Saxidomus Giganteus Class: Bivalvia; Heterodonta Order: Veneroida Beefsteak Clam, Butter, Or Washington Clam Family: Veneridae

Phylum: Mollusca Saxidomus giganteus Class: Bivalvia; Heterodonta Order: Veneroida Beefsteak clam, butter, or Washington clam Family: Veneridae

Taxonomy: Originally described as Shell: The shell is oval in shape (Coan and Venerupis gigantea, other synonyms include Carlton 1975), and the posterior is truncate conflicts of taxonomic genus-species gender (Keen and Coan 1974). agreement, as Saxidomus is feminine (article Interior: The valves are similar in 31.2, ICZN): S. gigantea (e.g., Paul et al. shape. The inner ventral margin is smooth 1976; Robinson and Breese, 1982; Bendell 2014), as well as Venus maxima. (Keen and Coan 1974), and the inner surface is white and porcelaneous. The muscle scars Description are dark and subequal in size. The pallial line Size: Adults average 10 cm in length (Paul et is continuous (but broken by a sinus), not a al. 1976; Kozloff 1993). series of scars (Fig. 3). The flesh is often Color: Shell exterior is whitish, but can also reddish, hence one common name, the have patches of blackish discoloration; beefsteak clam. juvenile exterior is sometimes tan in color Exterior: Exterior sculpture is with (Kozloff 1993). The shell interior is also white. raised concentric growth lines and grooves, General Morphology: Bivalve mollusks are with no radial lines (Fig. 1). The valves are bilaterally symmetrical with two lateral valves very similar, the shell is thick, heavy, and or shells that are hinged dorsally and deep (Fig. 2). The most prominent lines surround a mantle, head, foot and viscera representing periods of slowed growth (see Plate 393B, Coan and Valentich-Scott (Kozloff 1993). The valves gape only slightly 2007). ). The Veneroida is a large and at posterior end (gape less than 1/4 shell diverse bivalve heterodont order that is width) (Kozloff 1993). Individuals can retract characterized by well-developed hinge teeth. their siphon, but not feet. The shell There are 22 local families, and members of microstructure was described for many the Veneridae have three cardinal teeth on veneroid clams by Shimamoto (1986), where each valve (see Fig 302, Kozloff 1993; Plate Saxidomus species were characterized by a 396H, Coan and Valentich-Scott 2007) (Fig. Type I shell composed of both composite 4). prismatic and crossed lamellar structure Body: (Shimamoto 1986). Color: Hinge: The hinge is very thick, heavy, Interior: The ligament is completely and is posterior and external. There are three external, ad is seated on a long, massive cardinal hinge teeth, flanked by a long lateral nymph, or chondrophore (Fig. 4). The body tooth in each valve (Fig. 4). tissue is rubbery and is “superb for chowder” Eyes: (Kozloff 1993). Maximal systolic pressure Foot: was recorded for Tresus capax (see Siphons: description in this guide) to be 13 cm H20, Burrow: Inhabits burrows up to 30 cm deep which is higher than 11 cm H20 recorded for (Kozloff 1993). The burrow opening is Saxidomus giganteus (Florey and Cahill recognizable by a cigar-shaped or deflated 1977). figure eight-shaped hole that is 1.2–2 cm long Exterior: (Jacobson 1975). Byssus: Gills: Possible Misidentifications Veneroida is a large bivalve order, characterized by well-developed hinge teeth,

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12919 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] including most heterodonts. The family not extend into Oregon. (S. nuttalli is the only Veneridae is characterized by a hinge without Saxidomus in Humboldt Bay, however). lateral teeth, ligament that is entirely external, Saxidomus nuttalli, referred to as the “money radial ribs on shell exterior, and three cardinal clam” because of its representation as teeth on each shell valve. There are 12–16 currency for Californian native American species reported locally in this family within tribes (Ricketts and Calvin 1952), resembles the genera Nutricola, Saxidomus, and S. giganteus, but is larger (ironically, 12.7 Leukoma, with two species in each, and compared to 7.6 cm) and has more prominent Gemma gemma), Irusella lamellifera), growth lines and a shell that is purplish at the Tivelatultorum, Venerupis philippinarum, siphonal end ((Ricketts and Calvin 1952; Mercenaria mercenaria, Callithaca tenerrima, Kozloff 1993). Saxidomus nuttalli is more each with a single species represented common in the southern end of its locally. distribution, while S. giganteus is more Nutricola species are small, with shells common north (Ricketts and Calvin 1952). usually less than 10 mm in length. Gemma Panopea generosa, the deep- gemma also has a small shell, but it is burrowing geoduck, is quadrate, and gapes triangular in shape compared to Nutricola widely. Tresus capax, the gaper clam, (family species with elongate or oval shells. Tivela Mactridae, see description in this guide), is stultorum also has a triangular shell, but also quadrate, fairly smooth with chalky white individuals are larger than G. gemma and shell exterior. The truncated posterior gapes have a smooth shell surface with shiny moderately, its ligament is partly internal, the periostracum. cardinal teeth are "A" shaped, and the shell The remaining species have shells has a dark, eroded partial covering. larger than 10 mm in length. Some species have shell sculpturing that is dominated by Ecological Information commarginal ribs with fine radial ridges and Range: Type locality is not specified (see Orr others have shells that have radial ridges with et al. 2013). Known range includes the inconspicuous, or not predominating, Aleutian Islands, Alaska to Monterey, commarginal ribs. Of those in the former California; S. giganteus is rare in the southern category, I. lamellifera has widely spaced range. commarginal lamellae and a shell that is short Local Distribution: Locally occurs in bays compared to M. mercenaria and C. tenerrima. and estuaries, rarely on open coast or inlets The two latter species have elongated shells, with oceanic influence (Packard 1918). no anterior lateral teeth and valves that do not Common from Alaska to San Francisco Bay, gape. Saxidomus species also have an California, but rare south of Humboldt bay, elongate shell, when compared to I. California (Kozloff 1993). lamellifera, but they possess anterior lateral Habitat: Occurs in mud or sand (Coan and teeth and valves that are separated by a Carlton 1975), gravelly beaches (Puget narrow gape, posteriorly. Saxidomus nuttalli Sound, Washington). “Clam gardens”, and S. giganteus can be differentiated as the created adjacent to intertidal rock walls former species has an elongate and thinner constructed by human populations in the shell as well as a narrow escutcheon (not Holocene, have four times as many S. present in S. giganteus). The shell giganteus and twice as many P. staminea sculpturing in S. giganteus also appears (see description in this guide) individuals as smooth as the commarginal ribs are thin, low non-walled beaches, and transplanted and tightly spaced, while the opposite is true juveniles of the latter species also grow faster for S. nuttalli. Its shell is more elongate, the (1.7 times faster) in clam gardens (Groesbeck ribs heavier, rougher and more conspicuous et al. 2014). (Coan and Carlton 1975) and the interior is Salinity: Occurs in sites with average yearly often marked posteriorly with purple. salinity is 29 (range 24–32, Puget Sound, Saxidomus nuttalli, the larger, more southern Washington Goong and Chew 2001). species, is found in California in the same Temperature: Individuals prefer temperate- habitat as S. giganteus, but apparently does cold waters (see Range).

Hiebert, T.C. 2015. Saxidomus giganteus. 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: Individuals most commonly begins 30 minutes later; trochophore larvae collected from just under the sediment develop after 24 hours, which become bivalve surface, but also found up to 30 cm deep. veliger larvae 24 hours later (18˚C, see Fig. 1, Associates: Occasionally infested with Breese and Phibbs 1970). immature specimens of commensal pea crab Larva: Bivalve development generally Pinnixa littoralis, but usually free of symbiotic proceeds from external fertilization via or parasitic associates (Ricketts and Calvin broadcast spawning through a ciliated 1971). Co-occurs with other clams, Tapes trochophore stage to a veliger larva. Bivalve philippinarum and Protothaca staminea as veligers are characterized by a ciliated velum well as the shore crab, Hemigrapsus that is used for swimming, feeding and (Nickerson 1977; Goong and Chew 2001). respiration. The veliger larva is also found in Protothaca staminea and S. giganteus co- many gastropod larvae, but the larvae in the occur on Kiket Island, Washington, where the two groups can be recognized by shell greatest diversity and richness of other morphology (i.e. snail-like versus clam-like). marine invertebrates are found (Houghton In bivalves, the initial shelled-larva is called a 1977). Co-occurs with other clams (e.g., D-stage or straight-hinge veliger due to the Tresus capax and T. nuttallii, Gillispie and “D” shaped shell. This initial shell is called a Bourne 2004; Sanguinolaria nuttallii, Peterson prodissoconch I and is followed by a and Andre 1980), and the presence of the prodissoconch II, or shell that is subsequently latter species is negatively effected by S. added to the initial shell zone (see Fig. 1, nuttallii (Peterson and Andre 1980). Caddy 1969). Finally, shell secreted following Abundance: “The most abundant clam of the metamorphosis is simply referred to as the Northwest" (Ricketts and Calvin 1971), dissoconch (see Fig. 2, Brink 2001). Once Saxidomus giganteus was a commercially the larva develops a foot, usually just before harvested species in Puget Sound, metamorphosis and loss of the velum, it is Washington (Kozloff 1974). Up to 352 called a pediveliger (see Fig. 1, Caddy 1969; individuals/m2 were reported from beaches in Kabat and O’Foighil 1987; Brink 2001). (For British Columbia, Canada (Gillespie and generalized life cycle see Fig. 1, Brink 2001). Bourne 2005). In British Columbia beaches, Veliger larvae of S. giganteus are free- assessed in 1993, S. giganteus density was swimming for up to 30 days and grow as high as 376 individuals/m2 (Gillispie and approximately 7 µm per day (Breese and Bourne 2004). Phibbs 1970). They are straight hinge (see Fig. 4, Brink 2001) until they are 160 µm in Life-History Information length after 2 weeks (Fraser and Smith 1928). Reproduction: Separate sexes reproduce by They have an anterior end that is longer and free-spawning, external fertilization and more pointed than the posterior, which is development via a free-swimming larva. broadly rounded (Brink 2001). Throughout Oocytes are 80–90 µm in diameter and development, the umbo and both ends (ant surrounded by a jelly layer that is 230 µm in and post) become broadly rounded and diameter (see Fig. 1, Breese and Phibbs larvae are longer than they are tall. Larvae 1970). Spawning from March–June has metamorphose at about 230 µm and (Brink been reported for the Oregon coast (Fraser 2001) have a pelagic duration of 4 wks 1929; Robinson and Breese 1982; Kabat and (Fraser and Smith 1928; Kabat and O’Foighil O’Foighil 1987). Gametogenesis occurs in fall 1987). Optimal growth and survival for larvae months and is complete by August and were obtained at 15˚C, salinity 20–29, when September in the Strait of Georgia (Fraser fed a mixture of three algal species 1929). Like Protothaca staminea, spawning (settlement at 20–25 days when larvae were in response to dense algal blooms has been 230–250 µm, Bourne 1971). reported (Robinson and Breese 1982). There Juvenile: Juvenile growth was 18 µm per is considerable variation in spawning times, day for 150 days post metamorphosis even in neighboring beds with variable water (Breese and Phibbs 1970, see also Walne temperatures. Polar body formation occurs 1973). 60 minutes post fertilization and cleavage

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12919 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Longevity: To 20 years or more (Paul et al. Predation by crab species, which break open 1976; Haderlie 1980). the shells of many bivalves, is reduced by a Growth Rate: There is little growth of young larger and thicker shell, an inflated shell individuals immediately after settling. Instead shape with steep ventral margin, and the juveniles grow considerably the following ability to burrow deeply. Other bivalves (e.g., spring (Fraser and Smith 1928). Growth rates Protothaca staminea, see description in this varied for clams collected in different sites guide) also close tightly, further reducing around Puget Sound, Washington, with oldest predation, however, the narrow posterior clams (e.g., 30 years) being 95–140 mm in gape in S. giganteus allows for potential length (Goong and Chew 2001, see also breaking by crab claws (Boulding 1984). Gillespie and Bourne 2005). Growth rates are Octopus dofleini are known to prey upon S. measured by annular rings, which are formed giganteus by drilling holes in their shells; during periods of slowed growth, usually in increased shell thickness may reduce winter months (Paul et al. 1976). Periods of predation as incomplete boreholes were growth may be slowed by reduction in salinity observed on thicker shelled clams (Ambrose (Gillikin et al. 2005) and growth may be et al. 1988). Saxidomus giganteus was density dependent (Kline 1982). Specimens historically (e.g., Burchell et al. 2013) and is reached 65 mm in length after 8–9 years on currently a commercially important and Porpoise Island, southeast Alaska (Paul et al. harvested species; the most important food 1976). At three beaches in British Columbia clam in British Columbia, Canada (Bourne where populations were measured in 1993, 1971; Haderlie 1980; Kozloff 1993, see also individuals 40–71 mm in length were 8 years Fig. 1 Gillispie and Bourne 2005). The fishery old, 24–93 mm were 2–16 years, and 25–67 in southeast Alaska began in 1930 with a mm were 2–12 years old; estimating that harvest of 11,340 kg (Paul et al. 1976) and in individuals 6.5 years old are approximately 63 the Broughton Archipelago, British Columbia, mm in length (Gillispie and Bourne 2004). Canada harvests as high as 500,000 kg were Legal catch size is 63 mm in length, which reported in 1970 (Dunham et al. 2006). (see occurs when individuals are approximately 6– Bechtol and Gustafson 1998 for commercial 10 years old (Gillispie and Bourne 2004). summary). Food: A filter-feeder, that feeds by straining Behavior: material from currents of water that are pumped through the gills. The ingestion and Bibliography concentration of toxic algae (e.g., from the genera Alexandrium, Gymnodinium, 1. AMBROSE, R. F., B. J. LEIGHTON, Pyrodinium, Smolowitz and Doucette 1995) and E. B. HARTWICK. 1988. leads to paralytic shellfish poisoning, Characterization of boreholes by rendering the clams dangerous for human Octopus dofleini in the bivalve consumption (Kitts et al. 1992; Kitts and Saxidomus giganteus. Journal of Smith 1992). Clams accumulate toxins in Zoology. 214:491-503. their siphon tips, in part, to reduce predation 2. BECHTOL, W. R., and R. L. (Price and Lee 1972; Smolowitz and Doucette GUSTAFSON. 1998. Abundance, 1995). This suite of neurotoxins (50 structural recruitment, and mortality of Pacific variants) are collectively known as saxitoxins littleneck clams Protothaca staminea as they were first isolated from S. giganteus at Chugachik Island, Alaska. Journal (Oshima et al. 1977; Vale 2010) and the of Shellfish Research. 17:1003-1008. chemical composition of this toxin was 3. BENDELL, L. I. 2014. Evidence for described by Schantz et al. (1974). declines in the native Leukoma Predators: Known predators include sting staminea as a result of the intentional rays, fishes, shore birds (e.g., gulls, Maron introduction of the non-native 1982), drilling snails, and sea otters (Kvitek Venerupis philippinarum in coastal and Oliver 1992; Kvitek et al. 1993, but see British Columbia, Canada. Estuaries reduction in sea otter predation due to and Coasts. 37:369-380. presence of saxitoxin, Kvitek et al. 1991).

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