Scleroplax Granulata

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Phylum: Arthropoda, Crustacea Sc leroplax granulata Class: Malacostraca Order: Decapoda Section: Brachyura A burrow-dwelling pea crab Family: Pinnotheridae

Taxonomy: The monotypic genus Scleroplax present on the merus (Rathbun 1918). was erected for S. granulata in 1893 by Characteristics of the third maxilliped are Rathbun, but its systematic position was taxonomically important for this species. The controversial until it was recently confirmed, propodus of the third maxilliped extends to elevated and separated from Pinnixa based the end of the dactyl rather than in Pinnixa on characters of the carapace and third where the dactyl extends beyond the short maxilliped (Campos 2006). propodus (Campos 2006). Carapace: Rounded carapace. Oval, Description smooth, hard, convex and granular. Male Size: Up to 11 mm (males) and 12.9 mm carapace smoother than females. Carapace (females) in width (California, Garth and width almost 1½ x length (Kozloff 1974). Abbott 1980). The illustrated specimen Antero- and posterolateral edges are rounded (female from Coos Bay) is 5.5 mm in width and curve to meet gradually, without distinct (Fig. 1). Males can be larger than females angles (Scleroplax, Rathbun 1918). (MacGinitie and MacGinitie 1949), an unusual Frontal Area: Frontal area entire, characteristic among pea crabs. blunt, slightly convex with no teeth between Color: The illustrated specimen is dark gray eyes. with light outlines and red eyes. Males are Teeth: light tan and orange (Bodega Bay Harbor, Pereopods: Legs 2–5 very short CA, Garth and Abbott 1980). (Rathbun 1918), they are slender, somewhat General Morphology: The body of decapod rounded (Kuris et al. 2007) and with slender crustaceans can be divided into the dactyls. First walking legs are smaller than cephalothorax (fused head and thorax) and second while the third is longest (slightly). abdomen. They have a large plate-like The fourth walking legs are not greatly smaller carapace dorsally, beneath which are five than others (Figs. 1, 4). pairs of thoracic appendages (see chelipeds Chelipeds: The chelipeds of females and pereopods) and three pairs of are small, feeble, with thumb horizontal, tip maxillipeds (see mouthparts). The abdomen acute and fingers not gaping (Fig. 1). Male and associated appendages are reduced and chelipeds, on the other hand, are prominent, folded ventrally (Decapoda, Kuris et al. 2007). large and very wide. Their dactyls are curved, Cephalothorax: smooth, gaping and their propodus is with Eyes: Oval and small. Eyestalks very granulate surface and convex margins. short and thick with orbits small. Thumb is shorter than wide and bears one Antennae: large tooth (Garth and Abbott 1980) (Fig. 2). Mouthparts: The mouth of decapod Abdomen (Pleon): Female abdomen is crustaceans comprises six pairs of wide, smooth, fringed with hair and not appendages including one pair of mandibles reaching beyond sternum (Schmitt 1921). (on either side of the mouth), two pairs of Male abdomen is narrow and tapering maxillae and three pairs of maxillipeds. The gradually (Schmitt 1921) (see Pinnixa faba, maxillae and maxillipeds attach posterior to Fig. 5). the mouth and extend to cover the mandibles Telson & Uropods: (Ruppert et al. 2004). In S. granulata the Sexual Dimorphism: Male and female outer maxillipeds have 3-jointed palps where brachyuran crabs are easily differentiable. third article is joined to second proximally, not The most conspicuous feature, the abdomen, distally (Fig. 3). A winged extension is is narrow and triangular in males while it is

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12733 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] wide and flap-like in females (Brachyura, carapace has a granular cardiac ridge, curved Kuris et al. 2007). teeth along the anterolateral margin and a conspicuous subhepatic tooth in P. scamit. Possible Misidentifications Little is known about the final species, P. All members of the Pinnotheridae are small, weymouthi (Kuris et al. 2007). Pinnixa have a wide, rounded carapace, small eyes, schmitti (Rathbun, 1918) occurs from Alaska and short eyestalks. There are 15 pinnotherid to San Francisco Bay (Garth and Abbott species reported from central California to 1980). It lives in well-drained loose beach Oregon (Kuris et al. 2007). Pea crabs are material, not with any particular host (Wells very particular to a specific habitat and/or host 1940), but in tubes, cavities or burrows within (see Pinnixa faba). The genus Scleroplax is 5 cm of the surface. It has a low tooth on the monotypic and characterized by a hard, inner margin of the cheliped dactyl (Kozloff subheptagonal and convex carapace. 1974). The dactyls of its fourth walking legs Additional characters include a third are longer than those of the third pair (Kozloff maxilliped with propodus that extends to the 1974) and carapace is about 1¾ times wider end of the dactyl (Campos 2006). than long, and tapers laterally, unlike that of Pinnixa, Opisthopus and Scleroplax all Scleroplax, which is rounded. have a large maxillipedal palps and a wide The other local pinnotherid genera carapace. Opisthopus transversus has a include Pinnotheres (symbiotic with oysters), carapace just a little wider than long and Parapinnixa (symbiotic with polychaetes walking legs that are sub-equal, the second Terebella californica and Loimia), Fabia being slightly longer than the others. Its hosts (symbiotic with bivalves, especially Mytilus) are nearly always molluscan (Garth and Opisthopus (symbiotic with various molluscs Abbott 1980) and it has not been reported including Tresus, and some holothurians). north of Monterey, California (Schmitt 1921). Parapinnixa is a southern California genus Most local pea crab species are in the with a wide carapace, and legs that diminish genus Pinnixa: P. littoralis, is often found in greatly in size (unlike those of Scleroplax). the clam Tresus capax; P. longipes, with exceptionally large third walking legs, is Ecological Information commensal with tube worms; P. barnharti, is Range: Type locality is Ensenada, Baja commensal with a holothurian; P. California, Mexico (Campos 2006). Range occidentalis, with cylindrical fourth and fifth includes the north end of Vancouver Island, walking legs, is found in echiuroid worm B.C. south to El Coyote estuary, Punta burrows and associated with P. franciscana, Abreojos, Baja California Sur, Mexico P. tubicola, and P. schmitti, species also (Campos 2006; Campos and Campos 2012). found in worm burrows and tubes. Pinnixa Local Distribution: Coos Bay distribution at species have third walking legs markedly several sites. The illustrated specimen is longer than the others (not just slightly longer from Jordan Cove (North Spit). Distribution as in Scleroplax (Kuris et al. 2007)) and third also includes other Oregon estuaries. maxillipeds with propodus shorter than dactyl Attempts to find S. granulata in Coos Bay (they are of equal length in Scleroplax) have proven ineffective (Puls 2002). (Campos 2006). Their carapace is Habitat: Sandy mud and mudflats of membranous, not hard, and it has a protected bays (Garth and Abbott 1980). distinctive angle where the antero- and Free-living in burrows with Neotrypaea (= posterolateral carapace margins meet – in Callianassa) or Upogebia, etc. (see contrast to the rounded margins of associates), where it uses protection of Scleroplax. Pinnixa franciscana, a large (to burrow, and food and oxygen circulating 22 mm wide) crab, with a broad carapace with there. Males migrate between burrows (Garth pointed sides, a sharp line of granules on the and Abbott 1980). cheliped propodus and a widened merus on Salinity: Occurs with Neotrypaea, which is the third walking legs (Garth and Abbott found at salinities from 35–30 (Coos Bay). 1980), are also found in Neotrypaea or Temperature: Upogebia burrows with Scleroplax. The

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 Biology, Charleston, OR. Tidal Level: Mid to low intertidal to 55 m Juvenile: (Garth and Abbott1980; Jaffe et al. 1987). Longevity: Associates: Scleroplax granulata can be Growth Rate: Growth that is punctuated by found in burrows of Neotrypaea or Upogebia. molting and pre-molting periods are defined It is also found in the burrows and, by the separation of the epidermis from the sometimes, clinging to the body of the old cuticle and the dramatic increase in echiuroid, Urechis caupo in the southern part epidermal cell growth. Post-molt periods are of its distribution. Scleroplax granulata is recognizable by individuals that have soft among those pea crabs least intimately shells as the cuticle gradually hardens and associated with its host (Wells 1940) where it deposits a thin membranous layer. is a commensal, not parasitic, species Furthermore, decapods have the ability to (compare to Pinnixa faba). Additional regenerate limbs, which have been associates include the goby, Clevelandia ios, autonomized as necessary, at subsequent the polynoid polychaete, Hesperonoe, which molts (Kuris et al. 2007). clings to burrow walls to escape Scleroplax Food: Ingests food that falls into burrow and (MacGinitie and MacGinitie 1949). Bryozoan particles brought by goby Clevelandia. Also Walkeria lives on legs of Scleroplax and screens material with second maxillipeds bryozoan Triticella elongata is on its (Garth and Abbott 1980). carapace, appendages and in gill cavities Predators: (Garth and Abbott 1980). Scleroplax has also Behavior: Males move around among been observed with Mya arenaria (Friday burrows and are known to exhibit a "possum" Harbor, WA, Rathburn 1918). posture for up to two minutes if disturbed Abundance: Up to six individuals per (Garth and Abbott 1980). burrow, but can also occur singly. Scleroplax granulata is the most prevalent of all Bibliography commensals with Upogebia (Garth and Abbott 1980). 1. CAMPOS, E. 2006. Systematics of the genus Scleroplax Rathbun, 1893 Life-History Information (Crustacea: Brachyura: Reproduction: All decapod crustacean Pinnotheridae). Zootaxa. 1344:33-41. females attach recently laid gelatinous egg 2. CAMPOS, E., and A. DE CAMPOS. masses to their pleopods. The outer embryo 2012. The intertidal brachyuran crabs membrane thickens and a strand develops from estuaries of the west coast Baja that attaches each embryo to pleopod setae California, Mexico (Crustacea: (Decapoda, Kuris et al. 2007). Egg-bearing Brachyura). Marine Biodiversity female Scleroplax granulata have been Records. 5:1-7. observed from January to March in California 3. GARTH, J. S., and D. P. ABBOTT. and Oregon (Jaffe et al. 1987). Most larval 1980. Brachyura: The True crabs, p. release occurs at twilight (Rasmuson and 594-630. In: Intertidal invertebrates of Morgan 2013). California. R. H. Morris, D. P. Abbott, Larva: The larvae of pinnotherids proceed and E. C. Haderlie (eds.). Stanford through planktonic prezoea, zoea (two University Press, Stanford, CA. stages) and megalopa stages. The zoea 4. JAFFE, L. A., C. F. NYBLADE, R. B. have large compound eyes and four spines: FORWARD, and S. SULKIN. 1987. one each dorsal and rostral and two lateral Phylum or subphylum Crustacea, (see Fig. 54.5, Martin 2014). The most class Malacostraca, order Decapoda, definitive feature of pea crab zoea is the fifth Brachyura, p. 451-475. In: abdominal segment, which is expanded Reproduction and development of laterally (see http://invert- marine invertebrates of the northern embryo.blogspot.com/2012/04/identifying- Pacific coast. M. F. Strathmann (ed.). pinnotherid-larvae.html; Puls 2001). The University of Washington Press, specific larval morphology of S. granulata has Seattle, WA. not been described.

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12733 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] 5. KOZLOFF, E. N. 1974. Keys to the 11. RASMUSON, L. K., and S. G. marine invertebrates of Puget Sound, MORGAN. 2013. Fish predation after the San Juan Archipelago, and weakly synchronized larval release in adjacent regions. University of a coastal upwelling system. Marine Washington Press, Seattle. Ecology Progress Series. 490:185- 6. KURIS, A. M., P. S. SADEGHIAN, J. 198. T. CARLTON, and E. CAMPOS. 2007. 12. RATHBUN, M. J. 1918. The grapsoid Decapoda, p. 632-656. In: The Light crabs of America. Bulletin of the and Smith manual: intertidal United States Natural Museum. invertebrates from central California to 97:128-145. Oregon. J. T. Carlton (ed.). University 13. RUPPERT, E. E., R. S. FOX, and R. of California Press, Berkeley, CA. D. BARNES. 2004. Invertebrate 7. MACGINITIE, G. E., and N. zoology: a functional evolutionary MACGINITIE. 1949. Natural history of approach. Thomson Brooks/Cole, marine animals. McGraw-Hill Book Belmont, CA. Co., New York. 14. SCHMITT, W. L. 1921. The marine 8. MARTIN, J. W. 2014. Brachyura, p. decapod crustacea of California. 295-310. In: Atlas of crustacean University of California Publications in larvae. J. W. Martin, J. Olesen, and J. Zoology. 23:1-470. T. Høeg (eds.). Johns Hopkins 15. WELLS, W. 1940. Ecological studies University Press, Baltimore, MD. on the pinnotherid crabs of Puget 9. PULS, A. L. 2001. Arthropoda: Sound. University of Washington Decapoda, p. 179-250. In: Publications in Oceanography. 2:19- Identification guide to larval marine 50. invertebrates of the Pacific Northwest. A. Shanks (ed.). Oregon State University Press, Corvallis, OR. 10. —. 2002. Transport of zooplankton in South Slough, Oregon. M.S. University of Oregon.