Thyroscyphus longicaulis Splettstösser, 1929

Galea, Horia R., 2013, New additions to the shallow-water hydroids (Cnidaria: Hydrozoa) of the French Lesser Antilles: Martinique, Zootaxa 3686 (1), pp. 1-50 : 25

Thyroscyphus longicaulis Splettstösser, 1929

( Fig. 6 Q–T)

Thyroscyphus longicaulis Splettstösser, 1929: 49 , figs. 43–45.― Vervoort, 1968: 35, fig. 16.

Material examined. Stn. 3, 19.ii.2012, 10– 15 m, M229: a 2.3 cm high fragment bearing five female gonothecae with acrocysts (MHNG-INVE-83067). Stn. 7, 23.i.2012, 6 m, M022: several stems 0.8–4 cm high, of which one bears a male gonotheca (MHNG-INVE-82944). Stn. 8, 31.i.2012, 12– 15 m, M107: a 2.1 cm high colony with 3 female gonothecae bearing acrocysts (MHNG-INVE-82972). Stn. 9, 16.ii.2012, 5– 15 m, M204: several stems and fragments up to 2.5 cm high, some bearing male gonothecae (MHNG-INVE-82947). Stn. 11, 03.ii.2012, 9– 15 m, M135: numerous sterile stems up to 7.5 cm high (MHNG-INVE-82945). Stn. 15, 11.ii.2012, 10– 15 m, M175: several sterile stems 1–5.2 cm high (MHNG-INVE-82946).

Description. Hydrorhiza creeping on, or partly embedded in, tissues of demosponge, with spongin fibers firmly attached to the hydrorhiza and, occasionally, to the basal parts of cauli. Stems erect, always unbranched, reaching 7.5 cm high, tapering gradually from base to tip; no basal constriction at origin from stolon; slightly geniculate, divided into up to 31 internodes by means of transverse to slightly oblique nodes. Each internode, 1830–3535 µm long, 350–520 µm wide at node, bearing a latero-distal apophysis supporting a hydrotheca; apophyses alternate on stem, rounded-conical in shape, 245–305 µm long. Hydrothecae in plane of stem, directed outwards and upwards, 2195–2490 µm long, tubular, 620–680 µm wide, tapering basally and merging imperceptibly with an indistinct pedicel, convex on adcauline side and more or less straight on abcauline. Margin 575–620 µm wide, provided with four triangular, sharp cusps separated by deep, rounded embayments. Diaphragm absent; on adcauline side, a blister-like, internal reduplication of the perisarc, leaving an empty cavity between the two layers thus formed. Hydranths with ca. 28 filiform tentacles, all raised at same level. Gonothecae borne on apophyses supporting the hydrothecae; both sexes similar: smooth, cylindrical, tapering basally into indistinct pedicel, truncated distally; female ca. 3020 µm long and 870 µm wide, male ca. 2575 µm long and 810 µm wide. Life specimens with bright orange hydranths and the perisarc slightly horn colored.

Remarks. The attachment of the hydranth to the inner wall of hydrotheca occurs distally to the abcauline reduplication of the perisarc, as illustrated by Splettstösser (1929, Fig. 44). In the absence of a basal diaphragm, the demarcation between the hydrotheca and its pedicel could be not fixed other than arbitrarily, at the level of the perisarcal reduplication, as Splettstösser did. However, since the hydrotheca merges imperceptibly into its pedicel, the length given above was measured from its insertion on apophysis to the tip of one of the lateral cusps.

The gonothecae of this species were unknown to both Splettstösser and Vervoort (1968). Within female ones, a single, large egg matures into a huge, externally held, gelatinous acrocyst.

Geographical distribution. Possibly endemic to the Caribbean, known only from St. Thomas ( Splettstösser 1929, Vervoort 1968) and Martinique (present study).

Figures

FIGURE 6. A, B: Diphasia digitalis (Busk, 1852) ― stem internode in frontal (left) and lateral (right) views (A); optical cross section through internode at level of hydrothecal apertures (B). C – G, J – M: Sertularella calderi sp. nov. ― fragments of stem (C, D); hydrothecae (E) and aperture viewed from above (F); comparison of the hydrotheca (G) with those of S. fraseri Galea, 2010 a (H) and S. peculiaris Leloup, 1974 (I); male (J) and female (K) gonothecae; apertures of male (L) and female (M) gonothecae viewed laterally (below) and apically (above). N – P: Sertularelloides cylindritheca (Allman, 1888) ― internodes (N); lateral view of hydrotheca (O) with thickened internal ring of perisarc at base of apophysis (right), and frontal view of the latter (left); apical view of hydrotheca (P). Q – T: Thyroscyphus longicaulis Splettstösser, 1929 ― fragment of stem (Q); internode and hydrotheca (R); aperture (S); male (left) and female (right) gonothecae (T). U – Z: Hincksella formosa (Fewkes, 1881) ― hydrotheca (U); gonotheca seen laterally (V), and in optical cross section (X); aperture (Y). Scale bars: 10 µm (Z), 200 µm (F, L, M), 300 µm (P), 500 µm (A, B, E, G – I, O, S, U, Y), 1 mm (C, D, J, K, N, R, T, V, X), 4 mm (Q).