Adult specimens live in U-shaped, opaque, parchment-like tubes (Fig. 5). Tube lengths vary from 2-50 cm; animals vary from 1-30 cm. Larger tubes house larger animals with more gametes than do smaller ones. The two ends of each tube protrude from the bottom of sand flats. Specimens from southern latitudes are either benthic and can be collected by diving or are intertidal and can be collected with a shovel at very low tides. Specimens from Woods Hole are benthic and are collected by diving.
At Woods Hole, where we obtain animals from the Aquatic Resources Department of the Marine Biological Laboratory (7 MBL Street, Woods Hole, MA 02543), the reproductive season of Chaetopterus lasts from early July to the middle of August. The reproductive season is longer in Southern populations. Fertile specimens may be obtained from Cape Fear Biological Supply (PO Box 10218, Southport, NC 28461) from March until November. This species is also very common in Florida, but we have not investigated these specimens. Another, much smaller species, Chaetopterus variopedatus, is available on the Pacific Coast, and (presumably) the same species is also present in the Mediterranean [Appendix 3].
The functional anatomy of the worm (Fig. 1) was beautifully described and illustrated last century in a monograph (Joyeux-Laffuie, 1880). Early work by Enders (1909) and Berrill (1927, 1928) further laid the groundwork for our understanding of the morphology and behavior of this unusual worm. Somites comprising different regions have become so highly specialized that, in many cases, their components are almost unrecognizable. The notopodia of the 14th to the 16th somites are large fans that move back and forth rhythmically, in a piston-like fashion, creating a flow of water through the tube (Berrill, 1927; Riisgard, 1989; Riisgard and Larsen, 1995). Those of the 12th somite are drawn out to form two wing-like structures (the aliform notopodia). In the tube, they fold over the dorsal surface of the worm, creating a small aperture through which all the water must pass. A copious amount of secreted mucus extends as a sac from the aliform notopodia to the ciliated cup midway down somite 13. Planktonic food particles, trapped by the mucus as water is pumped through the tube, accumulate. Food and mucus are wrapped into a pellet by the ciliated cup and transported to the mouth (MacGinitie, 1939; Barnes, 1965). Posterior to segment 16 are the genital somites that produce eggs and sperm.