I use a cheat sheet to help me keep it all straight. I thought I'd share it.

Part I - Nomenclatural Classification Types

Holotype - If an author relies upon a single specimen to describe a species, that single specimen is the holotype.

Syntypes - If an author uses a group of specimens (sometimes referred to as the type series) to describe a species, the shells in the group are called syntypes. In this circumstance, there is no holotype. (Note: Authors do make mistakes. If a type series actually contains more than one species, the description the author produces may be flawed. This circumstance has been the source of much confusion with species named by not so meticulous authors. See neotype, below.) Member Charlie Sturm notes that "Sometimes, in older literature, syntype is known as co-type."

Holotype - If an author uses a group of specimens to describe a species and designates one to represent the species, then that one becomes the holotype.

Paratypes - If an author uses a group of specimens to describe a species and designates one to represent the species (the holotype), then the others in the group are called paratypes. (Note that authors do make mistakes and all specimens in a group examined may not be the species described and represented as the holotype. That is why identification comparisons should be made to the holotype, lectotype or neotype if at all possible.)

Lectotype - If, after an author names a species based upon a group of syntypes, a later author designates one of the syntypes to represent the species, it is called a lectotype. If the original author relied upon syntypes and included an illustration of one of the specimens, that specimen is also often referred to as the lectotype.

Paralectotypes - If a lectotype is designated, then the other paratypes in the original syntypes group become paralectotypes.

Neotype - If all the above types for a species are lost and descriptions/illustrations are ambiguous, an author can select a suitable specimen to represent the species, clarify the description, and designate that specimen as the neotype.

Hypotype - A described or figured specimen used in a publication to extend or correct the knowledge of a previously defined species. A hypotype would be any images/descriptions published after the holotype, syntypes, lectotype, or neotype have been established, but does not replace them. Rather, hypotyes are later publications that serve to illustrate and provide further information about a species. All Marlo's presentations of species here on LTS are hypotypes.

Iconotype - The illustration of the type created with and to facilitate the original description. If the original type material is lost this illustration may serve as the type. If the illustration is a photograph, then Phototype might be used instead of Iconotype.

Type locality - The type locality is the locality for the holotype, lectotype or neotype.

Topotype - A specimen taken from the type locality.

Part II - Biological/Description Types

Genotype – The genetic coding that determines the form, structure, function and behavior of a species. However, the ultimate display of form, structure, function and behavior of a specific species population, subpopulation or individual will also reflect the environmental conditions acting upon the organism(s) during development.

Phenotype – The generally accepted, “normal” properties of form, structure, function and behavior of a species resulting from its genetic coding and the environment. Usually, based upon the characters of those representatives of a species found in the largest, most predominant habitats or populations.

Morphology – The form and structure part of the description of a phenotype. Usually, based upon the characters of those representatives of a species found in the largest, most predominant habitats or populations.

Morph (from the Latin meaning "form") - A variant of the generally accepted, “normal” morphological description of a species (a phenotype) with unique characters that persist among some members of the species population. Morphs can (and often do) exist within the same randomly breeding population or may arise in isolated or widely separated populations. Morphs are often identified as subspecies. Some classic morphs would be the high spired morph of Melongena corona (Gmelin, 1791) often identified as M. altispira Pilsbry & Vanatta, 1934 and the clubbed spines morph of Strombus pugilis Linneaus, 1758 often identified as S. sloani Leach, 1814.

Morphs can be environmentally driven or result from within species genetic variation. In both cases, with time environmental morphs can disappear with the disappearance of the environmental drivers or genetic morphs can be bred out of existence. For more, look up Polymorphism.

Morphotype - A specimen chosen to illustrate a morphological variation (a morph) within a species population.

Ecotype - A within species morphological variation adapted to or driven by the ecological surroundings it inhabits.
Often called a “form” or “subspecies.”

Phenoplasticity – The alteration of a species’ genetically coded form, structure, function or behavior in response to differing environmental conditions. Some species’ genetic coding allows for greater variations than others in form, structure, function and behavior in response to environmental conditions . The phenoplasticity of some species can be so great as to result in forms with such differing morphology as to be mistaken as separate species. See discussion of Puperita pupa and Puperita tristis for example.

 

Cryptic species - When the species name is known to apply to two or more actual genetically separate species grouped under one species name because they cannot reliably be morphologically distinguished.  To apply the label "cryptic species" to a taxon means it is known (through some mechanism) that it is one of a group of genetically separate species that morphologically cannot be distinguished one from the other.  The label "cryptic species" is often applied to groups of similar taxa when it is uncertain as to whether or not they are actually genetically separate.  Then, later, when a reliable mechanism is used to distinguish among them, and it becomes known that they are not simply within species variations, morphological differences may be able to be described and new taxa names applied. 

Discussion:

Species descriptions we read created by the naming author may be based upon a holotype, group of syntypes or a neotype. A holotype, syntype or neotype description might be based upon the morphological description of a phenotype, a morph, or an ecotype. It all depends upon from where and how many specimens of a shell the author believes is the same species and relies on to write the description. This is one of the contributing factors as to why species identification can be so difficult. Many species were described and names assigned from single or only a few specimens (which may have been morphs, ecotypes, freaks or otherwise distinctly different from the species' more generally accurate morphological description). Add to this such factors as the specimens relied upon when assigning a name potentially having been juveniles, hybrids, damaged/incomplete, dead, or not all really the same species (but assumed to be), and you can see why identification is difficult and we are often confronted with a species having many assigned names.

Part III - Nomenclature we see with species names

cf. An abbreviation for the latin meaning "compare to." When used with a species name (Cerithiopsis cf. fusiformis) it means the specimen in question is sufficiently similar to this species that it probably is, but may not be. It means more research is needed to ascertain with certainty. Although you will most often see the term used as illustrated, Dr. Gary Rosenberg, creator of Malacolog - A Database of Western Atlantic Marine Mollusca, The Academy of Natural Sciences, has pointed out that technically it should be written as Cerithiopsis cf. C. fusiformis. The use of "cf." should precede the entire species name since a species name is binomial and the second term does not by itself identify a species.

aff. or sp. aff. An abbreviation for the latin "affinis," in this application meaning a close relationship between biological groups involving resemblance in structure. When used with a species name (Cerithiopsis aff. fusiformis; or Cerithiopsis aff. C. fusiformis) it means the specimen is probably not this species, but is very closely related and more research is needed to know.

My interpretation is that the use of "cf." or "aff." refect the two ends of the range of uncertainty as to to whether a specimen may or may not be a particular species. Which is used is obviously each observer's subjective judgment.

auct. non - auctorum non - of authors, but not of the original author. Follows the citation of a misidentified taxon. "Auct. non" should be read as: as used by author(s), but not of the original author. In other words, author(s) have incorrectly applied the concept of the species of the original author to a specimen [the specimen to which the author(s) are applying a species name is actually not the taxon of the original author].

s. l. - sensu lato; in the broad sense, i.e. of a taxon — including all its subordinate taxa and/or other taxa sometimes considered as distinct.

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The species/subspecies issue:

The ICZN accepts only one rank below that of species, namely the rank of subspecies (“subsp.” or “ssp.”) - a taxonomical rank subordinate to species, or a taxonomic unit within a rank.

A species will either be recognized as having no subspecies at all or two or more (including any that are extinct), never just one. Monotypic species have no subspecies. Polytypic species have subspecies [at least the "nominate" and one "autonymous"(see below)].

Nomenclature for a subspecies:

In Zoology:
Genus species subspecies
Strombus pugilis sloanii

In Botany:
Strombus pugilis ssp. sloanii

Marlo's preference: Strombus pugilis form sloanii.

If a species is polytypic, then the originally described/named shell is the “nominate subspecies” and written Strombus pugilis pugilis. And, later described variations are the “autonymous” subspecies, and written Strombus pugilis sloanii.


Part III - Nomenclature we see on data slips

Leg. - From Latin legere, to gather, choose, pluck. Most commonly used to mean "collected by." Preference is given to leg. over coll. because the latter is more usually used to mean "in the collection of." (Thanks to Henk K. Mienis)

coll. - In the collection of...

det. - From Latin determinavit, used to mean "identified by." (Thanks to Manfred Herrmann)