Obelia Longissima Class: Hydrozoa, Hydroidolina Order: Leptothecata a Floating Dock Hydroid Family: Campanularidae

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Phylum: Cnidaria Obelia longissima Class: Hydrozoa, Hydroidolina Order: Leptothecata A floating dock hydroid Family: Campanularidae

Taxonomy: Obelia longissima was first green (Puget Sound) (Arai and Brinckmann- described by Pallas in 1766. Synonymous Voss 1980). include Campanularia flabellata, Gonothyraea Body: longissima, Laomeda flabellata, L. longissima, Bell: The bell is very thin and O. flabellata, Sertularia longissima (WoRMS flat, with a small stomach, no peduncle, and a 2015). O. lucifera may also be a synonym rudimentary velum (Fig. 3). It is eversible (Arai (especially of the medusa form), but further and Brinckmann-Voss 1980). research is necessary to be sure. There has Radial Canals: There are four been much debate over the species identities straight radial canals, each containing a within the genus Obelia (Cornelius 1975; Arai globular gonad (Fig. 3). and Brinckmann-Voss 1980). The taxonomy Ring Canal: The ring canal is above was taken from the World Register of narrow, with eight statocysts (balance Marine Species (WoRMS 2015). In addition to structures) (Arai and Brinckmann-Voss 1980) confusion in the lower taxonomy, the higher and no ocelli (Fig. 3). taxonomy has undergone revision. The order Mouth: The mouth has 4 Hydroida was determined to be synonymous small, simple lips (Arai and Brinckmann-Voss with subclass Hydroidolina in 2004 (Schuchert 1980); in mature specimens these contain 2015). nematocysts (Boero et al. 2007). Tentacles: Tentacles are Description numerous, solid (as opposed to hollow), and General Morphology: Obelia longissima has short. There are usually 16-26 in young two forms. The sexual form is a gelatinous medusae (Ricketts et al. 1985; Mills and hydromedusa. It has radial canals that run Strathmann 1987), and more develop as they from the top of the peduncle to the bell mature. margin, where they are connected by a ring Velum: Reduced (Arai and canal. Suspended from the inside of the bell Brinckmann-Voss 1980) by a peduncle is the manubrium, or mouth. A Gonads: There are 4 round gonads velum rings the inside of the bell margin (Fig. on the middle of each radial canal (Arai and 3). Its asexual morphology is a large polyp. Brinckmann-Voss 1980). Each polyp has a stem (hydrocaulus), and Polyp: most have a sheathed (thecate) hydranth with Size: Each colony can be up to 60 cm a mouth (manubrium), stomach, and long (Mills et al. 2007) (Fig. 1). Older side tentacles. Rather than having hydranths, branches are all about the same length some polyps have gonothecae (Fig. 2). (towards the base), but younger branches Medusa: gradually get shorter near the growing tip Size: Newly-released medusae are (Mills et al. 2007). about 0.5 mm in diameter; as they mature, Color: The polyp is transparent white they grow to 5 mm in diameter (Cornelius when young, while old, mature colonies look 1975; Kozloff 1983). dirty. Stems are brown to black (Mills el al. Color: Medusae are primarily clear. 2007). Their tentacle bases, mouths, gonads, and Body: Lacks nematophores (non- stomachs are sometimes yellow to brown, feeding defensive polyps) (Mills et al. 2007) while their gonads and mouths can be bright Pedicel: Stems are thread-like and often monosiphonic (consist of a single

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12643 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] tube or row of cells) except sometimes near (Fig. 4a). Colony size is also a difference; the the base. Internodes of the stem are straight maximum size of an O. geniculata colony is 2 or curve very slightly (Mills et al. 2007). Each cm (Cornelius 1975), much smaller than the stem has many branches, which are ringed at 60 cm maximum of O. longissima. This size the joints, alternate, and have short stalks also gives O. geniculata a delicate white and (Fig. 2). Stems hold many hydranths rather fuzzy appearance (Kozloff 1983). The species than just one (Mills et al. 2007). are similar in that they both have ringed Hydranth: The hydranth is branches and axillary gonothecae that are covered by a theca (hydrothecae), which is urn-shaped, with a raised center and a short campanulate (bell-shaped, hence family ringed stalk. Their hydromedusae are also name) and deep enough to contain the similar enough that they are often not hydranth when contracted. The margin is identified past the genus level (Arai and crenulate rather than cusped, and lacks an Brinckmann-Voss 1980). operculum (Mills et al. 2007). Each hydranth Obelia dichotoma is very similar to O. is on the end of a long, ringed pedicels (Fig. longissima. Both have slender and annulated 2d, f). stems, though O. dichotoma has curved Gonangium: The reproductive internodes and is irregularly branched while buds (gonotheca, gonangia) asexually O. longissima has a straight stem and is produce medusae (Fig. 2c) (Ricketts et al. alternately branched. These are essentially 1985). These buds are axillary (i.e., grow out the only differences. Both have hydrothecae of the angle between the stem and the that are broad, bell-shaped, with slightly hydrotheca). They are oval-shaped and sinuated margins; their gonothecae are smooth, with a raised central aperture (Parker axillar, slender, and smooth. They widen from et al. 1951) and a terminal collar (Mills et al. the base, and end in a “raised, somewhat 2007). conical aperture” (Russell 1953) (Fig. 4b). No Cnidae: one has yet been able to definitively identify differences in the hydromedusae forms. Possible Misidentifications Other hydroids, which have stalks, and The family Campanulariidae includes thecae within which their hydranths can be leptomedusae possessing four radial canals, retracted (Fig. 2b) include those of the and lacking excretory pores and marginal or families Campanulinidae and Phialellidae lateral cirri. The polyps in the family have a (Rees and Hand 1975), which are very small club or trumpet-shaped manubrium, and lack and have tubular thecae with a pointed operculum. The genus Obelia includes operculum. Other Campanularidae (bell- species that have a nearly flat and eversible shaped hydrothecae) include Phialidium sp. bell, a reduced velum, eight statocysts, and and Campanularia sp. both of which have solid (rather than hollow) tentacles (Arai and colonies of less than 2 cm in height, and are Brinckmann-Voss 1980). Within the genus, rarely branched. the species look so similar (especially in the The genus most closely related to hydromedusa stage) that it is common for Obelia is Gonothyraea, which does not researchers to identify only to the genus level release free medusae, but retains them within (Arai and Brinckmann-Voss 1980). the gonotheca (Kozloff 1983). There are two very closely related species of Obelia: (Fig. 4) Ecological Information Obelia geniculata has a central zig zag Range: The type locality is Belgium (Ralph stem, thickened at the joints, while O. 1957). The genus Obelia is found worldwide. longissima has a much straighter and Obelia longissima is found from Alaska to San narrower stem. Obelia geniculata has a rather Pedro, California (Ricketts et al. 1985). conical hydrothecae (as opposed to bell- Local Distribution: All three closely related shaped) that is only slightly longer than wide, species (O. longissima, O. geniculata, O. and has plain margins rather than cusped dictotoma) are found from northern California

Piazzola, C.D. and T.C. Hiebert. 2015. Obelia longissima. In: Oregon Estuarine Invertebrates: Rudys' Illustrated Guide to Common Species, 3rd ed. T.C. Hiebert, B.A. Butler and A.L. Shanks (eds.). University of Oregon Libraries and Oregon Institute of Marine Biology, Charleston, OR. to Puget Sound, Washington; other species al. 1985). Medusa blooms and subsequent may be present as well, some of them massive shoreline settlement are not common introduced (Rees and Hand 1975). but do occasionally occur (Genzano et al. Habitat: This is a frequent fouling organism, 2008). common in harbors (Mills et al. 2007), on docks, kelp, and floats in bays, and in Life-History Information eelgrass beds (Elkhorn Slough, CA) (Ricketts Reproduction: Like other hydroids, O. et al. 1985). Healthy colonies are found on longissima has both a sexual reproductive exposed pilings, particularly where water is cycle and an asexual one. In sexual clean and fast-moving. Medusae are found reproduction, the medusae produce either floating, probably not far from their hydroid eggs or sperm (dioecious). After the egg is parents. They probably are not light- fertilized, it develops into a planula larva, dependent for vertical distribution (Parker and which settles and becomes the polyp stage. Haswell 1951). Polyps usually do not grow in In asexual reproduction, the gonangia of the pollution or direct sunlight (Ricketts et al. polyp bud to form juvenile medusae. The 1985). production of medusae by the polyp may be Salinity: Collected at 30, though it can tied to lunar periodicity: specifically, to the tolerate some fresh water (Ricketts et al. third week of the moon (Elmhirst 1925, in 1985). An Atlantic species, O. bidentata was Russell 1953). The complete life cycle found to have a wide distribution across the (swimming larvae to hydroid colony estuarine gradient, down to 0.5. O. dichotoma discharging medusae) takes one month was found down to 12 (Cornelius 1975). (MacGinitie and MacGinitie 1968). Lab reared Temperature: Specimens have been found in medusae are sexually mature six days after cold and temperate waters; settling may occur emergence (Russell 1953). O. longissima are in cooler temperatures during the year present all year, but are most numerous in (Standing 1976). spring to late summer. Settling may Tidal Level: They are most abundant in mid- correspond to low water temperatures intertidal and just below, and have been found (Standing 1976). Budding and release of from low tide to 128 m (Mills et al. 2007). medusae only occurs below 12° C (lab) Associates: The hydroid colonies serve as a (Haderlie et al. 1980). good habitat for many epibionts. Some of Larva: The hydromedusae form produces these include caprellid and garnmarid planula larvae (Kozloff 1983). Planulae are amphipods; asellote isopods; copepods; usually oval or club-shaped and ciliated diatoms; the sea slug Eubranchus; evenly all over their bodies. These larvae are nudibranchs Dendronotus frondosus and non-feeding and free-swimming. They are Phidiana crassicornis (Bodega Bay); and armed with nematocytes, but lack an apical pycnogonid Halosoma veridintestinale. The ciliary tuft and septa (see Fig. 3, Sadro 2001). medusa form plays host to pycnogonid larvae Juvenile: The juvenile medusa is about 0.5 of Anaphia (England). Despite both species’ mm in diameter had has 16-26 tentacles prevalence as fouling organisms, barnacle (Ricketts et al. 1985; Mills and Strathmann larvae cannot settle where O. longissima 1987). It lacks nematocysts on its lips (Boero growth is heavy (Standing 1976). et al. 2007). Abundance: Obelia longissima is particularly Longevity: One generation (from newly- common in harbors in northern California released larva to medusae-releasing hydroid) (Rees and Hand 1975), British Columbia, and takes about one month (Ricketts et al. 1985). Puget Sound (Arai and Brinckmann-Voss Growth Rate: Because of the quick 1980; Ricketts et al. 1985). In the Strait of generation time and rapid hydroid growth, Georgia, it is collected from March to Sept., several generations are possible in a year and common from April to June (Arai and (Ricketts et al. 1985). Obelia dichotoma grows Brinckmann-Voss 1980). Medusae are to 2.5 mm in 19 days (from 1 mm) (Browne in released primarily during summer, but also in Russell 1953). Growth is directly correlated smaller quantities throughout year (Ricketts et

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12643 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] with temperatures of 8-20° C (Haderlie et al. 3. HADERLIE, E. C., C. HAND, and W. 1980). B. GLADFELTER. 1980. Cnidaria Food: The medusa stage is considered a (Coelenterata): the sea anemones and microphagous filter-feeder, especially as a allies, p. 40-75. In: Intertidal juvenile (O. dichotoma) (Boero et al. 2007). invertebrates of California. R. H. Older individuals can sometimes consume Morris, D. P. Abbott, and E. C. crustaceans and their larvae, arrowworms, Haderlie (eds.). Stanford University and small fish. The polyp stage primarily eats Press, Stanford. phytoplankton (diatoms and dinoflagellates), 4. KOZLOFF, E. N. 1983. Seashore life and secondarily eats detritus from of the northern Pacific coast. macroalgae (De Rosa et al. 1999). University of Washington Press, Predators: Opisthobranch Eubranchus and Seattle. several nudibranch species eat hydroid buds 5. MACGINITIE, G. E., and N. (Ricketts et al. 1985; Mills et al. 2007). Other MACGINITIE. 1968. Natural history of hydrodmedusae prey upon the medusa stage marine animals. McGraw-Hill Book (Arai and Jacobs 1980). Co., New York. Behavior: The medusa is noted for its quick 6. MILLS, C. E., A. C. MARQUES, A. E. movements, and it is often found inverted MIGOTTO, D. R. CALDER, and C. (Fig. 3). Because of its flat bell, it uses bell- HAND. 2007. Hydrozoa: polyps, flapping rather than jet-propulsion to move hydromedusae, and siphonophora, p. through the water (see Fig. 2, Boero et al. 118-168. In: The Light and Smith 2007). This undulation is also how medusae manual: intertidal invertebrates from maintain waterflow to their manubrium in central California to Oregon. J. C. order to continue filter-feeding. Juvenile Carlton (ed.). University of California medusae must flap their bells continuously Press, Berkeley. (and thus feed continuously); they will 7. MILLS, C. E., and M. F. undulate their bell while at the surface of the STRATHMAN. 1987. Phylum Cnidaria, water to create waterflow while maintaining a Class Hydrozoa, p. 44-71. In: single position (Boero et al. 2007). Medusae Reproduction and development of are bioluminescent, and are the source of the marine invertebrates of the northern protein obelin (Ohmiya and Hirano 1996). Pacific coast: data and methods for the study of eggs, embryos, and Bibliography larvae. M. F. Strathman (ed.). University of Washington Press, 1. DE ROSA, S., A. MILONE, S. Seattle, WA. POPOV, and S. ANDREEV. 1999. 8. OHMIYA, Y., and T. HIRANO. 1996. Sterol composition of the Black Sea Shining the light: the mechanism of Hydrozoan, Obelia longissima (Pallas the bioluminescence reaction of 1766). Comparative Biochemistry and calcium-binding photoproteins. Physiology B: Biochemistry & Chemistry & Biology. 3:337-347. Molecular Biology. 123:229-233. 9. PARKER, T. J., O. LOWENSTEIN, C. 2. GENZANO, G., H. MIANZAN, L. DIAZ- F. COOPER, and W. A. HASWELL. BRIZ, and C. RODRIGUEZ. 2008. On 1951. A textbook of zoology. the occurrence of Obelia medusa Macmillan and Co., London. blooms and empirical evidence of 10. RALPH, P. M. 1957. New Zealand unusual massive accumulations of thecate hydroids. Part I. Obelia and Amphisbetia hydroids on Campanulariidae and the Argentina shoreline. Latin Campanulinidae. Transactions of the American Journal of Aquatic Royal Society of New Zealand. Research. 36:301-307. 84:811-854.