Phylum: Mollusca Hiatella arctica Class: Bivalvia, Heterodonta, Eugeterodonta Order: Imparidentia, Adapedonta A gammarid amphipod Family: Hiatelloidea, Hiatellidae Taxonomy: There are many synonyms for Color: H. arctica due to the potentially cosmopoli- Interior: Ligament is external (Figs. 2– tan distribution of this species. Research by 3) in members of the family Hiatellidae (Coan Strauch (1968) and Beu (1969) synony- and Carlton 1975). This primary ligament mized all Hiatella species worldwide (except initially forms at the shell posterior in newly H. australis from southern Australia) as H. metamorphosed juveniles before moving to arctica (Beu 1969). Commonly seen syno- the middle of the shell (Flyachinskaya and nyms include Saxicava arctica, H. pholaids, Lezin 2008). and H. solida. Due to the extensive synony- Exterior: mizations, it is possible that there are actual- Byssus: These attachment threads ly two species currently under the name H. are present in nestling specimens, but not in arctica, locally (Coan and Valentich-Scott boring ones (e.g., H. pholadis). Adult attach 2007). with byssal threads and can also bore into rock (Coan and Valentich-Scott 2007). A Description single, long byssal thread produced by post- Size: Individuals to 50–76 mm in length larval clams allows them to be moved by (Kozloff 1993). The illustrated specimen weak water currents (see Juvenile) (Haderlie (from Coos Bay) is 38 mm in length (Quayle 1980), in a process called thread drifting (see 1970). Macoma balthica, Nutricola tantilla, Color: Exterior is white, chalky, granular, descriptions in this guide). and with tan, thin, and ragged periostracum Gills: (Hiateila, Keen and Coan 1974). The Shell: (For amino acid shell composition see interior is porcelain-like and white Brigham 1983.) Right valve slightly larger (Hiatellidae, Hunter 1949). Periostracum is than the left (Khalaman 2005) (Fig. 2). light brown or tan. Interior: Pallial line is faint and broken General Morphology: Bivalve mollusks are into discontinuous scars (Fig. 3) (Hiatellidae, bilaterally symmetrical with two lateral valves Coan and Valentich-Scott 2007), unlike or shells that are hinged dorsally and sur- Entodesma navicula (see description in this round a mantle, head, foot and viscera (see guide). Adductor muscle scars are Plate 393B, Coan and Valentich-Scott approximately equal in size, but not shape. 2007). The Veneroida is a large and diverse There is no pallial sinus (Kozloff 1974). bivalve heterodont order that is character- Exterior: The shape is highly variable ized by well-developed hinge teeth. There due to their nestling habit. Right and left val- are 22 local families, and members of the ves are equal, oblong, and gaping. The Hiatellidae are characterized by a pallial line posterior is broader and more square than the that is divided into patches (see Plate 395D, anterior end, which is broadly truncated (Fig. Coan and Valentich-Scott 2007) (Fig. 3). 1). Elongate, boring specimens have been Body: A nestling species with a thin shell reported as H. pholadis (Coan and Carlton (see Fig. 257, Kozloff 1993). 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. Hiatella arctica. 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. 1975) (Fig. 1a). Shell sculpture is concentric abrupta and Hiatella arctica. Panopea abrup- only and the periostracum is light tan and ta tends to be larger (up to 200 mm in length) thin (Figs. 1, 2) (Hiatella, Keen and Coan than H. arctica and have a continuous pallial 1974). line, not broken into patches like in H. arctica. Hinge: Adult specimens are without Panopea abrupta, also known as the ge- (or very worn) hinge teeth (Fig. 3). Howev- oduck, is a very deep burrower with long si- er, young clams have 1–2 weak, peg-like phons (up to several feet) in soft sediments. cardinal teeth. Umbones are depressed, It has one cardinal tooth in either hinge and is nearer anterior end than middle and do not rarely found in Oregon. Also, Saxicavella touch one other (Fig. 2). pacifica, a small offshore species in soft sedi- Eyes: ments is reported (Coan and Valentich-Scott Foot: 2007). Siphons: Siphons are fused and with crim- Entodesma navicula is probably most son siphon tips (Fig. 1) (Kozloff 1993). likely to be confused with H. arctica, as it is of Burrow: a comparable size, shape, and habitat. Entodesma navicula has a dark, rough Possible Misidentifications periostracum, not a pale, thin one, an external Three bivalve families including the ligament (like H. arctica), and short, fused Lyonisiidae, Hiatellidae, and Thraciidae are siphons, but without red tips. Inside the shell characterized by their lack of dorsal margin is very pink and pearly. Entodesma navicula ears or projecting teeth or chondrophores, has no hinge teeth, but does have a large and two adductor muscles. In thraciids, the internal ligament and its pallial line is ligament can be both internal and external continuous. and the pallial line is continuous; in hiatellids Other bivalves that can be easily con- the ligament is always external and the palli- fused with H. arctica include Protothaca al line is broken into patches (see below). staminea, Petricola carditoides, Platyodon On the other hand, in the lyonisiids (e.g., cancellatus, and Cryptomya californica. The see Entodesma navicula in this guide) the venerid clam Protothaca staminea, like H. arc- pallial line is continuous, as in thraciids, but tica, is white with an external ligament, and the ligament is always internal, unlike thraci- can be found nestling in old pholad burrows. id species (Coan and Valentich-Scott 2007). It has radial as well as concentric striations, Burrowing and nestling clams, of however, and interiorly has three cardinal which there are many genera, can be diffi- hinge teeth and a strong pallial line and sinus. cult to separate by shell shape as their nestl- Petricola carditoides is a nestling clam which ing habits tend to produce a varied shell has an external ligament and a chalky white shape. Useful characteristics for differentiat- shell, as in H. arctica. It has 2–3 hinge teeth ing species include the hinge teeth, pallial in the adult, not just in the juveniles. Petricola line, and siphons. Most Pholadidae can be carditoides also has purple-tipped siphons, distinguished by their two distinct shell sec- not crimson, and its shell has some radial tions (see Penitella penita, Zirfaea pilsbryi in sculpture. The myid clam Platyodon cancella- this guide). All pholads have file-like dentic- tus is a white borer with a heavy shell with ulations and (except for Netastoma) an inter- fine, almost lamellar concentric exterior sculp- nal myophore. ture. Inside it has a chondrophore and tooth There are only two local species re- in its hinges, and a well-developed, deep pal- ported in the family Hiatellidae: Panopea lial sinus. Cryptomya californica, also a myid 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] clam, can nestle among rocks, although its have been collected at salinities of 30. Heart usual habitat is sand or mud. It is small (to rates 10 to 16 beats per minute at normal sa- 30 mm), thin-shelled and has a chondro- linities but drops dramatically in response to a phore. Interiorly it has an entire pallial line, change in salinity, returning to normal after 2– and an inconspicuous pallial sinus (Coan 7 days (Bakhmet et al. 2012). and Carlton 1975). Temperature: Temperature may affect shell growth and structure (see Larva) leading Ecological Information Lezin et al. (2015) to question the relevance Range: Type region is the Arcitc coast of of shell structure as taxonomic characters and Norway (Keen 1971) A circumpolar species for estimation of sea surface temperature (but with known range from Arctic Ocean to see Strauch 1968, 1971). Shell shape is also Panama (Oldroyd 1924). Range is certainly certainly affected by the nestling habits of in- influenced by many human introductions dividuals (see Rowland and Hopkins 1971). (Beu 1971; Narchi 1973; Russell-Hunter Tidal Level: Intertidal to 120 m deep, but also 1949; Yonge 197), and potentially includes low or subtidal when attached (with byssus) two species as a result (Coan and Valentich- under rocks, on floats or pilings (Morgan and Scott 2007) (see Taxonomy). In Cow Head, Allen 1976; Morton 1987; Yonge 1952, 1976; Newfoundland, radiocarbon age of H. arctica Coan and Valentich-Scott 2007). The highest fossils embedded in rock were abundance of individuals (57 per square me- approximately 8,250 years BP (Brookes and ter) was observed at 20-meter depths in the Stevens 1984). The genus Hiatella is Young Sound, northeast Greenland (Sejr et widespread in polar latitudes dating to 150 al. 2002). million years ago (Laakkonen et al. 2015). A Associates: Associates include other nestling recent molecular analysis of over 350 and boring molluscs (e.g., Entodesma navicu- specimens using three gene regions la, Penitella penita, Zirfaea pilsbryi). A poten- suggests cryptic speciation rather than tial competitor affecting settlement of Pecten widespread distribution, including at least 13 maximus, the great scallop in the Bay of Brest different putative species, several of them in France (Chauvard et al. 1996). Hiatella living sympatrically (Laakkonen et al. 2015). arctica is a facultative epibionts of the crab These authors found several distinct line- Hemigrapsus sanguineus in Japan (Isaeva et ages within the northeast Pacific (see Laak- al.