Acryptolaria operculata Stepanjants, 1979

Peña Cantero, Álvaro L., 2020, Species of Acryptolaria Norman, 1875 (Cnidaria: Hydrozoa) collected by US Antarctic and sub-Antarctic expeditions, Zootaxa 4767 (2), pp. 277-294 : 288-290

Acryptolaria operculata Stepanjants, 1979

( Figs 1E , 6B , 7E )

Acryptolaria operculata Stepanjants, 1979: 52 , pl. 9 fig. 5A, B; Peña Cantero et al., 2007: 258–261 , figs 12, 16D, 18D, 19E; Soto Àngel & Peña Cantero, 2015: 988, fig. 3b.

Acryptolaria patagonica El Beshbeeshy, 1991: 67–70 , fig. 14; 2011: 57–59, fig. 13.

? Acryptolaria patagonica— Watson, 2003: 162, 163, fig. 12A–C; Vervoort & Watson, 2003: 51–53, fig. 7A–G.

? Acryptolaria cf. operculata— Peña Cantero & Vervoort, 2010: 311–312 , figs 22, 30.

Material examined. Eltanin: 6/339, four fragments up to 22 mm long; 8/558, several fragments up 83 mm long; 9/740, several fragments up to 100 mm long, on anthozoans; 11/970, several fragments up to 30 mm long; 22/1536, at least two fragmented stems (longest fragment 85 mm long); 22/1592, stem fragment 9 mm long (on a microslide); 22/1595, numerous fragments and stems up to 60 mm high, on dead gorgonians and Halecium sp.; 26/1818, several stems up to 110 mm high, with coppinia, basibiont of Plumularia sp. and Hebella plana ; 26/1826, three stems up to 100 mm high, with coppinia, on anthozoans, basibiont of Hebella plana and Sertularia sp. Hero : 715/881, several stems up to 125 mm high, basibiont of Lafoea dumosa , Hebella plana and Serturalella sp.; 715/885, a fragment 30 mm long.

Description. Stems up to 125 mm high, strongly polysiphonic. Hydrorhiza rhizoidal little developed, sometimes forming a basal plaque. Branching usually alternate in one plane, up to third order. Branches and stems slightly geniculate. Sometimes with anastomoses. Hydrothecae alternate in one or two planes, making an angle up to 110°. Hydrotheca tubular, free part cylindrical; diameter decreasing basally at basal third. Hydrotheca curved outwards. Hydrotheca adnate to internode over half its adcauline length. Adcauline wall faintly convex at free part; more at adnate part, but for the most basal part. Abcauline wall concave. Hydrothecal aperture circular, directed up- and outwards. Rim even, usually without renovations or with a few short ones. Some hydrothecae with closing apparatus consisting of a deciduous circular flap of variable attachment.

Coppiniae fusiform, up to 35 mm long. Gonothecae arranged around stem and branches, tightly packed, polygonal in cross section. Aperture at the end of a long neck. Without defensive tubes.

Measurements (in µm). Hydrothecae: abcauline wall 1900–2400, free part of adcauline wall 820–1240, adnate part of adcauline wall 960–2000, adcauline wall 2160–3140, diameter at aperture 420–500, diameter at base 180–220. Cnidome: larger microbasic mastigophores, range 14–15 x 4.5–5.5, mean 14.4±0.4 x 5.0±0.2 (n=10); ratio, range 2.7–3.2, mean 2.9±0.1 (n=10); smaller microbasic mastigophores 8 x 3–3.5.

Measurements (in µm) (Tasman Sea material). Hydrothecae: abcauline wall 1300, free part of adcauline wall 700–900, adnate part of adcauline wall 840–940, adcauline wall 1640, diameter at aperture 300–390, diameter at base 140–200. Cnidome: larger microbasic mastigophores, range 14–14.5 x 5; ratio, range 2.8–2.9; smaller microbasic mastigophores 7.5 x 3.

Remarks. The combination of characters, such as the shape and size of the hydrotheca, the small size of the larger nematocysts, and the arrangement of the hydrothecae, usually in two planes, makes identification of this species easy.

The coppinia was first described by Vervoort & Watson (2003). Those in the present material perfectly agree with that description.

The material from the Tasman Sea (26/1826 and 26/1818) has distinctly smaller hydrothecae than the material from the south-west Atlantic, but it agrees in the remaining features, including the size of the nematocysts. It is also worth mentioning that the hydrothecal aperture reaches the minimum size reported by Vervoort & Watson (2003) in waters of New Zealand. The Tasman material also agrees with the material from CHACAL 2 DW 76, from the Norfolk Ridge area, a 14-mm-high stem dubiously assigned by Peña Cantero & Vervoort (2010) to A. operculata .

Peña Cantero & Vervoort (2010) considered doubtful the records by Watson (2003) and Vervoort & Watson (2003), because they did not include information about the cnidome and the genus has shown to have an unexpected diversity. Our material from the Tasman Sea has however larger nematocysts similar to those from the southwest Atlantic. As a result, it is likely that Watson’s (2003) material and that studied by Vervoort & Watson (2003) also belong to this species. Of course, it would be necessary to study the cnidome to be completely certain, but the remaining characters point to it.

Ecology and distribution. Acryptolaria operculata had been reported at depths from 98 ( El Beshbeeshy 2011) to 1420 m ( Watson 2003); the present material was collected between 124 and 2044, in the southwest Atlantic, and between 913 and 4740 m, in the Tasman Sea, considerably extending its lower bathymetric limit. Coppiniae in material collected in December in the Tasman Sea. Peña Cantero & Vervoort (2010) found the species on corals, Soto Àngel & Peña Cantero (2015) on dead gorgonians, Watson (2003) on primnoid gorgonian, and Vervoort & Watson (2003) on rock, stylasterids and corals.

Acryptolaria operculata seems to be a sub-Antarctic species, penetrating into Antarctic waters along the Scotia Arc (at least up to Discovery Bank). Its confirmed known distribution only included sub-Antarctic waters of the Patagonian shelf ( Stepanjants 1979; El Beshbeeshy 2011). Soto Àngel & Peña Cantero (2015) first recorded it also from Antarctic waters; in particular, apart from the sub-Antarctic Burdwood Bank, they reported it along the Scotia Arc islands, from Shag Rocks to Discovery Bank. As indicated above, the species has also been recorded from the Macquarie region ( Watson 2003) and New Zealand waters ( Vervoort & Watson 2003). Present material mostly comes from the area between Staten Island (Tierra del Fuego), the Falkland Islands and South Georgia, but also from the Tasman Sea, west of New Zealand.

Figures

FIGURE 1. Branch fragments showing hydrothecal arrangement and shape of hydrothecae:A, Acryptolaria conferta (Allman, 1877); B, Acryptolaria crassicaulis (Allman, 1888); C, Acryptolaria flabellum (Allman, 1888); D, Acryptolaria minuta Watson, 2003; E, Acryptolaria operculata Stepanjants, 1979. (A from 715/885; B from 2/11; C from 22/1520; D from 27/1852; E from 715/885). Scale bar: 500 µm.

FIGURE 6. Hydrothecae showing operculum (arrow): A, Acryptolaria frigida Peña Cantero, 2014; B, Acryptolaria operculata Stepanjants, 1979; C, Acryptolaria sp. (A from 2/2; B from 6/339; C from 22/1595). Scale bar: 200 µm.

FIGURE 7. Nematocysts:A, Acryptolaria conferta (Allman, 1877); B, Acryptolaria flabellum (Allman, 1888); C, Acryptolaria frigida Peña Cantero, 2014; D, Acryptolaria longitheca (Allman, 1877); E, Acryptolaria operculata Stepanjants, 1979; F, Acryptolaria sp. (A from 715/885; B from 5/221; C from 2/2; D from 27/1974; E from 22/1595; F from 715/885). Scale bar: 10 µm.