Gnorimosphaeroma Insulare Class: Malacostraca Order: Isopoda, Flabellifera Family: Sphaeromatidae

Phylum: Arthropoda, Crustacea Gnorimosphaeroma insulare Class: Malacostraca Order: Isopoda, Flabellifera Family: Sphaeromatidae

Taxonomy: The genus Gnorimosphaeroma Eyes: was described in 1954 by Menzies with six Antenna 1: First antenna longer than species including G. insulare as well as G. second and basal articles are separated by lutea, G. oregonensis, each a subspecies of the rostrum (Fig. 3) (see Fig. 4 Hoestlandt, G. oregonensis, differentiable by pleotelson 1977). morphology. Some authors later elevated Antenna 2: Shorter than first antenna these two subspecies to species status based (see Fig. 4 Hoestlandt, 1977). on habitat and physiology (e.g. Riegel 1959). Mouthparts: Mandible with a palp Furthermore, G. insulare and G. lutea were and maxilliped with four articles. Hairs synonymized by Hoestlandt in 1977 and, present on antero-lateral edge of articles 2–4 although some authors (including those for are less than ½ the length of the article (see our current, local intertidal guide, Brusca et al. Figs. 5–8, Hoestlandt 1977). 2007) also consider G. oregonensis a Pereon: synonym of G. insulare, others differentiate Pereonites: Seven free pereonites the two based on habitat: G. insulare is strictly total. marine while G. insulare is estuarine Pereopods: Seven pereopod pairs. (Stanhope et al. 1987). The basis of the first pereopod is hairless and distal extremity with one hair or hairless (Fig. Description 6). Size: Males up to 8 mm in length (Miller Pleon: Pleon consists of three parts. The 1975) and almost twice as long as wide. first is concealed under the last pereonite, the Color: White with small black second consists of of several coalesced chromatophores. pleonites often with partial sutures (Fig. 1), General Morphology: Isopod bodies are and the third part is the large pleotelson. dorso-ventrally flattened and can be divided Pleonites: Only two of three reach into a compact cephalon, with eyes, two the lateral margin, third pleonite is under the antennae and mouthparts, and a pereon second (Figs. 1, 4). (thorax) with eight segments, each bearing Pleopods: Five pleopod pairs. The similar pereopods (hence the name “iso- first pair is not widely separated at the base, pod”). Posterior to the pereon is the pleon, or and is similar in size to the second. The first abdomen, with six segments, the last of which three pairs are with marginal plumose setae. is fused with the telson (the pleotelson) (see The fourth and fifth pairs are fleshy and Fig. 1, Harrison and Ellis 1991; Plate 231, without transverse folds, and the fourth is with Brusca et al. 2007). The Isopoda can be a bent exopod (Fig. 2, 1-v). The number and divided into two groups: ancestral (“short- arrangement of these folds of the endopods tailed”) groups (i.e. suborders) that have short and exopods is considered an important telsons and derived (“long-tailed”) groups with taxonomic character by some authors (e.g. long telsons. Members of the Flabellifera, to Cassidinidae, Fig. 2, Iverson 1982; Fig. 1, which G. insulare belongs, fall into the long- Harrison and Ellis 1991). tailed variety. Body surface in Uropods: Two branched uropods visible Gnorimosphaeroma insulare is smooth and dorsally, with rigid endopod and flexible with eight segments from cephalon to pereon. exopod (Fig. 5) (see Fig. 9, Hoestlandt 1977). Individuals able to roll into a ball Pleotelson: Rounded and convex (Fig. 1). (Sphaeromatidae). Sexual Dimorphism: Conspicuous sexual Cephalon: Frontal border smooth (Fig. 3). dimorphism is rare among isopods, however, Rostrum: mature females are often broader and bear a

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12708 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] thoracic marsupium while males have Cassidinidae, Fig. 2, Iverson 1982; Fig. 1, modified first pleopods, called gonopods Harrison and Ellis 1991), the first pereopod is (Sadro 2001; Boyko and Wolff 2014). ambulatory and the uropod is with an Protogyny has been observed (see exopod. In G. noblei the first article of the Reproduction) in G. insulare and females left and right antennae peduncles are can have rudimentary penes after brood touching while they are not in G. release (Brook et al. 1994). oregonense. Gnorimosphaeroma rayi. so far found only in Tomales Bay, California and in Possible Misidentifications Japan, is an estuarine species found also The order Isopoda contains 10,000 species, above the mid-tide line, and also under 1/2 of which are marine and comprise 10 stones. In this species, the basis of the first suborders, with eight present from central pereopod has a tuft of 7–9 setae and 2–3 California to Oregon (see Brusca et al. setae are present on the sternal crest of the 2007). Among isopods with elongated ischium. Gnorimosphaeroma oregonense, is telsons (with anuses and uropods that are found above the mid-tide line, usually under subterminal), there are several groups (i.e. stones. Gnorimosphaeroma oregonense is suborders) including Valvifera, Anthuridea, stouter than G. insulare, being 1.5 to 1.75 Gnathiidea, Epicaridea and Flabellifera. times longer than wide and all three The Flabellifera is a large pleonites reach the lateral margin and the assemblage contains 3,000 species with frontal border of its head has several curves seven families occurring locally, three of (compare Plate 243C to 252C1, Brusca et al. 2 which are not present north of Point 2007). The exopod of the uropod is only /3 Conception, California (Brusca et al. 2007). as long as the endopod (Richardson 1905). The Flaberllifera are characterized by body Gnorimosphaeroma rayi also has three length that is rarely less than 3 mm and a pleonites reaching the lateral margin (Fig. pleon with less than three free pleonites 4b) and the basis of the first pereopod is (plus the pleotelson). The family setose. It is stout like G. oregonense, and Sphaeromatidae is almost certainly has longer antennae than either G. paraphyletic (Brandt and Poore 2003) and oregonense or G. insulare. includes 37 species in 11 genera in the western coast of North America (Wall et al. Ecological Information 2015) and has a pleon with 1–2 free Range: Type locality is San Nicolas Island, pleonites, a convex body that is not California (Menzies 1954). Known range from depressed, antennae that are widely Alaska to California (Menzies 1954a), where it separated, indistinct frontal lamina and is most common north of Point Conception subequal pleopods, where pleopods 4–5 (Miller 1968). are ovate in shape (see also Iverson 1982). Local Distribution: Oregon distribution in There are 17–24 species in this family from the Siuslaw estuary and Cox Island as well as central California to Oregon (Brusca et al. the Medcalf Preserve (South Slough of Coos 2007). These species belong to the Bay) and Carter Lake (Wones and Larson following genera: Ancinus, Clianella, 1991). Dynamene, Paradella, Pseudosphaeroma, Habitat: Estuarine intertidal, among Fucus Tecticeps (all with one species), Paracereis, and under logs in Salicornia marshes and in Sphaeroma (each with two species), mud or drainage channels (e.g. Metcalf Dynamenella, Exosphaeroma (each with 4– Preserve) as well as sedge marshes, 5 species) (for detailed key of amongst wood debris and within algal beds Exosphaeroma see Wall et al. 2015) and and banks (Stanhope et al. 1987). Benthic in Gnorimosphaeroma has two to four species Tomales Bay. locally. Salinity: Euryhaline (Wones and Larson The fourth and fifth pleopods in 1991). Estuarine to fresh water and can Gnorimosphaeroma lack pleats (see

Hiebert, T.C. 2015. Gnorimosphaeroma insulare. 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. tolerate salinities from 6–35 (Welton and Larva: Since most isopods are direct Miller 1980). developing, they lack a definite larval stage. Temperature: Instead this young developmental stage Tidal Level: -1.4 meters to subtidal (Metcalf resembles small adults (e.g. Fig. 40.1, Boyko Preserve, Hoestlandt 1969a). and Wolff 2014). Most isopods develop from Associates: Alga Fucus, amphipod embryo to a manca larva, consisting of three Orchestia, littorine snail Ovatella (Metcalf stages. Manca larvae are recognizable by Preserve) and amphipod Anisogammarus lacking the seventh pair of pereopods, but (Siuslaw estuary). Co-occurs, but is not otherwise resemble small adults. They negatively affected by the non-native mud usually hatch from the female marsupium at snail, Potamopyrgus antipodarum (Brenneis the second stage and the molt from second to et al. 2010). third manca produces the seventh pair of Abundance: Individuals have a tendency to pereopods and sexual characteristics (Boyko congregate. Individuals were abundant at and Wolff 2014). Isopod development and some depth in the coastal dune lake, Carter larval morphology can vary between groups Lake (Oregon National Dunes Recreational (e.g. Gnathiidae, Cryptoniscoidea, Area, Wones and Larson 1991). Bopyroidae, Cymothoidae, Oniscoidea) (see Boyko and Wolff 2014). Parasitic isopods, for Life-History Information example, have larvae that are morphologically Reproduction: Most isopods have separate dissimilar from adults (Sadro 2001). Isopod sexes (i.e. dioecious, Brusca and Iverson larvae are not common members of the 1985), although protogynous and protandric plankton, with parasitic larvae most likely to species are known (Brook et al. 1994; Araujo be observed. Occasionally, suspended et al. 2004; Boyko and Wolff 2014). benthic juveniles or pelagic species are Protogyny has been observed in both G. collected in plankton samples, but these can insulare (as G. luteum) G. oregonense, where be differentiated from larvae by their larger females have rudimentary penes and grow to size (Sadro 2001). The release of manca sexually mature males following several molts larvae in G. insulare occurred in July after brood release (see Table 1, Brook et al. (Stanhope et al. 1987). 1994). Reproduction proceeds by copulation Juvenile: and internal fertilization where eggs are Longevity: The longevity of the congeners deposited within a few hours after copulation G. rayi and G. oregonense are one year and and brooded within the female marsupium 2.3 years, respectively (Hoestlandt 1969). An (Brusca and Iverson 1985). The biphasic annual, semelparous species, molting of isopods allows for copulation; the Gnorimosphaeroma insulare males die after posterior portion of the body molts and mating and females die shortly after larvae individuals mate, then the anterior portion, hatch (Stanhope et al. 1987). which holds the brood pouch, molts (Sadro Growth Rate: Growth among isopods occurs 2001). Embryonic development proceeds in conjunction with molting where the within the brood chamber and is direct with exoskeleton is shed and replaced. Post-molt individuals hatching as manca larvae that individuals will have soft shells as the cuticle resemble small adults, with no larval stage gradually hardens. During a molt, arthropods (Boyko and Wolff 2014). Little about the have the ability to regenerate limbs that were reproductive and developmental biology of G. previously autonomized (Kuris et al. 2007), insulare is known, but ovigerous females however, isopods do not autotomize limbs as were observed in March, larger females readily as other groups (Brusca and Iverson produce larger brood, egg sizes vary from 1985). Compared to other arthropods, 450–480 µm, and the average developmental isopods exhibit a unique biphasic molting, in time is 120 days (Squamish estuary, British which the posterior 1/2 of the body molts Columbia Canada, Stanhope et al. 1987). before the anterior 1/2 (Brusca et al. 2007). Gnorimosphaeroma rayi reproduces in spring Growth rates in G. insulare were faster in only, on a one year cycle and G. oregonensis males than females (see Fig. 5, Stanhope et has young in spring and fall (Hoestlandt al. 1987). 1969). A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12708 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Food: A detritivore and scavenger. The BRENNEIS, V. E. F., A. SIH, and C. E. DE congener, G. oregonense, co-occurs with and RIVERA. 2010. Coexistence in the readily eats egg capsules of the gastropod intertidal: interactions between the Nucella emarginata. In fact, predation by this nonindigenous New Zealand mud isopod may cause N. emarginata to produce snail Potamopyrgus antipodarum and egg capsules with thicker walls that are more the native estuarine isopod resistant to predation (Rawlings 1994). Gnorimosphaeroma insulare. Oikos. Predators: Isopods play a significant role as 119:1755-1764. intermediate food web links, like amphipods, —. 2011. Integration of an invasive consumer (e.g. see Americorophium salmonis, this into an estuarine food web: direct and guide) that are consumed by more than 20 indirect effects of the New Zealand species of marine fish (Welton and Miller mud snail. Oecologia. 167:169-179. 1980; juvenile salmonids, sculpins, flounder BROOK, H. J., T. A. RAWLINGS, and R. W. and rockfish, Stanhope et al. 1987; cabezon, DAVIES. 1994. Protogynous sex Best and Stachowicz 2012) and whales change in the intertidal isopod (Brusca et al. 2007). The presence of the Gnorimosphaeroma oregonense non-native mud snail, Potamopyrgus (Crustacea, Isopoda). Biological antipodarum, increases predation on G. Bulletin. 187:99-111. insulare as well as the native isopod BRUSCA, R. C., C. R. COELHO, and S. Americorophium salmonis (Brenneis et al. TAITI. 2007. Isopoda, p. 503-541. In: 2011). The Light and Smith manual: intertidal Behavior: invertebrates from central California to Oregon. J. T. Carlton (ed.). University Bibliography of California Press, Berkeley, CA. ARAUJO, P. B., A. F. QUADROS, M. M. BRUSCA, R. C., and E. W. IVERSON. 1985. AUGUSTO, and G. BOND-BUCKUP. A guide to the marine isopod 2004. Postmarsupial development of crustacea of Pacific Costa Rica. Atlantoscia floridana (van Name, Revista de Biologia Tropical. 33:1-77. 1940) (Crustacea, Isopoda, HARRISON, K., and J. P. ELLIS. 1991. The Oniscidea): sexual differentiation and genera of the Sphaeromatidae size at onset of sexual maturity. (Crustacea: Isopoda): A key and Invertebrate Reproduction and distribution list. Invertebrate Development. 45:221-230. Taxonomy. 5:915-952. BEST, R. J., and J. J. STACHOWICZ. 2012. HOESTLANDT, H. 1969. Characteristics Trophic cascades in seagrass morphologiques d'une espece meadows depend on mesograzer nouvelle de la cote pacifique variation in feeding rates, predation americaine (G. lutea). Comptes susceptibility, and abundance. Marine Rendus Hebdomadaires des Seances. Ecology Progress Series. 456:29-42. Academie des Sciences. 267:1600- BOYKO, C. B., and C. WOLFF. 2014. 1601. Isopoda and Tanaidacea, p. 210-215. —. 1977. Description complementaire de In: Atlas of crustacean larvae. J. W. Isopode flabellifere Margtin, J. Olesen, and J. T. Høeg Gnormosphaeroma insulare Van (eds.). Johns Hopkins University Name et synonimie de G. luteum Press, Baltimore. Menzies avec cette espece. BRANDT, A., and G. C. B. POORE. 2003. Crustaceana. 32:45-54. Higher classification of the flabelliferan IVERSON, E. W. 1982. Revision of the isopod and related isopoda based on a family Sphaeromatidae (Crustacea, reappraisal of relationships. Isopoda, Flabellifera) 1. Subfamily Invertebrate Systematics. 17:893-923. names with diagnoses and key.