Penitella Penita Class: Bivalvia, Heterodonta, Euheterodonta

Penitella penita Class: Bivalvia, Heterodonta, Euheterodonta

Order: Imparidentia, Myida Common piddock Family: Pholadoidea, Pholadidae, Martesiinae

Taxonomy: The taxonomies of both pholad species are intertidal or subtidal, some can be species in this guide (Z. pilsbryi and Penitel- found boring into wood at great depths (e.g. la penita) are extensive and complicated, 7,250 meters Xylophaga, Kennedy 1974; Reft including many synonyms and overlapping and Voight 2009; Voight 2009; Marshall and descriptions (for full list of synonymies see Spencer 2013). Kennedy 1974). Penitella penita was origi- Body: nally described as Pholas penita by Conrad Color: Foot and mantle white (Turner in 1837. The current name was designated 1955). by Gabb in 1869 and the most common syn- Interior: onym seen today is Pholadidea penita. Exterior: However, Pholadidea species differ from Byssus: those in the genus Penitella by having a Gills: mesoplax that is divided longitudinally into Shell: Shell shape is elongate, and divided two pieces, a feature not present in the latter into two distinct parts (Fig. 1). Shell anterior genus (see Penitella, Kennedy 1974). becomes worn away from burrowing abrasion (Evans and LeMessurier 1972), the addition Description of new shell creates a rough and bulbous Size: Individuals to 70–95 mm in length and anterior (Kozloff 1993). No periostracum is 50 mm in height (Turner 1955; Haderlie and present. Abbott 1980; Kozloff 1993). The illustrated Interior: Divided into three areas by specimen (from Coos Bay) is 40 mm long, pallial lines. The pallial sinus and posterior is 18 mm high (Fig. 1). with a large posterior muscle scar. The ante- Color: White, inside and out (Haderlie and rior muscle scar and accessory are unusually Abbott 1980; Kozloff 1993). dorsal and a ventral muscle scar is also pre- General Morphology: Bivalve mollusks are sent (Fig. 4). An apophysis (myophore) is a bilaterally symmetrical with two lateral valves short, narrow, spoon-shaped structure of each or shells that are hinged dorsally and sur- valve, which serves as an extra muscle at- round a mantle, head, foot and viscera (see tachment site for powerful grinding muscles Plate 393B, Coan and Valentich-Scott (Keen 1971) (Fig. 4). In P. penita it is "weakly 2007). Myoid bivalves are burrowers and blade-like” (Turner 1955). borers, with long siphons and hinges with Exterior: The shell anterior is rounded, few teeth (Coan and Valentich-Scott 2007). bulbous, and with rasp-like radial and concen- Members of the Pholadidae bore into a vari- tric striae. These heavy file-like denticulations ety of substrates, possess no pallets on si- consist of a triangular rasping section which phon tips and have an anterior end that is covers less than 1/2 valve area (Fig. 1, 3) pointed or curved with no notch (contrast to (Kozloff 1993). The posterior is wedge- Teredinidae species, e.g. Bankia setacea, shaped, with regular concentric striations on- this guide) (see Plate 427F, 430D, Coan and ly, and a truncated end. Valves gape does Valentich-Scott 2007). While most pholad

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. P. penita. 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.

not extend to the middle of the shell type from 50 mm/year (soft substrates) to 50 (Penitella, Keen and Coan 1974). A callum mm/12 years (hard substrates, Evans 1968b), is present in adults (but not in young (Fig. 5)) i.e., harder rock leads to a shallower burrow at the anterior end (Fig. 1). Umbones are not (Evans 1970). In Monterey, California, Hader- prominent and umbonal reflection (where lie (1981a) reported boring rates of 32 mm/ umbones turn posterior, Fig. 1) are closely year (2.6 mm/month). (see also Habitat and appressed for the entire length (Coan and Behavior.) Valentich-Scott 2007). Siphonoplax is Pholadidae-specific character brown, membranous, heavy, flexible flaps, Mesoplax: A small accessory plate on dorsal and is not lined with calcareous granules edge (Fig. 2) has no accessory plates (e.g., (Coan and Valentich-Scott 2007). protoplax. metaplax, hypoplax) present. The Hinge: No hinge teeth or ligament mesoplax is pointed posteriorly, and truncate present. anteriorly, with swept back lateral wing-like Eyes: projections (Turner 1955). Foot: Foot atrophies in adult individuals after the callum seals the shell anterior Possible Misidentifications (Haderlie and Abbott 1980). There are several families of burrow- Siphons: Long, white, and retractible. The ing clams and the Pholadidae can be distin- tips are marked with small red spots, but not guished by their distinctively marked body ar- solidly, red-tipped smooth. No warts or or- eas (Fig. 1). Members of the Teredinidae and ange chitinous patches are present. No pal- Pholadidae can be found locally. They can be lets are on siphon tips (compare to Teredini- distinguished by the absence of pallets on si- dae, e.g., Bankia setacea, this guide). Inhal- phon tips in the latter family as well as an an- ant siphons with six large, and several small terior end that is not notched, as in the Tere- branched cirri around aperture (Turner dinidae. The Pholadidae includes 10 species 1955). locally, within the following genera: Barnea Burrow: (for burrow shape, see Fig 1B, Ev- (B. subtruncata), Chaceia (C. ovoidea), ans 1968d). Burrows are pear- (Haderlie Netastoma (N. rostratum), Parapholas (P. cal- 1981b) or cone-shaped (Evans and Fisher ifornica), Penitella (five local species) and 1966; Evans 1968d). Burrows into stiff clay, Zirfaea (Z. pilsbryi). The genus Zirfaea is sandstone, soft rock, shale and concrete characterized by adults that burrow into sand (Haderlie and Abbott 1980; Kozloff 1993), up or mud, the absence of a callum in mature in- to 15 cm below the surface (at least 3 times dividuals, and a shell sculpture that is divided the shell length). Burrowing mechanism is into two distinct zones (see Plates 427C, like that of the common local pholad, Zirfaea 429D, Coan and Valentich-Scott 2007). The pilsbryi (see description in this guide): The genus Barnea, for example, also lacks a cal- foot is sucker-like and attaches to the sub- lum, but does not have these two distinct strate so that the shell can rotate slowly and zones. All other local genera are character- create a cylindrical burrow. Shell valves ized by the presence of a callum and all ex- rock back and forth by contractions of anteri- cept Netastoma have a myophore as well. or and posterior adductor muscles. Individu- Parapholas species have shell sculpture with als rotate after each stroke, making a cylin- three distinct zones, where members of Cha- drical burrow (Lloyd 1896; Ricketts and Cal- ceia and Pentilla have two. None of the other vin 1952; Haderlie and Abbott 1980). Esti- local burrowing clams (e.g. in the genera Hia- mated burrowing rates varied with substrate tella. Entodesma, Barnea, Petricola, Bankia) 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]

have distinct body areas or the bulbous, pressed to the anterior end, a character also denticulated anterior of Penitella. found in C. ovoidea. Penitella richardsoni dif- The genus closest to Penitella, and fers from C. ovoidea by having a callum that most likely to be confused with it, is Zirfaea. does not gap and an more elongated shell As mentioned above, Penitella’s valves are (Coan and Valentich-Scott 2007). A new spe- also divided into two distinct sections, but it cies of Penitella, P. hopkinsi, was described differs in having a calcareous anterior cal- from Alaska, but it not yet reported in our area lum, or accessory plate (in the adult) as well (Kennedy and Armentrout 1989). With adult as a posterior which gapes only at the end, specimens, it should be easy to tell Penitella not to the middle of the shell (it has no ante- from Zirfaea because the latter species has a rior gape) and the apophysis is narrow, not long, non-retractable siphon and a broad. No Penitella species have a siphon membraneous covering of the anterior, longer than its body (Evans and Fisher instead of a calcareous callum. Small shells 1966) and all Penitella species have without the callum could be young Penitella retractable siphons. There are five species as well as mature Zirfaea and size at maturity of Penitella in our area (see Coan and varies greatly with environmental condition. Valentich-Scott 2007). Ecological Information Penitella conradi is very small and is Range: Type locality is San Diego, California found in Mytilus or Haliotus (abalone) shells. (Turner 1955). Eastern Pacific distribution It has a siphonoplax lined with coarse granu- includes the Gulf of Alaska (e.g., Chirikof Is- les (Zirfaea has no siphonoplax) (Evans and land) to Pequena, Baja California. The first Fisher 1966) and can bore into nephrite presence of P. penita in the fossil record is in (Monterey, California, Wilson and Kennedy the Oligocene in California (for pholad palaeo- 1984). Penitella penita has a heavy mem- ecology see Kennedy 1974, 1993) and fossil braneous siphonoplax, a calcified callum pholad beds can be observed at 2–15 meters and a distinctive mesoplax. Its anterior ras- above the high tide line on cliffs in Coos Bay ping surface covers less than half the valve and southward (Evans 1968d). area (Kozloff 1974) (Fig. 1, 3). It can be up Local Distribution: Coos Bay distribution at to 70 mm in length. Penitella fitchi also has Pigeon Point, Fossil Point, and Coos Head. a heavy siphonoplax, but has a callum with Other Oregon sites include Yaquina and Ne- a gap. This is a rare species, found low in tarts Bays (Turner 1955). the intertidal up to 25 meters deep. Penite- Habitat: Individuals found in open coast habi- lla turnerae is larger than P. penita (to 125 tats as well as exposed bays (Haderlie and mm), and less common. It is stout, and like Abbott 1980), where they bore into mud and Zirfaea lacks a siphonoplax. It has a distinc- rock and prefer northeast surfaces, where al- tive, rounded mesoplax, however, and its gae and light are reduced (similar to long, white, retractable siphons are tipped barnacles). The ability of P. penita to utilize a with solid red. Like Zirfaea, it has a strongly wide variety of substrates leads to the wide angled anterior ventral edge, but unlike Zir- geographic distribution (Evans 1968d). faea, P. turnerae has a callum. Penitella ri- Harder substrates produce individuals with chardsoni (=gabbi, Kennedy 1989) is also heavier, less elongate shells and larger small (up to 75 mm) with a warty, creamy- muscles (Evans and LeMessurier 1972). The lemon colored siphon and it is not common. substrate also affects the burrowing speed, as It is different from the other members of this harder rock leads to individuals that burrow genus as its umbone reflection is not ap-

and grow more slowly. For example, widely distributed rock boring clam in the individuals in soft rock may mature (and stop eastern Pacific (Evans 1968d). However, in burrowing) at three years, while those in California, P. penita was less abundant than harder rock may mature as late as 21 years. the congeners, P. conradi and P. richardsoni Such timing corresponds to burrowing (Haderlie and Abbott 1980). Fossil records speeds that are 4 (hard substrate) to 50 mm (El Rosario, Baja California) suggest densities (soft substrate)/year (Haderlie and Abbott as high as 200 individuals/m2 (Ledesma- 1980). Substrate type (e.g., hard versus Vazquez and Johnson 1994). soft) has been shown to alter the piddock Life-History Information shell shape, size and hardness (Evans Reproduction: Reproductive strategies are 1968c; Tajima and Kondo 2003). Piddock variable among the Pholadidae (e.g., repro- burrows have the ability, particularly when duction in Barnea candida includes hermaph- individuals are present in large numbers, of roditic, dioecious, oviparous and larviparous, compromising the stability of shorelines Evans 1970). Penitella penita is dioecious throughout their lifetimes (e.g., Pholas and oviparous. Sexual maturity is postponed dactylus, Barnea candida, B. parva, Pinn et until growth stops (Evans 1970), as individuals al. 2005; Davidson and de Rivera 2012). become sexually mature once callum is The ability of P. penita to burrow into a formed and their foot atrophies (Haderlie and variety of substrates (e.g., clay, sandstone, Abbott 1980). Gonad morphology in mature cement, Coan and Valentich-Scott 2007) individuals suggests gamete development in renders it a significant species in the erosion February, ripe gametes in June and spawning and destruction of marine structures (e.g., in July (Fossil Point, Coos Bay, Evans 1970). jetties). For example, erosion from physical The development of P. penita has not yet factors leads to roughly 0.5 mm substrate been described. Boyle and Turner (1976) eroded/year while that due to erosion from described the reproduction and development P. penita is 12 mm/year (Fossil Point, Coos of the east coast pholad, Martesia striata. Bay, Evans 1968a). This species spawns in February and eggs Salinity: Collected at salinities of 30. are translucent white and 45–46.8 µm in Temperature: Cold to temperate waters. diameter (33˚C, Turner and Johnson 1968; Tidal Level: Intertidal and subtidal (Evans 21˚C, Boyle and Turner 1976). 1967), with a broad distribution vertically, Larva: Bivalve development, including mem- individuals are found as high as +0.6 m bers of the Pholadidae, generally proceeds (Coos Bay, Evans 1968a) and as low as -91 from external fertilization via broadcast m (Kofoid and Miller 1927). spawning through a ciliated trochophore stage Associates: Other nestling and burrowing to a veliger larva. However, in the deep water invertebrates utilize the burrows of Penitella pholad genus, Xylophaga, species brood lar- penita (e.g. polychaetes Thelepus, vae until late veliger stages (Kennedy 1974; Halosydna, clams Hiatella, Entodesma, Voight 2009). Bivalve veligers are character- Zirfaea, Coos Bay, Table 2, Evans 1967). ized by a ciliated velum that is used for swim- Abundance: Often co-occurs with other ming, feeding and respiration. The veliger lar- pholads (e.g., Zirfaea pilsbryi, Penitella spp., va is also found in many gastropod larvae, but Netastoma rostratum) (Haderlie 1979). In the larvae in the two groups can be recog- Oregon, Penitella penita accounted for up to nized by shell morphology (i.e. snail-like ver- 90% of all boring species in the low intertidal sus clam-like). In bivalves, the initial shelled- and has been called the most common and

larva is called a D-stage or straight-hinge Longevity: Lives until substrate surrounding veliger due to the “D” shaped shell. This ini- the burrow erodes enough to make it subject tial shell is called a prodissoconch I and is to predators. Longevity is thus dependent on followed by a prodissoconch II, or shell that erosion rate and varies with rock hardness is subsequently added to the initial shell (Haderlie and Abbott 1980). At Fossil Point, zone. Finally, shell secreted following meta- erosion process takes about six years follow- morphosis is simply referred to as the disso- ing metamorphosis (nine years total lifespan, conch (see Fig. 2, Brink 2001). Once the Evans 1970). larva develops a foot, usually just before Growth Rate: Once they settle, growth pro- metamorphosis and loss of the velum, it is ceeds at a rate of 22 growth bands/year called a pediveliger (see Fig. 1, Kabat and (Haderlie and Abbott 1980). Growth occurs in O’Foighil 1987; Brink 2001). (For general- two distinct phases: the first where individu- ized life cycle see Fig. 1, Brink 2001.) Lar- als are actively boring and growing, and the vae of P. penita are free swimming with a second where both boring and growth stops pelagic duration of two weeks (Haderlie and (Evans 1970). Abbott 1980) with peaks in settlement occur- Food: A suspension feeder, P. penita uses ring from August to September (Evans long siphons and gills to filter food. 1970). The development of other pholads Predators: Flatworms Stylochoplana, Noto- (e.g. Barnea truncata, Chanley 1965; Cyrto- plana inquieta, where worms enter the shell, pleura costata, Chanley and Andrews 1971; eat the flesh, and lay eggs (Evans 1967). Ad- Martesia striata, Boyle and Turber 1976) ditionally, interference from Botula cali- proceeds as planktotrophic veliger larvae. forniensis, which settles on the burrow en- After 24 hours, M. striata larvae are straight trance may lead to the death of P. penita indi- hinge veligers (68 µm in length and 59 µm in viduals (Evans 1967). Other invertebrates height, Boyle and Turner 1976). After eight predators include Ceratostoma foliatum, days, they are umbo larvae (129–224 µm) Roperia poulsoni (Haderlie and Abbott 1980). and they are pediveligers by 28–32 days Behavior: Pholads are the most efficient bur- (224–236 µm) post fertilization. Metamor- rowers of the seven families of rock-boring phosis in M. striata occurs after 48–53 days bivalves (Evans 1968a). Grinding is assisted (see Table 1, Figure 1, Boyle and Turner by keeping algae out of burrow with sea 1976). (see also Campos and Ramorino water, by loosening rock grains, and by ciliary 1990 for planktonic pholad larvae from currents which flush out cavity (Keen 1971). Chile). The callum shape is determined by the Juvenile: Average time to maturity is 33 contours of the burrow and, in artificial months and metamorphosis is marked by burrows, the callum can be rather square the resorption of the foot (Evans 1968a, (versus pear-shaped, Haderlie 1981b). 1970). This species is unusual in having de- Bibliography terminate growth where, at about three years, individuals metamorphoses into non- 1. BOYLE, P. J., and R. D. TURNER. 1976. boring adults (about 55 mm in length). Larval development of wood boring pid- Crowding may induce early metamorphosis dock Martesia striata (L.) (Mollusca: Bival- (Evans 1968d). Anterior end of juveniles is via: Pholadidae). Journal of Experimental soft (without callum), while animal is actively Marine Biology and Ecology. 22:55-68. burrowing. Exposed foot is circular and has 2. BRINK, L. A. 2001. Mollusca: Bivalvia, p. developed as a suction disc (Fig. 5). 129-149. In: Identification guide to larval

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