Phylum: Arthropoda, Crustacea Scleroplax granulata Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Eucarida, Decapoda, Pleocyemata, Brachyura, A burrow-dwelling pea crab Eubrachyura, Thoracotremata Family: Pinnotheroidea, Pinnotheridae, Pinnotherinae Taxonomy: The monotypic genus Sclero- and maxillipeds attach posterior to the mouth plax was erected for S. granulata in 1893 by and extend to cover the mandibles (Ruppert Rathbun, but its systematic position was et al. 2004). In S. granulata the outer controversial until it was recently confirmed, maxillipeds have 3-jointed palps where third elevated and separated from Pinnixa based article is joined to second proximally, not dis- on characters of the carapace and third tally (Fig. 3). A winged extension is present maxilliped (Campos 2006). on the merus (Rathbun 1918). Characteristics of the third maxilliped are taxonomically im- Description portant for this species. The propodus of the Size: Up to 11 mm (males) and 12.9 mm third maxilliped extends to the end of the dac- (females) in width (California, Garth and tyl rather than in Pinnixa where the dactyl ex- Abbott 1980). The illustrated specimen tends beyond the short propodus (Campos (female from Coos Bay) is 5.5 mm in width 2006). (Fig. 1). Males can be larger than females Carapace: Rounded carapace. Oval, (MacGinitie and MacGinitie 1949), an smooth, hard, convex and granular. Male car- unusual characteristic among pea crabs. apace smoother than females. Carapace Color: The illustrated specimen is dark gray width almost 1½ x length (Kozloff 1974). An- with light outlines and red eyes. Males are tero- and posterolateral edges are rounded light tan and orange (Bodega Bay Harbor, and curve to meet gradually, without distinct CA, Garth and Abbott 1980). angles (Scleroplax, Rathbun 1918). General Morphology: The body of decapod Frontal Area: Frontal area entire, crustaceans can be divided into the cepha- blunt, slightly convex with no teeth between lothorax (fused head and thorax) and abdo- eyes. men. They have a large plate-like carapace Teeth: dorsally, beneath which are five pairs of tho- Pereopods: Legs 2–5 very short racic appendages (see chelipeds and pere- (Rathbun 1918), they are slender, somewhat opods) and three pairs of maxillipeds (see rounded (Kuris et al. 2007) and with slender mouthparts). The abdomen and associat- dactyls. First walking legs are smaller than ed appendages are reduced and folded ven- second while the third is longest (slightly). trally (Decapoda, Kuris et al. 2007). The fourth walking legs are not greatly smaller Cephalothorax: than others (Figs. 1, 4). Eyes: Oval and small. Eyestalks Chelipeds: The chelipeds of females very short and thick with orbits small. are small, feeble, with thumb horizontal, tip Antenna: acute and fingers not gaping (Fig. 1). Male Mouthparts: The mouth of decapod chelipeds, on the other hand, are prominent, crustaceans comprises six pairs of append- large and very wide. Their dactyls are curved, ages including one pair of mandibles (on ei- smooth, gaping and their propodus is with ther side of the mouth), two pairs of maxillae granulate surface and convex margins. and three pairs of maxillipeds. The maxillae 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. and L. Rasmuson. 2015. Scleroplax granulata. 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 Biol- ogy, Charleston, OR. Thumb is shorter than wide and bears one occidentalis, with cylindrical fourth and fifth large tooth (Garth and Abbott 1980) (Fig. 2). walking legs, is found in echiuroid worm Abdomen (Pleon): Female abdomen is burrows and associated with P. franciscana, wide, smooth, fringed with hair and not P. tubicola, and P. schmitti, species also reaching beyond sternum (Schmitt 1921). found in worm burrows and tubes. Pinnixa Male abdomen is narrow and tapering grad- species have third walking legs markedly ually (Schmitt 1921) (see Pinnixa faba, Fig. longer than the others (not just slightly longer 5). as in Scleroplax (Kuris et al. 2007)) and third Telson & Uropods: maxillipeds with propodus shorter than dactyl Sexual Dimorphism: Male and female (they are of equal length in Scleroplax) brachyuran crabs are easily differentiable. (Campos 2006). Their carapace is membra- The most conspicuous feature, the abdo- nous, not hard, and it has a distinctive angle men, is narrow and triangular in males while where the antero- and posterolateral cara- it is wide and flap-like in females (Brachyura, pace margins meet – in contrast to the Kuris et al. 2007). rounded margins of Scleroplax. Pinnixa fran- ciscana, a large (to 22 mm wide) crab, with a Possible Misidentifications broad carapace with pointed sides, a sharp All members of the Pinnotheridae are line of granules on the cheliped propodus and small, have a wide, rounded carapace, small a widened merus on the third walking legs eyes, and short eyestalks. There are 15 (Garth and Abbott 1980), are also found in pinnotherid species reported from central Neotrypaea or Upogebia burrows with California to Oregon (Kuris et al. 2007). Pea Scleroplax. The carapace has a granular crabs are very particular to a specific habitat cardiac ridge, curved teeth along the and/or host (see Pinnixa faba). The genus anterolateral margin and a conspicuous Scleroplax is monotypic and characterized subhepatic tooth in P. scamit. Little is known by a hard, subheptagonal and convex cara- about the final species, P. weymouthi (Kuris pace. Additional characters include a third et al. 2007). Pinnixa schmitti (Rathbun, 1918) maxilliped with propodus that extends to the occurs from Alaska to San Francisco Bay end of the dactyl (Campos 2006). (Garth and Abbott 1980). It lives in well- Pinnixa, Opisthopus and Scleroplax drained loose beach material, not with any all have a large maxillipedal palps and a particular host (Wells 1940), but in tubes, ca- wide carapace. Opisthopus transversus has vities or burrows within 5 cm of the surface. It a carapace just a little wider than long and has a low tooth on the inner margin of the walking legs that are sub-equal, the second cheliped dactyl (Kozloff 1974). The dactyls of being slightly longer than the others. Its its fourth walking legs are longer than those of hosts are nearly always molluscan (Garth the third pair (Kozloff 1974) and carapace is and Abbott 1980) and it has not been re- about 1¾ times wider than long, and tapers ported north of Monterey, California (Schmitt laterally, unlike that of Scleroplax, which is 1921). rounded. Most local pea crab species are in the The other local pinnotherid genera in- genus Pinnixa: P. littoralis, is often found in clude Pinnotheres (symbiotic with oysters), the clam Tresus capax; P. longipes, with Parapinnixa (symbiotic with polychaetes exceptionally large third walking legs, is Terebella californica and Loimia), Fabia commensal with tube worms; P. barnharti, is (symbiotic with bivalves, especially Mytilus) commensal with a holothurian; P. Opisthopus (symbiotic with various molluscs 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] including Tresus, and some holothurians). roplax (MacGinitie and MacGinitie 1949). Parapinnixa is a southern California genus Bryozoan Walkeria lives on legs of Scleroplax with a wide carapace, and legs that diminish and bryozoan Triticella elongata is on its greatly in size (unlike those of Scleroplax). carapace, appendages and in gill cavities (Garth and Abbott 1980). Scleroplax has also Ecological Information been observed with Mya arenaria (Friday Range: Type locality is Ensenada, Baja Cal- Harbor, WA, Rathburn 1918). ifornia, Mexico (Campos 2006). Range in- Abundance: Up to six individuals per burrow, cludes the north end of Vancouver Island, but can also occur singly. Scleroplax granula- B.C. south to El Coyote estuary, Punta ta is the most prevalent of all commensals Abreojos, Baja California Sur, Mexico with Upogebia (Garth and Abbott 1980). (Campos 2006; Campos and Campos 2012). Life-History Information Local Distribution: Coos Bay distribution at Reproduction: All decapod crustacean fe- several sites. The illustrated specimen is males attach recently laid gelatinous egg from Jordan Cove (North Spit). Distribution masses to their pleopods. The outer embryo also includes other Oregon estuaries. Attem- membrane thickens and a strand develops pts to find S. granulata in Coos Bay have that attaches each embryo to pleopod setae proven ineffective (Puls 2002). (Decapoda, Kuris et al. 2007). Egg-bearing Habitat: Sandy mud and mudflats of pro- female Scleroplax granulata have been ob- tected bays (Garth and Abbott 1980). Free- served from January to March in California living in burrows with Neotrypaea (= and Oregon (Jaffe et al. 1987). Most larval Callianassa) or Upogebia, etc. (see release occurs at twilight (Rasmuson and associates), where it uses protection of Morgan 2013). burrow, and food and oxygen circulating Larva: The larvae of pinnotherids proceed there. Males migrate between burrows through planktonic prezoea, zoea (two stag- (Garth and Abbott 1980). es) and megalopa stages. The zoea have Salinity: Occurs with Neotrypaea, which is large compound eyes and four spines: one found at salinities from 35–30 (Coos Bay). each dorsal and rostral and two lateral (see Temperature: Fig. 54.5, Martin 2014). The most definitive Tidal Level: Mid to low intertidal to 55 m feature of pea crab zoea is the fifth abdominal (Garth and Abbott1980; Jaffe et al. 1987). segment, which is expanded laterally (see Associates: Scleroplax granulata can be http://invert-embryo.blogspot.com/2012/04/ found in burrows of Neotrypaea or identifying-pinnotherid-larvae.html; Puls Upogebia.