Thamnopteros

urn: lsid: zoobank. org: act: 687 DE 3 EB- 696 E- 49 DC- 8 E 12 - 22 C 1 D 62020 D 2

Diagnosis Colonies tall, branched or unbranched; stems and, when present, side branches stiff, thick and strongly fascicled, giving rise regularly or irregularly to hydrocladia-bearing branchlets from individual deeper tubes; branchlets monosiphonic, Halopteris - like, with basal prosegment, followed by a regular succession of modules (separated or not by nodes), each carrying a hydrotheca, its associated nematothecae, and a cladial apophysis laterally; cladia alternate, except for 1 st and / or 2 nd cormidium of each branchlet, where they can be opposite; cladia with short, proximal, athecate internode, followed by a succession of modules (either divided or undivided by nodes) composed of a hydrotheca and its associated nematothecae. Lateral nematothecae of varied length, occasionally exceedingly long, members of a pair usually of different lengths. Gonothecae provided with several basal, bithalamic nematothecae.

Remarks The species under discussion herein (see below) shows obvious similarities with a hydroid described by Stechow (1923 c) under the basionym Heteroplon valdiviae. The latter forms large, ramified, fascicled colonies, giving rise irregularly, from the deeper tubes, to monosiphonic, Halopteris - like branchlets facing in all directions around the stem and / or its branches. The axes of branchlets are provided proximally with a prosegment, and occasionally with as many as four (Millard 1962); the prosegment bears a hydrotheca, its complement of nematothecae, and a pair of opposite cladial apophyses; the remainder of axis comprises a succession of hydrothecate internodes, each bearing a cladial apophysis lateral to a hydrotheca (proximalmost hydrotheca occasionally has a pair of opposite cladial apophyses); the apophyses are arranged alternately along the axis. With the exception of a short, proximal, athecate internode, followed by a nematothecate internode, the remainder of cladium is composed of a succession of thecate internodes separated by oblique nodes. Each hydrotheca, on both axes and cladia, is surrounded by 5 nematothecae: a mesial (well below its basis), a pair of laterals (of varied length and borne on short, conical apophyses), and a pair of axillar (Millard 1975). Stechow’s (1923) species was sometimes assigned to Halopteris (e. g., Millard 1957, 1962) and sometimes to Corhiza (Millard 1975; Schuchert 1997). Millard (1975) argued that a genus allocation to Corhiza was more opportune, for the “ appearance of the colony is very similar to C. scotiae, differing from it in the fact that the diverging tubes of the stem form sub-branches instead of hydrocladia ”. The diagnosis of Corhiza was modified accordingly, so as to include species with “ branches […] bearing cauline hydrothecae and pinnately arranged hydrocladia ”, as well (Millard 1975: 334). However, Millard’s (1975) opinion that unites into a single genus species whose fascicled stems and, if present, branches give rise to either Antennella - like hydrocladia or Halopteris - like branchlets, is not shared here. If this principle is applied to the genera Antennella and Halopteris, they must also be regarded as congeneric, although increasing evidence demonstrates that both are polyphyletic (Moura et al. 2018). The new genus comprises presently two species, Thamnopteros valdiviae (Stechow, 1923), its type species, and T. uniserius Galea gen. et sp. nov., described below.

Etymology From Ancient Greek ‘ θάμνΟς ’, meaning ‘ bush’, and ‘ πτΕρόν ’, meaning ‘ wing’ or ‘ feather’, to illustrate the appearance of the colonies of hydroids assignable to the present genus. The genus is masculine.

Type species Heteroplon valdiviae Stechow, 1923, designated herein (see below).