Phylum: Arthropoda, Crustacea Detonella papillicornis Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Peracarida, Isopoda, Oniscidea A sow bug Family: Detonidae Taxonomy: Detonella papillicornis was orig- al. 2007). The suborder, Oniscidea is the inally described by Richardson in 1904 as largest isopod suborder and the only fully- Trichoniscus papillicornis. Richardson de- terrestrial crustacean group (Brusca et al. scribed “about seven” articles on the flagel- 2007). lum of antenna two, but Lohmander later Cephalon: Cephalon without rostrum, but found 4–5 articles (including observations of slightly pronounced anteriorly and with con- the type specimen) and moved this species cavity at apex (Fig. 2). Large anterior lobes at to a new genus, Detonella (Schultz 1972; antero-lateral angles. Garthwaite 1988). Interspecific variation in Eyes: Eyes with approximately eight characters (e.g. protopodite setae and pleo- (sometimes six) ocelli (Lohmander 1927). telson margin, Schmidt 2000) lead subse- Antenna 1: First antenna is vestigial quent taxonomists to name new species, among the suborder Oniscoidea. which were eventually synonymized as D. Antenna 2: Peduncle of second an- papillicornis (for full list of synonyms see tenna with 5–6 joints and the last three bear Schmidt 2000). setose tubercules. The fifth joint has a distal process (Fig. 3) and the flagellum is Description composed of four articles (Richardson 1905; Size: Individuals 3.8 mm (Friday Harbor, Schultz 1972). Washington, Hatch 1947) to 6 mm in length Mouthparts: (South Slough of Coos Bay). Rostrum: Absent (Fig. 2). Color: Body dark red and white mottled Pereon: Body elongate and depressed with (Miller 1975). thorax composed of seven segments, the first General Morphology: Isopod bodies are of which is not fused with the head (Brusca et dorso-ventrally flattened and can be divided al. 2007). into a compact cephalon, with eyes, two an- Pereonites: Thoracic segments about tennae and mouthparts, and a pereon equal in size, each with two rows of tubercu- (thorax) with eight segments, each bearing les and postero-lateral angles directed back- similar pereopods (hence the name “iso- wards (Lohmander 1927). pod”). Posterior to the pereon is the pleon, Pereopods: Seven pairs of pereopods. or abdomen, with six segments, the last of Pleon: Pleon narrower than pereon, but not which is fused with the telson (the pleo- abruptly so (Fig. 1). telson) (see Plate 231, Brusca et al. 2007). Pleonites: Five free pleonites are pre- The Isopoda can be divided into two groups: sent (Brusca et al. 2007) (Fig. 1). ancestral (“short-tailed”) groups (i.e. subor- Pleopods: ders) that have short telsons and derived Uropods: Styliform and extend beyond body (“long-tailed”) groups with long telsons, D. with outer branch stouter and longer than the papillicornis groups among the former (see inner branch. Uropods are inserted postero- Fig. 9, Garthwaite and Lawson 1992; Brandt laterally, and the base is not expanded (Fig. and Poore 2003; see Plate 249C, Brusca et 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. Detonella papillicornis. 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. 4). rowing of the pleon. Their uropods have ex- Pleotelson: Spatulate (Fig. 4) and morpho- panded bases and all four branches (which logically variable. The pleotelson of the pre- are small) are near the center line. The exo- sent specimen is more triangular in original pods are inserted on the medial margin in Ar- description (Richardson 1905). madilloniscus and are terminal in Detonella Sexual Dimorphism: The first and second and conspicuously extend from body outline pleopods are also elongated in males for (Brusca et al. 2007). Armadilloniscus lindahli copulation in oniscideans and reproductive has a convex body and can roll into a ball. females have a conspicuous marsupium. Armadilloniscus coronacapitalis has a spur- like extension on the lateral margin of the an- Possible Misidentifications tenna penduncle article while A. holmesi does The order Isopoda contains 10,000 not. Both A. lindahli and A. coronacapitalis species, 1/2 of which are marine and com- have a southern distribution from Marin Coun- prise 10 suborders, with eight present from ty, California south, while D. papillicornis oc- central California to Oregon (see Brusca et curs from San Francisco Bay, California al. 2007). Among isopods with small, short northward (Brusca et al. 2007). Armadillo- telsons, there are several groups (i.e. subor- niscus holmesi occurs from Friday Harbor, ders) including Phreatoicidea, Asellota, Mi- Washington to Bahia Megdalena, Baja Cali- crocerberidea, Calabozoidea and Oniscidea. fornia (Schultz 1972). The monophyletic Oniscidea (previously part of the paraphyletic Scyphac- Ecological Information idae, see Holdrich et al. 1984 in Schmidt Range: Type region is Alaska (Trichoniscus 2000, 2002) is a fully-terrestrial group com- papillicornis, USNM# 28772, Garthwaite and posed of 4,000 described species, with 22 Lawson 1992). Essentially an Arctic and Ant- known locally (among 10 families, Schmidt arctic species (Lohmander 1927) with known 2002; Brusca et al. 2007). Members are range from Southern Alaska, to Washington characterized by seven pereonites, the first and, recently, in San Francisco Bay area not fused with the head, seven pairs of pere- (Garthwaite and Lawson 1992). opods, male penes on the sternum of pere- Local Distribution: Coos Bay distribution at onite seven, a pleotelson that does not Day's Creek in the South Slough. curve dorsally, vestigal (or very small) anten- Habitat: Preferable substrates include sand nules and a pleon with five free pleonites and beach debris. (Brusca et al. 2007). The first and second Salinity: pleopods are also elongated in males for Temperature: copulation, many species have a water con- Tidal Level: Upper intertidal of beaches. ducting system and some have respiratory Associates: The amphipod, Orchestra and structures on pleopods called pseudotrache- other Oniscoidea, including Armadilioniscus ae. tuberculatus and Philoscia richardsona (Hatch The Detonidae have antennae flagel- 1947). la with four articles and the family comprises Abundance: Somewhat sparse locally, but four species locally, three of which are in the rather common in littoral sites throughout San genus Armadilloniscus; Detonella is mono- Francisco Bay, California (Garthwaite and typic locally (D. papillicornis is the only spe- Lawson 1992). cies). Armadilloniscus species have a defi- Life-History Information nite rostrum and an oval body with no nar- Reproduction: Most isopods have separate 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] sexes (i.e. dioecious, Brusca and Iverson larvae by their larger size (Sadro 2001). 1985) (although protogynous and protandric Juvenile: species are known, Araujo et al. 2004; Boy- Longevity: ko and Wolff 2014). Reproduction proceeds Growth Rate: Growth among isopods occurs by copulation and internal fertilization where in conjunction with molting where the exoskel- eggs are deposited within a few hours after eton is shed and replaced. Post-molt individ- copulation and brooded within the female uals will have soft shells as the cuticle gradu- marsupium (Brusca and Iverson 1985). The ally hardens. During a molt, arthropods have biphasic molting of isopods allows for copu- the ability to regenerate limbs that were lation; the posterior portion of the body molts previously autonomized (Kuris et al. 2007), and individuals mate, then the anterior por- however, isopods do not autotomize limbs as tion, which holds the brood pouch, molts readily as other groups (Brusca and Iverson (Sadro 2001). Embryonic development pro- 1985). Compared to other arthropods, ceeds within the brood chamber and is di- isopods exhibit a unique biphasic molting, in rect with individuals hatching as manca lar- which the posterior 1/2 of the body molts vae that resemble small adults, with no lar- before the anterior 1/2 (Brusca et al. 2007). val stage (Boyko and Wolff 2014). Food: Larva: Since most isopods are direct devel- Predators: Isopods play a significant role as oping, they lack a definite larval stage. In- intermediate food web links, like amphipods, stead this young developmental stage re- (e.g. see Americorophium salmonis, this sembles small adults (e.g. Fig. 40.1, Boyko guide) that are consumed by more than 20 and Wolff 2014). Most isopods develop species of marine fish (Welton and Miller from embryo to a manca larva, consisting of 1980; cabezon, Best and Stachowicz 2012) three stages. Manca larvae are recogniza- and whales (Brusca et al. 2007). ble by lacking the seventh pair of pereo- Behavior: pods, but otherwise resemble small adults. Bibliography They usually hatch from the female marsupi- um at the second stage and the molt from 1. ARAUJO, P. B., A. F. QUADROS, M. M. second to third manca produces the seventh AUGUSTO, and G. BOND-BUCKUP. pair of pereopods