Charles Messing's Crinoid Pages: Collecting and Curation

Crinoids are relatively fragile organisms. Collecting specimens in plastic bags with a substantial volume of water via scuba or snorkeling or, in deeper water, via a variety of submersible- or ROV-mounted collection devices, offer the best opportunities for obtaining intact material. Trawled specimens often fragment before they can be preserved. Immersion in 10% buffered formalin or 70% ethanol also often results in fragmentation, although many larger deep-water crinoids can usually be preserved intact using the latter. Formalin may be used for specimens intended for histological work, but as this fixative degrades DNA, a portion of an arm or pinnules should be fixed separately in 95% ethanol or other fixative appropriate for molecular sequencing (e.g, dimethyl sulfoxide (DMSO)). Colors tend to fade upon preservation, especially in ethanol, so detailed color notes should be made while the animals are alive.

To minimize fragmentation in shallow-water feather stars, David Meyer recommends immersing the specimen, oral side down and arms outspread in a shallow dish filled with 95% ethanol, until dead (usually 30-90 sec). Some taxa respond to preservative by flexing their arms aborally, others orally, so gentle finger pressure or covering with a glass dish (so you can see what’s happening) may be required to keep the animal flat. Some species autotomize some to all arms regardless of the method. Most stalked species and more highly-skeletonized deep-sea feather stars (e.g., Thalassometridae, Charitometridae) can just be immersed in 95% ethanol. Specimens can later (at least a few hours) be transferred to 70% ethanol for storage.

For shipping, remove the specimen from ethanol, and wrap it gently in ethanol-dampened paper toweling both for cushioning and to maintain moisture. Use just enough ethanol to thoroughly dampen the toweling; dab the toweling against a dry towel to remove excess ethanol—to ensure that no free liquid remains (to avoid shipping restrictions on flammable liquids). Alternatively, soak the specimen in glycerol to maintain flexibility. Place the wrapped specimen in a heat-sealed plastic envelope to maintain moisture and reduce shipment weight and volume. Do not use any kind of gauze, because it will catch and detach pinnules and delicate cirri.

Pinnules and cirri are best examined singly by gently prying them off an arm or centrodorsal with the tip of a fine forceps. This procedure normally destroys the attachment articulation, however. In specimens with adjacent arms closely apposed, an entire arm or ray may have to be separated in order to examine oral and genital pinnules. In taxa with numerous cirri, many may have to be removed in order to examine the centrodorsal and ray bases (Messing and Dearborn, 1990).

Although most ossicles are clearly visible through the thin epidermis, some tropical feather stars are a bit fleshier. In ethanol-preserved specimens, ray bases in particular may be enveloped in enough tissue so that application of a small drop of 5% sodium hypochlorite solution (commercial liquid bleach) may be needed to examine external surfaces of sutures and articulations. However, care must be taken to avoid too much tissue dissolution or ossicles will begin to disassociate. Such structures are better examined in dried specimens, but these, even when properly preserved, become brittle and prone to breakage. Nevertheless, individual pinnules and cirri are best examined when dry. I have had success in mounting such skeletal components with a small drop of white glue (e.g., Elmer’s) on cardboard micropaleontology slides. Examination of individual ossicles and articular faces requires maceration of the entire part in liquid bleach. While smaller components such as pinnules begin to fall apart in seconds and become clean enough to examine in minutes, larger arms and ray bases take longer. Ossicles tightly sutured to each other by synostoses (e.g., calyx and some stalk ossicles), often may only be separated by gentle prying with a fine forceps or needle even after lengthy immersion in bleach.

It goes without saying (but I’ll say it anyway) that every specimen should be accompanied by a label detailing collection information, i.e., date, depth, location, latitude/longitude, collector name, and, when appropriate, vessel name, station and gear, and associated organism(s) (e.g., attached to octocoral [with name or description if no name]). Some alphanumeric should be attached to every collected specimen to correspond to field notes on habitat (e.g., substrate, co-occurring benthos, and temperature, current, if known), color, behavior, and any other pertinent observations, as well as separate subsamples destined for other fates (e.g., sequencing, histology). A catalogue number will be attached when the specimen(s) is(are) added to a formal depository, e.g., museum collection.

[Updated from Messing 1997]

References