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Lafoeina amirantensis (Millard & Bouillon, 1973) (Figs. 1–3; Tables 1–3) Egmundella amirantensis Millard & Bouillon, 1973: 40; Millard, 1975: 133; Gibbons & Ryland, 1989: 389 –390; Ramil & Vervoort, 1992: 22 –24. Lafoeina amirantensis: Calder 1991 a: 10; Calder 1991 b: 2068; Calder 1991 c: 223; Nogueira et al., 1997: 368; Calder & Maÿal, 1998: 73; Calder, 1998: 1852; Calder & Vervoort, 1998: 15; Watson, 2000: 5; Calder et al., 2003: 1180. Holotype: Musée Royal de l’Afrique Centrale– MRAC 2665, Egmundella amirantensis Millard & Bouillon, 1973, colony on Dynamena disticha (Bosc), Amirante, Seychelles. Material examined. MZUSP 1409, 23º 49.69 ’S 045º 24.76 ’W, Farol dos Moleques, São Sebastião, Brazil, 3–5m, colony on calcareous algae, 18 February 2001; MZUSP 1410, same data as MZUSP 1409, two 1 dayold medusae, 22 February 2001; MZUSP 1411, same data as MZUSP 1409, five 1 dayold medusae, 22 February 2001; MZUSP 1412, 23º 46 ’S 045º 40 ’W, Praia da Baleia, São Sebastião, Brazil, colony on calcareous algae and Sargassum sp., 1m, 16 July 2001; Praia de Barequeçaba, São Sebastião, Brazil, colony on calcareous algae, 4 February 2002. Description of polyp stage. Colonies with stolonal growth; perisarc smooth throughout, without annuli (Fig. 1). Hydrothecae and nematophores widely separated from each other, both arising directly from a branching and anastomosing hydrorhiza. Hydrorhiza 16–40 µm in diameter, without internal septa. Hydrotheca 110–250 µm high, 54–110 wide, thinwalled, smooth, tubular, without pedicel, constricted basally and slightly enlarged near base of operculum (Fig. 1 D, E). Operculum thinwalled, not delimited from hydrotheca by a crease line; not segmented, a continuation of the hydrothecal wall which folds upon itself forming 10–14 pleats, becoming conical when hydranth retracts within hydrotheca (Fig. 1 E–G). No visible difference between operculum and hydrotheca wall when hydranth extended. Hydranth extensile, 2.0–4.0 times higher than hydrotheca when fully extended, with 9–14 slender tentacles, no intertentacular web. Basitrichous isorhiza (Fig. 2 C) capsules arranged in circular bands evenly spaced along the length of the tentacle; atrichous isorhiza (Fig. 2 B) on body and tentacles. Tentacles amphicoronate, those of upper whorl 180–380 µm in length, held at 45–60 º angles, longer than those of lower whorl (110–220 µm) which are held horizontally or slightly downward (Fig. 1 A). Hypostome conical. Nematotheca (Fig. 1 B) 30–63 µm high, 15–32 µm in diameter, clubshaped, with a bundle of large, elongated microbasic mastigophore nematocysts (Fig. 2 F) inside. Hydranth column with basitrichous isorhiza, atrichous isorhiza, and scarce microbasic mastigophores identical with the ones present on nematophores. Gonothecae similar to hydrothecae. Character variation of polyp stage is presented in Table 1. Nematocyst size and distribution are shown in Table 2. mean ± SD (range) (n) Hydrotheca Height from base to tip of operculum (m) 188.5 33.9 (110–250) (38) Height from base to margin (m) 148.5 34.5 (90–235) (33) Maximum diameter (m) 72.0 11.4 (54–110) (45) Diameter at diaphragm (m) 41.9 8.5 (23–60) (27) Hydranth Height from diaphragm to tip of hypostome (m) 550.6 115.3 (415–740) (10) Diameter of column (m) 36.0 5.4 (30–50) (14) Diameter at tentacular ring (m) 58.3 15.6 (42–100) (11) Diameter at diaphragm (m) 32.7 11.0 (20–40) (3) Height of hypostome 22.7 1.5 (20–24) (6) Number of tentacles 11 1 (9–14) (21) Length of upward tentacles (m) 259.2 56.9 (180–380) (20) Length of downward tentacles (m) 158.5 33.8 (110–220) (20) Diameter of tentacles (m) 16.2 11.5 (10–50) (13) Nematotheca Height (m) 44.0 7.8 (30–63) (25) Diameter (m) 18.8 3.7 (15–32) (25) Diameter of hydrorhiza (m) 28.5 8.0 (16–40) (27) Description of Medusa. Medusa released in immature condition, transparent, hemispherical, about 0.2–0.4 mm high, slightly wider than high (Fig. 3 A). Mesoglea thin, without apical process and apical canal; exumbrella with scattered nematocysts (microbasic mastigophores, Fig. 2 A). Radial canals four, simple and straight; circular canal narrow. Velum broad, aperture circular. Two opposed perradial marginal bulbs, pyriform or triangular, brownpigmented, with tentacles (Fig. 3 B). Other perradial bulbs inconspicuous or absent, a few nematocysts marking the site of the future tentacular bulb. Tentacles hollow, filiform, tapering gradually, with two types of nematocysts: basitrichous isorhiza (Fig. 2 D) and atrichous isorhiza (Fig. 2 F). Tentacle tip without terminal swelling. Four interradial statocysts, each with a single statolith (Fig. 3 B–D). With one or two marginal cirri on the sides of each statocyst (Fig. 3 B–D). Cirrus solid, with scattered nematocysts. Lateral cirri absent. Manubrium tubular, short, cruciform in crosssection. Mouth simple, with four oral lips. Stomach broad, quadrate; peduncle lacking (Fig. 3 E). Four incipient gonads on the proximal portion of the radial canals, near stomach. Medusae grew relatively fast; some individuals (Fig. 3 F–G.) had doubled their size after one day. Noteworthy was the development of the other pair of opposed perradial tentacles, which at this stage were shorter and with smaller bulbs than the former two (Fig. 3 F). Tentacles reached 12 mm when fully extended and cirri about 0.4 mm. The number of cirri remained variable, increasing in number (4–8). Exumbellar nematocysts were still present but fewer than in the newly liberated medusae. The gonads remained underdeveloped, but were more visible. The medusae did not accept the copepods and Artemia nauplii offered and died a few days later; during this time no significant morphological changes were seen. Measurements of many young medusae are in Table 3. Nematocysts size and distribution are presented on Table 2. Remarks. SEM images (Fig. 1 E) revealed that the hydrothecal wall has shallow, longitudinal depressions extending from the base of operculum downward to approximately the middle of the hydrotheca. These features are, however, not seen under low or high power light microscopy. Medusae were liberated two and three days after their parent colonies were collected, respectively, at Farol dos Moleques in 18 February 2001 and Praia de Barequeçaba on 4 February 2002. On both occasions gonothecae were noticed only when empty, probably because they resemble hydrothecae in shape and size (as documented in the description and figures of Millard and Bouillon 1973). Care was taken to ensure that other species of hydroids were not present in the culture bowls. After the pieces of colonies were tied on glass slides, the hydrorhiza grew along the glass substratum; a few days later ramifying sparingly and giving rise to new hydranths at regular intervals of about 1–2 mm. Nematophores were scarce or even absent on some sections of the hydrorhiza and often they were covered by debris or unicellular algae. In one of the cultures, the terminal regions of the hydrorhizae gave rise to free planuloids or frustules (Fig. 1 C). These planulalike bodies were flattened, 400–800 µm long, 50–75 µm wide, and had the same nematocyst types as polyps (microbasic mastigophores, basitrichous isorhizas, and atrichous isorhizas). Planuloids lacked external cilia and crept over the glass surface by means of peristaltic waves. Three to four days after release, some planuloids stopped moving, settled onto their sides, and secreted a perisarc. Within about 12 h, primary hydranths with 8–10 tentacles were formed. Additional hydranths (up to three were observed) appeared singly from unbranched hydrorhiza. Nematophores did not develop. The process of formation of planuloids in L. amirantensis is similar to the ones reported for, e.g., Coryne, by Berrill 1953, and Obelia, by Allman 1871, and is usually elicited as a response to rapid changes in temperature (Berrill 1953, Panteleeva 1999). Although with limited means of locomotion which results in settlement near the parent colony, the planuloids increase the possibilities of dispersal of the species. |
