Phylum: Arthropoda, Crustacea Ianiropsis derjugini Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Peracarida, Isopoda, Asellota An asellid isopod Family: Janiroidea, Janiridae Taxonomy: In 1952, Menzies characterized (Fig. 1). I. kincaidi and I. derjugini as subspecies of I. Antenna 1: The first antenna is quite kincaidi based on morphology and habitat. short and has a flagellum with 8–10 articles However, due to a lack of evidence of genet- (Fig. 2) (10 articles in males, Richardson ic introgression, most researchers consider 1905). them different species (e.g. Wilson and Antenna 2: The second antenna is Wagele 1994; Brusca et al. 2007). with "squama", or scales, on third article of the base (Fig. 3) (Miller 1975) and is about 2/ Description 3 length of body. The flagellum is with many Size: Up to 4 mm in length (Menzies 1952). segments and fine setae and the peduncle Figured specimen (from Charleston, Coos has six articles (Hatch 1947). Bay) was 3 mm long. Mouthparts: Maxilliped palps with arti- Color: White with brown chromatophores. cles two and three much wider than endite General Morphology: Isopod bodies are (not figured) (Miller 1975). dorso-ventrally flattened and can be divided Rostrum: Absent. into a compact cephalon, with eyes, two an- Pereon: tennae and mouthparts, and a pereon Pereonites: Seven thoracic segments (thorax) with eight segments, each bearing with variably shaped epimera (Fig. 1) and no similar pereopods (hence the name “iso- lateral spines. pod”). Posterior to the pereon is the pleon, Pereopods: The interior edge of the or abdomen, with six segments, the last of propodus is smooth, not serrated, on proximal which is fused with the telson (the pleo- third of the first pereopod (Fig. 4) (Miller telson) (see Plate 231, Brusca et al. 2007). 1975). The Isopoda can be divided into two groups: Pleon: ancestral (“short-tailed”) groups (i.e. subor- Pleonites: ders) that have short telsons and derived Pleopods: (“long-tailed”) groups with long telsons, I. Uropods: Biramous with inner branch a little derjugini groups among the former (see longer than the outer branch. The total Plate 233C, Brusca et al. 2007). The subor- uropod length is less than ½ the pleotelson der, Asellota is considered one of the ances- (Miller 1975) (Fig. 5). tral isopod groups (see Fig. 7, Brandt and Pleotelson: Shield-like with spineless lateral Poore 2003) and members are some of the borders spineless (Fig. 1) and at postero- most diverse isopods and are most success- lateral angles at insertion of uropods (Fig. 1) ful in deep sea habitats (Brusca et al. 2007; (Miller 1975) (no other Ianiropsis has this e.g. Jaera, Linse et al. 2014). character). Three posterior segments not Cephalon: Without rostrum or anteriorly pro- differentiated (Hatch 1947). jecting anterolateral angles (Fig. 1) Sexual Dimorphism: Males have a second (compare to I. k. kincaidi, Miller 1975). pleopod with modified copulatory morphology Eyes: Well-developed and reniform 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. Ianiropsis derjugini. 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. (enlarged protopod and knee-like endopod) ent: I. kincaidi lives in small pools created (Brusca et al. 2007). by wave splash and is subject to wide tem- perature variation (Menzies 1952). On the Possible Misidentifications other hand, I. derjugini is more common un- The order Isopoda contains 10,000 der rocks that are covered by algae (Brusca species, 1/2 of which are marine and com- et al. 2007). prise 10 suborders, with eight present from Ianiropsis analoga, I. epilittoralis and central California to Oregon (see Brusca et I. tridens have spine-like serrations on the al. 2007). Among isopods with elongated sides of the pleotelson (Miller 1975). telsons (with anuses and uropods that are Ianiropsis analoga occurs from Marin subterminal), there are several groups (i.e. County, California northward, I. epilittoralis suborders) including Flabellifera, Anthu- can be found from Marin County south to ridea, Gnathiidea, Epicaridea and Valvif- San Luis Obispo, California in the high era. intertidal and I. tridens has a large range The suborder Asellota is character- from San Juan Island, Washington to ized by uropods that are styliform (Brandt Monterey County, California as well as and Poore 2003) and terminal, pleonites 3, northern Chile. Ianiropsis minuta and I. 4 or 5 fused with the pleotelson, and 1–3 montereyensis lack these serrations, forming an operculum over those posterior however I. minuta can be recognized by and pereonites without coxal plates. Thirty evenly rounded head margins and the lack -eight species comprising nine families are of the postero-lateral angles of the telson reported from central California to Oregon, and I. montereyensis has uropods that are but only 18 species are intertidal (Brusca longer than the telson. The former species et al. 2007). is reported from Marin County, California The family Janiridae (174 species, while the latter occurs from Marin to 23 genera worldwide, Linse et al. 2014) is Monterey Counties in the intertidal and a non-monophyletic isopod family (Wilson shallow subtidal zones (Brusca et al. 2007). 1994) that have 2–3 claws on the dactyls of pereopods 2–7, antennae with long fla- Ecological Information gella, and well developed uropods. There Range: Type region is the Bering Sea. are 13 species locally and seven are in the Known range from Komandorskie Islands, genus Ianiropsis, all of which are found in Bering Sea to Monterey County, California the intertidal or shallow subtidal (Brusca et (Miller 1968). al. 2007). The remaining genera include Local Distribution: Coos Bay distribution at Caecianiropsis, Caecijaera, Iais (each with the Charleston small boat basin. one local species) and Janiralata (three Habitat: Under rocks of middle and lower in- local species). tertidal zones (Menzies 1952), on buoys from Both Ianiropsis kincaidi and I. der- the surface to 1.8 m (Miller 1968). The fig- jugini were formerly subspecies of I. kin- ured specimen was collected from a within a caidi and thus, are most morphologically decayed float with the shipworm, Bankia similar. Ianiropsis kincaidi has longer uro- setacea. pods, almost half to as long as pleotelson. Salinity: Collected at a salinity of 30. Its first antennae are elongate and it lacks Temperature: Apparently not adaptable to the postero-lateral angles of I. derjugini. extreme temperatures (compre to I. k. kin- Habitats of the two subspecies are differ- caidi, Miller 1968). 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] Tidal Level: Middle and lower intertidal ment and larval morphology can vary between zones (Menzies 1952) ranging from surface groups (e.g. Gnathiidae, Cryptoniscoidea, Bo- to 1.8 m deep (Miller 1968). The figured pyroidae, Cymothoidae, Oniscoidea) (see specimen was collected near the water line. Boyko and Wolff 2014). Parasitic isopods, for Associates: The shipworm, Bankia setacea example, have larvae that are morphologically and harpactacoid copepods. dissimilar from adults (Sadro 2001). Isopod Abundance: Fairly common in wood debris larvae are not common members of the plank- with Bankia setacea. ton, with parasitic larvae most likely to be ob- served. Occasionally, suspended benthic ju- Life-History Information veniles or pelagic species are collected in Reproduction: Most isopods have separate plankton samples, but these can be differenti- sexes (i.e. dioecious, Brusca and Iverson ated from larvae by their larger size (Sadro 1985) (although protogynous and protandric 2001). species are known, Araujo et al. 2004; Boy- Juvenile: ko and Wolff 2014). Reproduction proceeds Longevity: by copulation and internal fertilization where Growth Rate: Growth among isopods occurs eggs are deposited within a few hours after in conjunction with molting where the exoskel- copulation and brooded within the female eton is shed and replaced. Post-molt individ- marsupium (Brusca and Iverson 1985). The uals will have soft shells as the cuticle gradu- biphasic molting of isopods allows for copu- ally hardens. During a molt, arthropods have lation; the posterior portion of the body molts the ability to regenerate limbs that were and individuals mate, then the anterior por- previously autonomized (Kuris et al. 2007), tion, which holds the brood pouch, molts however, isopods do not autotomize limbs as (Sadro 2001). Embryonic development pro- readily as other groups (Brusca and Iverson ceeds within the brood chamber and is direct 1985). Compared to other arthropods, with individuals hatching as manca larvae isopods exhibit a unique biphasic molting, in that resemble small adults, with no larval which the posterior 1/2 of the body molts stage (Boyko and Wolff 2014). Ovigerous I. before the anterior 1/2 (Brusca et al. 2007). derjugini were collected in February, May Food: and June (northern California, Menzies Predators: Isopods play a significant role as 1952). intermediate food web links, like amphipods, Larva: Since most isopods are direct devel- (e.g. see Americorophium salmonis, this oping, they lack a definite larval stage. In- guide) that are consumed by more than 20 stead this young developmental stage re- species of marine fish (Welton and Miller sembles small adults (e.g. Fig. 40.1, Boyko 1980; cabezon, Best and Stachowicz 2012) and Wolff 2014). Most isopods develop from and whales (Brusca et al. 2007). embryo to a manca larva, consisting of three Behavior: stages. Manca larvae are recognizable by lacking the seventh pair of pereopods, but Bibliography otherwise resemble small adults.