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Natural
Natural In the November issue of Sean Raynon Sabado, on page 5, we mentioned that Elizabeth Kinloch was making a trek across about 2,500 miles of Africa. As busy as she was Elizabeth took time to send some striking photos of live sea shells collected in the Dar Es Salaam area of East Africa, the westernmost extension of the Indo-Pacific molluskan province.
Of the shells, she says, "A mixed bag, typical of the good days of shelling in Dar es Salaam, Tanzania. Living species in this slide include Cypraea lamarcki [left], C. lynx [top], C. vitellus dama [bottom center], C. carneola sowerbyi [upper right], C. cribraria comma [center] , C. limacina [lower right] and, now showing the jet black mantle, Trivia oryza [right, middle]."
Although mollusk shells have been collected and their intricate designs admired for centuries, they remain an enigma to most of us. The adaptive significance of elaborate shell ornamentation baffles us, especially in mollusks covered with dense periostraca so that the pattern is obscured. There is undoubtedly no single solution to this puzzle, as could be expected of a complex biological system. That is, some shell patterns may have obvious adaptive significance, for example the cryptic (or camouflage) coloration of many limpets and land snails which are subject to intensive visual predation by birds. Other species may have shells which have no manifest correlation with environmental factors, even though the ornamentation may be very intricate.
In studying the molluscan shell, one can think of it as conveying a certain amount of information. The information, however, is coded and it is this "code" which the investigator must decipher. The information recorded in the shell is comparatively permanent, a characteristic not shared by many other organisms. Thus, we know from the examination of fossil shells that most of the same sculpture and color patterns we observe presently existed as long ago as the Paleozoic and are fundamental traits of most molluscan groups.
The first step in deciphering the shell "code" is to ascertain the basic types of ornamentation. This involves the measurement of several variables; 1) shape, 2) size, 3) ornamentation, 4) intensity of pigment or degree of sculpture and 5) persistence of the ornamentation through time (temporal pattern).
Natural Upon return to the lab, the plankton sample is transferred to two-liter beakers and allowed to settle for a few minutes. The supernatant organisms are returned to the sea or used as food for aquarium fish. Upon swirling the remainder, more veligers are caught up in the vortex and deposited at the bottom. The process is repeated until quick scanning indicates veligers are no longer present in the supernatant sea water. The veliger portion is then scanned in petri dishes. Crowding 20 large veligers (greater than 0.75mm) or about 50 small veligers (0.1-.75mm) into a small (5.5cm in diameter) plastic petri dish greatly increases the chances of their metamorphosing into juveniles within the first week of captivity. If they do not metamorphose during that time, it is unlikely that they will have sufficient energy to do so later, thus they will not grow sufficiently to permit identification.
The care and feeding of veligers after capture is time-consuming, and refurbishment of the culture dishes must be accomplished every two days. Each small petri dish should be provided with 2-3 drops of a mature, but not dense, culture of Phaeodactylum tricornutum3 a golden diatom, or with the same amount of another acceptable culture. Clean, smooth coral chips with a thin covering of algae were provided to induce settlement; also, some clean, fine sand was included to insure an ion system favorable for shell deposition. The sea water should be renewed with the stored, filtered sea water every 48 hours to prevent build-up of detrimental protozoan and bacterial populations, to renew the oxygen supply and to eliminate waste products.
After metamorphosis, suspected herbivores (nerites, limpets, littorines, Bittium and cerithiids) are provided with rock chips with algal films, or small clumps of filamentous alga (Strombus), or algal fronds with detritus. These food supplies are found in most calm sea water localities. Suspected carnivores (naticids, miters, columbellids, cones, etc.) can be offered Rissoella sp. a tiny (1-2mm) black snail or minute polychaetes. Trivia juveniles eat small, transparent, colonial tunicates; juveniles of Epitonium favor corals or sea anemones such as Aiptasia. The food supplies of cypraeid juveniles appear to be variable and to depend on the species involved: C. caputserpentis is an algal feeder after metamorphosis.4
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