Hermissenda Crassicornis Class: Gastropoda Order: Nudibranchia an Opalescent Aeolid Nudibranch Family: Facelinidae

Phylum: Mollusca Hermissenda crassicornis Class: Gastropoda Order: Nudibranchia An opalescent aeolid nudibranch Family: Facelinidae

Taxonomy Foot: Split in front (“anteriorly bilabiate”) Hermissenda crassicornis is a complex of (Farmer 1980); lateral angles produced into three distinct species (Lindsay and Valdes horns (fig. 1); foot extends posteriorly into 2016). H. crassicornis is used for the species long, pointed tail. Foot corners or horns also found in the northeast Pacific. Those found called “pedal tentacles” (Kozloff 1974). from Northern California to the Sea of Cortez Cerata: Large, conical, in 11 clusters of are referred to as H. opalescens and those transverse rows (Farmer 1980) covering found in Japan fall under the name H. emurai animal's back. Cerata begin posterior to (Lindsay and Valdes 2016). rhinophores (Beeman and Williams 1980), are Hermissenda crassicornis can be longest in median region of 1st two groups distinguished from the other two species by (Behrens 1980). Each cera with a core of the presence of white longitudinal lines in the digestive gland (fig. 1), and at tip a cnidosac, cerata (Lindsay and Valdes 2016). H. which collects nematocysts from cnidarian opalescens lacks these white lines in the prey (MacFarland 1966). cerata, and H. emurai has been described as Oral Tentacles: Usually present, order having a pale yellow body, a broken mid- Nudibranchia (McDonald 1975). Long, white, dorsal vermillion line mid-way down from the pointed (fig. 1). anterior end, and with two parallel lines Gills: None (fig. 1). Cerata serve as gills. running down the sides of the body, bluish Eyes: Small, black; posterior to bases of and vermilion in color (Lindsay and Valdes rhinophores (fig. 1). Eyes consist of a lens 2016). and five photoreceptor cells. The photoreceptor cells have position sensitivity Description due to their asymmetrical arrangement and Size: 30 mm to 80 mm long (Beeman and send nerve impulses to the brain via an axon Williams 1980); illustrated specimen (Coos (Stensaas et al. 1969). H. crassicornis eyes Bay) 50 mm. are used in neurological studies (Beeman and Color: Ground color often white, transparent Williams 1980). (MacFarland 1966), with opalescent white or Radula and Jaws: Ribbon of horseshoe- blue line around foot, down each oral tentacle shaped teeth; each central cusp with a single (McDonald 1975). Line down back is light or row of up to 28 teeth; 4-6 sharp spines on bright orange (Lindsay and Valdes 2016). either side of middle cusp whose under- Line can form diamond shape between first surface has up to 15 small points cerata. Cerata cores (digestive glands) are (MacFarland 1966) (fig. 4). Hermissenda light to dark brown or bright orange and each found in Oregon have 4-5 denticles, these are cera has a distinct white stripe on the anterior smaller than those found in other members of side (Lindsay and Valdes 2016). the species complex and appear as bumbs Body: Oblong, flat-bottomed, with (Lindsay and Valdes 2016). rhinophores, cerata, and tail, but without Mouth: Jaw border with up to 50 denticles posterior plume of branched gills (fig. 1). (MacFarland 1966). (Mandibles not figured.) Rhinophores: Long; with 8 - 24 slanted, faint Genital Openings: Genital apertures on low st "leaves" or rings (Farmer 1980); “weakly posterior part of 1 group of cerata perfoliate” (McDonald and Nybakken 1980) or (MacFarland 1966) (not visible as drawn, but annulate, otherwise solid (fig. 1). Color: as see arrow, fig. 1). ground. Anus: Tubular, located on the right, between nd rd 2 and 3 groups of cerata (fig. 1) (MacFarland 1966). Concealed (MacFarland

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12748 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] 1966). Anus more anterior than in Aeolididae also lacks the blueish lines on the body found (Keen 1971). on Hermissenda. This species was formerly Renal Pore: Lateral, between 1st and 2nd called Antiopella barbarensis (Cooper 1863). group of cerata (not visible, but see arrow, fig. The Hermissenda suborder Aeolidacea 1). includes two superfamilies: Protoaeolidoidea, Eggs: In pink, sausage-like string; each with one family, Notaeolidiidae; and measures 1 mm in diameter, attached Euaeolidoidea, with 21 families. Only a few through much of its length to substrate. String species from this latter superfamily could be makes tight counterclockwise spiral, which confused with Hermissenda: measures between 0.24 cm and 3.62 cm Fiona pinnata is similar in morphology to (Harrington and Alkon 1979). Each capsule Hermissenda, but has smooth rhinophores can have 1 – 4 eggs (Beeman and Williams and sail-like flaps on its cerata. The cerata 1980) (fig. 5). are dense along the margins; a large part of the back is clear (Keen 1971); it has no blue Possible Misidentifications lines or orange spots. Cosmopolitan. Nudibranchs can be separated from other The Coryphellidae have produced foot apparently shell-less opisthobranchs by their corners, but not angular ones as in radulae and jaws (they are carnivorous), and Facelinidae (Keen 1971). Their numerous by their rhinophores, which are not rolled as cerata are clustered and elongate, as in they are in sacoglossans. Nudibranchs also Hermissenda. Coryphella trilineata has three have oral tentacles. In addition, they have lost white (not blue) lines on a white body, but all shell and opercula (as adults) as well as there are no orange spots within them. The mantle cavity and gills. Some may have cerata can look much like Hermissenda, but secondary gills on their backs (McDonald and have cadmium yellow tips. The rhinophores Nybakken 1980). Nudibranch genital are annulate and colored yellow or orange. openings are on the right side. Aeolidia papillosa, the shag rug The nudibranchs found in the nudibranch found with anemones, is white Hermissenda suborder, Aeolidiacea, are with gray to brown spots. It has sharp pedal relatively small, long, and narrow, gill-less, tentacles like Hermissenda, but its cerata and have cerata. They feed partly on cnidaria, begin anterior to the rhinophores and are and are able to store nematocysts in their lanceolate, i.e. broad-based and sharp-tipped, cerata (Keen 1971). not conical as in Hermissenda. The nudibranchs in the other major Spurillidae (genus Spurilla) have suborder, Doridacea, are larger, with a large rhinophores with quite oblique leaves, and flat foot, thick mantle and obvious gills, i.e. have orange head markings. The cerata of S. Onchidoris, Triopha (McDonald and olivae are quite like Hermissenda: orange, Nybakken 1980). white tipped brown cores. Both this species Another suborder, Dendronotacea, and S. chromosoma are found only from resemble aeolids, but have sheaths for their central California south however (McDonald rhinophores and a mid-lateral anus. Examples and Nybakken 1980). are Tritonia, Tethys, Melibe, and especially There are two other nudibranchs in the Dendronotus spp. family Facelinidae (was Phidianidae The Arminacea are a very diverse group (McDonald and Nybakken 1980). Both are of lacking rhinophore sheaths and usually the genus Phidiana and found only from lacking oral tentacles; the anus is anterior. central California south. Both P. hiltoni Some have cerata, but others do not. Janolus (=pugnax) and P. morrowensis have orange fuscus has cerata very like Hermissenda markings on the head and on the (orange and white tipped), but also has a red rhinophores. These two are closely related, cockscomb between the rhinophores, colored but not likely to be confused with each other like the cerata. Cerata begin anterior to the or with Hermissenda. rhinophores and fall off easily; they are found Several other nudibranchs of diverse only on the periphery of the dorsum families could resemble Hermissenda (McDonald and Nybakken 1980). Janolus superficially in color, so care must be taken to

Perez-Varona, M. and Thiel-Klare, K. 2017. Hermissenda crassicornis. 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. observe carefully the rhinophores, foot algae or Zostera (Harrigan and Alkon 1978). tentacles, and especially the blue/white lines Motile sperm found in 34 mg animals, and of Hermissenda. egg laying by 73 mg animals in lab (Harrigan and Alkon 1978). Sperm from one copulation Ecological Information enough to fertilize most eggs in about three Range: Sitka, Alaska to Baja California, egg masses (Rutowski 1983). Mexico (Beeman and Williams 1980). Copulation in Hermissenda is Local Distribution: Coos Bay: small boat relatively short compared to other sea slugs. basin, Charleston, seasonally, especially in The process of intromitting between summer. simultaneous hermaphrodites will last only a Habitat: Varied: rocky tidepools, floats, mud couple of seconds. Two individuals will meet and sand flats (Beeman and Williams 1980; head to head and will go through flagellation, Goddard 1985), eelgrass beds (Puget the process of sensing each other with their Sound), bare rock and on seaweed. tentacles. Following this process both animals Also found on boat docks (Hoover et al. will “slide” towards the right side of each other 2012). where the gonopores are located and Salinity: Collected at 30 (Coos Bay). simultaneously copulate by erecting their Temperature: Annual range 9-18 °C cerata and intromitting. Violent lunging and (Beeman and Williams 1980). biting behavior once thought to be aggressive Tidal Level: Low intertidal; subtidal down to now known to be part of brief mating 35m (Beeman and Williams 1980). sequence (Rutowski 1983); many attempts at Associates: Copepod Hemicyclops copulation are unsuccessful. thysanotus often found on its back (Beeman Eggs hatch after 5-6 days into a and Williams 1980). Found on fouling panels planktonic veliger stage that lasts at least 34 regardless of presence of other organisms. days. Veligers that are ready to Sea pen Ptilosarcus (Puget Sound) (Birkeland metamorphose have eyes, a shell measuring 1974). Also see “Food”. 300mm, and a developed foot. After Weight: 5-8 grams (Harrigan and Alkon completing the larval stage, veligers crawl 1978). onto a hydroid and 12-24 hours later the larva Abundance: One of the most common crawls out of its shell to complete aeolids in northeastern Pacific, especially in metamorphosis. The new juvenile uses middle of range, but its occurrence is hydroid tissue as a food source (Harrigan and temporally variable at any one part of the Alkon 1978). range (Ricketts and Calvin 1971). Dominant Growth Rate: Veligers hatch in 5-6 days in littoral opisthobranch in abundance and lab at 13-15 °C and obligatory veliger stage of geographical distribution, Humboldt Bay, at least 34 days (Harrigan and Alkon 1978). California (Jaeckle 1984). Occurs in Puget Metamorphosis occurs when veligers are at Sound sea pen beds at densities up to 2-3/m2 least 300µ and possess eyes, foot and (Birkeland 1974). enlarged propodium (Harrigan and Alkon 1978). Veligers can swim. Life History Information Longevity: Average life span in lab 163 days Reproduction: Hermissenda crassicornis (35 veliger + 128 day adult): a subannual are sub annual species that reproduce year species (Harrigan and Alkon 1978). round. They are hermaphroditic, but self- Food: A generalist predator: carnivore and fertilization is probably unlikely (Harrigan and scavenger. Locates food via chemotaxis Alkon 1978). Mating animals and egg masses (Tyndale et al. 1994). Actively uses are found all year (Puget Sound) (Beeman chemotaxis in prey selection and and Williams 1980). Egg-laying begins when chemoreception is elicited by polar animal is 45 days old, continues until death compounds (Hoover et al. 2012). (in lab) at 128+ days (Harrigan and Alkon Hermissenda has been found to exhibit a 1978). Eggs are pink and have a counter- preference for A. labiata (Hoover et al. 2012). clockwise spiral shape ranging in size from Eats hydroids, particularly Tubularia, 0.24 cm to 3.62 cm and are deposited on Eudendrium, Sarsia in eelgrass (Goddard

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12748 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] 1985). Also eats small sea anemones, 4. COOPER, J.G.1863. Some new bryozoans, colonial ascidian Aplidium, genera and species of California botyrllid ascidians, annelids, small Mollusca. Proceedings of the crustaceans, clams, and dead California Academy of Natural animals. Also feeds on cnidarians, tunicates, Sciences 2:202-207. sponges and other gastropods (Hoover et al. 5. CRANE, S. 1971. The feeding and 2012). Will eat other Hermissenda, but reproductive behavior of the probably only when other food not available sacoglossan gastropod Olea (Goddard 1985). Subtidally in Puget Sound hansineensis Agersborg, 1923. The has consumed sea pen Ptilosarcus (Birkeland Veliger. 14:57-59. 1974). In Humboldt Co., California, prey 6. FARLEY, J., GROVER, L.M., SUN, include anthomedusae, leptomedusae and L., HAUNG, S.J., Eisthen, H.L., chondrophore Velella velella (Jaeckle 1984). Girolami, C., and Wu, R. 1990. Veligers crawl on Obelia, a probable food Chemosensory conditioning of (Harrigan and Alkon 1978). Hermissenda crassicornis. Behavioral Predators: In rocky areas below Monterey, Neuroscience. 104:583-596. California, the large opisthobranch Navanax 7. FARMER, W. M. 1980. Sea-slug inermis (Beeman and Williams 1980). Seastar gastropods. W.M. Farmer Enterprises, Crossaster (Puget Sound) prefers Tempe, AZ. Hermissenda as summer food (Birkeland 8. GODDARD, J.H.R. 1985. Personal 1974). Eggs eaten by sacoglossan Olea communication. Oregon Institute of hansineensis (Crane 1971). Marine Biology, Charleston, OR. Behavior: Very aggressive toward other 9. HARRIGAN, J.F., and D.L. ALKON. nudibranchs and other Hermissenda. Head- 1978. Larval rearing, metamorphosis, on “combats” with the latter probably often growth and reproduction of the eolid part of mating sequence (see Reproduction). nudibranch Hermissenda crassicornis Small Hermissenda have a swimming escape (Eschscholtz, 1831) (Gastropoda: response to seastar predator Crossaster Opisthobranchia). The Biological (Birkeland 1974). Hermissenda found to bulletin. 154:430-9. exhibit learned behavior. In one study, 10. HOOVER, R.A., ARMOUR, R., DOW, Hermissenda was able to learn to avoid foods I. and PURCELL J.E. that displayed an aversive signal (Farley et al. 2012. Nudibranch predation and 1990). dietary preference for the polyps of Aurelia labiata (Cnidaria: Scyphozoa). Bibliography Hydrobiologia. 690:199-213. 1. BEEMAN, R. D., and G. C. 11. JAECKLE, W. B. 1984. The WILLIAMS. Opisthobranchia and opisthobranch mollusks of Humboldt Pulmonata: the sea slugs and allies., County, California. The Veliger. p. 308–354. In: Intertidal invertebrates 26:207-213. of California. R. H. Morris, D. P. 12. KEEN, A. M. 1971. Sea shells of Abbott, and E. C. Haderlie (eds.). tropical west America: marine Stanford University Press, Stanford, mollusks from Baja California to Peru. California. Stanford University Press, Stanford. 2. BEHRENS, D. W. 1980. Pacific coast 13. KOZLOFF, E. N. 1974. Keys to the nudibranchs: a guide to the marine invertebrates of Puget Sound, opisthobranchs of the northeastern the San Juan Archipelago, and Pacific. Sea Challengers, Los Osos, adjacent regions. University of Calif. Washington Press, Seattle and 3. BIRKELAND, C. 1974. Interactions London. between a sea pen and seven of its 14. LINSDAY, T. and VALDES, A. 2016. predators. Ecological Monographs. The model organism Hermissenda 44:211-232. crassicornis (Gastropoda: