Monostaechas sp.

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 : 54-56

Monostaechas sp.

( Fig. 10 ; Table 10)

MATERIAL EXAMINED. — Norfolk Ridge. SMIB 4, stn DW 55, 23°21.4’- 23°21.4’S, 168°04.5’- 168°04.8’E, 215-260 m, 9.III.1989, 2 colonies on sponge and 3 fragments, no gonothecae ( MNHN).

SMIB 5 stn DW 101, 23°21.2’S, 168°04.9’E, 270 m, 14.IX.1989, several fragments without gonothecae ( MNHN).

DISTRIBUTION. — The colonies were collected at the Norfolk Ridge, between 215 and 270 m depth.

DESCRIPTION (COLONIES FROM SMIB 4,

STN DW 55)

Hydrorhiza tubular, growing on sponge; hydrocaulus monosiphonic and sympodially branched.

Basal part of colony composed of several internodes separated by transverse nodes and without nematothecae; last internode with a variable number of nematothecae.

Each hydrocladium with one long, basal, ahydrothecate internode, with basal transverse and distal

A oblique node and three to five nematothecae. Rest of hydrocladium composed of a succession of hydrothecate and athecate internodes. Thecate internodes with basal oblique node and distal transverse node; athecate internodes reverse. Each thecate internode with one hydrotheca and four nematothecae: one

SMIB 4 stn DW 55

Height of colony (in mm) 19

Axial segments:

Length 650-830

Diameter at node 120-190

Hydrocladial internode:

Length ahydrothecate 270-350

Length hydrothecate 380-490

Diameter at node 50-100

Hydrotheca:

Length abcauline wall 160-220

Length free portion adcauline wall 110-140

Diameter at rim 210-230

Mesial infracalycine nematotheca:

Length 80

Diameter at rim 40-50

Lateral nematotheca:

Length 120-160

Diameter at rim 45-50

Nematotheca of ahydrothecate internode:

Length 80-90

Diameter at rim 30-35

mesial inferior, two laterals and one axillar behind adcauline hydrothecal wall.

Hydrotheca cup-shaped with abcauline wall slightly convex; adcauline wall adnate for half its length and free part slightly concave; hydrothecal rim circular and flat. Mesial nematotheca not reaching hydrothecal base; adcauline wall of upper chamber deeply scooped or absent. Lateral nematothecae conical, placed on well-developed apophyses on both sides of hydrotheca, surpassing the hydrothecal rim. One axillar nematotheca behind free part adcauline wall of hydrotheca, slightly displaced towards left or right side and sometimes placed in the middle.

Athecate internodes with one frontal nematotheca, resembling mesial inferior nematotheca but with the distal chamber better developed. All nematothecae bithalamic and movable.

Gonosome absent.

VARIABILITY

New secondary hydrocladia with identical structure develop on the first athecate internode, arising from a short apophyses placed on the opposite side of a normal hydrocladium.

The material from SMIB 4, stn DW 55 occasionally has two axillar nematothecae.

REMARKS

This material comes close to Monostaechas quadridens , but shows some differences. The colonies are characterized by the small size of the hydrothecae, the length of lateral nematothecae surpassing the hydrothecal rim and, as the most relevant feature, the shape of lateral nematothecae, that are conical. For these reasons, and because of the sterile condition of this material, it was not included into M. quadridens .

Figures

FIG. 10. — Monostaechas sp., SMIB 4, stn DW 55: A, internodes, lateral view; B, internode, frontal view; C, D, internodes from same hydrocladium with differently developed lateral nematothecae, frontal views. Scale bar: 0.1 mm.