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