Halopteris vervoorti

Description. Colonies forming up to 2 cm high plumes with straight, monosiphonic, unbranched stems. Coenosarc brownish in living material. Basal part of stem, varied in length, composed of 2 – 7 ahydrothecate segments separated by transverse nodes, last node oblique; segments bearing a variable number of frontal nematothecae (up to 18) in apparently two parallel, closely-set rows; nematothecae placed rather alternately. Remainder of stem homomerously divided by means of oblique nodes; transverse nodes present only distally. Segments with one hydrotheca, a latero-distal apophysis, and up to 8 nematothecae: 1 median inferior, 2 laterals, 2 axillar (always present), and generally 1 (rarely 2, exceptionally 3) above hydrotheca. Median superior nematotheca (e) placed on intersegments or their equivalents. Cladia alternate, except for the two (rarely four) basalmost, which are often opposite; up to 20 per cormoid. Cladium inserted on stem apophysis by means of short quadrangular segment; both devoid of nematothecae. Next segment long, with proximal node transverse and distal node oblique; one nematotheca on upper side. Remainder of cladium heteromerously segmented; oblique nodes always well marked, transverse ones less obvious to nearly invisible. Hydrothecate segments with proximal node oblique and distal node transverse; up to 5 per cladium. Ahydrothecate segments, of variable length, with proximal node transverse and distal node oblique; with invariably one nematotheca on upper side. Hydrothecate segments with one hydrotheca and up to 5 nematothecae. Hydrotheca cup-shaped, placed in middle of segment, walls parallel to slightly divergent in lateral view; rim slightly scooped in lateral view. Free adcauline wall straight, largely surpassing distal end of segment; abcauline wall nearly straight, flaring slightly distally. Nematothecae: one median inferior, 2 laterals, and 1 (rarely 2) axillar. All cauline and cladial nematothecae bithalamic and movable, except the median inferior one which is fixed. Lateral nematothecae borne on rather long apophyses and nearly reaching hydrothecal rim; invertedconical, with long basal chamber, and much shorter upper chamber; walls straight and divergent; rim with variable emargination on side facing the hydrothecal wall (fig. 9 D). Cladial axillar nematotheca with basal chamber slighty higher than upper one; walls slightly divergent, margin lowered on adaxial side. Pairs of axillar nematothecae on either cladia or stem with apertures directed sideways. Median inferior nematotheca wide, with diminuitive basal chamber and apical chamber deeply scooped on adaxial side. Ahydrothecate segments with nematotheca (e) resembling median inferior ones, but with much higher basal chamber. Gonothecae arising singly below stem hydrothecae by means of short pedicel; a quadrangular segment between gonotheca and pedicel. Gonotheca (presumably female) rounded-ovoid, slightly tapering towards base, with rounded apex. Basal part curved at 90 ° and provided with two long, bithalamic nematothecae; apical chamber much shorter than basal one. Nematocysts: large microbasic mastigophores (15.3 – 17.0) × (5.8 – 6.7) µm (undischarged), (15.8 – 16.1) × (5.6 – 6.0) µm (discharged), with shaft (15.8 – 16.1) × (1.3 – 1.5) µm; small microbasic mastigophores (5.3 – 5.5) × (1.5 – 1.7) µm (undischarged).

Halopteris polymorpha — Ansín Agís et al., 2001: 167, fig. 70.

Remarks. Among 150 cauline segments from 10 cormoids examined, 138 bore one median superior nematotheca (77 %), 40 bore two nematothecae (22 %), and 2 bore three nematothecae (1 %). Although 2 or 3 nematothecae occurred generally on the basalmost segments of caulus, 2 nematothecae were also variably observed on more distal segments. They were placed either on the same axis as that of caulus, or alternately on both sides of it. Among 150 cladial hydrothecate segments examined from the same 10 cormoids, 141 bore one axillar nematotheca (94 %), and 9 bore a pair of axillar nematothecae (6 %). The present material is identical in nearly every respect to that described and figured by Ansín Agís et al. (2001) as H. polymorpha (Billard, 1913), and both are thought to be conspecific. Their material was sterile and partly matched with both Billard’s species and H. liechtensternii (Marktanner-Turneretscher, 1890). The main difference with the former was the presence of one cladial axillar nematotheca, and with the latter the presence of a pair of cauline axillar nematothecae. The main difference between H. vervoorti and H. liechtensternii lies is the presence of one cladial axillar nematotheca instead of two, and between H. vervoorti and H. polymorpha in the presence of a pair of cauline axillar nematothecae instead of a single one. The above-mentioned features and the discovery of fertile specimens of H. vervoorti in the present collection allow a separation of the three species. Some of the useful distingushing characters are listed in table 15.

Distribution. Cape Verde (Ansín Agís et al. 2001), Guadeloupe and Les Saintes (present study). Probably occurs also in the Mediterranean, as illustrated by the sample MHNG INVE 30117 from Banyuls-sur-Mer, France (P. Schuchert, personal communication).

Etymology. This species honors Dr. Willem Vervoort for his remarkable contribution to the hydrozoan taxonomy.

Type material. Stn. 3: 22.01.2008 — on rocks, numerous plumes, all sterile but one, on rock (MHNG INVE 60985). Additional material examined. Stn. 2: 01.04.2008 — numerous stems, all but one sterile, 1.4 – 1.7 cm high, on rock and green algae. Stn. 3: 01.04.2008 — several sterile stems ca. 1 cm high, on hard substrate. Stn. 7: 25.03.2008 — numerous sterile stems, 8 – 9 mm high, on various algae and concretions; 27.03.2008 — several colonies, 1.4 – 2.0 cm high, with rare, immature gonothecae; on various algae, concretions, sponge, and ascidian. Type locality. Petite Anse, Basse-Terre, Guadeloupe.