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Abstract
A new hydrozoan, Sarsia bella sp. nov. is described in both its hydroid and medusa stage from north of Puget Sound, Washington in the San Juan Islands, USA and off the southernmost tip of Vancouver Island, Canada. The medusa is distinguished from other Sarsia species by 16 exumbrellar nematocyst patches and in being more transparent or glass like when living than any other known species of the genus. The exumbrellar nematocyst patches become indistinct in mature specimens and in those crowded in culture, with single nematocysts increasingly spaced out. The hydroid, both field-collected and raised in culture from its medusa, forms small, upright stolonal colonies not more than 1.5 mm high. The hydranths bear an oral whorl of four to five capitate tentacles, and immediately below a second whorl of slightly shorter capitate tentacles. In thriving colonies there is occasionally a whorl of small filiform tentacles on the lower part of the hydranth. Medusa buds develop in the middle of hydranth below the capitate tentacles and above the reduced filiform tentacles, if present. Young medusae are liberated with the typical 16 exumbrellar nematocyst patches. The hydroid of this species was originally mistaken for the hydroid of Polyorchis penicillatus . Brinckmann-Voss (1977) reported a small corynid hydroid living on the margin of rock scallop shells. Medusae liberated from this hydroid were at that time believed to be those of Polyorchis penicillatus (Eschscholtz) present in the plankton. Immature medusae of these two species appear strikingly similar, especially with regard to their exumbrellar nematocyst patches, four tentacles and abaxial ocelli. Since then however, this connection has been proven wrong, because an identical hydroid was raised from the medusae of the new species Sarsia bella . Second generation medusae raised in the laboratory were carefully compared with medusae liberated from field collected hydroids (thought to have been Polyorchis penicillatus ), and these were found to be identical with meduse of Sarsia bella. Young medusae of P. penicillatus from the plankton can be clearly distinguished from S. bella medusae by the number of their exumbrellar nematocyst patches. Both P. penicillatus and Sarsia bella have eight adradial rows of exumbrellar nematocyst patches when young, however each row in P. penicillatus consists of at least three vertically alligned patches whereas each row never has more than two patches in S. bella . In both species the patches consist of microbasic p-mastigophores, but capsules in the case of P. penicillatus are larger than those in S. bella . Later stages of the two species are easily distinguished using other morphological characters with only four tentacles in S. bella and more than four in P. penicillatus . No hydroid of the genus Polyorchis has been described to date.
Highlights
The taxonomy of the genus Sarsia, especially from the North East Pacific, has been problematic for a long time (Arai and Brinckmann-Voss, 1980; Mills, 1982; Brinckmann-Voss, 1985)
FIG. 6. – Sarsia bella; a. enlargement of box insert from Figure 5: magnified: part of bell of young medusa with group of microbasic p mastigophores photographed at kink of exumbrella, unexploded ; b
In contrast to this new species, the planulae of Sarsia apicula develop into primary hydranths after only 48 hours
Summary
The taxonomy of the genus Sarsia, especially from the North East Pacific, has been problematic for a long. Time (Arai and Brinckmann-Voss, 1980; Mills, 1982; Brinckmann-Voss, 1985) Those species of Sarsia having medusae with a long manubrium, treated by Miller (1982) as belonging to the “tubulosa complex” will be considered here. One of Miller’s morphotypes, designated by him as the “L” type on account of the large eggs in the females, proved to be a separate, yet undescribed, species. Based on both young and adult specimens, or its hydroid raised from the medusa in the laboratory, and on observation of field-collected hydroid material, this species is described here as Sarsia bella sp. Sarsia viridis is very rare and more information, especially about the hydroid, is needed
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