Introduction to molluscan life habits databases

Jonathan  A. Todd

Department of Palaeontology, The Natural History Museum,
Cromwell Road, London, U.K. SW7 5BD


This database has been assembled to present source data on the autecology of neotropical marine mollusks represented in the Panama Paleontology Project collections of Middle Miocene to Recent age. Its scope includes all of the gastropod and bivalve genera and subgenera identified to date in the 463 PPP mollusk collections which were databased and archived as the Mollusc Occurrence 2000 database (1st March 2000) and subsequently filtered and refined to produce an analyzable dataset: the ‘Occurrence 2000 database’ (archived.1st March 2000). Scaphopods, chitons and cephalopods, the last two of which are very rare, have not been subject to any ecological analyses and I have excluded them.


My overall approach has been to assess separately the life habits of bivalves and gastropods and to consider those which are known or which can be reliably inferred through functional morphology, or taxonomic uniformitarianism in the case of anatomically unknown Recent or extinct taxa. I have undertaken a literature search to establish life habits for taxa at the generic level. Where life-habits are known to vary across subgenera of a genus I have coded the habits separately for each subgenus. Holoplanktic forms have been indicated as such and have been excluded from our ecological analyses (Todd et al., in prep.), which are restricted to the benthos.

Scope of literature review

There is an abundant literature on benthic molluscan life habits but it is very widely scattered through ecological, systematic and faunal works. For each genus or subgenus I have tried to provide at least one reference to a work which provides some, if not all, of the life habit information coded. Additional information has been added where necessary -- from functional morphological analysis or more general habitat preferences. The cited references are not intended to be comprehensive, but are simply intended to support my life habit assignations. They vary from primary literature on a particular species or genus through to literature reviews of a particular lifestyle or taxonomic group. I have chosen to include more general works when they usefully summarise and serve as a bibliography to more detailed studies, particularly when numerous works exist on a particular taxon. All literature identifications have been assessed according to our current taxonomy, so that a name used in a listed paper may not agree with the genus or subgenus  to which it is now referred in the PPP databases.

Coding of citations

I have tried to indicate the specificity with which the cited literature refers to the taxon in question by using a capital letter code; A through D. With caution, this may in some cases serve as a guide to the accuracy of the assigned life habits.

A: Bibliographic reference applies to the genus, including different subgenera (as interpreted in our in-house PPP systematics).
B: No data available for genus; reference is to a genus in same subfamily or family (rarely superfamily) and which is believed, on functional morphological or other grounds, to have similar life habits.
C: Reference to subfamily or family-level data when members are believed to have uniform life habits, at least for taxon in question.
D: functional morphological interpretation only (bivalves).

Life habit variability

An individual may show distinct life habits through its post-larval (benthic) ontogeny. Here I have coded taxa solely for their adult condition. Similarly, within a species life habits of and between individuals may vary; where known I have reflected this variability in the coding. At a higher taxonomic level, individual species within a genus/subgenus may show a range of  life habits: this variation too is coded. However, there are exceptions, where particular morphotypes within a genus/subgenus are known to have distinct life habits, then I have coded for only those morphotypes represented in our collections; an example is the limopsid bivalves.

Bivalve life habit categories

Over the past 30 years our understanding of bivalve ecology has been revolutionized by the discovery of widespread chemautotrophs, carnivory, and recently reported probable suctorial feeding. This diversity of trophic mechanisms has put to rest the longstanding division into suspension and deposit feeding. Paradoxically, we are now discovering that these last two categories are in some cases at least not mutually exclusive (see below). Despite all of this, Stanley’s pioneering work into the functional morphology of the bivalve shell still holds up in demonstrating the strong correpondences between a range of shell characters and life habits, thus permitting accurate assessment of anatomically unknown Recent and extinct taxa.

I have followed Stanley (1972) in considering the major groups of life habits to be: 1) organism/substrate relationship or life position; 2) feeding type, and 3) mobility; from which I have separated another largely independent category, 4) shell fixation. In each of these four groups I have identified a range of states, 19 in total, which are largely distinct and, with the exception of relative mobility, can mostly be directly ascertained from shell morphology. I have recognised a larger number of potentially discrete life habit combinations than did Stanley in his study of shallow shelf bivalves (he also excluded the largely commensal Galeommatoidea from consideration: I have tried to include them here). Even allowing for the huge increase in knowledge, I have found the range of bivalve life habits to be inadequately characterised by Stanley’s very broad guilds. The data presented here allows analyses to be conducted down to individual life habit level.

Organism/Substrate Relationships

ER: epifaunal recliner
Bivalves lying unattached on unconsolidated substrate.
EP: epifaunal
On a range of substrates; including sediment; consolidated substrates including biogenic substrates (e.g. coral), and macroalgal and seagrass substrates.
SI: semi-infaunal (Stanley, 1972)
IS: infaunal siphonate
IA: infaunal asiphonate
Absence of siphons is a major adaptive constraint in burrowing taxa (see Stanley 1986).
WN: nestler on or within hard substrates
Excluding active borers (below).
WB: borer, nestling in hard substrate
WU: nestler within burrow of another organism in unconsolidated substrate
Chiefly the commensal Galeommatoidea.

Feeding type

SU: suspension feeder
DU: subsurface deposit feeder
DS: surface deposit feeder
Surface and subsurface deposit feeders food sources and strategies have been compared and contrasted by Jumars et al., (1990). Suspension feeders may ingest deposited material and surface deposit feeders may suck in material from the water column (Kamermans 1994). Despite this, the two groups reflect distinct feeding strategies with often very different food sources. There is growing evidence that some tellinid species, among surface deposit feeders, may facultatively suspension feed. This swop between suspension and deposit feeding may occur as a response to food quality and quantity, hydrodynamics and predation pressure. Nevertheless, this ability may vary between congeners (Levinton 1991). To help resolve ecological patterns, for the present I have simply coded all tellinoids as surface deposit feeders except those taxa which have been examined and are only known to suspension feed.
DC: chemosymbiotic deposit feeder
CAR: microcarnivore


IM: immobile
Includes cemented, boring, nestling and reclining taxa with no means of repositioning, apart from that which may result from growth.
SE: sedentary
Sluggish forms which have at least some capacity to reposition in response to disturbance.
MA: actively mobile
Including active crawlers and burrowers.
SW: swimming
Those which have the ability to swim and which are believed to do so not solely as an escape response.

Shell fixation

UN: unattached
BA: bysally attached
CE: cemented
Including those by the shell or by byssal cementation.

Gastropod feeding categories

In general, the functional morphology of gastropod shells is much more complicated and poorly understood than that of bivalves. Many gastropods have lifestyles in which their shell is less intimately associated with the substrate in or upon which it lives than the valves of an infaunal bivalve; even in actively burrowing forms there exists a wide range of morphologies. Consequently, I have limited our analyses of gastropods to the one feature which I believe can be most easily and reliably assessed: their diets. Although this may be undecipherable from their shell morphology, broad dietary habits of closely related taxa are usually very similar and permit confident assessment of extinct forms. For some easily studied families diets are well known, but for many widespread and common taxa, especially carnivores, we still know surprisingly little. In these cases, for example the whelk family (Buccinidae), I have been forced to extrapolate data for a few species of a genus or two to the whole family.

I have adapted the theoretical and more practical trophic classifications of Hughes (1980) and Taylor and Reid (1984). I have made modifications to allow a fairly precise yet practical distinction between diets. Although it stresses clear ecological differences, it also tries to link those dietary and feeding modes which are known to commonly vary within and between species of a genus, particularly bearing in mind our very patchy knowledge. The trophic classification is the following:

CP: predatory carnivores
Predators feeding on and killing whole sedentary and mobile macro-organisms and also selective ingesters of foraminifera (foraminiferivores). Included here are scavengers, which with just a few known exceptions, are also predators, shifting facultatively when carrion is present (Britton & Morton 1994).
CB: browsing canivores
Predators which feed on sedentary, and typically clonal, animals (e.g. corals and other cnidarians, sponges, ascidians) without killing them.This also includes those ‘parasites’, which are ectoparasitic upon mostly relatively larger sedentary or mobile prey. For our purposes, I believe there is no useful distinction between these categories, given the varying host specificities of parasites (e.g. within eulimids, epitoniids and pyramidellids); and a seemingly complete gradation in relative sizes of parasite and host.
HO: herbivorous omnivores
Browsing macroherbivores with unselective omnivory, typically of epifauna attached to macroalgae.
HM: herbivores on fine-grained substrates
Microalgivores, detritivores, microphages and unselective deposit feeder. Also included here is a miscellany of herbivorous non-HR and HP categories, including those living on wood or mangrove substrates.
HR: herbivores on rock, rubble or coral substrates
HP: herbivores on plant or algal substrates
Micro-and macroalgivores and detritivores on macroalgal and seagrass substrates.
SU: suspension feeders
Includes taxa feeding solely or dominantly upon suspended particles, including mucociliary feeders.


BRITTON, J. C. and MORTON, B. 1994. Marine carrion and scavengers. Oceanography and Marine Biology. An Annual Review, 32: 369-434.

HUGHES, R. N. 1980. Optimal foraging theory in the marine context. Oceanography and Marine Biology. An Annual Review, 1980, 18: 423-481.

JUMARS, P. A., MAYER, L. M., DEMING, J. W., BAROSS, J. A. and WHEATCROFT, R. A. 1990. Deep-sea deposit-feeding strategies suggested by environmental and feeding constraints. Philosophical Transactions of the Royal Society of London, Series A, Mathematical and Physical Sciences, 331: 85-101.

KAMERMANS, P. 1994. Similarity in food source and timing of feeding in deposit- and suspension-feeding bivalves. Marine Ecology Progress Series, 104: 63-75.

LEVINTON, J. S. 1991. Variable feeding behavior in three species of Macoma (Bivalvia: Tellinacea) as a response to water flow and sediment transport. Marine Biology, 110: 375-383.

STANLEY, S. M. 1970. Relation of shell form to life habits of the Bivalvia (Mollusca). Geological Society of America Bulletin, 125, xiii, 296 pp.

______________. 1986. Population size, extinction, and speciation: the fission effect in Neogene Bivalvia. Paleobiology, 12: 89-110.

TAYLOR, J. D. and REID, D. G. 1984. The abundance and trophic classification of molluscs upon coral reefs in the Sudanese Red Sea. Journal of Natural History, 18: 175-209.


Last updated on March 27, 2001-tsa.