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Sketch of C. tenuissimum showing the budding pattern from the ancestrula (at center in blue).  Drawing by J. Winston, courtesy of the American Museum of Natural History.  Used with permission.  

Voucher Specimen: 
American Museum of Natural History 
# 584

Common Name:
None

Species Description:
Colonies of C. tenuissimum form white crusts on seagrasses, shells, and other substrata. Primary buds usually form distally from the ancestrula (the original settled larva), with the next buds forming proximally. Growth proceeds in both directions, and intermediate buds aid in forming a double fan shape that eventually becomes rounded. Zooids are oval in shape and measure 0.53 X 0.25 mm. Each zooid has a pair of short distal spines, and 5 - 7 pairs of lateral spines. The operculum is chitinous. The lophophore averages 0.475 mm in diameter and bears an average of 12 tentacles. Old colonies have areas where degenerate zooids are partially closed or calcified, and filled with storage products, while other areas within the colony have new or regenerating zooids with functional polypides.

Other Taxonomic Groupings:
Suborder: Anasca

Potentially Misidentified Species:
C. tenuissimum could be mistaken for C. seurati, since the 2 species occupy the same substrata and are morphologically similar. However, the budding pattern in C. tenuissimum is slightly more regular than in C. seurati due to C. tenuissimum's somewhat larger zooid size and distal-proximal budding pattern. Additionally, lateral walls in individual zooids are more calcified in C. seurati, and its distal spines are longer and more pointed. C. seurati has fewer lateral spines than C. tenuissimum in water of the same salinity: 1 - 3 for C. seurati vs. 5 for C. tenuissimum. Seasonally, C. seurati is most common in the winter months, while C. tenuissimum is most common in spring and summer. In terms of salinity, C. seurati is more common in waters with lower salinity than is C. tenuissimum.

II.  HABITAT AND DISTRIBUTION 
Regional Occurrence:
C. tenuissimum is a common estuarine species along the east coast of the United States and the Gulf of Mexico. It is also found in some locations along the Pacific coast, and is believed to have been introduced, along with oysters, from the Gulf coast of the U.S. (Lagaaij and Cook 1973; Winston 1982).

IRL Distribution:
C. tenuissimum is one of the most abundant bryozoan species inhabiting the Indian River Lagoon (Winston 1982, 1995).

III.  LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Individual zooids of C. tenuissimum attain an average size of 0.53 X 0.25 mm. The lophophore has between 11 and 13 tentacles and measures approximately 0.475 mm in diameter.

Abundance:
C. tenuissimum is one of the most abundant bryozoans within the IRL and is considered a fouling organism (Winston 1995). While it is abundant in the IRL, it is found in its greatest numbers in the St. James River, near Jamestown.

Locomotion:
Sessile

Reproduction:
C. tenuissimum is able to grow to reproductive size in less than 1 month. No ovicells are present. Reproduction occurs in both spring and fall, and is accomplished by release of eggs into the water column via the intertentacular organs of polypides. Peak reproduction occurs in late fall (Winston 1982).

C. tenuissimum and C. seurati co-occur in estuarine habitats, but their reproductive seasons are apparently offset. During December, when C. tenuissimum larvae are settling in their greatest numbers, they can outnumber C. seurati by a ratio of 99:1. However, throughout January, their settlement rates tend to equalize and by May, only C. seurati is still settling.

Embryology:
Fertilized eggs released into the water column develop into planktonic larvae.

IV.  PHYSICAL TOLERANCES
Temperature:
C. tenuissimum is collected year-round, and thus is able to withstand seasonal fluctuations in water temperature. It is considered to be eurythermal.

Salinity:
C. tenuissimum is one of 3 species of truly estuarine bryozoans. It was not collected from coastal stations surveyed by Winston (1982, 1995), but was routinely collected from the IRL where salinity ranged from 18 - 40 ‰.

V.  COMMUNITY ECOLOGY
Trophic Mode:
C. tenuissimum, like all bryozoans, is a suspension feeder. Each individual zooid in a colony has an average of 12 ciliated tentacles that are extended to filter phytoplankton less than 0.045 mm in size (about 1/1800 of an inch) from the water column. Bullivant ( 1967; 1968) showed that the average individual zooid in a colony can clear 8.8 ml of water per day.

Competitors:
Winston (1982) reported that C. seurati may be a better space competitor than C. tenuissimum, because its colonies were often observed to overgrow C. tenuissimum.

Habitats:
Typical habitat for ectoprocts in the Indian River Lagoon include seagrasses, drift algae, oyster reef, dock, pilings, breakwaters, and man-made debris (Winston 1995). Because C. tenuissimum is a fast growing species and attains reproductive size in under 1 month, it is able to live successfully on small, unstable substrata. Even the seagrass Syringodium has been shown to provide suitable habitat for reproductively successful colonies of C. tenuissimum (Winston 1982).

Associated Species:
Seagrasses as well as floating macroalgae, provide support for bryozoan colonies. In turn, bryozoans provide habitat for many species of juvenile fishes and their invertebrate prey such as polychaete worms, amphipods and copepods (Winston 1995). Bryozoans are also found in association with other species that act as support structures: mangrove roots, oyster beds, mussels, etc.

VI.  SPECIAL STATUS
Special Status:
None.

Benefit in IRL:
Bryozoans are ecologically important in the Indian River Lagoon due to their feeding method. As suspension feeders, they act as living filters in the marine environment. For example, Winston (1995) reported that bryozoan colonies located in 1 square meter of seagrass bed could potentially filter and recirculate an average of 48,000 gallons of seawater per day.

Economic Importance:
None.

Report by:  K. Hill, Smithsonian Marine Station
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Page last updated: July 25,  2001