Hydractinia tenuis ( Browne, 1902 )

Galea, Horia R., 2007, Hydroids and hydromedusae (Cnidaria: Hydrozoa) from the fjords region of southern Chile, Zootaxa 1597 (1), pp. 1-116 : 25

Hydractinia tenuis ( Browne, 1902)

(fig. 6L, pl. 1H)

Dysmorphosa tenuis Browne, 1902: 277 .

Podocoryne tenuis: Mayer, 1910: 141 ; Kramp, 1959: 102, fig. 70; 1961: 70.

Material examined. Plankton — off the Huinay Scientific Field Station , 08, 09, 11, 12, 13, 18, 19.ii.2006, 50–0 m, several medusae ( MHNG INVE 49730 ) .

Type locality. Stanley Harbor , Falkland Islands .

Description. Umbrella ca 600 µm high and 580 µm wide; mesoglea thick on apical part, thin elsewhere. Bell margin with 5–8 solid tentacles (generally 8) borne on conical marginal bulbs, light brown in color; no ocelli. Manubrium quadrate in cross-section, mounted on peduncle of nearly same length. Mouth with four short lips ending in four clusters of nematocysts; lips not prolonged as mouth-arms. Several medusa buds often present on manubrium; buds with 8 well-developed tentacles. No gonads have been seen. Cnidome: microbasic euryteles and desmonemes on tentacles.

Remarks. A slight apical constriction above the level of peduncle base has been reported by Mayer (1910) and Kramp (1959). In the present material, such a constriction is only visible in some contracted postures of the medusa, but not in relaxed specimens (observations on living animals). The polyp stage of H. tenuis is unknown, but Hartlaub (1905) thought that H. humilis ( Hartlaub, 1905) could be its hydroid; however, this hypothesis needs to be proved. Medusae of H. tenuis were abundant in the plankton of fjord Comau during January and February.

World distribution. Falkland Islands ( Kramp 1959).

Records from Chile. Medusae herein were collected from fjord Comau. This is the first record of the species for Chile.