Phylum: Arthropoda, Crustacea Gnorimosphaeroma insulare Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Peracarida, Isopoda, Sphaeromatidea Family: Sphaeromatoidea, Sphaeromatidae Taxonomy: The genus Gnorimosphaeroma longs, fall into the long-tailed variety. Body was described in 1954 by Menzies with six surface in Gnorimosphaeroma insulare is species including G. insulare as well as G. smooth and with eight segments from cepha- lutea, G. oregonensis, each a subspecies of lon to pereon. Individuals able to roll into a G. oregonensis, differentiable by pleotelson ball (Sphaeromatidae). morphology. Some authors later elevated Cephalon: Frontal border smooth (Fig. 3). these two subspecies to species status Eyes: based on habitat and physiology (e.g. Riegel Antenna 1: First antenna longer than 1959). Furthermore, G. insulare and G. lu- second and basal articles are separated by tea were synonymized by Hoestlandt in the rostrum (Fig. 3) (see Fig. 4 Hoestlandt, 1977 and, although some authors (including 1977). those for our current, local intertidal guide, Antenna 2: Shorter than first antenna Brusca et al. 2007) also consider G. ore- (see Fig. 4 Hoestlandt, 1977). gonensis a synonym of G. insulare, others Mouthparts: Mandible with a palp and differentiate the two based on habitat: G. or- maxilliped with four articles. Hairs present on egonensis is strictly marine while G. insulare antero-lateral edge of articles 2–4 are less is estuarine (Stanhope et al. 1987). than ½ the length of the article (see Figs. 5–8, Hoestlandt 1977). Description Rostrum: Size: Males up to 8 mm in length (Miller Pereon: 1975) and almost twice as long as wide. Pereonites: Seven free pereonites to- Color: White with small black chromato- tal. phores. Pereopods: Seven pereopod pairs. General Morphology: Isopod bodies are The basis of the first pereopod is hairless and dorso-ventrally flattened and can be divided distal extremity with one hair or hairless (Fig. into a compact cephalon, with eyes, two an- 6). tennae and mouthparts, and a pereon Pleon: Pleon consists of three parts. The first (thorax) with eight segments, each bearing is concealed under the last pereonite, the se- similar pereopods (hence the name “iso- cond consists of of several coalesced pleoni- pod”). Posterior to the pereon is the pleon, tes often with partial sutures (Fig. 1), and the or abdomen, with six segments, the last of third part is the large pleotelson. which is fused with the telson (the pleo- Pleonites: Only two of three reach the telson) (see Fig. 1, Harrison and Ellis 1991; lateral margin, third pleonite is under the Plate 231, Brusca et al. 2007). The Isopoda second (Figs. 1, 4). can be divided into two groups: ancestral Pleopods: Five pleopod pairs. The (“short-tailed”) groups (i.e. suborders) that first pair is not widely separated at the base, have short telsons and derived (“long- and is similar in size to the second. The first tailed”) groups with long telsons. Members three pairs are with marginal plumose setae. of the Flabellifera, to which G. insulare be- 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. 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. The fourth and fifth pairs are fleshy and wi- species in 11 genera in the western coast of thout transverse folds, and the fourth is with North America (Wall et al. 2015) and has a a bent exopod (Fig. 2, 1-v). The number pleon with 1–2 free pleonites, a convex and arrangement of these folds of the en- body that is not depressed, antennae that dopods and exopods is considered an im- are widely separated, indistinct frontal lami- portant taxonomic character by some au- na and subequal pleopods, where pleopods thors (e.g. Cassidinidae, Fig. 2, Iverson 4–5 are ovate in shape (see also Iverson 1982; Fig. 1, Harrison and Ellis 1991). 1982). There are 17–24 species in this fam- Uropods: Two branched uropods visible ily from central California to Oregon (Brusca dorsally, with rigid endopod and flexible et al. 2007). These species belong to the exopod (Fig. 5) (see Fig. 9, Hoestlandt following genera: Ancinus, Clianella, Dy- 1977). namene, Paradella, Pseudosphaeroma, Pleotelson: Rounded and convex (Fig. 1). Tecticeps (all with one species), Paracereis, Sexual Dimorphism: Conspicuous sexual Sphaeroma (each with two species), Dy- dimorphism is rare among isopods, howev- namenella, Exosphaeroma (each with 4–5 er, mature females are often broader and species) (for detailed key of Exosphaeroma bear a thoracic marsupium while males have see Wall et al. 2015) and Gnorimosphaero- modified first pleopods, called gonopods ma has two to four species locally. (Sadro 2001; Boyko and Wolff 2014). Pro- The fourth and fifth pleopods in togyny has been observed (see Reproduc- Gnorimosphaeroma lack pleats (see Cas- tion) in G. insulare and females can have sidinidae, Fig. 2, Iverson 1982; Fig. 1, Harri- rudimentary penes after brood release son and Ellis 1991), the first pereopod is (Brook et al. 1994). ambulatory and the uropod is with an exo- pod. In G. noblei the first article of the left Possible Misidentifications and right antennae peduncles are touching The order Isopoda contains 10,000 while they are not in G. oregonense. Gnori- species, 1/2 of which are marine and com- mosphaeroma rayi. so far found only in prise 10 suborders, with eight present from Tomales Bay, California and in Japan, is an central California to Oregon (see Brusca et estuarine species found also above the mid- al. 2007). Among isopods with elongated tide line, and also under stones. In this spe- telsons (with anuses and uropods that are cies, the basis of the first pereopod has a subterminal), there are several groups (i.e. tuft of 7–9 setae and 2–3 setae are present suborders) including Valvifera, Anthuridea, on the sternal crest of the ischium. Gnori- Gnathiidea, Epicaridea and Flabellifera. mosphaeroma oregonense, is found above The Flabellifera is a large assem- the mid-tide line, usually under stones. blage contains 3,000 species with seven Gnorimosphaeroma oregonense is stouter families occurring locally, three of which than G. insulare, being 1.5 to 1.75 times are not present north of Point Conception, longer than wide and all three pleonites California (Brusca et al. 2007). The reach the lateral margin and the frontal bor- Flaberllifera are characterized by body der of its head has several curves (compare length that is rarely less than 3 mm and a Plate 243C to 252C1, Brusca et al. 2007). pleon with less than three free pleonites The exopod of the uropod is only 2/ as long (plus the pleotelson). The family Sphaero- 3 as the endopod (Richardson 1905). Gnori- matidae is almost certainly paraphyletic mosphaeroma rayi also has three pleonites (Brandt and Poore 2003) and includes 37 reaching the lateral margin (Fig. 4b) and 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] basis of the first pereopod is setose. It is 1985), although protogynous and protandric stout like G. oregonense, and has longer species are known (Brook et al. 1994; Araujo antennae than either G. oregonense or G. et al. 2004; Boyko and Wolff 2014). Protogy- insulare. ny has been observed in both G. insulare (as G. luteum) G. oregonense, where females Ecological Information have rudimentary penes and grow to sexually Range: Type locality is San Nicolas Island, mature males following several molts after California (Menzies 1954). Known range brood release (see Table 1, Brook et al. from Alaska to California (Menzies 1954a), 1994). Reproduction proceeds by copulation where it is most common north of Point Con- and internal fertilization where eggs are de- ception (Miller 1968). posited within a few hours after copulation Local Distribution: Oregon distribution in and brooded within the female marsupium the Siuslaw estuary and Cox Island as well (Brusca and Iverson 1985). The biphasic as the Medcalf Preserve (South Slough of molting of isopods allows for copulation; the Coos Bay) and Carter Lake (Wones and posterior portion of the body molts and indi- Larson 1991). viduals mate, then the anterior portion, which Habitat: Estuarine intertidal, among Fucus holds the brood pouch, molts (Sadro 2001). and under logs in Salicornia marshes and in Embryonic development proceeds within the mud or drainage channels (e.g. Metcalf brood chamber and is direct with individuals Preserve) as well as sedge marshes, hatching as manca larvae that resemble small amongst wood debris and within algal beds adults, with no larval stage (Boyko and Wolff and banks (Stanhope et al. 1987). Benthic 2014). Little about the reproductive and de- in Tomales Bay. velopmental biology of G. insulare is known, Salinity: Euryhaline (Wones and Larson but ovigerous females were observed in 1991). Estuarine to fresh water and can tol- March, larger females produce larger brood, erate salinities from 6–35 (Welton and Miller egg sizes vary from 450–480 µm, and the av- 1980). erage developmental time is 120 days Temperature: (Squamish estuary, British Columbia Canada, Tidal Level: -1.4 meters to subtidal (Metcalf Stanhope et al. 1987). Gnorimosphaeroma Preserve, Hoestlandt 1969a). rayi reproduces in spring only, on a one year Associates: Alga Fucus, amphipod cycle and G. oregonensis has young in spring Orchestia, littorine snail Ovatella (Metcalf and fall (Hoestlandt 1969).