Halopteris tenella ( Verrill, 1874 )

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 : 32-34

Halopteris tenella ( Verrill, 1874)

( Fig. 8A–H )

Plumularia tenella Verrill, 1874: 731 .

Schizotricha tenella ― Nutting, 1900: 80, pl. 4 figs 4, 5; 1901: 365, fig. 70.― Fraser, 1912: 383, fig. 52.― Calder, 1971, 73, pl. 5F–G; 1983: 18, fig. 10.

Halopteris tenella ― Schuchert, 1997: 52, fig. 16.

Halopteris diaphana ― Galea, 2008: 42 , fig. 8E.― Calder, 2013: 43, fig. 13B–D [not H. diaphana (Heller, 1868) ].

Halopteris constricta ― Migotto, 1996: 44, fig. 9A–C (not H. constricta Totton, 1930 ).

Material examined. Stn. 6, 28.i.2012, 4– 10 m, M100: female colonies on Halimeda sp. (MHNG-INVE-82933); 14.ii.2012, 10– 17 m, M192: male colonies on seaweed (MHNG-INVE-82934); M197: male and female colonies on Halimeda sp. (MHNG-INVE-82935).

Remarks. The present material fits the descriptions of this species given by Verrill (1874), Nutting (1900), Fraser (1912) and Calder (1983), except for the cladia, which are always unbranched9, and the presence of Antennella -like stems, as illustrated in sample M192. As a typical feature of this species, the stems10, as well as the cladia, are divided into three types of internodes: hydrothecate, long ahydrothecate, and short ahydrothecate.

The hydrothecate internodes of the stem are rather short and bear a hydrotheca in middle, an apophysis lateral to it, as well as 3 to 5 nematothecae: a mesial one and a pair of laterals, as well as commonly one ( Fig. 8D 1 , 3 ), rarely two ( Fig. 8D 2), nematothecae distal to hydrotheca. These could be absent in half of the cases in the material examined ( Fig. 8D 4 , 5). The cladial hydrothecate internodes recall those of the stem, but are always devoid of the nematothecae distal to hydrotheca ( Fig. 8A–C ).

The ahydrothecate internodes of the stem bear commonly 2 nematothecae, but 3 may also occur, and even 4 in rare instances ( Fig. 8F ). The first cladial ahydrothecate internode is very long, and bears 2 or 3 nematothecae, while 1 or 2 of these are indifferently found on the second internode, whereas the third and fourth (when present) internodes carry generally 1, rarely 2, nematothecae.

The short ahydrothecate internodes are situated distal to the hydrothecate internodes and make the junction between these and the long ahydrothecate internodes. They are provided with transverse nodes at both ends and are devoid of nematothecae. These internodes could be absent in some parts of the stem ( Fig. 8D 1 , 2, 5) and/or cladia ( Fig. 8B ).

The female gonothecae ( Fig. 8H ) are cornucopia-shaped, have 3 basal nematothecae11, a terminal aperture with thickened perisarc below the rim, and a watch glass shaped lid. The male gonothecae ( Fig. 8G ) are bottle-shaped and are provided with only 2 basal nematothecae. The gonothecae of both sexes are borne on a pedicel composed of a couple of short, rectangular segments12.

There is a peculiar situation occurring in H. tenella regarding its mesial nematothecae, which are morphologically indistinguishable from the others occurring within the cormoid. They have a very tall basal chamber and, unlike the other species of Halopteris , are entirely movable13. In addition, the pair of lateral nematothecae flanking the hydrothecae is sessile, as no apophyses supporting them are present.

The material assigned to H. constricta Totton, 1930 by Migotto (1996) may belong to the present species, for the following reasons: 1) the hydrothecate internodes of the stem are "followed by 2 athecate internodes, the first short, without nematotheca and the second long, with 1–4 frontal nematothecae (usually 3 in basal internodes and 1–2 in distal ones)"; 2) the hydrocladia are composed of "1–2 short basal, athecate internodes (short intersegments) without nematothecae, followed by 1 long athecate internode (long intersegments) usually with 2 nematothecae (rarely 1), and 1 thecate internode similar to those of the stem. Next internodes with pattern of the main stem, but long intersegments usually with only a single namtotheca; division into short and long intersegments not always distinct"; 3) the mesial nematothecae have a tall, well-developed basal chamber ( Migotto 1996, Fig. 9B); 4) the gonothecae in the Brazilian material are undoubtedly male ( Migotto 1996, Fig. 9B) and represent the first finding of these structures in H. tenella .

The rather scarce and sterile material from Guadeloupe identified earlier by myself ( Galea 2008) as H. diaphana (Heller, 1868) was reexamined, and the presence of extra nematothecae above the stem hydrothecae could be confirmed, as well as the characteristic trumpet-shaped, movable mesial nematotheca. In addition, the material assigned to Heller's species by Calder (2013) is included here in the synonymy of H. tenella , mainly on account of the typical segmentation of both cauli and cladia, and its occurrence outside the Mediterranean basin.

As to the cnidome, the large capsules occurring in this species were variably described as either pseudostenoteles ( Migotto 1996) or microbasic euryteles ( Schuchert 1997). Discharged capsules occur quite frequently in the present material, and their shaft is provided basally with strong, conspicuous spines, which suggest that they are undoubtedly pseudostenoteles.

Geographical distribution. Massachusetts to the Caribbean Sea ( Calder 1983), Brazil ( Migotto 1996, as H. constricta Totton, 1930 ; Calder & Maÿal 1998), and from southern California to Panama ( Calder 1983).

Figures

FIGURE 1. Map of Martinique [modified after Battistini (1978)] showing the location of hydroid sampling stations.

FIGURE 8. A – H: Halopteris tenella (Verrill, 1874) ― stem internodes and cladia (A – C); hydrothecate internodes of the stem (D); hydrotheca (E); stem ahydrothecate segments showing varied number of nematothecae (F); male (G) and female (H) gonothecae. I – N: Aglaophenia postdentata Billard, 1913 ― stem internodes in specimens from Martinique (I) and Guadeloupe (J); cormidia in specimens from Martinique (K) and Guadeloupe (L); corbula (M); internode of corbulacosta showing the shape of the nematothecae (N). Scale bars: 100 µm (N), 200 µm (I – L), 300 µm (D – H), 500 µm (A – C, M).

FIGURE 3. A, B: Clytia hemisphaerica (Linnaeus, 1767) ― hydro- (A) and gonotheca (B). C, D: Clytia noliformis (McCrady, 1859) ― hydro- (C) and gonotheca (D). E:? Gastroblasta sp. ― hydrotheca. F, G: Orthopyxis sargassicola (Nutting, 1915) ― hydro- (F) and gonotheca (G). H, I: Egmundella humilis Fraser, 1936 ― hydro- and nematothecae from samples M 231 (H) and M 007 (I). J – P: Relative sizes of the hydrothecae of the hebellids discussed in the text. J, Q, R: Anthohebella communis (Calder, 1991) ― hydrothecae (J, Q) and gonotheca with medusoid gonophore (R). K, S, T: Hebella dyssymetra Billard, 1933 ― hydrothecae. L, U – Y: Hebella scandens (Bale, 1888) ― hydrothecae (L, U); gonotheca seen laterally (V) and apically (X), showing the four-flapped operculum; gonophore (Y). M, Z: Hebella sp. 1 ― hydrotheca. N: Hebella sp. 2 ― hydrotheca. O: Hebella sp. 3 ― hydrotheca. P: Hebella sp. 4 ― hydrotheca. Scale bars: 200 µm (H, I, Z), 300 µm (A – E, S, T), 500 µm (Q, R, U – Y), 1 mm (F, G, J – P).

FIGURE 4. A: Hebella sp. 2 ― hydrothecae. B: Hebella sp. 3 ― hydrothecae. C: Hebella sp. 4 ― hydrothecae. D – J: Comparison of the cnidomes of Anthohebella communis (Calder, 1991) (D), Hebella dyssymetra Billard, 1933 (E), Hebella scandens (Bale, 1888) (F), Hebella sp. 1 (G), Hebella sp. 2 (H), Hebella sp. 3 (I), Hebella sp. 4 (J). K – Q: Halecium dichotomum Allman, 1888 ― various stems (K); male (L, M) and female (N, P) gonothecae; aperture of a female gonotheca in frontal view, showing twin hydrotheca (O); cnidome (Q). Scale bars: 10 µm (D – J, Q), 300 µm (K – P), 500 µm (C), 1 mm (A, B).