Phylum: Arthropoda, Crustacea Class: Multicrustacea, Hexanauplia, Thecostraca, Cirripedia Semibalanus cariosus Order: Thoracica, Sessilia, Balanomorpha A thatched barnacle Family: Balanoidea, Archaeobalanidae, Semibalaninae Taxonomy: Semibalanus cariosus originally sessile, or attached barnacle (Balanomorpha). belonged to the genus Balanus. Members Basis in S. cariosus is membraneous, in con- of the genus Semibalanus, which was de- trast to most barnacles which have calcare- scribed (initially as a subgenus) by Pilsbry in ous bases (Cornwall 1951) and base forms 1916, differ from Balanus species with the unique starry pattern (Fig. 1), especially in ju- presence of membranous bases (Newman veniles (Fig. 3) (Ricketts and Calvin 1971). and Ross 1976). Thus, a common known Wall: Formed by plates and is thick synonym for S. cariosus is B. cariosus. when isolated, but thinner when crowded. The internal surface is usually with faint ribs Description or wrinkled texture (Cornwall 1951) (Fig. 4). Size: Individuals typically up to 75 mm in Longitudinal Tubes: Within diameter (Henry 1940) and 80 mm in height. walls, tubes are irregular (Fig. 4) and with Size is highly variable, especially in cylindri- cross-septa. They are sometimes filled with cal specimens on vertical surfaces, but is powder (Pilsbry 1916). not limited by mechanical factors of a wave Plates: Six, unequal and calca- swept environment (Denny et al. 1985). For reous plates bear narrow longitudinal spines, example, individuals from Puget Sound, giving specimens a unique thatched ap- Washington can grow to 100 mm high while pearance (Fig. 1). Each plate is composed of only 15 mm in diameter (Pilsbry 1916). parietes (exposed triangular part), alae Color: Shell dirty white, gray with round or (overlapping plate edges) and radii (the plate uncrowded specimens chalky white. Ter- edge marked off from the parietes by a defi- gum beak can be purple (Pilsbry 1916) and nite change in direction of growth lines) cirri are brown to almost black. (Newman 2007). The plates themselves in- General Morphology: Members of the Cirri- clude the rostrum, opposite it the carina and pedia, or barnacles, can be recognized by between the carina and rostrum are the four their feathery thoracic limbs (called cirri) that side plates, the carinolateral and rostrolateral are used for feeding. There are six pairs of plates (see Fig. 3, Balanus glandula, this cirri in S. cariosus. Sessile barnacles are guide). When crowded, cylindrical specimens surrounded by a shell that is composed of a often lack spines (Cornwall 1977). Rostrum flat basis attached to the substratum, a wall overlaps adjacent lateral plates (see Plate formed by several articulated plates and 213, Newman 2007). Radii narrow (Cornwall movable opercular valves including terga 1951). and scuta (Newman 2007). Opercular Valves: Thin (Henry 1942) Shell: valves consist of two pairs of movable plates Shape: Conical when isolated (Fig. inside the wall, which close the aperture: the 2), but can be cylindrical if crowded (see Fig. tergum and the scutum (Figs. 5, 6). 108, Kozloff 1993). Scuta: Exterior with low growth Basis: Calcareous and flat, attached ridges, the lower ridges are fringed with mem- to hard substrate, rendering S. cariosus a 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. Semibalanus cariosus. 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. brane and usually with a weak longitudinal The remaining two families include the striation. Interior a small, well-reflexed artic- Balanidae and Archaeobalanidae. Balanidae ular ridge is present, which is continued as a encompasses the genera Megabalanus, Par- sharp, high, curved adductor oblique coarse aconcavus, and Menesiniella (each with one teeth (Henry 1940) (Figs. 5a, 6a). local species), Amphibalanus (three local Terga: Very narrow and species) and Balanus (four local species). beaked, with narrow furrow, and long and The Archaeobalanidae includes the genera acute articular ridge. Very narrow and long Armatobalanus, Conopea, Hesperibalanus spur (Pilsbry 1916) that continue as a raised and Semibalanus (each with one local spe- ridge on the inside with strongly developed cies). An isolated S. cariosus, is with splinter depressor muscle crests (Figs. 5b. 6b). -like spines, nearly black cirri and is not likely Aperture: The shell opening, from to be confused with another barnacle. It has which the cirri emerge when feeding, is con- a thatched appearance, being irregularly rib- trolled by movement of the terga and scuta bed and its walls have uneven, longitudinal in conjunction with adductor and depressor tubes (Pilsbry 1916). However, where it is muscles. The aperture is small in conical crowded or eroded, these spines may be specimens and large in cylindrical ones worn off or not developed, and the barnacle (Henry 1940), the aperture can be deeply would have to be distinguished from other toothed (Fig. 1). common barnacles by its tergum and scu- Cirri: Six pairs of conspicuous feathery tum, and by its unique and unusual membra- feeding appendages. neous base. Semibalanus cariosus have ter- ga with a long pointed spur, quite different Possible Misidentifications from either B. crenatus or B. glandula. Semi- There are three groups (i.e. superor- balanus cariosus commonly co-occurs with ders) of cirripeds including the Rhizocepha- B. crenatus, B. glandula, as well as with la (parasites among crustaceans), the Acro- Chthamalus dalli. Juvenile S. cariosus will thoracica (shell-less burrowing forms) and show a typical heavy ribbing and starry outli- the Thoracica. The Thoracica contains ne, which would distinguish it from young B. 1,000 species worldwide including the mon- crenatus or B. glandula. Generally, these ophyletic taxa, Lepadomorpha, the stalked latter two species are found higher in the in- barnacles, and the Balanomorpha, or ses- tertidal than is S. cariosus, which occurs sile barnacles (Perez-Losada et al. 2008; mostly subtidally. Chan et al. 2014). Among the sessile Balanus crenatus may be easily con- forms, there are four families represented fused with the ubiquitous B. glandula, but is locally. The family Chthamaloidea includes generally found lower in the intertidal. members of the genus Chthamalus, which Balanus glandula has no longitudinal wall has alae on its rostral plates, not radii. The tubes (except when young) and it differs in family Tetraclitoidea has one species local- the structure of terga and scuta: the tergum ly, Tetraclita rubescens, the southern is very wide and has longer spurs and the thatched barnacle, that is superficially simi- scutum has no adductor ridge. Balanus lar to S. cariosus. However, it is character- crenatus, on the other hand, has a shell wall ized by a wall that is composed of four with a single row of uniformly spaced tubes plates (rather than six in the S. cariosus). (Newman 2007). Balanus trigonus is a lower Tetraclita rubescens occurs as far north as intertidal species with a southern distribution Monterey Bay, California (Newman 2007). (to Monterey Bay, California). Balanus nu- 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] bilus, the giant acorn barnacle, reaches 100 20 degrees C (Nishizaki and Carrington mm in diameter, and has a shell aperture 2014). that is relatively large and flaring (Newman Tidal Level: From high in splash zone (e.g. 2007). Balanus nubilus, would be most OIMB Boat House, Coos Bay) to more pro- likely to be confused with S. cariosus at tected areas farther up bay. Also occurs in subtidal levels. Both species, as juveniles, the low intertidal zone and subtidally (e.g. have strong ribs: S. cariosus has the cha- floating docks in Charleston). Upper intertidal racteristic starry border (Figs. 1, 3), limit may be determined by desiccation and however, that B. nubilus lacks. Both by substrate temperature as S. cariosus and species have a tergal plate with a long B. glandula individuals showed a negative spur, but that of S. cariosus is pointed, whi- correlation in abundance with substrate tem- le it is truncate in B. nubilus (compare Figs. perature in the mid-intertidal (Salish Sea, 5, 6 with Figs. 3b, 4a in B. nubilus, this gui- Washington, Harley 2011). Predation by sea de). The cirri of S. cariosus are also cons- stars may determine lower vertical limit picuous and almost black. (Cochran et al. 1968). Associates: Commonly grows below B. glan- Ecological Information dula, a barnacle that is often found growing Range: Type locality is the Kurile Islands. on S. cariosus. Often grows on and amongst Known range includes the Bering Sea south Mytilus californianus, with Littorina scutulata to Morro Bay, California (Newman and Ab- (outer coast) and with B. crenatus and the bott 1980) and Japan. (For range map see goose barnacle, Lepas pectinata pacifica and Newman and Abbott 1980, p 507.) with masses of tube worms (e.g. Eudistylia). Local Distribution: Outer rocky coasts and Also co-occurs with the barnacles, protected sites in Oregon Bays. In Coos Chthamalus dalli and Pollicipes polymerus Bay, also found on floating docks in the (outer coast) (Henry 1942). Charleston Marina. Abundance: Most common barnacle of low Habitat: Hard surface needed for attach- estuarine zone, where the tall and crowded ment (i.e. rock, shell, wood). Southern variety can be as dense as 15,000 individuals specimens prefer protected spots, including per square meter (Ricketts and Calvin 1971). deep crevices and overhanging ledges, in The highest density observed locally, at the the presence of a strong current (Ricketts OIMB Boat House, Coos Head was 270 indi- and Calvin 1971).