Halopteris concava ( Billard, 1911 )

Agís, José Ansín, Vervoort, Willem & Ramil, Fran, 2009, Hydroids of the family Halopterididae (Cnidaria, Hydrozoa) collected in the western Pacific by various French expeditions, Zoosystema 31 (1), pp. 33-61 : 48-49

Halopteris concava ( Billard, 1911) ( Fig. 7 ; Table 7)

Plumularia concava Billard, 1911: 65 , fig. 6; 1913: 19, figs 9A, B, 10, pl. 1, fig. 14.

Thecocaulus concavus – Bedot 1921: 8. — Von Schenck 1965: 928.

Halopteris concava – Schuchert 1997: 121.

MATERIAL EXAMINED. — Makassar Strait. CORINDON 2, stn 210, 00°14.9’S, 117°53.5’E, 338 m, 31.X.1980, 1 colony, no gonothecae ( MNHN).

Philippines. MUSORSTOM 3, stn DR 117, 12°31.2’N, 120°39.3’E, 92-97 m, 3. VI.1985, 1 colony with 2 gonothecae and a few hydrothecae of Hebella dyssymetra Billard, 1933 ( MNHN).

DISTRIBUTION. — Known only from type locality, Duroa (Kei Islands) and Bay of Kwandang (01°0.5’N, 122°56’E), between 52 and 80 m deep.The present records extend the geographical distribution to the Philippines and Makassar Strait and the bathymetrical range to 338 m.

DESCRIPTION ( COLONY FROM MUSORSTOM 3, STN DR 117)

Hydrorhiza tubular and adhering to substrate; hydrocauli monosiphonic.

Basal part of axis with several internodes separated by transverse nodes and with many renovations; last internode with several nematothecae arranged in two frontal rows, separated from remainder of axis by an oblique node. Rest of hydrocaulus composed of hydrothecate internodes separated by oblique nodes. Each hydrothecate axial internode with one hydrotheca, a lateral apophysis (alternately directed left and right, supporting hydrocladia) and 10 or 11 nematothecae: one mesial inferior, two laterals on short apophyses reaching the hydrothecal margin, one behind hydrotheca and six or seven supracalycine nematothecae in two rows, usually in opposite pairs. Cauline hydrotheca in basal part of internode identical to those of hydrocladium.

Hydrocladia alternately directed left and right. First internode ahydrothecate, with basal node slightly oblique, distal node strongly oblique, and with two or three frontal nematothecae. Remain- der of hydrocladium composed of a succession of hydrothecate internodes separated by scarcely visible oblique nodes. Each internode with one hydrotheca and six or seven nematothecae: one mesial inferior, two laterals and three or four supracalycine nematothecae, with the most basal located just behind adcauline wall of hydrotheca. Hydrotheca cup-shaped, adcauline wall adnate for more than half its length, free portion of adcauline wall concave; abcauline wall nearly straight and longer than adcauline wall; hydrothecal aperture circular and rim smooth. Mesial inferior nematotheca immovable, not reaching hydrothecal base, deeply scooped on adcauline side. Lateral nematothecae placed on well-developed apophyses on both sides of hydrotheca, reaching hydrothecal margin; upper chamber deeply emarginated on inner and outer sides. Supracalycine nematothecae movable; upper chamber with adcauline wall scooped.

Gonothecae borne on axial, hydrothecate internodes, inserted laterally at hydrothecal base by means of a short pedicel. Gonotheca pyriform with latero-terminal circular aperture closed by a lid; two nematothecae on basal part.

VARIABILITY

Regeneration of broken hydrocladia leads towards development of ahydrothecate internodes with one to three nematothecae.

A new hydrocladium may develop from the inside of a hydrocladial hydrotheca.

In a colony from MUSORSTOM 3, stn DR 117 the hydrocladia of three basal internodes are disposed in opposite pairs; rest of the axis with hydrocladia pinnately arranged.

MUSORSTOM 3 stn DR 117 Height of colony (in mm) 25 Axial segments:

Length 450-840 Diameter at node 90-160 Cauline hydrotheca:

Length 100-120 Diameter at rim 100-120 Cauline nematothecae:

Length 60-80 Diameter at rim 30-40 Hydrocladial internode:

Length 400-450 Diameter at node 50-60 Hydrotheca:

Length abcauline wall 130-145 Length free portion adcauline wall 40-55 Diameter at rim 100-120 Mesial infracalycine nematotheca:

Length 48-55 Diameter at rim 25-30 Lateral nematotheca:

Length 55-70 Diameter at rim 40-45 Mesial supracalycine nematotheca:

Length 55-60 Diameter at rim 20-30 Gonotheca:

Length 390-400 Maximum diameter 180-210 Gonothecal nematotheca:

Length 60-70 Diameter at rim 30

Two mesial inferior nematothecae have been observed, but the basal one with identical structure as supracalycine nematothecae.

Material from MUSORSTOM 3, stn DR 117 shows a weakly developed oblique node separating the ahydrothecate basal part from the distal part of the colony. A strongly oblique node has been observed in the material from CORINDON 2, stn 210 and also in the syntypes of Halopteris concava (MNHN) .

The material from stn 210 usually has two supracalycine nematothecae and sometimes three.

REMARKS

The material agrees with the original description given by Billard (1911); it needs no further comments.

Figures

FIG. 7. — Halopteris concava (Billard,1911),MUSORSTOM 3,stn DR 117:A, internodes of stem and branching,frontal view;B, internode from apical part of hydrocladium, lateral view; C, internode, frontal view; D, internodes from basal part of hydrocladium, lateral view; E, several internodes from hydrocladium, lateral view; F, gonotheca, posterior view. Scale bars: A-D, F, 0.1 mm; E, 0.2 mm.