3.3 INVERTEBRATES 



Community Composition 



In the intertidal zone, sessile 

 invertebrates consist largely of 

 barnacles, oysters, and mussels (Figure 9) 

 (Stephenson and Stephenson 1952, 1972; 

 Wood 1968; Ortega 1981; Van Dolah et al . 

 1984; Fox and Ruppert 1985). The smallest 

 barnacle is Chthamalus fragil is (Figure 

 9A), which is white, easily destroyed with 

 a fingernail, and has no calcareous basal 

 plate. Other barnacles in the genus 

 Balanus are larger, more robust, and have 

 calcareous basal plates. B^ improvisus is 

 white, with a diamond or kite-shaped 

 aperture (Figure 9B). B^. triqonus has a 

 similar shaped aperture, but the shell 

 plates are rough, with red and white 

 coloration. B^ eburneus is white, but has 

 a pentagonal -shaped aperture (Figure 9C) . 

 ]L_ amphitrite has purple stripes on the 

 shell plates. In the south, the much 

 larger, solid-walled barnacle, Tetrad ita 

 squamosa v. stalactifera . becomes common. 

 Bivalves are represented by the common 

 oyster Crassostrea virgi nica , and the 

 small black mussel Brachidontes exustus , 

 which forms mats (Figure 9D, E). 



There are a few mobile organisms that 

 are intertidal, including the large isopod 

 Lyqia exotica , the predatory Atlantic 

 oyster drill, Urosalpinx cinerea (Figure 

 10E), and in the south, the siphonarid 

 limpet Siphonaria pectinata . Where the 

 structural matrix of the oyster zone is 

 well developed, it provides a habitat for 

 xanthid crabs such as Panopeus herbstii 

 (Figure 10B). 



Mussels and oysters are generally 

 absent subtidally, and the sessile animal 

 community consists of sponges, 

 coel enterates (anemones and hydroids), 

 bryozoans, tunicates, and barnacles 

 (McDougall 1943; Maturo 1959; Wells et al . 

 1950, 1964; Sutherland 1974, 1977, 1978, 

 1981; Sutherland and Karlson 1977; Karlson 

 1978; Mook 1981, 1983a, b; Van Dolah et 

 al . 1984; Fox and Ruppert 1985). Except 

 for the absence of Chthamalus fragil is , 

 the barnacles are the same as those found 

 in the intertidal zone. 



One of the most common sponges is 

 Microciona prol ifera , which is bright red 



Figure 9. Common intertidal invertebrates. (A) 

 Chthamalus fragilis (to 8 mm diameter), (B) Balanus 

 Improvisus (to 13 mm diameter), (C) Balanus 

 eburneus (to 25 mm diameter), (D) Crassostrea 

 virginica (to 150 mm length), and (E) Brachidontes 

 exustus (to 35 mm length). A, B, and C redrawn from 

 Lippson and Lippson (1984), D and E redrawn from 

 Van Dover and Kirby-Smith (1979). 



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