Halopteris enersis, Galea, 2006

Galea, Horia R., 2006, On two new species of Halopteris Allman, 1877 (Cnidaria: Hydrozoa) from Chile, Zootaxa 1165 (1), pp. 57-68 : 58-62

Halopteris enersis sp. nov.

( Figs. 1–5 ; Tables 1–2)

Type material

Holotype: MHNG INVE 38145 , several cormoids from a single colony, 1–4 cm high, without gonothecae, epizoic on a hydroid. Chile, Bernardo Area , Canal Farquhar, 48°29’18.7’’S, 74°12’25.7’’W, depth 32 m, 29 March 2005.

Description

Colony forming plumes up to 4 cm high, arising from creeping hydrorhiza. Stolon tubular, ramified, without nematothecae. Stems monosiphonic, unbranched, straight basally, slightly flexuose distally; composed of a basal part of varying length (1/4 to 1/3 the caulus length) lacking hydrothecae and hydrocladia, and a longer distal part bearing hydrothecae and hydrocladia. Basal part with 1–3 transverse nodes and a varied number of frontal nematothecae (up to nine) in a single row, separated from remainder of stem by an oblique node. Distal part of stem heteromerously segmented by alternating oblique and transverse nodes, often deeply constricted, forming intersegments and main segments. However, in distal part of stem, transverse nodes may be weaker due to perisarc thinning. Perisarc tending to be thickened near proximal and distal ends of intersegments and segments. Intersegments much longer than main segments. Hydrocaulus intersegments with proximal transverse node and distal oblique node; lacking hydrothecae and hydrocladia, but bearing five to six frontal nematothecae, in one row. Nematothecae bithalamic and movable, adaxial side of upper chamber lower, aperture wide. Main segments with proximal oblique node and distal transverse node. Each segment characteristically with one hydrotheca, a pair of lateral apophysis, and four nematothecae. Hydrothecae situated in lower half of main segments; deep, walls straight and slightly diverging, rim even, circular, slightly everted. Hydrothecae adnate for half of their adcauline length. Cauline nematothecae: one median inferior, two laterals, and one median superior; axillar nematotheca absent. Median inferior nematotheca not reaching base of hydrotheca; likely movable; bithalamic, lower chamber less voluminous; abcauline wall of upper chamber longer than adcauline one, aperture wide. Lateral nematothecae conical, both sides equal in length, bithalamic, borne on apophyses about as long as nematotheca itself; nematothecae pointing upwards, not reaching the hydrothecal rim. Median superior nematotheca situated behind adcauline wall of hydrotheca, but distal to axil, not overtopping hydrothecal rim; nematotheca bithalamic, adcauline wall of upper chamber much lower, aperture wide. Hydrocladia in opposite pairs, up to 13 pairs per plume, with as many as six hydrothecae or more in undamaged specimens; unbranched, directed laterally at an angle between 75–85° with caulus, pointing slightly forward. Hydrocladia attached on short apophyses lateral to cauline hydrothecae by one short quadrangular segment; both apophyses and segment devoid of nematothecae. Hydrocladia gently curving, with heteromerous segmentation similar to that of caulus. Intersegments much longer than main segments. Intersegments with two or often three nematothecae in one row. Nematothecae bithalamic and movable; adaxial side much lower. Main hydrocladial segments typically with one hydrotheca and three nematothecae. Hydrothecae situated in the middle of main segments, axis at 45° to that of hydrocladia, rim reaching beyond distal end of segment. Hydrothecae rather deep, cup­shaped, widening towards rim, one half of adcauline wall free and straight; abcauline wall straight, with slightly everted margin; aperture circular, rim smooth, perpendicular or nearly so to axis of hydrotheca. Intrathecal septum lacking. Hydrocladial nematothecae: one median inferior and two laterals, axillar nematotheca absent. Mesial inferior nematotheca not reaching hydrothecal base, abcauline wall longer than adcauline one, rim deeply scooped on adcauline side, aperture wide; likely movable. Lateral nematothecae conical, bithalamic, both sides equal in length, rim circular; borne on conspicuous apophyses of same length as nematotheca, adnate to hydrothecal wall; nematothecae movable, not reaching hydrothecal rim but the transverse node of main segment. Hydranths with about 16–18 filiform tentacles in a single whorl. Morphometric data of H. enersis are given in table 1.

Gonothecae unknown.

Nematocysts: microbasic euryteles in nematophores, with shaft indistinctly swollen and approaching mastigophore condition, shaft length in discharged capsule about slightly longer than capsule, size 15 × 4.5 µm. Smaller capsules in tentacles, size 6 × 2 µm.

Remarks

Halopteris enersis belongs to the Halopteris group, with opposite hydrocladia (see Schuchert 1997). It can be readily distinguished from other members of the group as follows: its caulus is unbranched and therefore different from that of H. geminata (Allman, 1877) , which is dichotomously branched. Caulus and cladia of H. enersis are heteromerously segmented, while those of H. zygocladia (Bale, 1914) are homomerously segmented. Hydrothecae of H. enersis possess one pair of lateral nematothecae, not two as in H. catharina (Johnston, 1833) ; the nematothecae are bithalamic and therefore different from the rather unique one­chambered lateral nematothecae of H. gemellipara Millard, 1962 . There is no internal transverse ridge in lower part of hydrothecae of H. enersis as in H. opposita (Mulder & Trebilcock, 1911) . In two species of the genus, but not in H. enersis , one or a pair of nematothecae are present in the axils of cauline and cladial hydrothecae; these species are H. prominens Vervoort & Watson, 2003 and H. gracilis (Clarke, 1879) , respectively.

Halopteris enersis is very close to the eighth member of the group, i.e. H. plagiocampa ( Pictet, 1893) , but some important features permit separation of the species. The main distinguishing characters are listed in table 2.

Etymology

The species was named after the company Enersis which promotes biodiversity research and conservation at the Huinay Scientific Field Station.

Distribution Known only from the type locality.

( Pictet, 1893). 1 Siboga stations 77, 164 and 258 (see Schuchert, 1997). 2 MHNG INVE 25021 (see

Schuchert, 2003).

Figures

FIGURE 1–5. Halopteris enersis, sp. nov. 1, two colonies of different size, frontal view. Scale bar 5 mm; 2, part of stem, lateral view. Scale bar 0.5 mm; 3, detail of colony with bases of opposite hydrocladia, frontal view. Same scale as in figure 2; 4, part of hydrocladium, lateral view. Scale bar 0.5 mm; 5, cauline (A–D) and cladial (A’–C’) nematothecae. A, A’—nematothecae from intersegments; B,B’—main segment median inferior nematothecae; C,C’—main segment lateral nematothecae; D—main segment superior nematotheca. Scale bar 100 µm.