The hydroid and medusa of Sarsia bella sp . nov . ( Hydrozoa , Anthoathecatae , Corynidae ) , with a correction of the “ life cycle ” of Polyorchis penicillatus ( Eschscholtz ) *

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). Only those species of Sarsia having medusae with a long manubrium, treated by Miller (1982) as belonging to the “tubulosa complex” will be considered here. The medusa stage of this species complex common in the eastern section SCI. MAR., 64 (Supl. 1): 189-195 SCIENTIA MARINA 2000

of the Juan de Fuca Strait and the San Juan Islands (Fig. 1), occurs in different forms either considered "species," "subspecies" or "morphotypes" (Miller, 1982) in the same habitat.Miller's paper dealt with the medusa stage and first cleavage of their embryos only.Brinckmann-Voss (1985) followed the development of some of Miller's "types" to the hydroid and next medusa generations comparing them with additional field-collected hydroids.Some of Miller's results were confirmed, while certain morphotypes were definitely assigned to valid species.However, 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.nov.The formerly mistaken connection (Brinckmann-Voss, 1977) of the hydroid of this new species with Polyorchis penicillatus will be discussed and corrected.
Sarsia viridis ( see Brinckmann-Voss, 1980) will not be discussed in this paper.Although it is sympatric with Sarsia bella and the other species of the genus listed in Table 1, it can be easily distinguished from them morphologically by its small size and persistant green colour.In addition, Sarsia viridis is very rare and more information, especially about the hydroid, is needed.

MATERIAL AND METHODS
Sarsia bella medusae were collected regularly from floats in Friday Harbor, Washington, Becher Bay, and occasionally in the harbour of Sooke, British Columbia (Fig. 1).Females and males were placed in pairs in small custard cups to spawn.Filtered sea water was used, being at least three days old to avoid contamination with sperm from other Sarsia medusae in the field.As an additional control, female medusae alone and their eggs were observed.Embryos developed from the mating pairs were left in the same container for observation of settlement and development of the hydroids.Primary hydranths were raised to colonies as described in Brinckmann-Voss (1985).As the hydranths of this species have a tendency to regress if not aerated, leaving only the hydrorhiza, small stones with barnacles from the intertidal were added to the colonies.This stirring by natural feeding action of the barnacle cirri was preferable to simple aeration with air stones because nauplii released from the barnacles acted also as perfect-sized prey for the small Sarsia bella hydranths.The hydroid cultures were kept at 5-10°C in an unheated room during the winter months, and outside or in a refrigerator during the summer (the research region of southern Vancouver Island region has cool summers with night temperatures rarely above 15ºC.) Field collected hydroids were collected from the outer and inner margin of rock scallop shells, Hinnites multirugosus (Gale) (syn.Hinnites giganteus Grey) from Departure Bay, British Columbia.Etymology: The new species was named Sarsia bella in reference to the delicate glass-like bell of the medusa.
Diagnosis: Medusae with 2 vertically alligned nematocyst patches in each of eight exumbrellar adradii; clearly visible in young specimens; individual cnidocysts more widely spaced and diminishing in numbers when medusae are crowded in culture or reaching maturity (compare Fig. 2 with Fig. 5).Gonads in distal half of manubrium only; female medusae with larger eggs than other Sarsia (Miller 1982, Table 1); Reddish (never blue) manubrium and marginal bulbs.Hydroids Sarsia-like, upright short stolonal colonies; hydranths emerging directly from hydrorhiza without distinct hydrocaulus; with feeble perisarc around base of hydranths; hydranths small, maximum length 1.5 mm (measured from hydrorhiza); with oral whorl of 4-5 tentacles, and second whorl with shorter tentacles just beneath the oral one; with or without minute filiform tentacles.
Description of medusa (Fig. 2): Living adult medusa with rounded to conical bell reaching a maximum 9 mm high, and 7.5 mm wide; with exumbrella thicker apically than laterally; with short, conical apical canal; with exumbrellar cnidocyst patches faintly visible or absent; with individual cnidocysts more widely separated than in young specimens; manubrium nearly three times as long as exumbrella, with gonads encircling distal part of manubrium except stomach leaving about proximal half of manubrium gonad free.Four marginal bulbs with abaxial ocelli , but without abaxial spurs; tentacles with cnidocyst clusters scattered proximally, becoming more moniliform distally.
Hydroid raised from medusa (Fig. 3): stolonal short colonies not more than 1.5 mm high with hydranths rising directly from a creeping net-like hydrorhiza without clear separation of hydranths and hydrocaulus (terminology used after Millard 1975, Cornelius 1996); with an oral whorl of 4-5 short capitate tentacles, each not more than 0.4 mm long; with tentacles of second whorl half the length of the oral ones; maximum thickness of oral tentacle bulb 56 µm, 40 µm in lower tentacles; usually only 10 endodermal cells in oral tentacles; up to five medusa buds in middle of hydranths; occasionally (Fig. 4) four small, reduced filiform tentacles in area below medusa buds, these present in thriving and relaxed colonies only; usually absent as in Figure 3. Hydroids from field-collected material (Fig. 4) on the shell margin of rock scallops appear identical to hydroids raised from the medusae in the laboratory, except for the hydrorhiza and proximal part of hydranth being imbedded in an incrusting sponge which often covers part of the margins of rock scallops.
Medusae liberated from their hydroids are 1 mm high and 1 mm wide.Exumbrella with 16 patches of nematocysts -two per each of eight adradii (Fig. 5); each patch consisting of 6-11 densely packed microbasic p-mastigophores.During growth of the exumbrella, the nematocysts become more scattered or widely separated and often disappear as the medusae mature; the upper patches tend to disappear before the lower ones.During development, the manubrium getting longer than the subumbrella and gonads develop.Initially when the manubrium has not reached its full length, gonads seem to be thicker distally than proximally, so that the manubrium appears spindle-shaped in juvenile specimens; but in mature medusae, the gonads are limited to the distal part of the manubrium, leaving its proximal part gonad-free.In alcohol-preserved specimens, mature medusae measure between 5.8/5.0 mm and 8.0/7.6 mm in height/diameter.Diameter of eggs is 129 µm (see Miller 1982 for Sarsia "L").In the present study the egg diameter is slightly less, 110-120 µm, but still considerably larger than those of the sympatric species Sarsia apicula (Murbach and Shearer 1902) (as Sarsia "S" in Miller, 1982;see Discussion).
The ciliated planula settles on the bottom of glass dishes and primary hydranths were observed 10 to 14 days after spawning.In contrast to this new species, the planulae of Sarsia apicula develop into primary hydranths after only 48 hours.Medusa buds develop between March and May in cultures kept at about 8-12°C.The field-collected hydroids off the British Columbia coast were found with medusa buds in the beginning of March at a sea-water temperature of 9°C.
Distribution: the medusa stage of Sarsia bella has been found occasionally in Sooke, frequently in Becher Bay and Friday Harbor (Fig. 1).The hydroid was collected in Departure Bay off Nanaimo, B.C.Although intensive collecting was done in Departure Bay, Sarsia bella medusae were not found there.

DISCUSSION
Generic distinctions within the Corynidae have been under discussion for a number of years.Petersen (1990), with the help of cladistic methods, improved earlier concepts by trying to arrange the family into three genera (Sarsia, Coryne and Dipurena) according to different characters of hydroid and medusae.Although Sarsia bella fits Petersen's definition of the genus Sarsia, some of the characters used by him seem to be unreliable as a generic distinction: these include shape of of marginal bulbs of the medusae and position of medusa buds on the hydroids (author's personal observation; Kubota and Takashima 1992).Additional characters such as morphology of the tentacles in the hydroid, should also be considered to define the three genera.
Sarsia bella is one of the two common "sibling"species of the genus Sarsia which occur in certain bays off southern Vancouver Island and Friday Harbor.Miller (1982) considered these belonging to a Sarsia tubulosa complex, but recent hybridization experiments between Friday Harbor and Becher Bay specimens and subsequent raising of the primary hydranths of both forms (Brinckmann-Voss, work in progress) reveal that Miller's Friday Harbor "S" type is actually Sarsia apicula (Murbach and Shearer, 1902) and not a morphotype of Sarsia tubulosa (M.Sars, 1835) as suggested in Figure 4 of his paper (Miller, 1982, p.161).The species Sarsia tubulosa (M.Sars, 1835) is present in Sooke Harbour, but much rarer or absent in Friday Harbor, where Miller did his work; Miller's "L" type is, as he suggested, a separate species described above as the new species Sarsia bella.Although Miller reported up to 37.7% successful early cleavage stages in his hybridization experiments of Sarsia bella sp.nov.and S. apicula (Murbach and Shearer,1902) (S and L morphotype in Miller, 1982) experiments (Brinckmann-Voss,A. work in progress) between the two species -or heterotypic matings of the two morphotypes as phrased by Miller (1982, p. 163) -did not result in any primary hydranths.Instead embryos from homotypic matings developed into primary hydranths about 90% of the time (Brinckmann-Voss, A. work in progress).Furthermore, Sarsia bella can be morphologically distinguished from a small blue Sarsia, " B" type in Miller (1982), collected in Parks Bay, Shaw Island (San Juan Islands), and considered by him belonging to the same "tubulosa" morphotype.In addition to their morphological distinction in the medusa and hydroid stage, both species are spatially or temporally separated from each other.Sarsia" P" type (Miller, 1982), or Sarsia princeps (Haeckel, 1879), can be easily distinguished from Sarsia bella (Table 1) by the morphology of the medusa as well as the hydroid (Arai, and Brinckmann-Voss, 1980;Brinckmann-Voss, 1985).
The hydroid now identified as Sarsia bella which occurs on the rim of the shells of the rock scallop, Hinnites giganteus, was mistakenly reported as the hydroid of Polyorchis penicillatus Eschscholtz in an earlier paper (Brinckmann-Voss, 1977).The mistake happened because of the similarity between newlyliberated medusae from the hydroid living on rock scallops and the youngest stages of the medusa P. penicillatus collected separately from the plankton.Although both species look strikingly similar in their youngest medusa stage, they can be easily distinguished from each other: Sarsia bella never has more than two vertically alligned nematocyst patches on each of the 8 adradii as shown earlier (Fig. 5 FIG.2.-Sarsia bella ; adult male medusa Becher Bay; 0 m; x: specific characters: gonad free part of manubrium and exumbrellar cnidocyst patches.Scale = 1.0 mm FIG. 4. -Sarsia bella, after sketch from living hydroid from fieldcollected rock scallop.Small filiform tentacles below medusa buds only occasionally present.Scale = 0.1mm 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. hydroid: large isorhiza with 2 adjacent stenoteles.Scale a,b = 10 µm.