Spheroma oregonensis Dana, 1853; now Gnorimosphaeroma oregonense (Dana, 1853); by original designation.

Body vaulted, dorsal surfaces smooth or polished in appearance, without setae. Eyes lateral, simple, without posterior lobe. Pleon consisting of 4 visible segments (as determined by lateral sutures), sutures (except first) long extending from lateral margin, separated medially by 24–28% pleon width; pleonite 1 entire, posterior margin even, narrower than remainder of pleon, not extending to pleon lateral margins. Pleotelson vaulted, anteriorly as wide as pleon, without dorsal process; posterior margin entire, simple, arcuate. Maxilliped palp articles 2–4 medial margins lobate, article 2 not expanded. Penial processes entirely separate, basally close set, short (not extending beyond pleopod peduncles). Uropod rami lamellar, similar in size, exopod shorter than endopod, inserted near anterolateral angle of peduncle; endopod lateral margin simple, finely serrate or smooth, distally broadly rounded; both rami distally broadly rounded or narrowly rounded.

Body vaulted, dorsal surfaces smooth or polished in appearance, without setae; coxal and other margins smooth, with ability to conglobate; not or weakly sexually dimorphic. Head with rostral point present, dorsally visible, simple, not separating antennular bases; without paired incisions in front of eyes, lateral margins not laterally extended to body outline (antennules more or less ventral). Eyes lateral, simple. Pereonite 1 lateral margins not anteriorly produced, not laterally enclosing head, pereonites 2–7 with posterior margin not raised, pereonite 1 anteriorly with keys. Sternite 1 without cuticular mesial extensions. Pereonite 6 simple, without bosses, processes or marginal extensions. Pereonite 7 as wide as pereonite 6, forming part of body outline, dorsally without bosses, processes, or marginal extensions. Coxae distally narrow, those of pereonites 2–7 overlapping the one behind, rounded, with ventral ‘lock and key’ processes, with grooved articulation; those of pereonite 6 not large, not overlapping those of pereonite 7. Pleon consisting of 4 visible segments (as determined by lateral sutures); pleonite 1 entire, posterior margin even, narrower than remainder of pleon, not extending to pleon lateral margins; sutures (except first) running to lateral margin, all separate, sutures long (separated medially by 24–28% pleon width); pleonal sternite absent; dorsal surface without process; posterior margin even, with ‘keys’. Pleonite 5 posterior margin entire (not fused with pleotelson). Pleotelson vaulted, anteriorly as wide as pleon, without dorsal process; posterior margin entire, simple, arcuate; ventrolateral margins forming ridge.

Marsupium formed from four pairs of oostegites, arising from pereonites 1–4; anterior pocket absent, posterior pocket absent, oostegites overlapping at mid-line (except 1).

Antennule peduncle with basal articles medially not in contact, 1 and 2 robust, article 3 slender; article 1 not produced, without anterior lobe; article 2 approximately 0.5 as long as article 1; with articles 2 and 3 colinear, article 3 longer than article 2; article(s) not flattened; flagellum shorter than peduncle, longer than peduncular article 3. Antenna peduncle articles all colinear (or curving regularly), less robust than antennule, peduncular articles all of similar thickness.

Epistome anteriorly narrow, with median weak constriction, anteriorly flush with head, not projecting; elongate. Mandible incisor wide, 4-cuspid; lacinia mobilis present; spine row normal; present, molar process gnathal surface with transverse ridges, rounded. Maxillula lateral lobe robust setae with some or all serrate, mesial lobe with major robust setae, these setae being heavily serrate. Maxilla with setae on middle and lateral lobes serrate. Maxilliped palp articles 2–4 medial margins lobate, article 2 not expanded; endite distal margin rounded, anteromesial (upper) marginal ridge without long curved serrate robust setae.

Mouthparts of female not metamorphosed.

Pereopod 1 ambulatory; dactylus secondary unguis short, robust, simple; setae on superodistal corner of merus only very long. Pereopod 2 similar in proportion to pereopod 3; dactylus with secondary unguis simple, short and stout. Pereopods 3–7 dactylus with secondary unguis simple. Pereopods with inferior margins of ischium to carpus without dense setulose fringe, ischium superior margin without sinuate acute robust seta, pereopods 1–3 or 4 ischium superior margin with few long stiff slender setae. Pereopods 1 (or 1–3), inferior margins of merus, carpus and propodus palm pereopod 1 only with robust setae on propodus inferior margin.

Penial processes entirely separate, basally close set, short (not extending beyond pleopod peduncles), widest near base, apex bluntly rounded.

Pleopod 1 rami not operculate; exopod lamellar; rami exopod with longitudinal axis weakly oblique; endopod of similar proportions to exopod, mesial margin lamellar, distally triangular, endopod proximomedial heel absent; exopod distally rounded or distally subtruncate or truncate, exopod distal margins not serrate. Pleopod 2 endopod ca. as long as exopod; exopod distal margins not deeply serrate; appendix masculina inserted basally, with straight margins, distally abruptly narrowed, longer than and extending beyond endopod (1.14 × as long as endopod), distally narrowly rounded. Pleopod 3 exopod transverse suture present, endopod of similar proportions to exopod. Pleopod 4 rami with PMS; exopod transverse suture present, incomplete, thickened transverse ridges absent, lateral margin not thickened, with short simple marginal setae; endopod thickened transverse ridges absent; mesial margin without deep distal notch; endopod without proximomedial lobe. Pleopod 5 exopod transverse suture present, entire, thickened transverse ridges absent, lateral margin with short simple setae, lateral margin not thickened, with 3 discrete scale patches; scale patches flush or weakly domed; endopod with thickened transverse ridges absent, endopod without proximomedial lobe.

Uropod rami not strongly flattened, not forming part of continuous body outline; exopod shorter in length than endopod, exopod lamellar, inserted near anterolateral angle of peduncle-endopod, lateral margin simple, finely serrate or smooth, distally broadly rounded; endopod lamellar, distally broadly rounded or narrowly rounded. Uropod endopods not in contact posteriorly.

Gnorimosphaeroma is in a general sense quite unremarkable in appearance, with no species showing any sort of dorsal ornamentation of tubercles, processes, or pereonal and pleonal ridges that characterize so many genera of Sphaeromatidae. As such, there is a lack of readily obvious characters by which to identify the genus. Gnorimosphaeroma, on morphological criteria, is most similar to the genera Bilistra Sket & Bruce, 2004, Exosphaeroma Stebbing, 1900, Lekanesphaera Verhoeff, 1943, Neosphaeroma Baker, 1926 and Sphaeroma Bosc, 1802. The latter three genera can be differentiated from Gnorimosphaeroma in the first instance by having the uropodal exopod lateral margin with one or more serrations or notches (among other characters).

Exosphaeroma is a large genus with 40 species at the last count (Boyko et al. 2008) that, as presently constituted, contains both smooth bodied species as well as some with coarsely pitted or ridged dorsal surfaces (e.g., see Kensley 1978; Espinosa-Pérez and Hendrickx 2001; Bruce 2003), and also species with greatly enlarged uropodal rami (e.g., see Kensley 1978; Bruce 2003; Wall et al. 2015). Some of the smooth-bodied species of Exosphaeroma are superficially similar to Gnorimosphaeroma, but can be distinguished by the pleonal sutures running to the posterior margin (to the free lateral margin in Gnorimosphaeroma), as well as pleonite 1 having two flat sub-median lobes on the posterior margin (see Bruce 2003: figs 14E, 18F).

Bilistra is similar in gross morphology and also occupies coastal freshwater habitats. Bilistra differs from Gnorimosphaeroma in having a far shorter uropodal exopod (ca. half as long as endopod), shorter pleonal sutures that run to the pleon posterior margin (not lateral margin); the inferior margins of pereopods ischium or merus to propodus have a dense setulose (fur-like) fringe while the superior margins lack long setae altogether. Bilistra is presently restricted to New Zealand, but there is also one species in South Africa, from supralittoral brackish pools and tidal streams that is currently classified as Pseudosphaeroma barnardi Monod, 1931 that is in need of redescription and formal reassignment to Bilistra (NLB, pers. obs.).

Gnorimosphaeroma pereopod setation is inconsistently illustrated, even within species, despite being a potentially significant character. The redescription given here, and figures of Hoestlandt (1975) show long setae on the superior or superodistal margin of the merus and long setae on the inferior margin of the ischium and merus. Such setae were not mentioned or figured in Menzies’ (1954) genus diagnosis or species descriptions. Such setae are also apparently absent from all northwestern species (e.g., Hoestlandt 1975, 1977; Kwon and Kim 1985; Nunomura 1998, 1999a, 2007).

It has been long established that all of Dana’s (1852) isopod material, and therefore all the type material for the many species of isopod that he named, was lost with the sinking of the ship USS ‘Peacock’ on the bar of the Columbia River in 1841 (Bruce 1986: 220; 2004: 228; 2009: 211; Poore and LewTon 1993: 234). Gnorimosphaeroma oregonense (Dana, 1853) is one such species.

Species of Gnorimosphaeroma are uniform in appearance, and to date no assessment has been made of intrinsic variability within species. Some species of Gnorimosphaeroma occur sympatrically and there are many exceedingly similar species. At present few species have been described in full detail. Furthermore, records of G. oregonense are somewhat inconsistent in the details presented and the material is not always available for re-examination, so that it is not always possible to confirm the correct identity of previous records and indeed also on occasion, new material. We consider that designating a neotype is necessary to clearly characterize the identity of this species, to allow for the genus to be precisely diagnosed based on the type species and to permit unambiguous identification and separation from other sympatric congeneric species.

Dana (1853) did not indicate a specific type locality, but stated that the species had been obtained from “Puget’s Sound, Oregon; also, Bay of San Francisco, California”. One may infer that the first mentioned location is the type locality but that remains an inference, and furthermore one cannot be certain that the material consists of only one species, given that there are four species in the region and also that the morphology of purported species apparently changes from low to high latitudes (present study). The neotype has been chosen from specimens collected as near as practically possible to the original type locality, and is now Stanley Park, 49.294°N, 123.155°W (British Columbia, Canada), ca. 150 km north of Puget Sound.

Gnorimosphaeroma albicauda Nunomura, 2005, G. akanense Nunomura, 1998, G. anchialos Jang & Kwon, 1993, G. boninense Nunomura & Satake, 2006, G. chejuense Kim & Kwon, 1988, G. chinense (Tattersall, 1921), G. hachijoense Nunomura, 1999b, G. hoestlandti Kim & Kwon, 1985, G. hokurikuense Nunomura, 1998, G. insulare (Van Name, 1940), G. iriei Nunomura, 1998, G. kurilense Kussakin, 1974, G. naktongense Kwon & Kim, 1987, G. noblei Menzies, 1954, G. oregonense (Dana, 1853), G. ovatum (Gurjanova, 1933), G. paradoxa (Nunomura, 1988), G. pulchellum Nunomura, 1998, G. rayi Hoestlandt, 1969, G. rebunense Nunomura, 1998, G. saijoense Nunomura, 2013, G. shikinense Nunomura, 1999b, G. tondaense Nunomura, 1999b, G. trigonocaudum Nunomura, 2011, G. tsutshimaense Nunomura, 1998.

The original diagnosis of the genus was provided by Menzies (1954: 5). A more complete diagnosis of the genus is provided here (see above). Menzies (1954) suggested that Neosphaeroma pentaspina Baker, 1926 could possibly be attributed to Gnorimosphaera were it to be redescribed, while Harrison and Holdich (1984) indicated some shared characters, notably the pleon suture, but the species is presently considered as incertae sedis. Smooth-bodied Sphaeromatidae similar to Gnorimosphaeroma are summarized in the genus remarks above and reoccur in several sphaeromatid clades. In their molecular analysis Wetzer et al. (2018) demonstrated that this a plesiomorphic trait and that Neosphaeroma is basal to or nested within the Cymodoce clade and is not closely related to Gnorimosphaeroma.

Neotype ♂ (8.5 mm): Canada, British Columbia, Vancouver, Stanley Park, 49.294°N, 123.155°W, mid intertidal, hand, fixed and preserved in 95% ethanol. 7 Jul 2010, coll. Regina Wetzer & N. Dean Pentcheff. Collection ID: RW10.003. LACM:DISCO:7028.

♀ Non-type with mancas (6.0 mm) LACM:DISCO:11164; ♂ (8.5 mm) LACM:DISCO:11161; subadult ♂ with penes beginning, without appendix masculina (6.0 mm) LACM:DISCO:11162; plus additional 20+ adults, juveniles, and mancas in this lot.

Body parts and appendages figured are as indicated in figure legends.

Body length 2.4 × width; widest at pereonite 6; pleotelson length 0.6 × width, distal margin broad and weakly convex. (Figs 1A, B, 2A). Pleotelson length 0.66 × width.

Figure 1. 

Gnorimosphaeroma oregonense. ♂ Neotype. LACM:DISCO:7028 A anterior dorsal B posterior dorsal and pleotelson.

Antennula peduncle article 1 length 1.3 × width; article 2 as long as wide; article 3 length 2.6 × width, inferior distal margin with one palm seta; flagellum with 13 articles, 11 basal articles with aesthetascs and small simple seta (Figs 2A, 3A, 4A). Antenna reaching slightly beyond anterior margin of pereonite 2; peduncle article 4 length 2.3 × width, flagellum with 14 articles, setation as figured (Figs 2A, 3B, 4B). Clypeus and labrum as in Figs 3A, 8B.

Figure 2. 

Gnorimosphaeroma oregonense A ♂ neotype. LACM:DISCO:7028, lateral B ♀ non-type LACM:DISCO:11164, lateral.

Figure 3. 

Gnorimosphaeroma oregonense ♀ Non-type. LACM:DISCO:11164 A clypeus and labrum B marsupium with three mancas.

Figure 4. 

Gnorimosphaeroma oregonense ♂ Neotype LACM:DISCO:7028. All appendages from right, unless otherwise indicated A antennula B antenna C left mandible D right mandible E maxillula lateral lobe F maxillula medial lobe G maxilla H maxilliped.

Left mandible incisor with 4 cusps; lacinia mobilis with a single cusp; lacinia mobilis spine row comprised of 4 serrate spines; crushing surfaces ridged (Fig. 4C). Right mandible incisor with 3 cusps, spine row comprised of 7 serrate spines (Fig. 4D). Maxillula mesial lobe with ca. 4 spines; lateral lobe with ca. 8 spines (Fig. 4F, E, respectively). Maxilla mesial lobe with 5 simple setae and 6 plumose RS on gnathal surface; middle lobe with 2 simple setae and 1 pectinate RS; lateral lobe with 2 simple setae, and 1 pectinate RS (Fig. 4G). Maxilliped endite distal surface with 7 plumose setae; distomesial margin with 3 plumose setae; palp article 2 distal apex with 9 long, simple RS; article 3 distal apex with 11 long, simple RS, lateral distal angle with 2 long, simple RS; article 4 distal apex with 15 long, simple RS, lateral distal angle with 1 long, simple RS; article 5 distal apex with 13 long, simple RS (Fig. 4H).

Pereopod 1 (Figs 5A, 7C) basis inferior distal angle with 1 long, RS, inferior proximal margin with setal patch; ischium length 1.6 × width, inferior medial margin with setal patch; merus lobate, 0.74 × ischium length, superior distal angle with 4 long, RS; carpus inferior medial margin with 1 robust, serrate, trident seta; propodus length 2.1 × width, 1.1 × ischium length, inferior margin with 3 robust, serrate, trident seta, and 3 plumose setae; dactylus length 1.2 × width, length 0.33 × propodus length, distal margin with 4 simple setae (Figs 5A, 7C). Pereopod 2 (Fig. 5B) basis inferior distal angle with 1 long, simple RS, inferior medial margin with setal patch; ischium length 2.2 × width, inferior medial margin with 12 long, simple RS, inferior distal angle with single simple RS; merus lobate, length 1.6 × width, 0.69 × ischium length, superior distal angle with cluster of 7 simple RS, distal medial margin with one palm seta; carpus length 1.2 × merus length, 2.5 × width, superior margin with 4 robust, biserrate setae on distal angle, inferior margin 2 palm setae; propodus weakly curved, length 2.6 × width, 1.2 × carpus length, superior distal margin with a palm seta; dactylus length 1.2 × width, length 0.27 × propodus length, inferior margin with scales, distal margin with 3 long, simple setae (Fig. 5B). Pereopods 3–6 progressively less setose (not figured). Pereopod 7 (Figs 5C, 7B) basis inferior medial margin with setal patch, inferior distal angle with 1 long, simple seta; ischium length 3.2 × width, inferior distal angle with 1 palm seta; merus lobate, merus length 1.3 × width, merus length 0.42 × ischium length, superior distal angle with 1 trident seta, inferior distal angle with 1 biserrate seta and 1 palm seta; carpus length 1.8 × width, carpus length 1.3 × merus length, superior distal angle with a cluster of 5 long, biserrate setae, inferior distal angle with a cluster of 1 long, biserrate seta, and 1 long, trident seta; propodus weakly curved, length 3.2 width, length 1.5 carpus length, superior distal angle with 1 simple seta, and 1 palm seta, inferior margin with 2 long, trident setae; dactylus length 1.3 × width, dactylus length 0.21 × propodus length, distal margin with 3 simple setae (Figs 5C, 7B).

Figure 5. 

Gnorimosphaeroma oregonense ♂ Neotype LACM:DISCO:7028. All appendages from right A pereopod 1 B pereopod 2 C pereopod 7.

Penial processes length 3.8 × basal width; close set (Fig. 6A).

Figure 6. 

Gnorimosphaeroma oregonense ♂ Non-type LACM:DISCO:11161 A penes in ventral view with relative position to pleopods. ♂ Neotype. LACM:DISCO:7028. All appendages from right B–F pleopods 1–5.

Pleopod 1 (Fig. 6B) peduncle length 0.38 × width with 4 coupling hooks; exopod length 1.5 × width, 1.1 × endopod length. Pleopod 2 (Fig. 6C) peduncle length 0.34 × width with 3 coupling hooks, appendix masculina length 8.5 × width, 1.1 × length of endopod, straight, proximally and medially slightly swollen, distally narrowing. Pleopod 3 (Fig. 6D) peduncle length 0.34 × width with 3 coupling hooks. Pleopods 1–4 exopods and endopods with PMS as figured (note: not all drawn, but indicated). Pleopod 4 (Fig. 6E) endopod and exopod subequal, exopod with transverse suture. Pleopod 5 (Fig. 6F) endopod and exopod subequal, endopod length 1.5 × width, exopod length 2.1 × width with 1 distal scale patch and 2 medial lateral scale patches.

Uropod extending to posterior margin of pleotelson. Exopod 0.83 × as long as endopod, 2.7 × as wide; apex narrowly rounded; mesial margin with continuous row of PMS. Endopod 3.8 × as long as wide, lateral margin weakly convex, apex bluntly rounded.

Body length 2.4 × width (Figs 2B, 3A, B, 7A, 8A–C, 9A, B). Pleotelson length 0.66 × width (Fig. 8C). Uropodal endopod (Figs 8C, 9B) as in male, longer than exopod, endopod just barely extending to posterior margin of pleotelson. Gravid female (Figs 3B, 9B) estimated to be able to brood 8–10 mancas.

Figure 7. 

Gnorimosphaeroma oregonense ♀ Non-type SEM. LACM:DISCO:11164 A dorsum B pereopod 1 seta C pereopod 7 setae.

Figure 8. 

Gnorimosphaeroma oregonense ♀ Non-type SEM. LACM:DISCO:11164 A head dorsum B clypeus and labrum ventral C pleotelson dorsal.

Figure 9. 

Gnorimosphaeroma oregonense Non-type SEM. LACM:DISCO:11164 A ♀ LACM:DISCO:11164 lateral B ♀ LACM:DISCO:11164 ventral view with oostegites.

Largest ♂ to 8.5 mm, largest ♀ to 6 mm. Dana (1853) gave no measurements. Fee (1926: 8, 9) records the largest specimens as being “ca. 1 cm. long; one-half as long as wide.”

When preserved in ethanol, specimens quickly become pale buff to whitish.

British Columbia, Vancouver to California, San Francisco.

The species occurs only in fully marine habitats in the intertidal to an unknown depth. A single lot indicated that it was collected by night light, and another that specimens were collected on floats among fouling organisms. None of the material examined indicates depth.

Kussakin (1979) reported G. oregonense from Alaska, Popov Island to San Francisco Bay, California. Kussakin (1979) figured G. oregonense from the collections of the Zoological Institute of the Academy of Sciences of the USSR. He noted that it is widely distributed with males reaching a length of 12 mm and females up to 8 mm, and that it occurred widely from Alaska to California. It is not clear what the specific localities of the figured specimens were (Kussakin 1979: 407) nor of those deposited in the Russian collections. We were unable to locate and access these specimens. Kussakin reported that the specimens he examined were predominantly littoral, but can be sublittoral to 22 m, on rocks, under rocks, less often on sand, and sometimes in empty shipworm tubes. Kussakin remarked it is a good swimmer, and sometimes turns up in night light samples. It can tolerate salinities as low as 9‰. Since we were not able to re-examine Kussakin’s specimens, we cannot verify that the Gnorimosphaeroma he identified are the same species as G. oregonense from the type locality and described here. Furthermore, our genetic data clearly distinguishes between fully marine and low salinity specimens and recognizes these as distinct species (see below). We do not include Kussakin’s specimens in the synonymy (Gnorimosphaeroma oregonense: Kussakin, 1979: 406, figs 260–262.)