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Phylum: Penitella penita (= penita) Class: , Order: Myoida, Pholadina Common piddock (Conrad, 1837) Family: , Martesinnae

Description  Hinge Area—no hinge teeth or ligament. Size—to 95 mm long; 50 mm high (Turner  Apophysis (myophore)—short. narrow, 1955). This specimen 40 rnm long, 18 mm spoon-shaped structure it each valve, high (fig. 1). which serves as an extra muscle Color—white, inside and out. attachment for powerful grinding muscles Shell Shape—elongate, divided into two (Keen 1971 (fig. 4); "weakly blade-like” distinct parts: (Turner 1955).  Anterior—rounded, bulbous, rasp-like  Body—foot and mantle white (Turner radial and concentric striae of heavy file- 1955). like dentic:uiations on the triangular  Young—anterior end soft (without rasping section which covets less than 1/2 callum), while is burrowing. valve area (fig. 1) (Kozloff 1974a). Exposed foot circular. developed as a  Posterior—wedge-shaped, with regular suction disc (fig. 5). concentric striations only, end truncate. Gapes at end only, not to middle of shell: Possible Misidentifications Penitella (Keen and Coan 1974). There are other burrowing clams in our  Callum (calcareous accessory plate)--- area, i.e. Hiatella. Entodesma, , present in adult at anterior end (fig. 1). Not Petricola, Bankia- None of them have distinct present in young (fig. 5). body areas or the bulbous, denticulated  Umbones—not prominent. Umbonal anterior of Penitella. A similar pholad is reflection (where urn-bones turn back, fig. Zirfaea pilsbryi (subfamily Pholadinae) a very 1): closely appresed for entire length large piddock to 150 mm; whose most (Coan and Carlton 1975). noticeable characteristic is its lack of a callum  Mesoplax—small accessory plate on protecting the anterior end; (it bores even as dorsal edge (fig. 2); (no accessory plates, an adult). Zirfaea has very long, nonretractible i.e. protoplax. metaplax, hypoplax, siphons (and no siphonoplax), a posterior present). Mesoplax pointed posteriorly, gape which extends to the middle of the truncate anteriorly, with swept back lateral animal; a broad apophysis, and a rasping wings: species penita (Turner 1955). surface which covers half the valve area  Siphons—long, white, retractible; tips (Kozloff 1974a). marked with small red spots, but not Other northeastern Pacific Pholadidae solidly red-tipped smooth: without warts or include: orange chitinous patches. No pallets on Netastoma rostrata (subfamily siphon tips (as in boring mollusc Bankia). Jouannetiinae), a short, anteriorly truncate Incurrent siphons with 6 large, and several species without an internal apophysis, and small branched cirri around aperture with a tubular, calcareous siphonoplax. Its (Turner 1955). callum is only a fluted band, not a round  Siphonoplax—brown, membranous, enclosing plate. heavy, flexible flaps, not lined with Chaceia ovoidea (= Pholadidea) which calcareous granules: species penita bores into shale, has non-retractible siphons (Coan and Carlton 1975). with orange chitinous patches and warty tips.  Periostracum—none. It is oval, not elongate, and its callum does  Interior—divided into three areas by not completely cover the anterior aperture pallial lines. Pailial sinus posterior; large (Coan and Carlton 1975). posterior muscle scar- Anterior muscle Paraphoias californica has no siphonoplax, scar and accessory unusually dorsal (fig. and is divided in-to three well-marked regions, 4); ventral muscle scar present as well. not two as is Penitella. It has two dorsal

Digitized 2010 – Last Updated 1979 – E-mail corrections to [email protected] plates, a mesoplax and a metaplax, not one; it Halosydna, clams Hiatella, Entodesma, can bore into hard rock. Zirfaea (Coos Bay). Three other species of Penitella can be present: Life History Information Penitella conradi is usually found in Mytilus Reproduction—dioecious, oviparous; sexual or abalone (Haliotis) shells. It is very small, to maturity postponed until growth stops (Evans 33 mm, its siphonoplax is lined with coarse 1970). calcareous granules and its mesoplax is Growth Rate—average time to maturity-33 truncate posteriorly, pointed anteriorly (the months (Evans 1968b). Unusual in having reverse of P. penita, see fig. 2). The determinate growth: at about 3 years mesoplax is large: almost equal in area to the metamorphoses into non-boring adult (about rasping surface (Kozloff 1974a). 55 mm long). Crowding may induce early Penitella gabbi can be found with P. metamorphosis (Evans 1968). penita, but is much less common (Coan and mature at smaller size in soft rock than in hard Carlton 1975). It is a cleancut, oval shell with rock a creamy-lemon siphon," covered with warts. Longevity—lives until burrow erodes enough It has no siphonoplax; its callum extends very to make it subject to predators (i.e. less than little beyond the beak, and the umbonal 3 x valve length); erosion rate varies with rock reflection is not attached anteriorly. P. gabbi hardness: at Fossil Point, erosion process can be up to 75 mm long and often has a takes about 6 years. gray-brown periostracum posteriorly (Quayle Food—a suspension feeder, using long 1970). siphons to feed. A very closely related species, Penitella Predators—flatworms Stylochoplana, turnerae, was described from Coos Bay in Notoplana inquieta. Worm enters the shell 1966 (Evans and Fisher 1966).This is a much and eats the flesh, laying its eggs there larger species than P. penita, (to 125 mm, (Evans 1967). Fossil Point, Coos Bay), stout and lacking a Behavior—pholads are the most efficient of siphonoplax. Its siphons are white, long and the seven families of rock-boring bivalves red-tipped. Its mesoplax is reduced to a (Evans 1968a). Boring is mechanical, not narrow crescent, rounded posteriorly and not chemical, and in this species is done only by sharply pointed as in P. penita. the young animal, after which it metamorphoses into a non-boring adult. Ecological Information Grinding assisted by keeping algae out of Range—Gulf of Alaska to Pta. Pequena, Baja burrow with sea water, by loosening rock California ; type locality San Diego. Calif grains, and by ciliary currents which flush out (Turner 1955). cavity (Keen 1971). Makes cone-shaped Local Distribution—Coos Bay, Pigeon Point, burrow (Evans and Fisher 1966). Fossil Point, Coos Head; Yaquina Bay, Netarts (Turner 1955). Literature Cited Habitat—bores into mud and rock; burrows at least 3 x valve length. Prefers northeast 1. COAN, E. V., and J. T. CARLTON. surfaces, where algae and light are least 1975. Phylum Mollusca: Bivalvia, p. (much like barnacles): also on cement jetties: 543-578. In: Light's manual; intertidal an important animal in erosion and concrete invertebrates of the central California destruction. coast. S. F. Light, R. I. Smith, and J. T. Salinity—collected at 30 ‰. Carlton (eds.). University of California Temperature—geographical distribution is in Press, Berkeley. cold to temperate waters. 2. EVANS, J. W. 1967. Relationship Tidal Level—intertidal and subtidal (Evans between Penitella penita (Conrad, 1967): found as high as 0.6 m (Coos Bay) 1837) and other organisms of the (Evans 1968a); broad distribution vertically. rocky shore. The Veliger. 10:148-151. Found as low as 91 m (Kofoid et al 1927). Associates—other nestling and burrowing invertebrates; i.e. polychaetes Thelepus,

Digitized 2010 – Last Updated 1979 – E-mail corrections to [email protected] 3. EVANS, J.W. 1968. Factors modifying mollusks from Baja California to Peru. the morphology of the rock-boring Stanford University Press, Stanford. clam, penitella penitaI (Conrad, 1837). 8. KEEN, A. M., and E. COAN. 1974. Journal of Molluscan Studies. 38:111- Marine Molluscan Genera of Western 119. North America: An Illustrated Key. 4. EVANS, J.W. 1968a. The role of Stanford University Press, Stanford, Penitella penita (Conrad 1837) (Family California. Pholadidae) as eroders along the 9. KOFOID, C. A. 1927. Biological Pacific coast of North America. section, p. Chapter 19. In: San Ecology. 49:156-159. Francisco Bay Maritime Piling 5. EVANS, J.W. 1970. Sexuality in the Committee: Marine Borers and Their rock-boring clam Penitella penita Relation to Marine Construction on the (Conrad 1837). Canadian Journal of Pacific Coast. Zoology. 48:625-627. 10. QUAYLE, D.B. 1970. The intertidal 6. EVANS, J. W., and D. FISHER. 1966. bivalves of British Columbia. British A new species of Penitella (family Columbia Provincial Museum, Victoria, Pholadidae) from Coos Bay, Oregon. Canada. The Veliger. 8:222-224. 7. KEEN, A.M. 1971. Sea shells of tropical west America; marine

Digitized 2010 – Last Updated 1979 – E-mail corrections to [email protected]

Digitized 2010 – Last Updated 1979 – E-mail corrections to [email protected]