All species currently recognized by the Southern California Association of Marine Invertebrate Taxonomists (SCAMIT 2021), as well as previously by the organization (SCAMIT 1994–2018) were reviewed and changes (e.g., additions, deletions, synonymies) verified. Additional species were added based on reviews of original species descriptions, taxonomic monographs, species or habitat guides, ecological studies, and published reports of site-specific or regional surveys conducted in the Southern California Bight (SCB) or elsewhere, as well as by personal observations and examination of field or museum specimens by the authors.

The higher-level classification of crustaceans and isopods has evolved over the past two decades, with 11 isopod suborders currently recognized, of which eight include marine species (e.g., see Martin and Davis 2001; Brandt and Poore 2003; Ahyong et al. 2011; Boyko et al. 2013; Wetzer et al. 2013; Martin et al. 2014; Wetzer 2015). The treatment followed herein for the SCB isopods reflects that presently accepted by the World Register of Marine Species (WoRMS: Boyko et al. 2008 onwards) and SCAMIT (2021), with any differences between these lists addressed in the endnotes or annotated species list following the keys.

The Isopoda Latreille, 1817 can be distinguished from the other peracarid orders, and crustaceans in general, by the following combination of characters (after Brusca and Iverson 1985; Wetzer et al. 1997; Brusca et al. 2007).

1. Body usually dorsoventrally depressed but may be cylindrical or tubular in some suborders (e.g., Anthuridea and Phreatoicidea).
2. Body without a carapace but with a cephalic shield.
3. Head (cephalon) compact, typically with compound eyes, two pairs of antennae (first pair minute in Oniscidea), and mouthparts comprising one pair of mandibles, two pairs of maxillae, and one pair of maxillipeds.
4. Compound eyes sessile (not stalked) but may be on ocular lobes in some Asellota, Cymothoida (i.e., Gnathiidae), and Valvifera.
5. First and second antennae (antennules and antennae, respectively) uniramous, but with minute scales in a few taxa.
6. Mandible usually with a 1- to 3-articulate palp and a multidentate incisor process, left and right lacinia mobilis often differ, molar process highly variable.
7. First and second maxillae (maxillules and maxillae, respectively) without palps.
8. First thoracic appendages (thoracopods) modified as maxillipeds comprising fifth pair of mouthparts.
9. Long thorax of eight segments (thoracomeres), the first (and second in Gnathiidae) fused to the cephalon and bearing the maxillipeds, the remaining seven segments (pereonites) being free and collectively comprising a region called the pereon.
10. Pereon with seven pairs of uniramous legs (pereopods), all generally alike; the exception being the Gnathiidae in which only five pairs of walking legs are present.
11. Abdomen (pleon) relatively short comprising six somites (pleonites), at least one of which is always fused to the telson to form a pleotelson.
12. Six pairs of biramous pleonal appendages, including five pairs of plate-like pleopods specialized for respiration and/or swimming, and one pair of fan-like or stick-like, uniarticulate uropods.
13. Heart located primarily in the pleon.
14. Young isopods develop within a brood pouch (female’s marsupium) and emerge as a manca before appearance of the last pair of pereopods. Mancas have six pairs of pereopods.
15. Biphasic molting in which the posterior half of the body molts before the anterior half.

In terms of reproductive status, isopods can be sexed based on the presence or absence of male or female secondary sex characters. If oostegites (or a marsupium) are present with or without eggs or developing embryos, an individual is obviously female. If oostegites are absent, males can be distinguished by the presence of paired penes (may be fused) on the sternum of pereonite 7 (or pleonite 1) and/or appendices masculinae on the endopods of the second pleopods. Absence of all these characters indicates that the individual is either a juvenile, an immature female, or an immature male that has not yet developed secondary sexual features.

Terminology in the keys follows that which is typical for isopods in general (see Brusca and Iverson 1985; Kensley and Schotte 1989; Brusca and Wilson 1991; Wetzer et al. 1997; Brusca et al. 2007). The generalized isopod body plan characteristic of most groups is diagrammed in Fig. 3A, while Fig. 4 shows the specialized body plan characteristic of an adult female bopyrid (i.e., representative epicaridean). See Cohen and Poore (1994: fig. 1) for a detailed diagram of a stylized male gnathiid isopod.

Figure 3. 

A Generalized isopod body plan (modified after Kensley and Schotte 1989: fig. 2) B ventral view of valviferan pleon and pleotelson showing opercular uropods (after Poore and Lew Ton 1993: fig. 25) C example of ambulatory pereopod (after Brusca 1983a: fig. 11G) D example of prehensile pereopod (after Brusca 1983a: fig. 11F).

Figure 4. 

Bopyrid isopod body plan (adult female). A dorsal view B ventral view. Modified after Markham (1985a: fig. 2).

In general, the isopod body is divided into three regions: the cephalon (head), pereon, and pleon. The cephalic region is referred to as “head” throughout the following keys. The segments of the pereon are referred to as pereonites 1–7 for most taxa or as pereomeres 1–7 for the epicarideans. Likewise, the segments of the pleon are referred to as pleonites 1–5 and the pleotelson (incorporating the fused pleonite 6 and telson) for most taxa (unless fused into fewer segments) or as pleomeres 1–6 plus telson for the epicarideans. The appendages of the pereon are numbered as pereopods 1–7, while the appendages of the pleon are referred to as pleopods 1–5 plus the uropods for all taxa. The first antennae (antenna 1) and second antennae (antenna 2) are referred to as antennules and antennae, respectively. Additional terminology is defined in glossaries of technical terms provided in Martin et al. (2022). Other useful glossaries are included in Kensley and Schotte (1989) and Wetzer et al. (1997), while Brusca and Wilson (1991) provide an extensive detailed description of isopod morphology. Key references regarding taxonomy, systematics, biogeography, and ecology of various isopod taxa are listed below for each suborder represented in this review, while specific references for each species are provided in the annotated species list.

Suborder Cymothoida: Primary references for the superfamily Anthuroidea include Menzies and Barnard (1959), Poore (1975, 1980, 1984a, 1984b, 2001a), Wägele (1984a), Poore and Lew Ton (1986, 1988a, 1988b, 1988c, 1988d), Cadien and Brusca (1993), and Annisaqois and Wägele (2021). Key references for the superfamily Cymothooidea are available for the families Aegidae (e.g., Brusca 1983a; Brusca and France 1992; Bruce 2009a), Cirolanidae (e.g., Bruce 1981; Brusca et al. 1995), Corallanidae (e.g., Delaney 1984, 1989), Cymothoidae (e.g., Brusca 1981; Bruce 1990; Smit et al. 2014; Hata et al. 2017), Gnathiidae (e.g., Cohen and Poore 1994; Smit and Davies 2004; Haney 2006; Tanaka 2007; Wilson et al. 2011), and Tridentellidae (e.g., Bruce 1984; Delaney and Brusca 1985). Within the infraorder Epicaridea, the family Bopyridae has been treated in detail in a long series of papers by Markham since the 1970s (e.g., Markham 1974a, 1975, 1977a, 1985a, 1986, 1992, 2001, 2003, 2004, 2008, 2016, 2020), while Boyko and Williams (2021a, 2021b) recently covered the two known local genera of the family Dajidae. Other valuable recent references for bopyrid and dajid isopods include Boyko et al. (2017), Williams et al. (2019), and Williams and Boyko (2021).

Suborder Limnoriidea: Key references for the family Limnoriidae include Menzies (1951a, 1957, 1958), Cookson (1991), and Borges et al. (2014).

Suborder Sphaeromatidea: Key references for the family Serolidae include Sheppard (1933), Harrison and Poore (1984), Brandt (1988), Wägele (1994), and Bruce (2009b), while important references for the family Ancinidae include Holmes and Gay (1909), Menzies and Barnard (1959), Schultz (1973), Glynn and Glynn (1974), Bruce (1993), and Shimomura (2008). Key references for the Sphaeromatidae include Menzies (1954), Harrison and Holdich (1982, 1984), Harrison and Ellis (1991), Bruce (1993), Schotte (2005), Wetzer et al. (2013, 2018, 2021), Wall et al. (2015), and Wetzer and Mowery (2017).

Suborder Valvifera: Key references for the valviferans include Menzies (1950a, 1951b), Sheppard (1957), Menzies and Barnard (1959), Menzies and Miller (1972), Brusca and Wallerstein (1977), Brusca (1983b, 1984), Brandt (1990), Poore and Lew Ton (1990, 1993), Rafi and Laubitz (1990), Wägele (1991), Poore (2001b, 2015), and King (2003).

Suborder Asellota: Key references for the asellotes include Menzies (1951b, 1952), Menzies and Barnard (1959), George and Strömberg (1968), Hessler et al. (1979), Wilson and Hessler (1980, 1981), Poore (1984c), Wilson (1987, 1994, 1997, 2008b), Wilson and Wägele (1994), Serov and Wilson (1995), Just and Wilson (2004, 2007, 2021), Doti and Wilson (2010), and Brix et al. (2021).

Suborder Oniscidea: Useful references for the oniscids include Van Name (1936, 1940, 1942), Garthwaite et al. (1985, 1992), Garthwaite and Lawson (1992), Leistikow and Wägele (1999), Schmalfuss (2003), Schmidt and Leistikow (2004), Schmidt (2008), and Sfenthourakis and Taiti (2015).

A total of 190 species of isopods are covered in this review of the Southern California Bight (SCB) isopod fauna, representing 105 genera, 42 families, and six suborders (Appendix 1). These include all but two of the 132 species-level taxa currently recognized by SCAMIT (2021)^{Endnote 1}. Approximately 84% of these isopods represent described species (see Boyko et al. 2008 onwards), while the remaining 16% represent well-documented “provisional” but undescribed species.

Of the six isopod suborders occurring in SCB coastal and offshore waters, the Cymothoida and Asellota are the most diverse, accounting for ~ 36% and 29% of the species, respectively (Table 1). The Valvifera and Sphaeromatidea are the next most speciose suborders, accounting for ~ 13–15% of species, while the suborder Limnorioidea is represented by only three species (< 2%) in SCB waters. Finally, the suborder Oniscidea is represented by nine species (~ 5%) that occur at the terrestrial-marine interface in several intertidal areas of the SCB. See Brusca et al. (2007) or contact R Wetzer for more complete lists of California oniscid isopods.

The suborder Cymothoida is represented by 69 species distributed amongst four superfamilies (Anthuroidea, Cymothooidea, Bopyroidea, Cryptnoniscoidea) and 15 families. The superfamily Anthuroidea, characterized by long, thin, cylindrical bodies usually at least 6 × longer than wide, includes 11 species in five families. Most anthuroids are thought to feed on other small invertebrates and occur in the SCB amongst fouling communities in marinas, bays, and harbors, and in both littoral and sublittoral habitats on the outer coast from the low intertidal to soft and hard-bottom benthos of the continental shelf, slope, and submarine canyons (0–1300 m depths).

The superfamily Cymothooidea is represented by six families with 38 species. Five of these families (Aegidae, Cirolanidae, Corallanidae, Cymothoidae, Tridentellidae) are generally similar in body form with sleek symmetrical bodies usually ~ 2–6 × longer than wide, the uropods and pleotelson forming a distinct tail fan, and the pereopods modified from ambulatory to prehensile reflecting their different lifestyles (e.g., Fig. 3C, D). For example, the family Cirolanidae is represented by seven species with mostly ambulatory pereopods, although pereopods 1–3 tend to have well-developed dactyli modified for grasping. In the SCB, these species occur intertidally on both sandy and rocky beaches, as well as in shallow to deep water habitats of the continental shelf, slope, and basins (0–1250 m depths). Corallanidae and Tridentellidae, represented by two species each in the SCB, are similar in shape to the cirolanids, but with the mouthparts and anterior pereopods modified for a predatory lifestyle. For example, the dactyli of pereopods 1–3 are usually as long or longer than the propodi and thus adapted for grasping prey. The two SCB corallanids occur from the intertidal to 138 m on the continental shelf, while the two SCB tridentellids have been reported from offshore depths of 53–360 m. The family Aegidae is represented by seven species in the SCB, all of which are temporary parasites of marine fishes and are characterized by prehensile pereopods 1–3 (dactylus strongly recurved and as long or longer than propodus). These species have been reported from the intertidal to deep waters of the continental shelf, slope, basins, and oceanic islands (0–2534 m depths). Although somewhat similar in general body form to the above four families, species of Cymothoidae are even more highly modified for a parasitic lifestyle with all seven pairs of pereopods being strongly prehensile. All cymothoids are obligate parasites of marine or freshwater fishes, most commonly being found attached in the gill chamber or buccal region of their host. Nine species of cymothoids are recognized herein as parasitizing a wide range of marine fishes in nearshore to offshore coastal waters of the SCB.

The sixth family of Cymothooidea occurring in SCB waters is Gnathiidae of which the males are highly modified and characterized by only six free pereonites and five pairs of pereopods. Eleven species of gnathiids are reported in the SCB, including three that are awaiting formal description. These 11 species occur in a wide range of habitats from the intertidal to shallow subtidal, and from the benthos of the offshore continental shelf, slopes, and submarine canyons to depths of ~ 1400 m.

Bopyroidea and Cryptoniscoidea comprise the remaining two superfamilies of Cymothoida, both of which are highly modified obligate parasites of other crustaceans. Bopyroidea is represented by 17 species in two families (Bopyridae and Ionidae) in shallow to deep SCB waters. Sixteen of these species are branchial parasites of a wide range of decapod crustaceans (e.g., hermit crabs, shrimp, mud shrimp, ghost shrimp, galatheid crabs, squat lobsters, porcelain crabs, grapsid crabs) while one species is an abdominal parasite of mud shrimp. In contrast, Cryptoniscoidea is represented by only three species in two families. These include Dajidae represented herein by at least two species that are ectoparasites on the dorsal carapace of several species of shrimp, and Hemioniscidae represented by a single species that is an ectoparasite of barnacles.

The suborder Limnoriidea is represented by three species of the family Limnoriidae in SCB waters. All three species occur in shallow waters (0–30 m depth) where they burrow into either wood (2 species) or algal holdfasts (1 species).

The suborder Sphaeromatidea is represented by 25 species in SCB waters distributed between two superfamilies (Seroloidea and Sphaeromatoidea) and four families. The serolids (family Serolidae) presently include only a single recognized species in the SCB, Heteroserolis carinata, which burrows just beneath the sediment surface from shallow waters in bays and harbors, and offshore to depths of ~ 100 m. However, it is possible that shallow vs. deep water populations in the region represent two distinct species (TDS, pers. obs.). In contrast, the superfamily Sphaeromatoidea includes 24 species in three families. Of these, the family Sphaeromatidae is the most diverse, represented herein by a total of 20 species. Most of these species occur from intertidal to shallow subtidal habitats < 30 m depth, although two species, Discerceis granulosa and Paracerceis gilliana, have been reported from slightly deeper waters between 37–73 m. The other two sphaeromatoid families, Ancinidae and Tecticipitidae, are represented by only three and one species, respectively. All four of these species occur in intertidal or shallow subtidal habitats (< 30 m depths).

The suborder Valvifera can be distinguished from all other local isopods by the possession of hinged opercular uropods that cover the ventral surface of the pleon and pleotelson enclosing the pleopods (see Fig. 3B). Four families and 29 species of valviferans are represented in SCB waters. Idoteidae is the most diverse of these families, comprising 23 species in the study area. Many of these species, especially within the genera Colidotea, Erichsonella, Eusymmerus, Idotea, Pentidotea, and Stenosoma are most common in intertidal and shallow subtidal habitats associated with various species of kelp or algae. In contrast, the two local species of Edotia occur in soft-bottom habitats of the continental shelf between depths of ~ 14–64 m, while three of the four SCB species of Synidotea (except S. harfordi) occur on the shelf or slope at depths of ~ 30–800 m. The remaining three families of SCB valviferans comprise a total of six species. The family Arcturidae is represented by four species that occur in the low intertidal (1 species) or offshore shelf benthos (3 species) at depths < 100 m. The last two families are each represented by a single species. These include Cleantioides occidentalis of the Holognathidae in relatively shallow waters (intertidal to ~ 50 m), and Califarcturus tannerensis of the Thermoarcturidae in deep waters (~ 1200–1300 m).

The suborder Asellota is represented by 55 species in SCB waters distributed between two superfamilies (Janiroidea and Stenetrioidea) and 12 families. However, only ~ 64% of these species are formally described, with the remaining 36% representing provisional species (see Appendix 1). Stenetrioidea includes a single species (Stenetrium sp. A) reported from 90–131 m in the Santa Maria Basin. In contrast, Janiroidea is represented by a diverse group of 11 families that occur in a wide range of habitats and depths from the intertidal to nearly 4000 m. Janiridae is the most diverse of these families, comprising 18 species; ca. two-thirds of the janirids occur in shallow waters from the intertidal to depths of ~ 30 m, while the remaining third occur on the continental shelf at depths between ~ 30–200 m. Paramunnidae is the next most diverse family with nine species, two of which occur in the shallow subtidal (9–20 m) and seven on the continental shelf (75–197 m). Munnidae is the third most diverse family with eight species, of which five species occur in intertidal to shallow subtidal habitats, two species occur at mostly shelf depths (12–237 m), and one species occurs in deeper slope waters (500 m). The Munnopsidae is represented by six species that occur at depths between 73–1118 m. The Joeropsididae is represented by five species that occur at depths from the intertidal to 161 m, while the Desmosomatidae includes three species that range in depth from ~ 100–3000 m. The remaining five families are each represented by a single species. These include Dendrotion­idae (Acanthomunna tannerensis at ~ 600–800 m), Haplomunnidae (Haplomunna caeca at ~ 4000 m), Lepidocharontidae (Microcharon sp. A at 75 m), Nannoniscidae (Nannonisconus latipleonus at ~ 300–500 m), and Pleurocopidae (Pleurocope sp. A at < 1 m).

The suborder Oniscidea is represented in this review by nine species distributed between six families. Each of these species typically occurs at or above the high tide mark in its respective habitat. The families Alloniscidae (2 species) and Tylidae (1 species) occur on sandy beaches in the SCB. The Detonidae (3 species) and Halophiloscidae (1 species) both occur in marshes, bays, and estuaries. The Platyarthridae (1 species) is reported to occur on both sandy beaches and at the edges of marshes. The Ligiidae is represented herein by a single species that typically occurs in the spray zone on rocky intertidal shores.

Ten keys were constructed to facilitate identification of the 190 species of isopods included in this guide. Key A represents a key to the suborders and main superfamilies, which are then identified to species in Keys B–J. Keys B–E cover the suborder Cymothoida (superfamilies Anthuroidea, Cymothooidea, Bopyroidea, and Cryptoniscoidea). Key B covers the Anthuroidea (5 families, 11 species). Key C covers the families Aegidae, Cirolanidae, Corallanidae, Cymothoidae, and Tridentellidae of Cymothooidea (27 species). Key D covers the remaining cymothooidean family, Gnathiidae (11 species). Key E covers the epicaridean superfamilies Bopyroidea and Cryptoniscoidea (4 families, 20 species). Key F covers the suborder Limnoriidea (1 family, 3 species). Key G covers the superfamilies Seroloidea and Sphaeromatoidea of the suborder Sphaeromatidea (4 families, 25 species). Key H covers the suborder Valvifera (4 families, 29 species). Key I covers the superfamilies Janiroidea and Stenetrioidea of the suborder Asellota (12 families, 55 species). Key J covers the suborder Oniscidea (6 families, 9 species).

Figs 5, 6

Figure 5. 

Isopoda, Cymothoida, Anthuroidea, Paranthuridae: A Paranthura elegans A1 lateral view of head (piercing mouthparts) A2 dorsal view of pereonite 7, free pleonites 1–5, pleotelson and uropods (after Menzies 1951b; Wetzer and Brusca 1997) B Paranthura japonica B1 dorsal close-up view of head B2 dorsal view of fused pleonites 1–5, pleotelson and uropods (after Richardson 1909; Brusca et al. 2007) C Califanthura squamosissima (male with antenna loaded with aesthetascs) C1 lateral view of head (piercing mouthparts) C2 dorsal view of pereonites 6 and 7, dorsally fused pleonites 1–5, pleotelson and uropods (after Menzies 1951b) D Colanthura bruscai, dorsal view of pereonites 6 and 7, free pleonites 1–5, pleotelson and uropods (after G. Poore, personal contribution).

Figure 6. 

Isopoda, Cymothoida, Anthuroidea, Anthuridae: A Amakusanthura californiensis A1 dorsal close-up view of head A2 dorsal view of pereonite 7, dorsally fused pleonites 1–5, pleotelson and uropods (after Wetzer and Brusca 1997) B Cyathura munda B1 lateral view of head (biting mouthparts) B2 dorsal view of pereonite 7, dorsally fused pleonites 1–5, pleotelson and uropods (after Menzies 1951b) C Haliophasma geminatum C1 dorsal view of head and pereonites 1 and 2 of male C2 dorsal view of pereonite 7, dorsally fused pleonites 1–5, pleotelson and uropods (after Wetzer and Brusca 1997) D Mesanthura occidentalis D1 dorsal view of pereonite 7, dorsally fused pleonites 1–5, pleotelson and right uropod (after Allen 1976). Antheluridae: E Ananthura luna E1 dorsal close-up view of head E2 dorsal view of pereonite 7, free pleonites 1–5, pleotelson and uropods (after Schultz 1966). Hyssuridae: F Kupellonura sp. A F1 dorsal close-up view of head F2 dorsal view of pereonite 7, free pleonites 1–5, pleotelson and uropods (after Wetzer and Brusca 1997).

Figs 7–11

Figure 7. 

Isopoda, Cymothoida, Cymothooidea, Cirolanidae: A Cirolana diminuta (after Brusca et al. 1995) B Cirolana harfordi (after Brusca et al. 1995) C Eurydice caudata (after Brusca et al. 1995) D Excirolana chiltoni (after Schultz 1969) E Excirolana linguifrons (after Schultz 1969) F Metacirolana joanneae (after Schultz 1966) G Natatolana californiensis (after Brusca et al. 1995).

Figure 8. 

Isopoda, Cymothoida, Cymothooidea, Corallanidae: A Excorallana tricornis occidentalis (after Delaney 1984) B Excorallana truncata (after Delaney 1984). Tridentellidae: C Tridentella glutacantha (after Delaney and Brusca 1985) D Tridentella quinicornis (after Delaney and Brusca 1985). Aegidae (in part): E Aega lecontii (after Schultz 1969) F Aegiochus plebeia (after Brusca 1983a).

Figure 9. 

Isopoda, Cymothoida, Cymothooidea, Aegidae (in part): A Rocinela angustata (after Brusca and France 1992) B Rocinela belliceps (after Brusca and France 1992) C Rocinela laticauda (after Brusca and France 1992) D Rocinela murilloi (after Brusca and Iverson 1985; Brusca and France 1992) E Rocinela signata (after Brusca and Iverson 1985; Brusca and France 1992) A1–E1 = pereopods 3 A2–E2 = uropods with medial process of peduncle indicated by arrows.

Figure 10. 

Isopoda, Cymothoida, Cymothooidea, Cymothoidae (in part): A Renocila thresherorum (after Brusca 1981) B Nerocila acuminata (after Brusca and Iverson 1985) C Smenispa convexa (after Brusca 1981) D Mothocya rosea (after Brusca et al. 2007).

Figure 11. 

Isopoda, Cymothoida, Cymothooidea, Cymothoidae (in part): A Ceratothoa gaudichaudii A1 pereopod 4 with arrow indicating carina (after Brusca 1981) B Ceratothoa gilberti B1 pereopod 4 (after Brusca 1981) C Elthusa californica C1 pereopod 4 (after Brusca 1981) D Elthusa menziesi D1 pereopod 4 (after Menzies 1962a; Brusca 1981) E Elthusa vulgaris E1 pereopod 4 with arrow indicating carina (after Brusca 1981).

Fig. 12

Figure 12. 

Isopoda, Cymothoida, Cymothooidea, Gnathiidae: A Caecognathia crenulatifrons (after Wetzer and Brusca 1997) B Caecognathia sanctaecrucis (after Wetzer and Brusca 1997) C Gnathia clementensis (after Schultz 1966) D Gnathia coronadoensis (after Schultz 1966) E Gnathia productatridens (after Wetzer and Brusca 1997) F Gnathia steveni (after Menzies 1962a) G Gnathia tridens (after Wetzer and Brusca 1997) H Gnathia trilobata (after Schultz 1966).

Figs 13–16

Figure 13. 

Isopoda, Cymothoida, Epicaridea, Bopyroidea, Ionidae: A Ione cornuta (after Richardson 1905a). Bopyridae (in part): B Bathygyge grandis (after Markham 2016) C Anathelges hyphalus (after Markham 1974a) D Leidya infelix (after Markham 2002) E Munidion pleuroncodis (after Markham 1975); F Phyllodurus abdominalis (after Richardson 1905a).

Figure 14. 

Isopoda, Cymothoida, Epicaridea, Bopyroidea, Bopyridae (in part): A Argeia pugettensis (after Richardson 1905a) B Aporobopyrus muguensis (after Markham 2008) C Aporobopyrus oviformis (after Shiino 1934) D Asymmetrione ambodistorta (after Markham 1985b) E Orthione griffenis E1 ventral view of pleon and pleopods (after Markham 2004) F Progebiophilus bruscai F1 ventral view of pleon and pleopods (after Campos and de Campos 1998).

Figure 15. 

Isopoda, Cymothoida, Epicaridea, Bopyroidea, Bopyridae (in part): A Bopyrella calmani (after Sassaman et al. 1984) B Capitetragonia alphei (Caribbean species = representative for Capitetragonia sp. A; after Markham 1985a) C Eremitione giardi (after Richardson 1905a) D Pseudione galacanthae (after Richardson 1905a) E Schizobopyrina striata (after Campos and de Campos 1990).

Figure 16. 

Isopoda, Cymothoida, Epicaridea, Cryptoniscoidea, Dajidae: A Holophryxus alaskensis (adult female) A1 dorsal view A2 ventral view (after Richardson 1905b) B Zonophryxus probisowa (adult female) B1 dorsal view B2 ventral view (Peruvian species = representative for unidentified SCB species of Zonophryxus; after Boyko and Williams 2021a). Hemioniscidae: C Hemioniscus balani C1 adult female C2 juvenile female (after Nierstrasz and Brender à Brandis 1926; Williams and Boyko 2012).

Fig. 17

Figure 17. 

Isopoda, Limnoriidea, Limnorioidea, Limnoriidae: A Limnoria algarum (after Menzies 1957) B Limnoria quadripunctata B1 inner surface of left mandible showing “rasp” (after Menzies 1957) C Limnoria tripunctata (after Allen 1976).

Figs 18–23

Figure 18. 

Isopoda, Sphaeromatidea, Seroloidea, Serolidae: A Heteroserolis carinata (shallow-water form after Menzies and Barnard 1959; deep-water form after Wetzer and Brusca 1997). Tecticipitidae: B Tecticeps convexus (after Richardson 1905a; Schultz 1969).

Figure 19. 

Isopoda, Sphaeromatidea, Sphaeromatoidea, Ancinidae: A Ancinus granulatus (after Holmes and Gay 1909) B Ancinus seticomvus (after Iverson 1982) C Bathycopea daltonae (after Menzies and Barnard 1959).

Figure 20. 

Isopoda, Sphaeromatidea, Sphaeromatoidea, Sphaeromatidae (in part): A Gnorimosphaeroma noblei (after Menzies 1954) B Gnorimosphaeroma oregonense B1 dorsal view (after Menzies 1954) B2 lateral view of pereonites 1–7 showing S-shaped coxae of anterior pereonites (e.g., arrow) C Discerceis granulosa (after Richardson 1899, 1905a) D Sphaeroma quoianum (after Harrison and Holdich 1984) E Sphaeroma walkeri (after Kensley and Schotte 1989).

Figure 21. 

Isopoda, Sphaeromatidea, Sphaeromatoidea, Sphaeromatidae (in part): A Paracerceis cordata (after Schultz 1969) B Paracerceis gilliana (after Allen 1976) C Paracerceis sculpta (after Brusca 1980) D Paracerceis sp. A (after Brusca 1980).

Figure 22. 

Isopoda, Sphaeromatidea, Sphaeromatoidea, Sphaeromatidae (in part): A Dynoides elegans (after Wetzer and Mowery 2017) B Paradella dianae (after Harrison and Holdich 1982) C Dynamenella dilatata (after Richardson 1899, 1905a) D Dynamenella glabra (after Richardson 1899, 1905a) E Dynamenella sheareri (after Brusca et al. 2007).

Figure 23. 

Isopoda, Sphaeromatidea, Sphaeromatoidea, Sphaeromatidae (in part): A Exosphaeroma amplicauda (after Wall et al. 2015) B Exosphaeroma aphrodita (after Wall et al. 2015) C Exosphaeroma inornata (after Iverson 1982) D Exosphaeroma pentcheffi (after Wall et al. 2015) E Exosphaeroma rhomburum (after Richardson 1899, 1905a).

Figs 24–30

Figure 24. 

Comparison of maxillipeds and number of articles in maxillipedal palps (3–5) between genera and families of SCB valviferan isopods: A 3-article maxillipedal palps B 4-article maxillipedal palps C 5-article maxillipedal palps.

Figure 25. 

Isopoda, Valvifera, Arcturidae: A Idarcturus allelomorphus (after Menzies and Barnard 1959) B Idarcturus hedgpethi (after Menzies 1951b) C Neastacilla californica (after Menzies and Barnard 1959). Thermoarcturidae: D Califarcturus tannerensis (after Schultz 1966). Holognathidae: E Cleantioides occidentalis E1 dorsal view (after Brusca and Wallerstein 1979a) E2 lateral view of C. verecundus from Florida showing reduced size of pereopod 4 characteristic of Cleantioides (after Kensley and Clark 1998).

Figure 26. 

Isopoda, Valvifera, Idoteidae (in part): A Stenosoma wetzerae (after Ormsby 1991) B Erichsonella crenulata (after Menzies 1950b) C Eusymmerus pseudoculata (after Menzies and Bowman 1956).

Figure 27. 

Isopoda, Valvifera, Idoteidae (in part): A Edotia sublittoralis (after Menzies and Barnard 1959) B Edotia sp. B (after Stebbins 2012c) C Colidotea findleyi (after Brusca and Wallerstein 1977) D Colidotea rostrata (after Allen 1976) E Colidotea wallersteini (after Brusca 1983b).

Figure 28. 

Isopoda, Valvifera, Idoteidae (in part): A Synidotea calcarea (after Schultz 1966) B Synidotea harfordi (after Menzies and Miller 1972) C Synidotea magnifica (after Menzies and Barnard 1959) D Synidotea media (after Iverson 1972).

Figure 29. 

Isopoda, Valvifera, Idoteidae (in part): A Idotea fewkesi (after Menzies 1950a) B Idotea metallica (after Brusca and Wilson 1991) C Idotea rufescens (after Menzies 1950a) D Idotea urotoma (after Menzies 1950a).

Figure 30. 

Isopoda, Valvifera, Idoteidae (in part): A Pentidotea aculeata (after Stafford 1913b) B Pentidotea kirchanskii (after Miller and Lee 1970) C Pentidotea montereyensis (after Menzies 1950a) D Pentidotea resecata (after Menzies 1950a) E Pentidotea schmitti (after Menzies 1950a) F Pentidotea stenops (after Brusca and Brusca 1978) G Pentidotea wosnesenskii (after Menzies 1950a).

Figs 31–41

Figure 31. 

Isopoda, Asellota, Janiroidea, Dendrotionidae: A Acanthomunna tannerensis (after Schultz 1966). Janiridae (in part): B Iais californica (after Menzies and Barnard 1951). Stenetrioidea, Stenetriidae: C Stenetrium sp. A C1 pereopod 1 (after Wilson 1997).

Figure 32. 

Isopoda, Asellota, Janiroidea, Joeropsididae: A Joeropsis concava A1 = antennule (after Wilson 1997) B Joeropsis dubia dubia B1 antennule B2 lateral margin of pleotelson (after Menzies 1951b) C Joeropsis dubia paucispinis C1 head C2 pleotelson (after Menzies 1951b) D Joeropsis lobata (after Richardson 1905a) E Joeropsis sp. A E1 antennule (after Wilson 1997).

Figure 33. 

Isopoda, Asellota, Janiroidea, Janiridae (in part): A Janiralata davisi (after Menzies 1951b) B Janiralata occidentalis (after Menzies 1951b) C Janiralata rajata (after Menzies 1951b) D Janiralata solasteri (after Menzies 1951b) E Janiralata sp. A (after Wilson 1997) F Janiralata sp. B (after Wilson 1997) G Janiralata sp. C (after Wilson 1997) H Janiralata sp. D (after Wilson 1997).

Figure 34. 

Isopoda, Asellota, Janiroidea, Janiridae (in part): A Ianiropsis analoga A1 enlarged dorsal view of pleotelson showing lateral spines (after Menzies 1952) B Ianiropsis derjugini (after Menzies 1952) C Ianiropsis kincaidi (after Menzies 1952) D Ianiropsis minuta (after Menzies 1952) E Ianiropsis montereyensis (after Menzies 1952) F Ianiropsis tridens F1 enlarged dorsal view of pleotelson showing lateral spines (after Menzies 1952).

Figure 35. 

Isopoda, Asellota, Janiroidea, Paramunnidae (in part): A Austrosignum latum (after Just and Wilson (2021) B Boreosignum sp. A (after Cadien 2008) C Munnogonium erratum, C1 male pereopod 2 (after Wilson 1997) D Munnogonium tillerae D1 male pereopod 2 (after Just and Wilson (2021). Pleurocopidae: E Pleurocope floridensis (Caribbean species = representative for Pleurocope sp. A; after Kensley and Schotte 1989).

Figure 36. 

Isopoda, Asellota, Janiroidea, Munnidae: A Munna chromatocephala (after Menzies 1952) B Munna fernaldi (after George and Strömberg 1968) C Munna halei (after Menzies 1952) D Munna magnifica (after Schultz 1964) E Munna spinifrons (after Menzies and Barnard 1959) F Munna stephenseni F1 close-up of pleotelson, arrow indicating sensory setae on left lateral margin (after Menzies 1952) G Munna sp. A (after Wilson 1997) H Uromunna ubiquita H1 close-up of pleotelson, arrow indicating spines or serrations on right lateral margin (after Menzies 1952).

Figure 37. 

Isopoda, Asellota, Janiroidea, Haplomunnidae: A Haplomunna caeca A1 dorsal view of brooding female A2 right lateral view of brooding female A3 left lateral view of pleotelson tip and 3-spined tubercle (after Wilson 1976).

Figure 38. 

Isopoda, Asellota, Janiroidea, Munnopsidae: A Belonectes sp. A (after Wilson 1997) B Eurycope californiensis (after Schultz 1966) C Ilyarachna acarina (after Thistle 1979) D Ilyarachna profunda (after Thistle 1979) E Munnopsurus sp. A (after Wilson 1997) F Munnopsurus sp. B (after Wilson 1997).

Figure 39. 

Isopoda, Asellota, Janiroidea, Janiridae (in part): A Caecijaera horvathi (after Menzies 1951c) B Caecianiropsis psammophila (northern California species = representative for Caecianiropsis spp. LA1 and LA2; after Menzies and Pettit 1956). Lepidocharontidae: C Microcharon sabulum C1 close-up of uropods (Caribbean species = representative for Microcharon sp. A; after Kensley 1984).

Figure 40. 

Isopoda, Asellota, Janiroidea, Desmosomatidae: A Desmosoma sp. A (after Wilson 1997) B Momedossa symmetrica (after Schultz 1966) C Prochelator sp. A (after Wilson (1997); Nannoniscidae: D Nannonisconus latipleonus (after Schultz 1966).

Figure 41. 

Isopoda, Asellota, Janiroidea, Paramunnidae (in part): A Paramunna quadratifrons (after Iverson and Wilson 1981) B Paramunna sp. A (after Cadien 1996) C Pleurogonium californiense C1 antennule (after Wilson 1997) D Pleurogonium sp. A D1 antennule (after Wilson 1997).

Figs 42, 43

Figure 42. 

Isopoda, Oniscidea, Oniscoidea, Ligiidae: A Ligia occidentalis (representative species for Ligia cf. occidentalis; after Allen 1976). Halophilosciidae: B Littorophiloscia richardsonae (after Brusca et al. 2007). Platyarthridae: C Niambia capensis (after Brusca et al. 2007). Tylidae: D Tylos punctatus, lateral view of whole body with posterior view of pleonites 4 and 5 plus pleotelson (after Brusca et al. 2007).

Figure 43. 

Isopoda, Oniscidea, Oniscoidea, Alloniscidae: A Alloniscus mirabilis (after Brusca et al. 2007) B Alloniscus perconvexus (after Richardson 1905a). Detonidae: C Armadilloniscus coronacapitalis (after Menzies 1950c) D Armadilloniscus holmesi (after Menzies 1950c) E Armadilloniscus lindahli (after Menzies 1950c).

1. The provisional species Sphaeromatidae sp. A listed in SCAMIT (2021) was reported based on immature female specimens collected off Catalina Island at a depth of 12–16 m. Although these isopods co-occurred with two other sphaeromatids, Dynamenella glabra and Paracerceis sculpta, they differed from females of both species as well as other known members of those two genera (but see Endnote 17 below regarding the correct generic assignment for some SCB Dynamenella). Although the voucher sheet developed for Sphaeromatidae sp. A included a note that these isopods could be immature Paracerceis gilliana, this hypothesis has not been confirmed. Consequently, this provisional species is not included in Key G because its correct generic assignment is not known. The second species listed in SCAMIT (2021) not included in this review is the oniscid Armadillidium vulgare, which is a strictly terrestrial species with a worldwide distribution.
2. No illustrations exist for the provisional anthuroid Eisothistos sp. A collected from Santa Barbara to Catalina Island at depths of 5–77 m, although Brusca and Cadien (1993) stated that the species is similar in gross morphology to Eisothistos antarcticus (see Wägele 1984a: fig. 2). However, neither E. antarcticus nor any of the other 30 species of Eisothistos currently recognized by WoRMS (Boyko et al. 2008 onwards) are known to occur near the SCB. For additional information on the genus see Wägele (1979, 1984a), Müller (1990), Poore (2001a), and Poore and Lew Ton (2002).
3. The aegid Aegiochus plebeia has not yet been reported from the SCB. However, the species is included in this guide since its known geographic range spans the region. See Brusca (1983a) and Bruce (2009a) for additional information.
4. It is currently unclear how to clearly distinguish juveniles of most cymothoid species from each other. Although Brusca (1978a, 1978b) provided detailed descriptions of the life histories of Elthusa vulgaris (as Lironeca vulgaris) and Nerocila acuminata (as N. californica), such information is not readily available for other local cymothoid species. Consequently, all juvenile cymothoids are treated as unidentified Cymothoidae in Key C.
5. Since its description in 1980, the cymothoid Renocila thresherorum has been considered primarily a Gulf of California species with only a few known records from elsewhere in the Eastern Pacific (see Brusca 1981). These include one SCB record of a female and an associated juvenile collected off Corona del Mar in southern California plus a couple of records from Magdalena Bay on the southwest coast of Baja California. The species, however, has also been reported recently from the Suez Canal area of Egypt (e.g., Eman et al. 2014; Mahmoud et al. 2016; Ali and Aboyadak 2018). Given this disjunct distribution, it would be useful to perform a comprehensive morphological and molecular comparison of Eastern Pacific vs. Egyptian specimens to confirm whether they represent the same or perhaps two similar looking species of Renocila.
6. The cymothoid Ceratothoa gaudichaudii is included in this guide based on historical distribution records (e.g., Brusca 1981). However, the species is listed as “taxon inquirendum” in WoRMS (Boyko et al. 2008 onwards) based on the review by Martin et al. (2015). Also see Hadfield et al. (2016) for a current list of accepted species in Ceratothoa Dana, 1852, and for information regarding taxonomic uncertainties within the genus.
7. Female and juvenile gnathiids key only to family in Key D. However, Haney (2006) provides a comprehensive discussion and guide to pairing unidentifiable females and juveniles with their male counterparts for many of the northeast Pacific species of Gnathia Leach, 1814 and Caecognathia Dollfus, 1901.
8. No illustrations exist for the three provisional species of gnathiids included in Key D (Caecognathia sp. A, Caecognathia sp. SD1, Gnathia sp. MBC1). However, photographs of these and all other known species of gnathiids that occur in SCB waters are available in Haney (2006).
9. The provisional species Capitetragonia sp. A was originally reported in 2011 as Probopyria sp. A (species voucher sheet available from SCAMIT Toolbox at https://www.scamit.org; T. D. Stebbins, 4 September 2011). However, the genus Probopyria Markham, 1985 was synonymized with Capitetragonia Pearse, 1953 by An et al. (2015). Because no illustrations exist for this provisional species, an image of the type species of Capitetragonia, C. alphei (Richardson, 1900), is provided as an example in Fig. 15B.
10. The bopyrid Eremitione giardi is listed in SCAMIT (2021) as Pseudione giardi, although this and eight other species previously included in Pseudione were transferred to the newly erected genus Eremitione by Williams et al. (2019). This species was originally added to the SCAMIT species list in 2011 (Edition 6) based on a trawl record from off the coast of Palos Verdes (D. Cadien, pers. comm.). However, the record may be questionable because E. giardi was not previously known from California waters (see Markham 1974b) except possibly for a report of an unconfirmed species identified as Pseudione sp. found infesting the hermit crab Pagurus hirsutiusculus in central California (J. Markham, pers. comm.). The record of E. giardi off Palos Verdes is likely valid if the host was a hermit crab, but not if the host was another type of crustacean (J. Markham, pers. comm.).
11. Two different adult body morphologies have been described for the dajid isopod Holophryxus alaskensis (see Richardson 1905a, 1905b: Butler 1964; Boyko and Williams 2021b), while Coyle and Mueller (1981) provided complete descriptions of the larval and juvenile stages of the species. In the original species description based on three adult female specimens collected off Alaska without any host information, Richardson (1905b) described and illustrated a stout and somewhat irregular body form, the dorsal and ventral views which are reproduced in Fig. 16A herein. Richardson (1908) later described a second species of the genus, H. californiensis, based on one adult female collected off Alaska attached to the shrimp Pasiphaea pacifica, plus one female and one male collected off Santa Barbara, southern California. In his subsequent redescription of H. alaskensis based on Richardson’s type material and additional specimens of both sexes from British Columbia, Butler (1964: figs 1, 3) synonymized H. californiensis with H. alaskensis and described a more typical elongate and symmetrical body form for adult females. Additionally, Boyko and Williams (2021b) recently provided a thorough review of the above with new records that extended the southern distribution of H. alaskensis to deep waters off the US-Mexico border. These authors also provided color photographs of typical female and male H. alaskensis, as well as an in-situ photo of an adult female attached to its host shrimp (Boyko and Williams 2021b: fig. 1).
12. Specimens of unidentified dajid isopods listed as Zonophryxus sp. in SCAMIT (2021) were collected in SCB waters during the 1990s parasitizing two species of caridean shrimp, Pantomus affinis and Plesionika trispinus (see Montagne and Cadien 2001; Boyko and Williams 2021a). Whether these isopods represent one or more species awaits further investigation. Because no illustrations exist for Zonophryxus sp., images of a recently described species from Peruvian waters, Zonophryxus probisowa Boyko & Williams, 2021, are provided in Fig. 16B as an example of the genus. Although it is not clear how closely this species resembles the SCB specimens, these images clearly show the notched appearance of the posterior end that is characteristic of species of Zonophryxus. In addition to describing Z. probisowa, Boyko and Williams (2021a) reviewed and provided a key to all seven species of Zonophryxus based on female characters. Finally, a couple of other eastern Pacific specimens of Zonophryxus recently discovered from mis-identified Gulf of California samples collected during the Talud VIII cruises in 2005 (TDS, pers. obs.) may represent an additional undescribed species of this genus (C. Boyko, pers. comm.).
13. There may be a new species of Heteroserolis in deeper waters of the SCB. Preliminary comparisons of specimens collected from depths > 100 m off San Diego with those from shallower waters in San Diego Bay (depth ≤ 15 m) reveal several differences in morphology. Whether these differences merit a new species requires further investigation. The differences between the shallow-water and deep-water specimens include: