Hermissenda Crassicornis Class: Gastropoda, Heterobranchia, Euthyneura, Ringipleura

Hermissenda crassicornis Class: Gastropoda, Heterobranchia, Euthyneura, Ringipleura

An opalescent aeolid nudibranch Order: Nudipleura, Nudibranchia, Cladobranchia

Taxonomy: Hermissenda crassicornis is a faint "leaves" or rings (Farmer 1980); “weakly complex of three distinct species (Lindsay perfoliate” (McDonald and Nybakken 1980) or and Valdes 2016). H. crassicornis is used annulate, otherwise solid (fig. 1). Color: as for the species found in the northeast Pacif- ground. ic. Those found from Northern California to Foot: Split in front (“anteriorly bilabiate”) the Sea of Cortez are referred to as H. opal- (Farmer 1980); lateral angles produced into escens and those found in Japan fall under horns (fig. 1); foot extends posteriorly into the name H. emurai (Lindsay and Valdes long, pointed tail. Foot corners or horns also 2016). called “pedal tentacles” (Kozloff 1974). Hermissenda crassicornis can be dis- Cerata: Large, conical, in 11 clusters of trans- tinguished from the other two species by the verse rows (Farmer 1980) covering animal's presence of white longitudinal lines in the back. Cerata begin posterior to rhinophores cerata (Lindsay and Valdes 2016). H. opal- (Beeman and Williams 1980), are longest in escens lacks these white lines in the cerata, median region of 1st two groups (Behrens and H. emurai has been described as hav- 1980). Each cera with a core of digestive ing a pale yellow body, a broken mid-dorsal gland (fig. 1), and at tip a cnidosac, which col- vermillion line mid-way down from the anteri- lects nematocysts from cnidarian prey or end, and with two parallel lines running (MacFarland 1966). down the sides of the body, bluish and ver- Oral Tentacles: Usually present, order Nudi- milion in color (Lindsay and Valdes 2016). branchia (McDonald 1975). Long, white, pointed (fig. 1). Description Gills: None (fig. 1). Cerata serve as gills. Size: 30 mm to 80 mm long (Beeman and Eyes: Small, black; posterior to bases of rhi- Williams 1980); illustrated specimen (Coos nophores (fig. 1). Eyes consist of a lens and Bay) 50 mm. five photoreceptor cells. The photoreceptor Color: Ground color often white, transparent cells have position sensitivity due to their (MacFarland 1966), with opalescent white or asymmetrical arrangement and send nerve blue line around foot, down each oral tenta- impulses to the brain via an axon (Stensaas cle (McDonald 1975). Line down back is light et al. 1969). H. crassicornis eyes are used in or bright orange (Lindsay and Valdes 2016). neurological studies (Beeman and Williams Line can form diamond shape between first 1980). cerata. Cerata cores (digestive glands) are Radula and Jaws: Ribbon of horseshoe- light to dark brown or bright orange and shaped teeth; each central cusp with a single each cera has a distinct white stripe on the row of up to 28 teeth; 4-6 sharp spines on ei- anterior side (Lindsay and Valdes 2016). ther side of middle cusp whose under- surface Body: Oblong, flat-bottomed, with rhino- has up to 15 small points (MacFarland 1966) phores, cerata, and tail, but without posterior (fig. 4). Hermissenda found in Oregon have 4- plume of branched gills (fig. 1). 5 denticles, these are smaller than those Rhinophores: Long; with 8 - 24 slanted,

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]

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.

found in other members of the species com- The nudibranchs in the other major plex and appear as bumbs (Lindsay and suborder, Doridacea, are larger, with a large Valdes 2016). flat foot, thick mantle and obvious gills, i.e. Mouth: Jaw border with up to 50 denticles Onchidoris, Triopha (McDonald and (MacFarland 1966). (Mandibles not figured.) Nybakken 1980). Genital Openings: Genital apertures on low Another suborder, Dendronotacea, re- posterior part of 1st group of cerata semble aeolids, but have sheaths for their rhi- (MacFarland 1966) (not visible as drawn, but nophores and a mid-lateral anus. Examples see arrow, fig. 1). are Tritonia, Tethys, Melibe, and especially Anus: Tubular, located on the right, be- Dendronotus spp. tween 2nd and 3rd groups of cerata (fig. 1) The Arminacea are a very diverse (MacFarland 1966). Concealed (MacFarland group lacking rhinophore sheaths and usually 1966). Anus more anterior than in Aeolidi- lacking oral tentacles; the anus is anterior. dae (Keen 1971). Some have cerata, but others do not. Janolus Renal Pore: Lateral, between 1st and 2nd fuscus has cerata very like Hermissenda group of cerata (not visible, but see arrow, (orange and white tipped), but also has a red fig. 1). cockscomb between the rhinophores, colored Eggs: In pink, sausage-like string; each like the cerata. Cerata begin anterior to the measures 1 mm in diameter, attached rhinophores and fall off easily; they are found through much of its length to substrate. only on the periphery of the dorsum String makes tight counterclockwise spiral, (McDonald and Nybakken 1980). Janolus also which measures between 0.24 cm and 3.62 lacks the blueish lines on the body found on cm (Harrington and Alkon 1979). Each cap- Hermissenda. This species was formerly sule can have 1 – 4 eggs (Beeman and Wil- called Antiopella barbarensis (Cooper 1863). liams 1980) (fig. 5). The Hermissenda suborder Aeolidacea includes two superfamilies: Protoaeolidoidea, Possible Misidentifications with one family, Notaeolidiidae; and Euae- Nudibranchs can be separated from olidoidea, with 21 families. Only a few species other apparently shell-less opisthobranchs from this latter superfamily could be confused by their radulae and jaws (they are carnivo- with Hermissenda: rous), and by their rhinophores, which are Fiona pinnata is similar in morphology not rolled as they are in sacoglossans. Nudi- to Hermissenda, but has smooth rhinophores branchs also have oral tentacles. In addition, and sail-like flaps on its cerata. The cerata are they have lost all shell and opercula (as dense along the margins; a large part of the adults) as well as mantle cavity and gills. back is clear (Keen 1971); it has no blue lines Some may have secondary gills on their or orange spots. Cosmopolitan. backs (McDonald and Nybakken 1980). Nu- The Coryphellidae have produced foot dibranch genital openings are on the right corners, but not angular ones as in Facelini- side. dae (Keen 1971). Their numerous cerata are The nudibranchs found in the Hermis- clustered and elongate, as in Hermissenda. senda suborder, Aeolidiacea, are relatively Coryphella trilineata has three white (not blue) small, long, and narrow, gill-less, and have lines on a white body, but there are no orange cerata. They feed partly on cnidaria, and are spots within them. The cerata can look much able to store nematocysts in their cerata like Hermissenda, but have cadmium yellow (Keen 1971). tips. The rhinophores are annulate and col-

ored yellow or orange. Temperature: Annual range 9-18 °C Aeolidia papillosa, the shag rug nudi- (Beeman and Williams 1980). branch found with anemones, is white with Tidal Level: Low intertidal; subtidal down to gray to brown spots. It has sharp pedal ten- 35m (Beeman and Williams 1980). tacles like Hermissenda, but its cerata begin Associates: Copepod Hemicyclops thysano- anterior to the rhinophores and are lanceo- tus often found on its back (Beeman and Wil- late, i.e. broad-based and sharp-tipped, not liams 1980). Found on fouling panels regard- conical as in Hermissenda. less of presence of other organisms. Sea pen Spurillidae (genus Spurilla) have rhi- Ptilosarcus (Puget Sound) (Birkeland 1974). nophores with quite oblique leaves, and Also see “Food”. have orange head markings. The cerata of Weight: 5-8 grams (Harrigan and Alkon S. olivae are quite like Hermissenda: or- 1978). ange, white tipped brown cores. Both this Abundance: One of the most common aeol- species and S. chromosoma are found only ids in northeastern Pacific, especially in mid- from central California south however dle of range, but its occurrence is temporally (McDonald and Nybakken 1980). variable at any one part of the range (Ricketts There are two other nudibranchs in and Calvin 1971). Dominant littoral opistho- the family Facelinidae (was Phidianidae branch in abundance and geographical distri- (McDonald and Nybakken 1980). Both are of bution, Humboldt Bay, California (Jaeckle the genus Phidiana and found only from 1984). Occurs in Puget Sound sea pen beds central California south. Both P. hiltoni at densities up to 2-3/m2 (Birkeland 1974). (=pugnax) and P. morrowensis have orange Life-History Information markings on the head and on the rhino- Reproduction: Hermissenda crassicornis are phores. These two are closely related, but sub annual species that reproduce year not likely to be confused with each other or round. They are hermaphroditic, but self- with Hermissenda. fertilization is probably unlikely (Harrigan and Several other nudibranchs of diverse Alkon 1978). Mating animals and egg masses families could resemble Hermissenda super- are found all year (Puget Sound) (Beeman ficially in color, so care must be taken to ob- and Williams 1980). Egg-laying begins when serve carefully the rhinophores, foot tenta- animal is 45 days old, continues until death (in cles, and especially the blue/white lines of lab) at 128+ days (Harrigan and Alkon 1978). Hermissenda. Eggs are pink and have a counter-clockwise Ecological Information spiral shape ranging in size from 0.24 cm to Range: Sitka, Alaska to Baja California, 3.62 cm and are deposited on algae or Zos- Mexico (Beeman and Williams 1980). tera (Harrigan and Alkon 1978). Motile sperm Local Distribution: Coos Bay: small boat found in 34 mg animals, and egg laying by 73 basin, Charleston, seasonally, especially in mg animals in lab (Harrigan and Alkon 1978). summer. Sperm from one copulation enough to fertilize Habitat: Varied: rocky tidepools, floats, mud most eggs in about three egg masses and sand flats (Beeman and Williams 1980; (Rutowski 1983). Goddard 1985), eelgrass beds (Puget Copulation in Hermissenda is relatively Sound), bare rock and on seaweed. Also short compared to other sea slugs. The pro- found on boat docks (Hoover et al. 2012). cess of intromitting between simultaneous Salinity: Collected at 30 (Coos Bay). hermaphrodites will last only a couple of sec-

onds. Two individuals will meet head to botyrllid ascidians, annelids, small crusta- head and will go through flagellation, the ceans, clams, and dead animals. Also feeds process of sensing each other with their ten- on cnidarians, tunicates, sponges and other tacles. Following this process both animals gastropods (Hoover et al. 2012). Will eat other will “slide” towards the right side of each oth- Hermissenda, but probably only when other er where the gonopores are located and food not available (Goddard 1985). Subtidally simultaneously copulate by erecting their in Puget Sound has consumed sea pen Ptilo- cerata and intromitting. Violent lunging and sarcus (Birkeland 1974). In Humboldt Co., biting behavior once thought to be aggres- California, prey include anthomedusae, lepto- sive now known to be part of brief mating medusae and chondrophore Velella velella sequence (Rutowski 1983); many attempts (Jaeckle 1984). Veligers crawl on Obelia, a at copulation are unsuccessful. probable food (Harrigan and Alkon 1978). Eggs hatch after 5-6 days into a Predators: In rocky areas below Monterey, planktonic veliger stage that lasts at least 34 California, the large opisthobranch Navanax days. Veligers that are ready to metamor- inermis (Beeman and Williams 1980). Seastar phose have eyes, a shell measuring Crossaster (Puget Sound) prefers Hermissen- 300mm, and a developed foot. After com- da as summer food (Birkeland 1974). Eggs pleting the larval stage, veligers crawl onto a eaten by sacoglossan Olea hansineensis hydroid and 12-24 hours later the larva (Crane 1971). crawls out of its shell to complete metamor- Behavior: Very aggressive toward other nudi- phosis. The new juvenile uses hydroid tissue branchs and other Hermissenda. Head-on as a food source (Harrigan and Alkon 1978). “combats” with the latter probably often part of Larva: mating sequence (see Reproduction). Small Juvenile: Hermissenda have a swimming escape re- Longevity: Average life span in lab 163 sponse to seastar predator Crossaster days (35 veliger + 128 day adult): a suban- (Birkeland 1974). Hermissenda found to ex- nual species (Harrigan and Alkon 1978). hibit learned behavior. In one study, Hermis- Growth Rate: Veligers hatch in 5-6 days in senda was able to learn to avoid foods that lab at 13-15 °C and obligatory veliger stage displayed an aversive signal (Farley et al. of at least 34 days (Harrigan and Alkon 1990). 1978). Metamorphosis occurs when veligers Bibliography are at least 300µ and possess eyes, foot and enlarged propodium (Harrigan and 1. BEEMAN, R. D., and G. C. WILLIAMS. Alkon 1978). Veligers can swim. Opisthobranchia and Pulmonata: the sea Food: A generalist predator: carnivore and slugs and allies., p. 308–354. In: Intertidal scavenger. Locates food via chemotaxis invertebrates of California. R. H. Morris, D. (Tyndale et al. 1994). Actively uses chemo- P. Abbott, and E. C. Haderlie (eds.). Stan- taxis in prey selection and chemoreception ford University Press, Stanford, California. is elicited by polar compounds (Hoover et al. 2. BEHRENS, D. W. 1980. Pacific coast nu- 2012). Hermissenda has been found to ex- dibranchs: a guide to the opisthobranchs hibit a preference for A. labiata (Hoover et of the northeastern Pacific. Sea Challeng- al. 2012). Eats hydroids, particularly Tubu- ers, Los Osos, Calif. laria, Eudendrium, Sarsia in eelgrass 3. BIRKELAND, C. 1974. Interactions be- (Goddard 1985). Also eats small sea anem- tween a sea pen and seven of its preda- ones, bryozoans, colonial ascidian Aplidium, tors. Ecological Monographs. 44:211-232.

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