard’s species. Ecology and distribution. Material collected at a depth of 159–161 m , off Cape Adare. Etymology. The specific name “ antarctica ” refers to the Antarctic region where this species was found.