Phylum: Mollusca Macoma inquinata Class: Bivalvia, Heterodonta, Euheterodonta Order: Imparidentia, Cardiida Irus clam Family: Tellinoidea, Tellinidae, Macominae Taxonomy: Macoma balthica, M. nasuta (see Plate 393B, Coan and Valentich-Scott and M. inquinata were all originally de- 2007). Among the bivalves, the Heterodonta scribed as members of the genus Tellina. are characterized by ctenidia (or gills) that Tellina inquinata and T. irus, initially de- are eulamellibranchiate, fused mantle margins scribed as different species (the former with and the presence of long siphons. Veneroid eastern Pacific distribution, the latter with bivalves have well-developed hinge teeth and western), were synonymized in the genus members of the family Tellinidae have short Heteromacoma. Later, this synonymization lateral hinge teeth (when present – see Pos- was reversed based on characters of shell sible Misidentifications), shells with external morphology and Macoma inquinata striations or ribs, and deep pallial sinuses (previously, and confusingly, called M. irus) (Coan and Valentich-Scott 2007). When was deemed a member of the genus Maco- holding closed shell in both hands with the ma, with an eastern Pacific distribution while hinged area up and the ligaments toward you, H. irus, remained a Heteromacoma, with a the right valve is in the right hand (Fig. 4) the western Pacific (see Keen 1962; Coan (Keen and Coan 1974). 1971). Thus, known synonyms for M. in- Body: quinata include T. inquinata as well as M. Color: irus. Subspecific designations are also Interior: Ligament is long, strong, nar- sometimes seen (e.g. Macoma heteromaco- row, and prominent (Figs. 1, 4). It is not ma inquinata, Kabat and O’Foighil 1987). seated on a nymph, but is entirely external Macoma inquinata is the name almost exclu- (Tellinidae, Coan and Valentich-Scott 2007). sively used in current intertidal guides (e.g. Exterior: Coan and Valentich-Scott 2007). Byssus: Gills: Description Shell: Shape ovate or subovate, but not circu- Size: Individuals up to 55 mm in length lar. Posterior end is narrower and less roun- (Coan 1971). The illustrated specimen (Fig. ded than anterior end. Shell is heavy, not fra- 1) is 44 mm in length, 35 mm in height, and gile and inflated, with subcentral umbones 18 mm in diameter. (Fig. 1). Occasionally, there is a slight gape Color: Shell is dull white, with a dark and and flex to right on the posterior end (Dunnill opaque periostracum (not shiny) (see Fig. and Ellis 1969). 294, Kozloff 1993). Interior shell is porce- Interior: Pallial line is not detached llanous white and feebly polished (Dunnill from the anterior ventral end of pallial sinus and Ellis 1969). Siphons are only barely ye- (Fig. 2) and is longer in the left valve (Fig. 3). llowish in color (Kozloff 1993). The pallial sinus reaches almost to the General Morphology: Bivalve mollusks are anterior adductor scar, or just to its base in bilaterally symmetrical with two lateral the left valve (Fig. 3) (Coan 1971). The pallial valves or shells that are hinged dorsally and sinuses are similar in the two valves (e.g. surround a mantle, head, foot and viscera 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. Macoma inquinata. 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. compare to M. nasuta, this guide). valves, a dark and deciduous periostracum, Exterior: External shell bears con- two cardinal teeth, the absence of lateral teeth spicuous concentric sculptural undulations and a pallial sinus that is deeper on the left (Fig. 1). valve (Scott and Blake 1998; Arruda and Do- Hinge: Hinge with ligament is entirely maneschi 2005). Macoma species may also external and no lateral teeth (Macoma, Coan have a more northern geographic distribution and Valentich-Scott 2007). Hinge area in- whileTellina are elongate, relatively compres- cludes two cardinal teeth in each valve, but sed, conspicuously sculptured, brightly colo- no lateral teeth (Fig. 5). red, and usually warm water dwellers (Coan Eyes: 1971). Eleven species in the infaunal genus Foot: Macoma (Luttikhuizen et al. 2012) are repor- Siphons: The inhalant and exhalant siphons ted locally (although 30 have been identified are completely separate (Fig. 1a) (Quayle in the northeastern Pacific, Dunnill and Ellis 1970; Kozloff 1993). 1969), but only seven are described in local Burrow: keys (e.g. Coan and Valentich-Scott 2007), the four most common species of Macoma in Possible Misidentifications our area are M. balthica, M. nasuta, M. Tellinids can be distinguished from inquinata, and M. secta (Kabat and O’Foighil other small or young bay clams (i.e. 1987). Mactridae: Tresus; Veneridae: Protothaca, Two species, M. secta and M. inden- Saxidomus; Myidae: Mya, Cryptomya) an tata have a posterior dorsal flange extending external ligament, an ovate shell, an incons- from posterior end to the external ligament, picuous nymph (or supporting projection for this is absent in other Macoma species. The the external ligament), sometimes reddish former species is called the the sand clam hue and lateral teeth as well as a shell with and has a quadrate and truncate posterior. ribs or striations (no radial pattern) and she- The latter is elongate, has a pointed posterior, lls that never gape. Lateral teeth may or unique muscle scars, is relatively rare and may not be present in the Tellinidae (Coan small (to 2.5 cm) and occurs from Trinidad, 1971). Myids have a hinge with a spoon- California southward. Macoma secta, also shaped chondrophore (left valve) and a pro- has a white shell, with a yellowish epidermis. jecting tooth (right valve) (see Mya arenaria, Its right valve is more inflated than the left, this guide). Venerids have three cardinal and it can be large (to 120 mm) and is more teeth in each valve. Mactrids have an inter- common in clean sand, not in estuarine mud. nal ligament, A-shaped cardinal teeth, and The morphology of the pallial sinus dif- gaping valves (Coan and Valentich-Scott ferentiates the other species. In species with- 2007). The Tellinidae has around 16 spe- out a posterior dorsal flange, M. acolasta and cies distributed between two genera locally M. yoldiformis, the anterior ventral edge of the – Tellina and Macoma. These genera can pallial sinus is detached for a portion of the be differentiated by the hinge teeth, Tellina distance to the posterior adductor muscle species have a hinge with lateral teeth, while scar. Macoma acolasta also has a rounded Macoma species do not. Macoma species posterior, rather than pointed as in M. yoldi- have shells that are also more rounded and formis and is rare, sand-dwelling, and occurs inflated thanTellina, and are smooth, white, from Bodega Bay, California, southward. often chalky. They are characterized by ha- Macoma yoldiformis is elongate, inflated, and ving a ovate shell consisting of two equal thin, with the pallial sinus detached from the 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] pallial line. Although the range of this clam valves. Macoma incongrua averages 30–40 is from Vancouver south to Baja California, it mm in length (Dunnill and Ellis 1969). is not included in Puget Sound or British (The following species may be present Columbia work (Dunnill and Ellis 1969). It locally, but are not included in local dichoto- can be found in silt in low intertidal of mous keys). Macoma expansa, is a rare, protected bays (Coan and Valentich-Scott usually offshore species (to 50 mm) whose 2007). pallial sinuses are perpendicular to the pallial Macoma inquinata, M. nasuta and M. line. Macoma elimata is found only in 15– balthica (see descriptions in this guide) are 476 meters of water. Macoma calcarea is all species with an anterior ventral edge of found from 35 meters and lower, from 37° pallial sinus that is not detached and they north. Other northern subtidal species tend to be larger (up to 110 mm) than M. ac- include the large M. brota and M. lipara olasta or M. yoldiformis (less than 30 mm). (Dunnill and Ellis 1969). Macoma balthica has a pinkish hue and a Ecological Information pallial sinus that ends ¾ of the way to anteri- Range: Type locality is Columbia River, OR or adductor muscle scar and is generally (Keen 1962). Known range includes Siberia, more oval than M. nasuta or M. inquinata Aleutian Islands, British Columbia, south to (Kozloff 1993). In M. inquinata, the pallial Oregon and rare further south of Santa Bar- sinus does not reach the ventral end of the bara, California (Coan 1971). anterior adductor muscle. Macoma nasuta, Local Distribution: Distribution in many on the other hand, is not as round and Oregon bays, particularly Tillamook, Coos, heavy as M. inquinata and its pallial sinus Siuslaw, Yaquina, and less common in Alsea, reaches and joins the anterior adductor scar Nestucca, Netarts Bays (Hancock 1979). above its base (left valve). (Its right valve Habitat: Usually in soft muddy sand (Dunnill may be more like M. inquinata’s). and Ellis 1969; Kabat and O’Foighil 1987) and Furthermore, its siphons are orange and its in protected areas. Individuals have also shell posterior is bent to the right (hence the been found in coarse sand with shell hash, name, bent-nose clam). Macoma inquinata intertidal sand, and in fine sediment overlying can also bend slightly posteriorly, and may flat rocks (British Columbia, Canada, Dunnill be confused with the thinner M.