Halopteris plumosa, Galea, Horia R. & Schories, Dirk, 2012

Galea, Horia R. & Schories, Dirk, 2012, Some hydrozoans (Cnidaria) from Central Chile and the Strait of Magellan, Zootaxa 3296, pp. 19-67 : 56-59

Halopteris plumosa sp. nov.

(fig. 8A–H, table 9)

Antennella diaphana diaphana — Leloup, 1974: 47, fig. 42 [not Halopteris diaphana (Heller, 1868) ]. Halopteris constricta — Blanco, 1973: 76, figs 4–6. — Blanco, 1994c: 220, figs 1, 2 [not H. constricta Totton, 1930 = H. minuta (Trebilcock, 1928) ].

Material examined. Stn. RHO — 01.xi.2009, DS279 (25 m): a dozen small (ca. 4 mm high), sterile stems, epizoic on Symplectoscyphus flexilis (MHNG-INVE-79643). Stn. AMI — 26.v.2010, S01 (5 m): holotype (MHNG- INVE-79668)—five sterile stems, 1.9–3.4 cm high, on sponge; S02 (10 m): a single sterile plume, 2.9 cm high, basal part missing.

Description. Colonies forming upright, up to 3.4 cm high plumes, arising from creeping, ramified, tubular stolons. Hydrocaulus monosiphonic, unbranched, straight to imperceptibly geniculate. Basal part of varied length, devoid of both hydrothecae and hydrocladia; divided into several segments by transverse nodes, distalmost node oblique; segments with varied number of nematothecae in one row. Caulus above basal part homomerously segmented by oblique nodes into up to 60 internodes; young stems heteromerously segmented distally. Hydrocladia alternate, basalmost ones often broken off. Cladia, at origin, slightly shifted towards front of stem, then curving dorsally and reaching back a common plane for the whole cormoid. Cauline internodes carrying one hydrotheca, an apophysis lateral to it, and up to 6 nematothecae: one mesial inferior, a pair of laterals, and one or two (rarely three) above hydrotheca, the latter placed on ahydrothecate internodes in young cormoids. Axillar nematothecae missing. Stem apophyses rather long, distal end transverse, with no associated nematothecae. Adult plumes with up to 9 hydrothecae per cladium; hydrocladia homomerously divided into internodes by means of oblique nodes; heteromerous division often occurs in young plumes only. First cladial segment with proximal end transverse and distal end oblique, carrying one or two nematothecae in a row. Remainder of cladial segments of moderate length, with a centrally-placed hydrotheca, and up to five nematothecae: one mesial inferior, a pair of laterals, and one (exceptionally two) median superior, the latter carried on short ahydrothecate segments in young cormoids with heteromerous division of cladia. First cladial internode may occasionally bear a lateral apophysis for the insertion of a second order cladium; the latter with similar morphology and carrying up to 5 hydrothecae. Hydrotheca cupshaped, rim even, not reaching distal node, long axis forming an angle of about 45° with internode; abcauline wall slightly sigmoid, adcauline 2/3rd adnate, free part markedly concave; aperture tilted uprightly. All nematothecae bithalamic, with adaxial wall of upper chamber significantly lowered; all but mesial inferior nematotheca movable. Gonothecae unknown.

Remarks. In rare instances, some cauline internodes from middle part of stem may give raise laterally to two apophyses supporting opposite cladia. There are one to three nematothecae above each hydrotheca, placed along either one or two parallel rows. In young stems, these nematothecae are situated on a separate ahydrothecate segment, due to a secondary heteromerous segmentation.

Large cormoids have cladia homomerously segmented into intersegments, while younger ones have a mix of homo- and heteromerous segmentation. In the latter case, the mesial superior nematotheca(e) are borne on a short, distal intersegment, delimited from the preceding segment by an oblique node (fig. 8D). The first hydrocladial intersegment bears very often a single nematotheca in the smallest stems, but two were occasionally present. Conversely, two nematothecae are often found in larger stems, occasionally a single one is present.

Leloup (1974) assigned to “ Antennella (= Halopteris ) diphana (Heller, 1868)” two cormoids having alternate, occasionally branched hydrocladia, hydrothecae with the free adaxial wall distinctly concave, and associated nematothecae arranged as in our specimens. These were in perfect agreement with specimens described above, and his material is considered conspecific with S. plumosa .

Argentinean material assigned by Blanco (1973) to Halopteris constricta Totton, 1930 undoubtedly belongs to the present species as well. Comparisons of morphology and size are provided in table 9. A single, minor difference exists in Blanco's account, namely the presence of two cladial segments between the cauline process and the first hydrothecate internode. However, this is not supported by her figs 4 & 5, which show a well-developed apophysis followed by a single ahydrothecate segment. Indeed, it appears that this earlier account was an error. In a subsequent paper, Blanco (1994c) clearly stated that there was a single athecate internode between the cauline apophysis and the first thecate internode.

Gonothecae of this species remain undescribed.

Halopteris plumosa is readily distinguished from its congeners by its moderately tall, robust plumes provided with regularly alternate, close-set hydrocladia, with stem and cladia homomerously divided into internodes, the hydrothecae curved adaxially, and the lack of axillar nematothecae. Microscopically, it comes closer to H. campanula (Busk, 1852) , but some specific differences exist: 1) not all the cauline internodes bear cladia in H. campanula , a situation never met with in the present species; 2) two nematothecae occur in pairs above the hydrothecae of H. plumosa (occasionally a 3rd one exists), while only one is present in H. campanula ; 3) the first hydrocladial segment in H. plumosa bears one or two nematothecae, while only one occurs in H. campanula ; 4) the hydrothecae are as deep as broad in H. campanula , and comparatively deeper and with a distinctly concave adaxial wall in H. plumosa ; 5) the size of the hydrothecae of H. campanula is nearly twice as that of H. plumosa . Macroscopically, H. campanula is a highly polymorphic species ( Schuchert 1997), while only erect, monosiphonic cormoids, with regulary alternate cladia have been observed in H. plumosa . Additionally, the new species occurs in a geographically remote area from the known zone of distribution of H. campanula .

Etymology. The specific epithet refers to the feather-like shape of the colonies.

Distribution in Chile. Previously recorded from Canal Calbuco ( Leloup 1974). The present records are from Punta de Choros and Corral, but the species likely occurs soutwards to Tierra del Fuego.

World records. Gulf of San Matias, Argentina ( Blanco 1973, 1994c).