Idotea Resecata Class: Malacostraca Order: Isopoda a Valviferan Isopod Family: Idoteidae

Home , Atlantoscia floridana, Idotea, Idoteidae, Pentidotea, Pentidotea resecata

Phylum: Arthropoda, Crustacea Idotea resecata Class: Malacostraca Order: Isopoda A valviferan isopod Family: Idoteidae

Taxonomy: The genus Idotea was described General Morphology: Isopod bodies are by Fabricius in 1798, and although originally dorso-ventrally flattened and can be divided spelled Idotea, several authors adopted the into a compact cephalon, with eyes, two spelling Idothea, since then. The genus antennae and mouthparts, and a pereon Pentidotea was described by Richardson in (thorax) with eight segments, each bearing 1905 and was reduced to subgeneric level by similar pereopods (hence the name “iso- Menzies in 1950. The two subgenera (or pod”). Posterior to the pereon is the pleon, or genera), Pentidotea and Idotea differ by the abdomen, with six segments, the last of which articles on maxilliped palps, the former with is fused with the telson (the pleotelson) (see five and the latter with four (Miller and Lee Plate 231, Brusca et al. 2007). The Isopoda 1970), but are not always currently can be divided into two groups: ancestral recognized (Rafi and Laubitz 1990). (“short-tailed”) groups (i.e. suborders) that Furthermore, this character may be vary with have short telsons and derived (“long-tailed”) age and other characters may reveal more groups with long telsons. Valviferan concrete differences to define the two (Poore (including the Idoteidae) are a distinct group and Ton 1993). Thus synonyms for I. of isopods (Brusca 1984) and have an resecata include, Idothea resecata, elongated telson (Fig. 73, Ricketts and Calvin Pentidotea resecata and Idotea Pentidotea 1952). resecata. Idothea rufescens may also be a Cephalon: Entire, not notched (compare to synonym having been described from an Mesidotea entomon, this guide), sides of immature specimen (Menzies and Waidzunas head straight. First thoracic segment fused 1948). We follow the most recent intertidal with head (Isopoda, Brusca et al. 2007). guide for the northeast Pacific coast (Brusca Rostrum: Slight rostrum (Fig. 3) with et al. 2007), which uses the name Idotea frontal process narrow, pointed and resecata. exceeding frontal lamina visible from ventral side (Fig. 2). Description Eyes: Eyes oval, not markedly Size: Individuals 39–50 mm in length elongate transversely (Fig. 3). (Ricketts and Calvin 1952; Welton and Miller Antenna 1: 1980) and can be 4 ½ times longer than wide Antenna 2: The number of flagellum (Richardson 1905). segments on the second antennae increase Color: Light green, with black with individual size (Menzies and Waidzunas chromatophores when closely associated with 1948). Zostera and yellowish-brown when on kelp Mouthparts: Maxilliped palp with five (Rickets and Calvin 1952; Welton and Miller articles (although juveniles may have only 1980). The body color is a results of four, Poore and Ton 1993) and one coupling carotenoids and carotenoproteins (for hook (Fig. 4). The number of setae on the carotenoid pigments, see Lee and Gilchrist maxilliped increases with individual size 1972) within the cuticle and may serve as (Menzies and Waidzunas 1948). camouflage from fish predation (Best and Pereon: Body elongate and depressed with Stachowicz 2012). Color polymorphism is thorax composed of seven segments (Fig. 1) high in the congener, I. baltica and variation is (Brusca et al. 2007). determined by habitat and predation pressure Pereonites: All seven thoracic but not sexual selection (Jormalainen and somites (pereonites) are free (Idoteidae) with Merilaita 1995). epimeral sutures visible dorsally (except the first somite) (Fig. 1).

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12715 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected]

Pereopods: Seven pairs of Most local species in the Idoteidae ambulatory and similar walking legs (Fig. 1). are within the genus Idotea (12 species), Pleon: Short pleon with six pleonites which includes those with a pleon composed (Brusca et al. 2007). of two complete and one incomplete Pleonites: Two pleonites complete, pleonite(s), a maxillipedal palp with five with one partial horizontal suture (Fig. 1). articles and one coupling seta, eyes that are Pleopods: Appendages of the pleon not elongated transversely and a large include five respiratory pairs and a single pair shield-like pleotelson (Brusca et al. 2007). of uropods (Brusca et al. 2007). The first Idotea sensu Poore and Ton 1993 refers three pairs are particularly locomotory (e.g. for only to individuals with free pleonites, swimming), while the posterior two pairs are anterior spiniform pereopod setae and free strictly respiratory (Alexander 1988; penes, while many northeastern Pacific Alexander et al. 1995). species have fused pleonites, partially fused Uropods: Ventral, not visible dorsally, and penes and reduced coxae (Poore and Ton forming opercular doors or valves covering 1993). Based on these characters, authors pleopods (Valvifera). differentiate Idotea from Pentidotea (see Pleotelson: Large, elongated and shield-like Taxonomy). Idotea resecata is the only with posterior border bearing concave margin, member of the genus to have a concave keels (Fig. 1). pleotelson. Thus it is easy to distinguish it Sexual Dimorphism: Conspicuous sexual from other light green idoteids, such as l. dimorphism is rare among isopods. Mature aculeata and I. montereyensis. females bear a thoracic marsupium and Among the Idotea, I. urotoma, I. males have modified first pleopods, called rufescens, and I. ochotensis have a gonopods (Sadro 2001; Boyko and Wolff maxilliped palp with four articles (rather than 2014). five in the remaining eight Idotea species) a character that previously defined two sub- Possible Misidentifications genera, Idotea Idotea (with four articles) and The order Isopoda contains 10,000 species, Idotea Pentidotea (with five articles) (Menzies 1/2 of which are marine and comprise 10 1950; Miller and Lee 1970). suborders, with eight present from central Of the Idotea species with five California to Oregon (see Brusca et al. maxilliped palp articles (Idotea Pentidotea, 2007). Among isopods with elongated Menzies 1950), I. aculeata, a reddish idoteid, telsons (with anuses and uropods that are has a long projection on its narrowing subterminal), there are several families pleotelson. It has oval eyes (not reniform), including Flabellifera, Anthuridea, long antennae and blunt lateral borders on Gnathiidea, Epicaridea and Valvifera. The the first pleonite. Idotea montereyensis is Valvifera are characterized by hinged doors slender and small (up to 16 mm), red, green- or valves covering the pleopods, well- brown, or black and white and is found on developed coxal plates, the absence of Phyllospadix species and red algae. It has a mandibular palps, occasionally fused rounded telson and with a short projection. pleonites and males with modified sexual Idotea stenops is olive-green to brown, found appendages arising from the first pleonite, on brown algae and with narrow eyes, a rather than the thorax. This suborder slender pointed telson, and 2–3 coupling includes three local families and 34 species: hooks on its maxillipeds, not one. Idotea the Chaetiliidae (see Mesidotea entomon, schmitti has pleonite one with acute lateral this guide), the Arturidae and the Idoteidae. borders and an anterior margin of pereonite The Arturidae is composed of species with one that does not encompass the cephalon. narrow but cylindrical bodies, with the Idotea kirchanskii is bright green and found anterior four pleopods larger and less setose on Phyllospadix species. It has a rounded than the posterior three. Characteristics of telson (lacking a medial projection), oval the Idoteidae include a dorso-ventrally eyes and the epimera of pereonal somites compressed body, similar pereopods, and are visible dorsally only on segments 5–7. seven free pereonites and is composed of 22 species, locally (Brusca et al. 2007).

Hiebert, T.C. 2015. Iodetea resecata. 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. Ecological Information resemble small adults, with no larval stage Range: Type locality is Strait of Juan de (see I. granulosa and I. neglecta Fuca (Menzies 1950). Known range is from development, Stromberg 1965; Boyko and Alaska to Baja, California (Ricketts and Calvin Wolff 2014). Ovigerous I. resecata have been 1952; Iverson 1974; Welton and Miller 1980). observed in July (central California, Welton Idotea as a genus is cosmopolitan (see Fig. 9, and Miller 1980). Idotea baltica and I. Brusca 1984). chelipes produce 1–3 broods per year with Local Distribution: Coos Bay distribution brood sizes that range from 60 to 120 eggs northwest of the Charleston Bridge in South per brood (Limfjord, Denmark, Kroer 1989; Slough. Baltic, Jormalainen and Tuomi 1989). Habitat: Frequently found on or clinging to Larva: Since most isopods are direct eelgrass Zostera or Macrocystis (Ricketts and developing, they lack a definite larval stage. Calvin 1952; Miller 1975), even on drifting Instead this young developmental stage kelp rafts (Hobday 2000). Preferable resembles small adults (e.g. Fig. 40.1, Boyko substrate is mud, but individuals also occur and Wolff 2014). Most isopods develop from under rocks, in crevices and cracks, within embryo to a manca larva, consisting of three empty shells and worm tubes (Brusca et al. stages. Manca larvae are recognizable by 2007). lacking the seventh pair of pereopods, but Salinity: Can survive one hour in fresh water otherwise resemble small adults. They (Welton and Miller 1980). usually hatch from the female marsupium at Temperature: Scarce where surface the second stage and the molt from second to temperatures exceed 18°C (Welton and Miller third manca produces the seventh pair of 1980). North Pacific Idotea species exhibit a pereopods and sexual characteristics (Boyko wide temperature tolerance as their ranges and Wolff 2014). Isopod development and extend across several zoogeographic larval morphology can vary between groups provinces that are associated with (e.g. Gnathiidae, Cryptoniscoidea, temperature barriers for other invertebrates Bopyroidae, Cymothoidae, Oniscoidea) (see (Wallerstein and Brusca 1982). Boyko and Wolff 2014). Parasitic isopods, for Tidal Level: Intertidal, near + 0.15 meters example, have larvae that are morphologically (South Slough of Coos Bay), ranging from dissimilar from adults (Sadro 2001). Isopod surface to 6.4 meters (Richardson 1905). larvae are not common members of the Associates: Gastropods and hermit crabs in plankton, with parasitic larvae most likely to the genera Littorina and Pagurus, as well as be observed. Occasionally, suspended amphipods. benthic juveniles or pelagic species are Abundance: Common in Puget Sound. collected in plankton samples, but these can be differentiated from larvae by their larger Life-History Information size (Sadro 2001). The development of the Reproduction: Most isopods have separate congener I. emarginata was described in sexes (i.e. dioecious, Brusca and Iverson 1955 by Naylor where, within the brood 1985) (although protogynous and protandric chamber, three stages were observed over a species are known, Araujo et al. 2004; Boyko 30 day period (at 9˚C): 1) green eggs 700 µm and Wolff 2014). Reproduction proceeds by in diameter encased in a membrane, 2) copulation and internal fertilization where elongated embryo with rudimentary eggs are deposited within a few hours after appendages and 3) hatched individuals, 1.8 copulation and brooded within the female mm in length, with fully formed appendages. marsupium (e.g. I. emarginata, Naylor 1955; Following hatching individuals molt every two Brusca and Iverson 1985). The biphasic weeks (British Isles, Naylor 1955). molting of isopods allows for copulation; the Juvenile: Juvenile development follows the posterior portion of the body molts and third manca stage, where males have individuals mate, then the anterior portion, gonopods (modified first pleopods) and which holds the brood pouch, molts (Sadro females have plate-like limbs on pereopods 2001). Embryonic development proceeds 2–5, called oostegites (that, together with the within the brood chamber is direct and sternites, form the marsupium) (Boyko and individuals hatch as manca larvae that Wolff 2014). Females begin to brood once

body length is at least 14 mm (Wallerstein Bibliography and Brusca 1982). Longevity: The longevity of the congeners, Idotea baltica and I. chelipes is 11–12 months 1. ALEXANDER, D. E. 1988. Kinematics and 10–11 months, respectively (Limfjord, of swimming in two species of Idotea Denmark, Kroer 1989). (Isopoda, Valvifera). Journal of Growth Rate: Growth among isopods occurs Experimental Biology. 138:37-49. in conjunction with molting where the 2. ALEXANDER, D. E., J. BLODIG, and exoskeleton is shed and replaced. Post-molt S. Y. HSIEH. 1995. Relationship individuals will have soft shells as the cuticle between function and mechanical gradually hardens. During a molt, arthropods properties of the pleopods of isopod have the ability to regenerate limbs that were crustaceans. Invertebrate Biology. previously autonomized (Kuris et al. 2007), 114:169-179. however, isopods do not autotomize limbs as 3. ARAUJO, P. B., A. F. QUADROS, M. readily as other groups (Brusca and Iverson M. AUGUSTO, and G. BOND- 1985). Compared to other arthropods, BUCKUP. 2004. Postmarsupial isopods exhibit a unique biphasic molting, in development of Atlantoscia floridana which the posterior 1/2 of the body molts (van Name, 1940) (Crustacea, before the anterior 1/2 (Brusca et al. 2007). Isopoda, Oniscidea): sexual Food: Idotea resecata is an herbivore, differentiation and size at onset of primarily eating kelp, eelgrass blades (Welton sexual maturity. Invertebrate and Miller 1980), sea grasses (Holbrook et al. Reproduction and Development. 2000; Best and Stachowicz 2012) and their 45:221-230. epiphytes (Williams and Ruckelshaus 1993; 4. BERNSTEIN, B. B., and N. JUNG. Houghes et al. 2010). Populations have the 1979. Selective pressures and ability to destroy entire kelp canopies when coevolution in a kelp canopy predators are lacking (Bernstein and Jung community in southern California. 1979). Idotea species produce a phenolic Ecological Monographs. 49:335-355. compound that reduces feeding on eelgrass 5. BEST, R. J., and J. J. STACHOWICZ. (Zostera species) by other grazers (e.g. 2012. Trophic cascades in seagrass Ampithoe valida, this guide) (Lewis and Boyer meadows depend on mesograzer 2014). Algal feeding rates in Idotea species variation in feeding rates, predation can range from 0.1–71.3 mg per individual susceptibility, and abundance. Marine per day (Trowbridge 1993). Ecology Progress Series. 456:29-42. Predators: Isopods play a significant role as 6. BOYKO, C. B., and C. WOLFF. 2014. intermediate food web links, like amphipods Isopoda and Tanaidacea, p. 210-215. (e.g. see Americorophium salmonis, this In: Atlas of crustacean larvae. J. W. guide), that are consumed by more than 20 Margtin, J. Olesen, and J. T. Høeg species of marine fish (e.g. Oxyjulis (eds.). Johns Hopkins University californica, Bernstein and Jung 1979; Welton Press, Baltimore. and Miller 1980; cabezon, Best and 7. BRUSCA, R. C. 1984. Phylogeny Stachowicz 2012) and whales (Brusca et al. evolution and biogeography of the 2007). marine isopod subfamily Idoteinae Behavior: Always orients on kelp blades, (Crustacea: Isopoda: Idoteidae). along the same axis as the blade. Swimming Transactions of the San Diego Society is accomplished by propulsion from the first of Natural History. 20:99-133. three pairs of pleopods. In Idotea resecata 8. BRUSCA, R. C., C. R. COELHO, and and I. wosnesenskii, the power strokes from S. TAITI. 2007. Isopoda, p. 503-541. each pleopod occur in succession, but the In: The Light and Smith manual: recovery strokes occur simultaneously intertidal invertebrates from central (Alexander 1988). California to Oregon. J. T. Carlton (ed.). University of California Press, Berkeley, CA.

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