Idotea Resecata Class: Multicrustacea, Malacostraca, Eumalacostraca

Home , Chaetiliidae, Eumalacostraca, Idotea, Idoteidae, Pentidotea, Pentidotea resecata

Phylum: Arthropoda, Crustacea

Idotea resecata Class: Multicrustacea, Malacostraca, Eumalacostraca

Order: Peracarida, Isopoda, Valvifera A valviferan isopod Family: Idoteidae

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

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]

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.

maxilliped increases with individual size telsons (with anuses and uropods that are (Menzies and Waidzunas 1948). subterminal), there are several families in- Rostrum: Slight rostrum (Fig. 3) with cluding Flabellifera, Anthuridea, Gnathiidea, frontal process narrow, pointed and exceed- Epicaridea and Valvifera. The Valvifera are ing frontal lamina visible from ventral side characterized by hinged doors or valves cov- (Fig. 2). ering the pleopods, well-developed coxal Pereon: Body elongate and depressed with plates, the absence of mandibular palps, oc- thorax composed of seven segments (Fig. 1) casionally fused pleonites and males with (Brusca et al. 2007). modified sexual appendages arising from the Peronites: All seven thoracic somites first pleonite, rather than the thorax. This (pereonites) are free (Idoteidae) with suborder includes three local families and 34 epimeral sutures visible dorsally (except the species: the Chaetiliidae (see Mesidotea en- first somite) (Fig. 1). tomon, this guide), the Arturidae and the Ido- Pereopods: Seven pairs of ambula- teidae. The Arturidae is composed of spe- tory and similar walking legs (Fig. 1). cies with narrow but cylindrical bodies, with Pleon: Short pleon with six pleonites the anterior four pleopods larger and less se- (Brusca et al. 2007). tose than the posterior three. Characteristics Pleonites: Two pleonites complete, of the Idoteidae include a dorso-ventrally with one partial horizontal suture (Fig. 1). compressed body, similar pereopods, and Pleopods: Appendages of the pleon seven free pereonites and is composed of 22 include five respiratory pairs and a single species, locally (Brusca et al. 2007). pair of uropods (Brusca et al. 2007). The Most local species in the Idoteidae are first three pairs are particularly locomotory within the genus Idotea (12 species), which (e.g. for swimming), while the posterior two includes those with a pleon composed of two pairs are strictly respiratory (Alexander complete and one incomplete pleonite(s), a 1988; Alexander et al. 1995). maxillipedal palp with five articles and one Uropods: Ventral, not visible dorsally, and coupling seta, eyes that are not elongated forming opercular doors or valves covering transversely and a large shield-like pleo- pleopods (Valvifera). telson (Brusca et al. 2007). Idotea sensu Pleotelson: Large, elongated and shield- Poore and Ton 1993 refers only to individu- like with posterior border bearing concave als with free pleonites, anterior spiniform margin, keels (Fig. 1). pereopod setae and free penes, while many Sexual Dimorphism: Conspicuous sexual northeastern Pacific species have fused ple- dimorphism is rare among isopods. Mature onites, partially fused penes and reduced females bear a thoracic marsupium and coxae (Poore and Ton 1993). Based on males have modified first pleopods, called these characters, authors differentiate Idotea gonopods (Sadro 2001; Boyko and Wolff from Pentidotea (see Taxonomy). Idotea 2014). resecata is the only member of the genus to have a concave pleotelson. Thus it is easy Possible Misidentifications to distinguish it from other light green The order Isopoda contains 10,000 idoteids, such as l. aculeata and I. montere- species, 1/2 of which are marine and com- yensis. prise 10 suborders, with eight present from Among the Idotea, I. urotoma, I. ru- central California to Oregon (see Brusca et fescens, and I. ochotensis have a maxilliped al. 2007). Among isopods with elongated palp with four articles (rather than five in the

remaining eight Idotea species) a character under rocks, in crevices and cracks, within that previously defined two sub-genera, empty shells and worm tubes (Brusca et al. Idotea Idotea (with four articles) and Idotea 2007). Pentidotea (with five articles) (Menzies Salinity: Can survive one hour in fresh water 1950; Miller and Lee 1970). (Welton and Miller 1980). Of the Idotea species with five maxil- Temperature: Scarce where surface tempe- liped palp articles (Idotea Pentidotea, Men- ratures exceed 18°C (Welton and Miller zies 1950), I. aculeata, a reddish idoteid, 1980). North Pacific Idotea species exhibit a has a long projection on its narrowing pleo- wide temperature tolerance as their ranges telson. It has oval eyes (not reniform), long extend across several zoogeographic antennae and blunt lateral borders on the provinces that are associated with first pleonite. Idotea montereyensis is slen- temperature barriers for other invertebrates der and small (up to 16 mm), red, green- (Wallerstein and Brusca 1982). brown, or black and white and is found on Tidal Level: Intertidal, near + 0.15 meters Phyllospadix species and red algae. It has (South Slough of Coos Bay), ranging from a rounded telson and with a short projec- surface to 6.4 meters (Richardson 1905). tion. Idotea stenops is olive-green to Associates: Gastropods and hermit crabs in brown, found on brown algae and with na- the genera Littorina and Pagurus, as well as rrow eyes, a slender pointed telson, and 2– amphipods. 3 coupling hooks on its maxillipeds, not Abundance: Common in Puget Sound. one. Idotea schmitti has pleonite one with Life-History Information acute lateral borders and an anterior mar- Reproduction: Most isopods have separate gin of pereonite one that does not encom- sexes (i.e. dioecious, Brusca and Iverson pass the cephalon. Idotea kirchanskii is 1985) (although protogynous and protandric bright green and found on Phyllospadix species are known, Araujo et al. 2004; Boyko species. It has a rounded telson (lacking a and Wolff 2014). Reproduction proceeds by medial projection), oval eyes and the copulation and internal fertilization where epimera of pereonal somites are visible dor- eggs are deposited within a few hours after sally only on segments 5–7. copulation and brooded within the female Ecological Information marsupium (e.g. I. emarginata, Naylor 1955; Range: Type locality is Strait of Juan de Fu- Brusca and Iverson 1985). The biphasic molt- ca (Menzies 1950). Known range is from ing of isopods allows for copulation; the pos- Alaska to Baja, California (Ricketts and Cal- terior portion of the body molts and individuals vin 1952; Iverson 1974; Welton and Miller mate, then the anterior portion, which holds 1980). Idotea as a genus is cosmopolitan the brood pouch, molts (Sadro 2001). Embry- (see Fig. 9, Brusca 1984). onic development proceeds within the brood Local Distribution: Coos Bay distribution chamber is direct and individuals hatch as northwest of the Charleston Bridge in South manca larvae that resemble small adults, with Slough. no larval stage (see I. granulosa and I. ne- Habitat: Frequently found on or clinging to glecta development, Stromberg 1965; Boyko eelgrass Zostera or Macrocystis (Ricketts and Wolff 2014). Ovigerous I. resecata have and Calvin 1952; Miller 1975), even on drift- been observed in July (central California, Wel- ing kelp rafts (Hobday 2000). Preferable ton and Miller 1980). Idotea baltica and I. substrate is mud, but individuals also occur chelipes produce 1–3 broods per year with

brood sizes that range from 60 to 120 eggs sternites, form the marsupium) (Boyko and per brood (Limfjord, Denmark, Kroer 1989; Wolff 2014). Females begin to brood once Baltic, Jormalainen and Tuomi 1989). body length is at least 14 mm (Wallerstein Larva: Since most isopods are direct devel- and Brusca 1982). oping, they lack a definite larval stage. In- Longevity: The longevity of the congeners, stead this young developmental stage re- Idotea baltica and I. chelipes is 11–12 months sembles small adults (e.g. Fig. 40.1, Boyko and 10–11 months, respectively (Limfjord, and Wolff 2014). Most isopods develop Denmark, Kroer 1989). from embryo to a manca larva, consisting of Growth Rate: Growth among isopods occurs three stages. Manca larvae are recogniza- in conjunction with molting where the exoskel- ble by lacking the seventh pair of pereo- eton is shed and replaced. Post-molt individ- pods, but otherwise resemble small adults. uals will have soft shells as the cuticle gradu- They usually hatch from the female marsupi- ally hardens. During a molt, arthropods have um at the second stage and the molt from the ability to regenerate limbs that were second to third manca produces the seventh previously autonomized (Kuris et al. 2007), pair of pereopods and sexual characteristics however, isopods do not autotomize limbs as (Boyko and Wolff 2014). Isopod develop- readily as other groups (Brusca and Iverson ment and larval morphology can vary be- 1985). Compared to other arthropods, tween groups (e.g. Gnathiidae, Cryptoniscoi- isopods exhibit a unique biphasic molting, in dea, Bopyroidae, Cymothoidae, Oniscoidea) which the posterior 1/2 of the body molts (see Boyko and Wolff 2014). Parasitic iso- before the anterior 1/2 (Brusca et al. 2007). pods, for example, have larvae that are mor- Food: Idotea resecata is an herbivore, pri- phologically dissimilar from adults (Sadro marily eating kelp, eelgrass blades (Welton 2001). Isopod larvae are not common mem- and Miller 1980), sea grasses (Holbrook et al. bers of the plankton, with parasitic larvae 2000; Best and Stachowicz 2012) and their most likely to be observed. Occasionally, epiphytes (Williams and Ruckelshaus 1993; suspended benthic juveniles or pelagic spe- Houghes et al. 2010). Populations have the cies are collected in plankton samples, but ability to destroy entire kelp canopies when these can be differentiated from larvae by predators are lacking (Bernstein and Jung their larger size (Sadro 2001). The develop- 1979). Idotea species produce a phenolic ment of the congener I. emarginata was de- compound that reduces feeding on eelgrass scribed in 1955 by Naylor where, within the (Zostera species) by other grazers (e.g. brood chamber, three stages were observed Ampithoe valida, this guide) (Lewis and Boyer over a 30 day period (at 9˚C): 1) green eggs 2014). Algal feeding rates in Idotea species 700 µm in diameter encased in a mem- can range from 0.1–71.3 mg per individual per brane, 2) elongated embryo with rudimen- day (Trowbridge 1993). tary appendages and 3) hatched individuals, Predators: Isopods play a significant role as 1.8 mm in length, with fully formed append- intermediate food web links, like amphipods ages. Following hatching individuals molt (e.g. see Americorophium salmonis, this every two weeks (British Isles, Naylor 1955). guide), that are consumed by more than 20 Juvenile: Juvenile development follows the species of marine fish (e.g. Oxyjulis third manca stage, where males have gono- californica, Bernstein and Jung 1979; Welton pods (modified first pleopods) and females and Miller 1980; cabezon, Best and have plate-like limbs on pereopods 2–5, Stachowicz 2012) and whales (Brusca et al. called oostegites (that, together with the 2007).

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