Obelia Longissima Class: Hydrozoa, Hydroidolina

Home , Campanulariidae, Hydroid (zoology), Leptothecata, Obelia, Obelia dichotoma, Obelia longissima

Obelia longissima Class: Hydrozoa, Hydroidolina

Order: Leptothecata A floating dock hydroid Family: Campanularidae

Taxonomy: Obelia longissima was first de- about 0.5 mm in diameter; as they mature, scribed by Pallas in 1766. Synonymous in- they grow to 5 mm in diameter (Cornelius clude Campanularia flabellata, Gonothyraea 1975; Kozloff 1983). longissima, Laomeda flabellata, L. longissi- Color: Medusae are primarily clear. ma, O. flabellata, Sertularia longissima Their tentacle bases, mouths, gonads, and (WoRMS 2015). O. lucifera may also be a stomachs are sometimes yellow to brown, synonym (especially of the medusa form), while their gonads and mouths can be bright but further research is necessary to be sure. green (Puget Sound) (Arai and Brinckmann- There has been much debate over the spe- Voss 1980). cies identities within the genus Obelia Body: (Cornelius 1975; Arai and Brinckmann-Voss Bell: The bell is very thin and flat, with 1980). The taxonomy above was taken from a small stomach, no peduncle, and a rudi- the World Register of Marine Species mentary velum (Fig. 3). It is eversible (Arai (WoRMS 2015). In addition to confusion in and Brinckmann-Voss 1980). the lower taxonomy, the higher taxonomy Radial canals: There are four has undergone revision. The order Hydroida straight radial canals, each containing a glob- was determined to be synonymous with sub- ular gonad (Fig. 3). class Hydroidolina in 2004 (Schuchert Ring canal: The ring canal is 2015). narrow, with eight statocysts (balance struc- tures) (Arai and Brinckmann-Voss 1980) and Description no ocelli (Fig. 3). General Morphology: Obelia longissima Mouth: The mouth has 4 small, has two forms. The sexual form is a gelati- simple lips (Arai and Brinckmann-Voss 1980); nous hydromedusa. It has radial canals that in mature specimens these contain nemato- run from the top of the peduncle to the bell cysts (Boero et al. 2007). margin, where they are connected by a ring Tentacles: Tentacles are nu- canal. Suspended from the inside of the bell merous, solid (as opposed to hollow), and by a peduncle is the manubrium, or mouth. short. There are usually 16-26 in young me- A velum rings the inside of the bell margin dusae (Ricketts et al. 1985; Mills and Strath- (Fig. 3). Its asexual morphology is a large mann 1987), and more develop as they ma- polyp. Each polyp has a stem (hydrocaulus), ture. and most have a sheathed (thecate) hy- Velum: Reduced (Arai and dranth with a mouth (manubrium), stomach, Brinckmann-Voss 1980) and tentacles. Rather than having hy- Gonads: There are 4 round gonads on dranths, some polyps have gonothecae (Fig. the middle of each radial canal (Arai and 2). Brinckmann-Voss 1980). Medusa: Polyp: Size: Newly-released medusae are Size: Each colony can be up to 60 cm

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: https://oimb.uoregon.edu/oregon-estuarine-invertebrates and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected]

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 Biol- ogy, Charleston, OR.

long (Mills et al. 2007) (Fig. 1). Older side lack operculum. The genus Obelia includes branches are all about the same length species that have a nearly flat and eversible (towards the base), but younger branches bell, a reduced velum, eight statocysts, and gradually get shorter near the growing tip solid (rather than hollow) tentacles (Arai and (Mills et al. 2007). Brinckmann-Voss 1980). Within the genus, Color: The polyp is transparent white the species look so similar (especially in the when young, while old, mature colonies look hydromedusa stage) that it is common for re- dirty. Stems are brown to black (Mills el al. searchers to identify only to the genus level 2007). (Arai and Brinckmann-Voss 1980). Body: Lacks nematophores (non- There are two very closely related spe- feeding defensive polyps) (Mills et al. 2007) cies of Obelia: (Fig. 4) Pedicel: Stems are thread-like Obelia geniculata has a central zig zag and often monosiphonic (consist of a single stem, thickened at the joints, while O. longis- tube or row of cells) except sometimes near sima has a much straighter and narrower the base. Internodes of the stem are straight stem. Obelia geniculata has a rather conical or curve very slightly (Mills et al. 2007). hydrothecae (as opposed to bell-shaped) that Each stem has many branches, which are is only slightly longer than wide, and has plain ringed at the joints, alternate, and have short margins rather than cusped (Fig. 4a). Colony stalks (Fig. 2). Stems hold many hydranths size is also a difference; the maximum size of rather than just one (Mills et al. 2007). an O. geniculata colony is 2 cm (Cornelius Hydranth: The hydranth is 1975), much smaller than the 60 cm maxi- covered by a theca (hydrothecae), which is mum of O. longissima. This size also gives O. campanulate (bell-shaped, hence family geniculata a delicate white and fuzzy appear- name) and deep enough to contain the hy- ance (Kozloff 1983). The species are similar dranth when contracted. The margin is cren- in that they both have ringed branches and ulate rather than cusped, and lacks an oper- axillary gonothecae that are urn-shaped, with culum (Mills et al. 2007). Each hydranth is a raised center and a short ringed stalk. Their on the end of a long, ringed pedicels (Fig. hydromedusae are also similar enough that 2d, f). they are often not identified past the genus Gonangium: The reproductive level (Arai and Brinckmann-Voss 1980). buds (gonotheca, gonangia) asexually pro- Obelia dichotoma is very similar to O. duce medusae (Fig. 2c) (Ricketts et al. longissima. Both have slender and annulated 1985). These buds are axillary (i.e., grow out stems, though O. dichotoma has curved inter- of the angle between the stem and the hy- nodes and is irregularly branched while O. drotheca). They are oval-shaped and longissima has a straight stem and is alter- smooth, with a raised central aperture nately branched. These are essentially the (Parker et al. 1951) and a terminal collar only differences. Both have hydrothecae that (Mills et al. 2007). are broad, bell-shaped, with slightly sinuated margins; their gonothecae are axillar, slender, Possible Misidentifications and smooth. They widen from the base, and The family Campanulariidae includes end in a “raised, somewhat conical aper- leptomedusae possessing four radial canals, ture” (Russell 1953) (Fig. 4b). No one has yet and lacking excretory pores and marginal or been able to definitively identify differences in lateral cirri. The polyps in the family have a the hydromedusae forms. club or trumpet-shaped manubrium, and

Other hydroids, which have stalks, was found down to 12 (Cornelius 1975). and thecae within which their hydranths can Temperature: Specimens have been found in be retracted (Fig. 2b) include those of the cold and temperate waters; settling may occur families Campanulinidae and Phialellidae in cooler temperatures during the year (Rees and Hand 1975), which are very small (Standing 1976). and have tubular thecae with a pointed oper- Tidal Level: They are most abundant in mid- culum. Other Campanularidae (bell-shaped intertidal and just below, and have been found hydrothecae) include Phialidium sp. and from low tide to 128 m (Mills et al. 2007). Campanularia sp. both of which have colo- Associates: The hydroid colonies serve as a nies of less than 2 cm in height, and are good habitat for many epibionts. Some of rarely branched. these include caprellid and garnmarid amphi- The genus most closely related to pods; asellote isopods; copepods; diatoms; Obelia is Gonothyraea, which does not re- the sea slug Eubranchus; nudibranchs Den- lease free medusae, but retains them within dronotus frondosus and Phidiana crassicornis the gonotheca (Kozloff 1983). (Bodega Bay); and pycnogonid Halosoma veridintestinale. The medusa form plays host Ecological Information to pycnogonid larvae of Anaphia (England). Range: The type locality is Belgium (Ralph Despite both species’ prevalence as fouling 1957). The genus Obelia is found worldwide. organisms, barnacle larvae cannot settle Obelia longissima is found from Alaska to where O. longissima growth is heavy San Pedro, California (Ricketts et al. 1985). (Standing 1976). Local Distribution: All three closely related Abundance: Obelia longissima is particularly species (O. longissima, O. geniculata, O. common in harbors in northern California dictotoma) are found from northern Califor- (Rees and Hand 1975), British Columbia, and nia to Puget Sound, Washington; other spe- Puget Sound (Arai and Brinckmann-Voss cies may be present as well, some of them 1980; Ricketts et al. 1985). In the Strait of introduced (Rees and Hand 1975). Georgia, it is collected from March to Sept., Habitat: This is a frequent fouling organism, and common from April to June (Arai and common in harbors (Mills et al. 2007), on Brinckmann-Voss 1980). Medusae are re- docks, kelp, and floats in bays, and in eel- leased primarily during summer, but also in grass beds (Elkhorn Slough, CA) (Ricketts smaller quantities throughout year (Ricketts et et al. 1985). Healthy colonies are found on al. 1985). Medusa blooms and subsequent exposed pilings, particularly where water is massive shoreline settlement are not common clean and fast-moving. Medusae are found but do occasionally occur (Genzano et al. floating, probably not far from their hydroid 2008). parents. They probably are not light- dependent for vertical distribution (Parker Life-History Information and Haswell 1951). Polyps usually do not Reproduction: Like other hydroids, O. longis- grow in pollution or direct sunlight (Ricketts sima has both a sexual reproductive cycle et al. 1985). and an asexual one. In sexual reproduction, Salinity: Collected at 30, though it can toler- the medusae produce either eggs or sperm ate some fresh water (Ricketts et al. 1985). (dioecious). After the egg is fertilized, it devel- An Atlantic species, O. bidentata was found ops into a planula larva, which settles and be- to have a wide distribution across the estua- comes the polyp stage. In asexual reproduc- rine gradient, down to 0.5. O. dichotoma tion, the gonangia of the polyp bud to form

juvenile medusae. The production of medu- and small fish. The polyp stage primarily eats sae by the polyp may be tied to lunar perio- phytoplankton (diatoms and dinoflagellates), dicity: specifically, to the third week of the and secondarily eats detritus from macroal- moon (Elmhirst 1925, in Russell 1953). The gae (De Rosa et al. 1999). complete life cycle (swimming larvae to hy- Predators: Opisthobranch Eubranchus and droid colony discharging medusae) takes several nudibranch species eat hydroid buds one month (MacGinitie and MacGinitie (Ricketts et al. 1985; Mills et al. 2007). Other 1968). Lab reared medusae are sexually hydrodmedusae prey upon the medusa stage mature six days after emergence (Russell (Arai and Jacobs 1980). 1953). O. longissima are present all year, Behavior: The medusa is noted for its quick but are most numerous in spring to late movements, and it is often found inverted summer. Settling may correspond to low wa- (Fig. 3). Because of its flat bell, it uses bell- ter temperatures (Standing 1976). Budding flapping rather than jet-propulsion to move and release of medusae only occurs below through the water (see Fig. 2, Boero et al. 12° C (lab) (Haderlie et al. 1980). 2007). This undulation is also how medusae Larva: The hydromedusae form produces maintain waterflow to their manubrium in or- planula larvae (Kozloff 1983). Planulae are der to continue filter-feeding. Juvenile medu- usually oval or club-shaped and ciliated sae must flap their bells continuously (and evenly all over their bodies. These larvae thus feed continuously); they will undulate are non-feeding and free-swimming. They their bell while at the surface of the water to are armed with nematocytes, but lack an ap- create waterflow while maintaining a single ical ciliary tuft and septa (see Fig. 3, Sadro position (Boero et al. 2007). Medusae are bio- 2001). luminescent, and are the source of the protein Juvenile: The juvenile medusa is about 0.5 obelin (Ohmiya and Hirano 1996). mm in diameter had has 16-26 tentacles Bibliography (Ricketts et al. 1985; Mills and Strathmann 1987). It lacks nematocysts on its lips 1. DE ROSA, S., A. MILONE, S. POPOV, (Boero et al. 2007). and S. ANDREEV. 1999. Sterol composi- Longevity: One generation (from newly- tion of the Black Sea Hydrozoan, Obelia released larva to medusae-releasing hy- longissima (Pallas 1766). Comparative Bi- droid) takes about one month (Ricketts et al. ochemistry and Physiology B: Biochemis- 1985). try & Molecular Biology. 123:229-233. Growth Rate: Because of the quick genera- 2. GENZANO, G., H. MIANZAN, L. DIAZ- tion time and rapid hydroid growth, several BRIZ, and C. RODRIGUEZ. 2008. On the generations are possible in a year (Ricketts occurrence of Obelia medusa blooms and et al. 1985). Obelia dichotoma grows to 2.5 empirical evidence of unusual massive ac- mm in 19 days (from 1 mm) (Browne in Rus- cumulations of Obelia and Amphisbetia sell 1953). Growth is directly correlated with hydroids on the Argentina shoreline. Latin temperatures of 8-20° C (Haderlie et al. American Journal of Aquatic Research. 1980). 36:301-307. Food: The medusa stage is considered a 3. HADERLIE, E. C., C. HAND, and W. B. microphagous filter-feeder, especially as a GLADFELTER. 1980. Cnidaria juvenile (O. dichotoma) (Boero et al. 2007). (Coelenterata): the sea anemones and al- Older individuals can sometimes consume lies, p. 40-75. In: Intertidal invertebrates of crustaceans and their larvae, arrowworms, California. R. H. Morris, D. P. Abbott, and

E. C. Haderlie (eds.). Stanford University HEDGEPETH, and D. W. PHILLIPS. 1985. Press, Stanford. Between Pacific tides. Stanford University 4. KOZLOFF, E. N. 1983. Seashore life of Press, Stanford, CA. the northern Pacific coast. University of 13. RUSSELL, F. S. 1953. The medusae of Washington Press, Seattle. the British Isles. University Press, Cam- 5. MACGINITIE, G. E., and N. MACGINI- bridge [Eng.]. TIE. 1968. Natural history of marine ani- 14. SADRO, S. 2001. Cnidaria (Coelenterata), mals. McGraw-Hill Book Co., New York. p. 13-23. In: An identification guide to the 6. MILLS, C. E., A. C. MARQUES, A. E. larval marine invertebrates of the Pacific MIGOTTO, D. R. CALDER, and C. Northwest. A. L. Shanks (ed.). Oregon HAND. 2007. Hydrozoa: polyps, hydro- State University, Corvallis. medusae, and siphonophora, p. 118-168. 15. SCHUCHERT, P. 2015a. Hydroidolina. In: The Light and Smith manual: intertidal World Register of Marine Species: http:// invertebrates from central California to www.marinespecies.org/aphia.php? Oregon. J. C. Carlton (ed.). University of p=taxdetails&id=19494. [Accessed California Press, Berkeley. 7/17/15]. 2015. 7. MILLS, C. E., and M. F. STRATHMAN. 16. —. 2015b. World Hydrozoa Database. 1987. Phylum Cnidaria, Class Hydrozoa, http://www.marinespecies.org/aphia.php? p. 44-71. In: Reproduction and develop- p=taxdetails&id=117389 [Accessed 2015- ment of marine invertebrates of the 07-27]. 2015. northern Pacific coast: data and methods 17. STANDING, J. D. 1976. Fouling communi- for the study of eggs, embryos, and lar- ty structure: effects of the hydroid Obelia vae. M. F. Strathman (ed.). University of dichotoma on larval recruitment. In: Coe- Washington Press, Seattle, WA. lenterate ecology and behavior. G. O. 8. OHMIYA, Y., and T. HIRANO. 1996. Mackie (ed.). Plenum Press, New York. Shining the light: the mechanism of the Updated 2015 bioluminescence reaction of calcium- C.D. Piazzola and T.C. Hiebert binding photoproteins. Chemistry & Biol- ogy. 3:337-347. 9. PARKER, T. J., O. LOWENSTEIN, C. F. COOPER, and W. A. HASWELL. 1951. A textbook of zoology. Macmillan and Co., London. 10. RALPH, P. M. 1957. New Zealand thecate hydroids. Part I. Campanulariidae and Campanulinidae. Transactions of the Royal Society of New Zealand. 84:811- 854. 11. REES, J. T., and C. H. HAND. 1975. Class Hydrozoa, p. 65-84. In: Light's manual: intertidal invertebrates of the central California coast. S. F. Light, R. I. Smith, and J. T. Carlton (eds.). University of California Press, Berkeley. 12. RICKETTS, E. F., J. CALVIN, J. W.