Saxidomus Giganteus Class: Bivalvia, Heterodonta, Euheterodonta

Home , Euheterodonta, Leukoma staminea, Mercenaria, Paphia, Pea crab, Saxidomus

Saxidomus giganteus Class: Bivalvia, Heterodonta, Euheterodonta

Order: Imparidentia, Venerida Beefsteak clam, butter, Family: Veneroidea, Veneridae or Washington clam

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

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. 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.

Foot: valves that do not gape. Saxidomus species Siphons: also have an elongate shell, when compared Burrow: Inhabits burrows up to 30 cm deep to I. lamellifera, but they possess anterior lat- (Kozloff 1993). The burrow opening is rec- eral teeth and valves that are separated by a ognizable by a cigar-shaped or deflated fig- narrow gape, posteriorly. Saxidomus nuttalli ure eight-shaped hole that is 1.2–2 cm long and S. giganteus can be differentiated as the (Jacobson 1975). former species has an elongate and thinner shell as well as a narrow escutcheon (not pre- Possible Misidentifications sent in S. giganteus). The shell sculpturing in Veneroida is a large bivalve order, S. giganteus also appears smooth as the characterized by well-developed hinge teeth, commarginal ribs are thin, low and tightly including most heterodonts. The family Ven- spaced, while the opposite is true for S. nut- eridae is characterized by a hinge without talli. Its shell is more elongate, the ribs heavi- lateral teeth, ligament that is entirely exter- er, rougher and more conspicuous (Coan and nal, radial ribs on shell exterior, and three Carlton 1975) and the interior is often marked cardinal teeth on each shell valve. There posteriorly with purple. Saxidomus nuttalli, are 12–16 species reported locally in this the larger, more southern species, is found in family within the genera Nutricola, Saxido- California in the same habitat as S. giganteus, mus, and Leukoma, with two species in but apparently does not extend into Oregon. each, and Gemma gemma), Irusella lamellif- (S. nuttalli is the only Saxidomus in Humboldt era), Tivelatultorum, Venerupis philippinar- Bay, however). Saxidomus nuttalli, referred um, Mercenaria mercenaria, Callithaca ten- to as the “money clam” because of its repre- errima, each with a single species repre- sentation as currency for Californian native sented locally. American tribes (Ricketts and Calvin 1952), Nutricola species are small, with resembles S. giganteus, but is larger shells usually less than 10 mm in length. (ironically, 12.7 compared to 7.6 cm) and has Gemma gemma also has a small shell, but it more prominent growth lines and a shell that is triangular in shape compared to Nutricola is purplish at the siphonal end ((Ricketts and species with elongate or oval shells. Tivela Calvin 1952; Kozloff 1993). Saxidomus nutta- stultorum also has a triangular shell, but in- lli is more common in the southern end of its dividuals are larger than G. gemma and distribution, while S. giganteus is more com- have a smooth shell surface with shiny peri- mon north (Ricketts and Calvin 1952). ostracum. Panopea generosa, the deep- The remaining species have shells burrowing geoduck, is quadrate, and gapes larger than 10 mm in length. Some species widely. Tresus capax, the gaper clam, (family have shell sculpturing that is dominated by Mactridae, see description in this guide), is commarginal ribs with fine radial ridges and also quadrate, fairly smooth with chalky white others have shells that have radial ridges shell exterior. The truncated posterior gapes with inconspicuous, or not predominating, moderately, its ligament is partly internal, the commarginal ribs. Of those in the former cardinal teeth are "A" shaped, and the shell category, I. lamellifera has widely spaced has a dark, eroded partial covering. commarginal lamellae and a shell that is short compared to M. mercenaria and C. Ecological Information tenerrima. The two latter species have elon- Range: Type locality is not specified (see Orr gated shells, no anterior lateral teeth and et al. 2013). Known range includes the

Aleutian Islands, Alaska to Monterey, presence of the latter species is negatively California; S. giganteus is rare in the effected by S. nuttallii (Peterson and Andre southern range. 1980). Local Distribution: Locally occurs in bays Abundance: “The most abundant clam of the and estuaries, rarely on open coast or inlets Northwest" (Ricketts and Calvin 1971), with oceanic influence (Packard 1918). Saxidomus giganteus was a commercially Common from Alaska to San Francisco Bay, harvested species in Puget Sound, Washing- California, but rare south of Humboldt bay, ton (Kozloff 1974). Up to 352 individuals/m2 California (Kozloff 1993). were reported from beaches in British Colum- Habitat: Occurs in mud or sand (Coan and bia, Canada (Gillespie and Bourne 2005). In Carlton 1975), gravelly beaches (Puget British Columbia beaches, assessed in 1993, Sound, Washington). “Clam gardens”, cre- S. giganteus density was as high as 376 indi- ated adjacent to intertidal rock walls con- viduals/m2 (Gillispie and Bourne 2004). structed by human populations in the Holo- Life-History Information cene, have four times as many S. giganteus Reproduction: Separate sexes reproduce by and twice as many P. staminea (see de- free-spawning, external fertilization and devel- scription in this guide) individuals as non- opment via a free-swimming larva. Oocytes walled beaches, and transplanted juveniles are 80–90 µm in diameter and surrounded by of the latter species also grow faster (1.7 a jelly layer that is 230 µm in diameter (see times faster) in clam gardens (Groesbeck et Fig. 1, Breese and Phibbs 1970). Spawning al. 2014). from March–June has been reported for the Salinity: Occurs in sites with average yearly Oregon coast (Fraser 1929; Robinson and salinity is 29 (range 24–32, Puget Sound, Breese 1982; Kabat and O’Foighil 1987). Washington Goong and Chew 2001). Gametogenesis occurs in fall months and is Temperature: Individuals prefer temperate- complete by August and September in the cold waters (see Range). Strait of Georgia (Fraser 1929). Like Pro- Tidal Level: Individuals most commonly col- tothaca staminea, spawning in response to lected from just under the sediment surface, dense algal blooms has been reported but also found up to 30 cm deep. (Robinson and Breese 1982). There is con- Associates: Occasionally infested with im- siderable variation in spawning times, even in mature specimens of commensal pea crab neighboring beds with variable water Pinnixa littoralis, but usually free of symbiotic temperatures. Polar body formation occurs or parasitic associates (Ricketts and Calvin 60 minutes post fertilization and cleavage 1971). Co-occurs with other clams, Tapes begins 30 minutes later; trochophore larvae philippinarum and Protothaca staminea as develop after 24 hours, which become bivalve well as the shore crab, Hemigrapsus veliger larvae 24 hours later (18˚C, see Fig. 1, (Nickerson 1977; Goong and Chew 2001). Breese and Phibbs 1970). Protothaca staminea and S. giganteus co- Larva: Bivalve development generally pro- occur on Kiket Island, Washington, where ceeds from external fertilization via broadcast the greatest diversity and richness of other spawning through a ciliated trochophore stage marine invertebrates are found (Houghton to a veliger larva. Bivalve veligers are charac- 1977). Co-occurs with other clams (e.g., terized by a ciliated velum that is used for Tresus capax and T. nuttallii, Gillispie and swimming, feeding and respiration. The veli- Bourne 2004; Sanguinolaria nuttallii, ger larva is also found in many gastropod lar- Peterson and Andre 1980), and the

vae, but the larvae in the two groups can be stead juveniles grow considerably the follow- recognized by shell morphology (i.e. snail- ing spring (Fraser and Smith 1928). Growth like versus clam-like). In bivalves, the initial rates varied for clams collected in different shelled-larva is called a D-stage or straight- sites around Puget Sound, Washington, with hinge veliger due to the “D” shaped shell. oldest clams (e.g., 30 years) being 95–140 This initial shell is called a prodissoconch I mm in length (Goong and Chew 2001, see and is followed by a prodissoconch II, or also Gillespie and Bourne 2005). Growth shell that is subsequently added to the initial rates are measured by annular rings, which shell zone (see Fig. 1, Caddy 1969). Finally, are formed during periods of slowed growth, shell secreted following metamorphosis is usually in winter months (Paul et al. 1976). simply referred to as the dissoconch (see Periods of growth may be slowed by reduction Fig. 2, Brink 2001). Once the larva develops in salinity (Gillikin et al. 2005) and growth may a foot, usually just before metamorphosis be density dependent (Kline 1982). Speci- and loss of the velum, it is called a pediveli- mens reached 65 mm in length after 8–9 ger (see Fig. 1, Caddy 1969; Kabat and years on Porpoise Island, southeast Alaska O’Foighil 1987; Brink 2001). (For general- (Paul et al. 1976). At three beaches in British ized life cycle see Fig. 1, Brink 2001). Veli- Columbia where populations were measured ger larvae of S. giganteus are free- in 1993, individuals 40–71 mm in length were swimming for up to 30 days and grow ap- 8 years old, 24–93 mm were 2–16 years, and proximately 7 µm per day (Breese and 25–67 mm were 2–12 years old; estimating Phibbs 1970). They are straight hinge (see that individuals 6.5 years old are approximate- Fig. 4, Brink 2001) until they are 160 µm in ly 63 mm in length (Gillispie and Bourne length after 2 weeks (Fraser and Smith 2004). Legal catch size is 63 mm in length, 1928). They have an anterior end that is which occurs when individuals are approxi- longer and more pointed than the posterior, mately 6–10 years old (Gillispie and Bourne which is broadly rounded (Brink 2001). 2004). Throughout development, the umbo and Food: A filter-feeder, that feeds by straining both ends (ant and post) become broadly material from currents of water that are rounded and larvae are longer than they are pumped through the gills. The ingestion and tall. Larvae metamorphose at about 230 µm concentration of toxic algae (e.g., from the and (Brink 2001) have a pelagic duration of genera Alexandrium, Gymnodinium, Pyrodini- 4 wks (Fraser and Smith 1928; Kabat and um, Smolowitz and Doucette 1995) leads to O’Foighil 1987). Optimal growth and surviv- paralytic shellfish poisoning, rendering the al for larvae were obtained at 15˚C, salinity clams dangerous for human consumption 20–29, when fed a mixture of three algal (Kitts et al. 1992; Kitts and Smith 1992). species (settlement at 20–25 days when lar- Clams accumulate toxins in their siphon tips, vae were 230–250 µm, Bourne 1971). in part, to reduce predation (Price and Lee Juvenile: Juvenile growth was 18 µm per 1972; Smolowitz and Doucette 1995). This day for 150 days post metamorphosis suite of neurotoxins (50 structural variants) (Breese and Phibbs 1970, see also Walne are collectively known as saxitoxins as they 1973). were first isolated from S. giganteus (Oshima Longevity: To 20 years or more (Paul et al. et al. 1977; Vale 2010) and the chemical com- 1976; Haderlie 1980). position of this toxin was described by Growth Rate: There is little growth of young Schantz et al. (1974). individuals immediately after settling. In- Predators: Known predators include sting

rays, fishes, shore birds (e.g., gulls, Maron Protothaca staminea at Chugachik Island, 1982), drilling snails, and sea otters (Kvitek Alaska. Journal of Shellfish Research. and Oliver 1992; Kvitek et al. 1993, but see 17:1003-1008. reduction in sea otter predation due to pres- 3. BENDELL, L. I. 2014. Evidence for de- ence of saxitoxin, Kvitek et al. 1991). Pre- clines in the native Leukoma staminea as dation by crab species, which break open a result of the intentional introduction of the shells of many bivalves, is reduced by a the non-native Venerupis philippinarum in larger and thicker shell, an inflated shell coastal British Columbia, Canada. Estuar- shape with steep ventral margin, and the ies and Coasts. 37:369-380. ability to burrow deeply. Other bivalves 4. BOULDING, E. G., and T. K. HAY. 1984. (e.g., Protothaca staminea, see description Crab response to prey density can result in this guide) also close tightly, further re- in density-dependent mortality of clams. ducing predation, however, the narrow pos- Canadian Journal of Fisheries and Aquatic terior gape in S. giganteus allows for poten- Sciences. 41:521-525. tial breaking by crab claws (Boulding 1984). 5. BOURNE, N. 1971. The effects of temper- Octopus dofleini are known to prey upon S. ature, salinity and food on the develop- giganteus by drilling holes in their shells; in- ment of the larvae of butter clams, Saxido- creased shell thickness may reduce preda- mus giganteus. Proceedings National tion as incomplete boreholes were observed Shellfisheries Association. 61:1971-1971. on thicker shelled clams (Ambrose et al. 6. BREESE, W. P., and F. D. PHIBBS. 1969. 1988). Saxidomus giganteus was historical- Some observations on the spawning and ly (e.g., Burchell et al. 2013) and is currently early development of the butter clam, a commercially important and harvested Saxidomus giganteus. Proceedings Na- species; the most important food clam in tional Shellfisheries Association. 60:95-98. British Columbia, Canada (Bourne 1971; 7. BRINK, L. A. 2001. Mollusca: Bivalvia, p. Haderlie 1980; Kozloff 1993, see also Fig. 1 129-149. In: Identification guide to larval Gillispie and Bourne 2005). The fishery in marine invertebrates of the Pacific North- southeast Alaska began in 1930 with a har- west. A. Shanks (ed.). Oregon State Uni- vest of 11,340 kg (Paul et al. 1976) and in versity Press, Corvallis, OR. the Broughton Archipelago, British Colum- 8. BURCHELL, M., A. CANNON, N. HALL- bia, Canada harvests as high as 500,000 kg MANN, H. P. SCHWARCZ, and B. R. were reported in 1970 (Dunham et al. 2006). SCHOENE. 2013. Intersite variability in (see Bechtol and Gustafson 1998 for com- the season of shellfish collection on the mercial summary). central coast of British Columbia. Journal Behavior: of Archaeological Science. 40:626-636. 9. COAN, E. V., and P. VALENTICH-SCOTT. Bibliography 2007. Bivalvia, p. 807-859. In: The Light 1. AMBROSE, R. F., B. J. LEIGHTON, and and Smith manual: intertidal invertebrates E. B. HARTWICK. 1988. Characteriza- from central California to Oregon. J. T. tion of boreholes by Octopus dofleini in Carlton (ed.). University of California the bivalve Saxidomus giganteus. Jour- Press, Berkeley, CA. nal of Zoology. 214:491-503. 10. DUNHAM, J. S., B. KOKE, G. E. GILLES- 2. BECHTOL, W. R., and R. L. GUS- PIE, and G. MEYER. 2007. An exploratory TAFSON. 1998. Abundance, recruitment, survey for littleneck clams (Protothaca and mortality of Pacific littleneck clams staminea) in the Broughton Archipelago,

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