Chiton (Sea Cradle) Ecology and Natural History in Between Pacific Tides
Direct Quotations By
Edward F. Ricketts
1939 (first edition -1,000 copies) and 1948 (second edition)

Compiled in 2002 by
Robert 'Roy' J. van de Hoek, Field Biologist & Geographer
Sierra Club, Wetlands Action Network, National Audubon Society
Chitons of the Pacific Coast
(See 127, pp. 90-91, 330)

Names of chitons shown on the plate opposite are given below, by rows, left to right. Those followed by a question mark are uncertain varieties which have not yet been clearly determined, an dover which at present there is much controversy.

First row: (1) Mopalia ciliataSowerby; (2) Ischnochiton (Lepidozona) mertensii Middendorff; (3) Mopalia ciliata wosnessenskii Middendorff ?; (4) Mopalia ciliata wosnessenskii Middendorff ?.

Second row: (1) Cyanoplax hartwegii Carpenter; (2) Tonicella lineata Wood; (3) Ischnochiton (Stenoplax) fallax Carpenter; (4) Tonicella lineata Wood (color variation).

Third row: (1) Ischnochiton (Lepidizona) mertensii Middendorff; (2) Ischnochiton (Stenoplax) magdalenensis Hinds (color variation); (3) Mopalia muscosa swanii Carpenter ?; (4) Placiphorella velata Dall.

Fourth row: (1) Mopalia lignosa Gould; (2) Mopalia ciliata wosnessenskii Middendorff ? (color variation); (4) Mopalia lignosa Gould.

Protected Outer Coast: Rocky Shores - Mid-tide Horizon
36. "Some of bolder chitons or sea cradles can be considered characteristic members of this zone. Most of them live under rocks, coming out to forage at night; but the delicately marked Lepidchitona (Tonicella) lineata, the line chiton (Pl.VI), is often in plain sight during the day. Although this is a small species, usually not much over an inch in length, it is the most strikingly beautiful sea cradles found in the Pacific coast intertidal. in semi-sheltered areas it maintains the high station (that is, high for a chiton) that characterizes Nuttallina (169) on the surf-swept open coast. in southeastern Alaska lineata is the most abundant shore chiton, but it occurs there with the leather chiton, Katherina, which on the California coast is restricted to surf-swept areas. The lined chiton ranges from Alaska to San Diego and is common as far south as Monterey."

"Another chiton, Cyanoplax* hartwegi (237), an oval olive-green form, may be found almost at will, although not in great numbers, by lifting up the clusters of Pelvetia on vertical rocks. In such places it spends its days, protected from sunlight and drying winds. It seems more at home, however, in quieter regions like Puget Sound."

"The natural history of chitons is discussed in 76."

*Dr. Berry prefers Cyanoplax.

Protected Outer Coast: Rocky Shores - Low-tide Horizon
76. "The collector who, from seeing Lepidochitona (36) and occasional Nuttallina, has become familiar with the chitons for which the Pacific is famous will surprise himself some day by turning up a perfectly enormous sea cradle without any apparent shell, dull brick-red in color. This giant, Cryptochiton stelleri, sometimes called the "gum boot," is the largest chiton in the world, being as much as 13" long. It is reputed to have been used for food by the coast Indians, and was eaten by the Russian settlers in southeastern Alaska. After one experiment the writers decided to reserve the animals for times of famine; one tough, paper-thin steak was all that could be obtained from a large cryptochiton, and it radiated such a penetrating fishy odor that it was discarded before it reached the frying pan."

"Although it is sensitive to light and feeds mostly at night, as do other chitons, this giant form may remain out in the tide pools and on the rocks all days when there is fog. Cryptochiton feeds on fixed algae, rasping its food into small particles , snail fashion, with a large radula, which may be examined by reaching into the mouth with a pair of blunt forceps and drawing out the file-like ribbon."

"Chitons, although usually placed in a separate class, are at least closely related to snails. Like snails they have a long flat foot, with the internal organs between it and the shell; but chitons retain teh symmetrical double gills, one on each side of the foot, whereas most snails have their anatomy so convoluted and twisted that only one gill remains. The shell consists of eight articulated plates, which allow the animal to curl up almost into a ball when disturbed. In Cryptochiton, however, the plates are not visible externally, the fleshy girdle having completely overgrown them. The hard white disarticulated plates of dead specimens are often cast up on the beach as "butterfly shells."

"Sometimes in the spring great congregation of Cryptochiton gather on rocky beaches, having presumably come in from deep water to spawn. The range is from Alaska westward to Japan and southward to San Nicolas Island off southern California, although specimens are not numerous below Monterey Bay. An account of the breeding habits of a related chiton (Ischnochiton magdalenensis) is given in 127."

More than twenty-five percent of the cryptochitons examined examined will be found to have a commensal scale worm, Acholoe vittata (Pl. XXVIII), formerly Halosydna (Polynoe) lordi, living on the gills. These very fragile worms, shedding some of their 25 or more pairs of scales at the slightest disturbance, may be 3" or 4" long, and are of a clear, light-yellow color. The same worm, never found free-living, is found commensal in the gill groove of the keyhole limpet, Diadora aspersa (181).

Protected Outer Coast: Rocky Shores - Low-tide Horizon
127 (p.90:1948,1939): "The other molluskan inhabitants of the under-rock areas are chitons - sea cradles - several species of which have already been mentioned. A majority of the 110- 125 species of chitons that inhabit the West coast are light sensitive and will be found underneath the rocks in this zone, carefully protected from daylight and especially from the sun."

"Probably all chitons are vegetable feeders, and in most cases the sexes are separate. According to observations made by Dr.Heath, the females will never release their eggs until the males have liberated their sperm into the water. Spawning takes place on May and June days when low tides occur in the early morning - not, apparently, because of the influence of the moon or merely because the tide is low, but because the water in the pools is then undisturbed. Egg-laying may continue over a period of several hours, but it ceases the momen the returning tide sends the first wave breaking into the pool. Another investigator, however, Grave (1922) finds that moonlight is the chief factor influencing the sexual maturity of an East-coast form similar to Nuttallina that he has studied."

"Along a considerable stretch of coast all the Ischnochiton magdalenensis (Pl. XIX) will spawn on the same day and almost at the same hour....

"Ischnochiton magdalensensis (up to 3" long) is a rather beautifully marbled, elongated, light gray to white chiton, ranging from Oregon to Magdalena Bay in Lower California and particularly common in Monterey Bay."

"In the La Jolla tide pools the most abundant large animal to be found at present ....

Protected Outer Coast: Rocky Shores - Low-tide Horizon
128 (p.91:1948,1939): "Other common chitons (Pl.XIX) are distinguished readily by their shape and color. Ischnochiton regularis, reported from Mendocino to Monterey only, is a uniform and beautiful slaty blue, and up to 2" long. Another Ischnochiton, ................................. We have found fine healthy specimens living on the walls and ceilings of caves, and during foggy weather they may often be found on rocks. Ordinarily, however, they are under-rock animals like their relatives."

"Through a method recently devised at the University of California (for which we have to thank Mrs. Grant), the common species of Mopalia may be differentiated in the field. . . .................."

Open Coast: Rocky Shores - High-tide and Mid-tide Horizons
169. Nuttallina californica (Pl. XXVI) is a small sea cradle or chiton, rarely more than 1 1/2 " long, that is pretty well restricted to the middle intertidal of fairly exposed shores. It can be distinguished by its rough uncouth appeaerance, spiny girdle, and color - dull brown streaked with white. It may be found occasionally well up toward the high-tide line, but never much below the middle zone. At Laguna Beach and other places in the south this chiton lives in sculptured furrows in the rock. If these furrows are of the chiton's own making, as they appear to be, they are comparable with the excavations made in rock by the owl liimpet and the purple urchin. In all three cases the object is apparently to go gain security of footing against the surf. The recorded range is Puget Sound to the Coronado Islands."

"Below the middle zone, nuttallina's place is taken by the larger Katherina (177). Both of these chitons are perfectly well able to take care of themselves at times of high surf, for they are very tough and attach to the rocks so tightly that a flat, sharp instrument must be used to pry them away. Detached from their supports, chitons promptly curl up like pill bugs."

Open Coast: Rocky Shores - Low-tide Horizon
177. "Katharina tunicata, (P.XXVII), whose dead black tunic has almost overgrown the plates of its shell, isone of the few chitons that does not retreat before daylight, or even sunlight, and next to the "gum boot" (Cryptochiton) it is the largest of the family. In the low-tide area Katherina assumes the position held in the middle zone of the same surf-swept regions by Nuttallina, but Katherina shows more definite zonation, occurring, in suitable locations, in well-defined belts a little above zero of the tide tables. In Alaska Katherina is the most abundant intertidal chiton, and it ranges plentifully as far south as Point Conception, where there is a great colony, and less commonly below there to the Coronado Islands."

"On the most exposed parts of the open coast Katherina's eggs are shed in July, at least in the central California region, but in Puget Sound sexual maturity comes a month or two earlier. Strangely enough, on at least one occasion Katherina was found to be not only the commonest chiton but one of the most prevalent of all littoral forms, in a British Columbia locality almost completely protected from wave shock (but directly fronting a channel to the open coast), an anomalous situation recalling the remarks of the ecologist Allee (1923) to the effect that if the search is long enough one can turn out very nearly any animal in any environment, however far-fetched."

Bay and Estuary: Rocky Shores - Low-tide Horizon
221. "Of chitons, the black Katharina (177) can be expected on relatively exposed shores. The giant brick-red Cryptochiton (76) occurs also, but the specimens are smaller than those found on the central California coast. One or more species of Mopalia will also be found, as differentiated in 128. M. muscosa is known to occcur in such sheltered localiaties as Elkhorn Slough (in the subspecies hindsii, according to MacGinitie, 1935c) and San Francisco Bay, with a total range extending from the Shumagin Islands to Lower California. Puget Sound specimens are sexually mature in July and August."
Bay and Estuary: Rocky Shores - Low-tide Horizon
237. "In the northern waters there are several under-rock chitons that we have met before, noticeably the small, red-marked Ischnochiton mertensii (128). Although the still smaller Lepidochitona hartwegii occurs from Alaska to Lower California, it is listed here as well as in 36 because it seems to be charactersistic of the quiet-water, under-rock associations in Puget Sound. It is a broad oval in outline, is colored a dull olive green, and is rarely more than an inch long."

Concluding Remarks
Robert Roy van de Hoek
The chitons (sea cradles) fascinated Ed Ricketts, more than many of the other invertebrates that he studied. The proof of this conclusion for me exists in following ways. For example, the only color plate in the 1948 edition is of the chitons as reproduced here in this web page. There are also numerous black & white photographs of chitons in both the 1939 and 1948 editions of Between Pacific Tides. In addition, it is noted in his comments in the books, Sea of Cortez, Between Pacific Tides, but also in his field notes of trips to British Columbia, Mexico, and southern California. To discover more about why chitons fascinated Ed Ricketts so much in the first place, one needs to begin by reading his published passages collectively on chitons (sea cradles). His writings exist in three books: Sea of Cortez, Between Pacific Tides, The Outer Shores.. The annotated appendices of his two books also enlighten us to his interest in sea cradles (chitons). The little things make all the difference such as the simple mention of Point Conception with a great colony of Katherina. Does that mean that Ed Ricketts was able to find access to Point Conception, because today there is no access for all, let alone one marine biologist, unless you have access to a wealthy individual with keys to the roads. Hopefully someday, this stretch of coast can become a National Seashore, so the public can see these wonderful chitons and the lighthouse. Perhaps the lighthouse might become a youth hostel or a visitor center to the public, where a marine naturalist watches over the delicate marine resources.