Antennella peculiaris, Galea, Horia R., 2013

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 : 26-29

Antennella peculiaris sp. nov.

(Plate 2A–F; Fig. 7A–D; Table 4 )

Material examined. Stn. 6, 28.i.2012, 4– 10 m, M092: fertile (female) colony on Halimeda sp. (MHNG-INVE- 82925); M099: fertile (female) colony on Halimeda sp. (MHNG-INVE-82926); 14.ii.2012, 10– 17 m, M197: fertile (female) colonies on Halimeda sp. (syntype: MHNG-INVE-82927). Additional material for comparison: Stn. 13, 29.i.2012, 6– 10 m, M118: fertile (female) colony of Antennella secundaria (Gmelin, 1791) , on Sargassum sp. (MHNG-INVE-82928). Mediterranean, France, La Ciotat, 05.viii.2009, 0.5 m, HRG-0124: fertile (female) colony of A. secundaria , on seaweed; Le Pradon, 27.viii.2008, 1 m, HRG-0153: sterile colony of A. secundaria , on seaweed.

Description. Stems up to 8 mm high arising from creeping, branching hydrorhiza. Stems with basal part of varied length, devoid of hydrothecae, carrying only nematothecae (up to 6) in two closely set, parallel rows; a basal constriction, just above origin from stolon, and 1–2 occasional transverse nodes above this; last node oblique. Stem heteromerously divided into hydrothecate and ahydrothecate internodes. Hydrothecate segments with proximal oblique node and distal transverse node, just as long as to accommodate a hydrotheca and its associated nematothecae: one mesial, a pair of laterals (not reaching the hydrothecal rim), as well as an axillar one, this occasionally missing. Ahydrothecate internodes with distal oblique node distally and transverse node proximally; there is characteristically a second, incomplete (not reaching the posterior side of stem) transverse node towards the proximal end of these internodes, delimiting a short, rectangular segment; whole ahydrothecate internodes comparatively longer than they hydrothecate counterparts, and carrying two distant nematothecae on their longest parts. All nematothecae bithalamic, wall of upper chamber lowered on adaxial side, except in lateral nematothecae, where there is a central, rounded lobe. Gonotheca (only female observed), arising singly or in pairs from below the hydrothecae through a pedicel composed of two short, rectangular pieces; shape typical of the genus, with two basal nematothecae; walls thin, except around aperture where the perisarc is conspiculously thickened; a watch glass shaped operculum. Gonophore of unidentified type: a darker, ovoid, central mass is envelopped in a coat of jelly, the latter being protected by the ectoderm of the blastostyle (Plate 2A–D). Cnidome: 1) small, rounded heteronemes, rare in the coenosarc and the gonophore; 2) small, banana shaped microbasic mastigophores, abundant in the tentacles and the coenosarc; 3) large, elongated microbasic mastigophores, in the nematophores, also common in the coenosarc; 4) fusiform microbasic heteronemes, occurring exclusively in the gonophore.

Remarks. The stems of A. peculiaris sp. nov. are indistinguishable macroscopically from those of the sympatric A. secundaria (Gmelin, 1791) , except for their more pigmented coenosarc (pale brown vs. transparent), and their preferential occurrence on Halimeda sp. rather than on Sargassum sp.

On one hand, the identification of Caribbean A. secundaria was made upon comparison with fertile, Mediterranean specimens from two localities from the south of France. Only differences related to the length of the internodes (compare Fig. 7E and H), so variable in this species (see Schuchert 1997), could be noted. However, the general structure of their tropho- and gonosomes (Fig. 7F and I), as well as their cnidome composition (Fig. 7G and J), leave little doubt about their conspecificity.

PLATE 2. A–F: Antennella peculiaris sp. nov. ―general view of the gonotheca with its gonophore (A); gonophore, mounted in glycerin, in lateral view (B) and cross section (C); microscopic structure of the gonophore (D); emptied gonotheca after expulsion of its gonophore (E); frontal view of gonotheca showing rounded hole in the ectoderm of blastostyle allowing the exit of the gonophore (F). G–I: Antennella secundaria (Gmelin, 1791) ―gonotheca and gonophore in lateral view (G) and crosssection (H), showing large oocyte enveloped by the ectoderm of the blastostyle, Caribbean material; gonophore of Mediterranean specimen in lateral view (I).

On the other hand, several microscopic differences with taxonomic significance could be noted between A. peculiaris and A. secundaria , as follows: 1) the presence, in the former, of a small, rectangular, intermediate, ahydrothecate and anematothecate internode, situated at the proximal end of the ahydrothecate stem internodes; 2) in A. peculiaris , the distal part of the hydrothecate segments above the theca is very reduced, just as long as to accommodate the insertion of the axillar nematotheca, while in A. secundaria this portion is much longer, and surpasses the level of the rim of hydrotheca; 3) the gonothecae of the new species appear slightly larger and wider compared to those of A. secundaria (compare Fig. 7B and I), and the gonophores they produce seem different, as seen in temporary preparations in glyceryne. While the female gonophore of A. secundaria is represented by a single, large oocyte enveloped by the ectoderm of the blastostyle (Plate 2G–I), that of A. peculiaris is a dark, FIGURE 7. A–D: Antennella peculiaris sp. nov. ―stem fragment in lateral (A1) and frontal (A2) views; female gonotheca (B); nematothecae: lateral and axillar (C1), mesial (C2), and of stem internode (C3); cnidome (D). E–J: Antennella secundaria (Gmelin, 1791) ―stem (E), female gonotheca (F), and cnidome (G) of Mediterranean specimen; stem (H), female gonothecae (I), and cnidome (J) of Caribbean specimen. K–N: Antennella aff. quadriaurita Ritchie, 1909 ―stem fragment in frontal view (K); gonotheca (L); comparison of lateral nematothecae and cnidomes between specimens from Martinique (M1 and N1, respectively) and Tristan da Cunha (M2 and N2, respectively). O –S: Antennella similis sp. nov. ―stem fragment in lateral ( O 1) and frontal ( O 2) views; female (P) and male (Q) gonothecae; nematothecae: of stem internode (R1), mesial (R2), lateral (R3), and axillar (R4); cnidome (S). T–W: Antennella tubitheca sp. nov. ―stem fragment (T); gonotheca (U); nematothecae: lateral and axillar (V1), of stem internodes and mesial (V2); cnidome (W). X–Z: Antennella sp.―stem fragment (X); lateral ( Y 1), mesial ( Y 2) and stem ( Y 3) nematothecae; cnidome (Z). Scale bars: 10 µm (D, G, J, N, S, W, Z), 100 µm (C, M, R, V, Y), 300 µm (A, B, E, F, H, I, K, L, O –Q, T, U, X).

compact, central mass contained in a thick jelly, itself enveloped by the ectoderm of the blastostyle (Plate 2A–C). Its microscopic structure (Plate 2D) could not be properly investigated in the absence of histological sections. No free gonophores have been observed. In numerous empty gonothecae, the ectoderm of the blastostyle retains the imprint of the expelled gonophore (Plate 2E), and shows apically a hole allowing the dispersive stage to become free (Plate 2F); 4) the large microbasic mastigophores of A. peculiaris differ in shape and, to a lesser extent in size, compared to their counterparts of A. secundaria from both Martinique (sample M118) and the Mediterranean (sample HRG-124). While these capsules are rather tubular in A. peculiaris , comparatively more ovoid nematocysts are seen in A. secundaria ; 5) an abundant microbasic heteroneme occurs specifically, and in high numbers, in the gonophore of A. peculiaris , while no nematocysts could be found in any of the available samples of A. secundaria from both the Caribbean and the Mediterranean.

Life cycle experiments on living material, as well as a histological study are necessary to ascertain the exact nature of the gonophore of A. peculiaris .

Etymology. From peculiaris (Latin) , meaning peculiar, with reference to the likely unusual structure of its stem and gonophore.

Geographical distribution. Only known from Martinique.