Anatomical Glossary Overview

This is an up-to-date, comprehensive glossary of anatomical and morphometric terms applied to the sclerotised structures of mosquitoes. It represents an extensively revised and updated amalgam of the Taxonomists’ Glossary of Mosquito Anatomy (Harbach & Knight, 1980) and its supplement of corrections and additions (Harbach & Knight, 1982).

The glossary is divided into nine sections: General, Adults, Eggs, Larvae, Larval chaetotaxy, Pupae, Pupal chaetotaxy, Vestiture and Morphometry. The General section includes anatomical terms for structures that are common to adults, larvae and/or pupae, and the Morphometric section includes terms for morphological measurements and ratios used in the descriptive taxonomy of adults, eggs, larvae and pupae. Each of the other sections includes terms that are specific to the title of the section.

Anatomical terms are arranged alphabetically and defined on separate pages within each section. Each page has as a basic pattern of five headings - Abbreviation, Variants, Definition, Synonyms and Explanation - and one or more images that illustrate the defined structure (morphometrics are not illustrated). All terms have a definition, nearly all have an abbreviation, many have variant spellings and synonyms, and relatively few are provided with additional information under the heading Explanation. In cases where information is not available for one or more of the headings, those headings are not displayed on a page.

Abbreviations consist of capital letters or a combination of upper and lower case letters. Abbreviations are not duplicated within a given section but in a few cases they are duplicated between sections. Individual elements of the larval and pupal chaetotaxy are denoted by a number and a hyphenated capital letter (except cephalothorax = CT; paddle = Pa) on pages, but are identified on illustrations with only the number. The abbreviations of the defined structures are circled in red on the illustrations, and the serial homologues of defined larval and pupal setae are encircled by turquoise rings.

The glossary sections can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Clicking on the name of a section in the side panel leads to an introduction to that section.

It is not currently possible to determine to which defined term a particular synonymic term applies. The glossary will eventually include an index of synonymic terms with links to the conventional terminology.

General

This section contains anatomical terms that are common to mosquito adults, larvae and/or pupae. In most cases, the terms refer to ontogenetically homologous structures; however, in some cases topological terms denote structures that are not clearly homologous.

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Adults

This section contains a comprehensive treatment of the specific terminology applied to the structures that comprise the external skeleton of adult mosquitoes. Users will note that it differs substantially from the section on adult morphology in Taxonomists’ Glossary of Mosquito Anatomy (Harbach & Knight, 1980). Corrections to illustrations, the addition of new illustrations and new terms, and the inclusion of updated information, e.g. the terminology applied to wing spots (Wilkerson & Peyton, 1990), are most noticeable.

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Eggs

The eggs of mosquitoes bear the general morphological characters of many insect eggs and consist, before fertilisation, of the ovum and the remains of the nurse cells surrounded by a covering, the chorion, formed from the follicular epithelium and consisting of an outer layer, the outer chorion, and an inner layer, the inner chorion, which together form the eggshell. Structural features of the outer chorion provide useful taxonomic information, but, unfortunately, the eggs of most mosquito species are known.

The morphological terminology listed and defined here for features of mosquito eggs was recommended for general use by Harbach & Knight (1980). A few terms more recently used in descriptive literature have yet to be included as either bona fide terms for general use or as unnecessary synonyms. Users who are aware of new or preferred terms for describing egg morphology are encouraged to contact the site manager.

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Larvae

Mosquito larvae have a greater number of anatomical characters amenable to taxonomic study than any other life stage. They possess many secondary adaptive features, but they also tend to show phyletic relationships better than the adults. This section defines the head, thoracic and abdominal structures of mosquito larvae, excluding sensory setae and other cuticular projections. The complement of setae (innervated sensory organs) that arise from various body parts of mosquito larvae is treated in the Larval chaetotaxy section, and the assortment of non-innervated projections of the cuticle are defined in the Vestiture section.

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Larval chaetotaxy

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Background  Beginning with Martini (1923), a number of individuals have participated in the development of a sound nomenclatural system for the setae of mosquito larvae. Their various systems are detailed in a comparative manner in Tables 2-15 of Harbach & Knight (1980) (setae of the mouth region are not included). This work crested with the detailed studies of Belkin (1950, 1952, 1953, 1954a, 1954b, 1960, 1962), and the system perfected by him has been in general use ever since.

The setal definitions all begin with the word seta and are arranged numerically for each body area. The body area treatments begin with the antenna and proceed posteriorly to abdominal segment X.

Because of the considerable variation that occurs throughout the Culicidae in vertical and horizontal orientation of the living larva and of its terminal parts, it is impractical to describe the positional relationships of the setae in terms of their true morphological orientation. Instead, all descriptions of positional relationships are based on a simple horizontal orientation of all sections of the body.

Two hundred and twenty-three (223) pairs of setae are found on mosquito larvae. The setae are distributed as follows:

Antenna  Six setae occur on the antenna, individually numbered by their approximate position from base to apex and bearing the hyphenated suffix “A”.

Cranium  A maximum of 20 pairs of setae are known to occur on the fourth-instar larval cranium. These are designated by numerals beginning anterodorsally and preceding posteriorly and ventrally, each numeral bearing the hyphenated suffix “C”.

Mouth region  A total of 29 setae (or multiple setae) are known to occur on the areas and appendages about the mouth. These are numbered individually on each area or appendage, each number being followed by a hyphen and the abbreviation for the appropriate area or appendage. Three pairs occur on the labropalatum (Lp), one at the margin of the mouth (Mo), four on the mandible (Mn), 15 on the maxilla (Mx) and six on the labiohypopharynx (Lh).

Thorax  A maximum of 15 pairs of setae are known on the prothorax, 14 on the mesothorax and 13 on the metathorax. Each of these setae is individually designated first by a numeral showing its actual, or in some cases presumed, primitive position in the “basic pattern” of the Culicidae in which seta 1 arises closest to the dorsal longitudinal midline with the positions of successively higher numbered setae following progressively and circumferentially toward the ventral longitudinal midline, and second by a hyphen and a capital letter P, M or T indicating a position on the prothorax, mesothorax or metathorax, respectively. In a series of publications by Belkin (1950, 1952, 1953, 1954, 1960, 1962), presumptive segmental homologies were established between all of the setae of the thorax and the first seven abdominal segments, except for seta 0-P.

Abdomen  A maximum of 12 pairs of setae are found on abdominal segment I, 15 pairs on abdominal segments II through VII, seven pairs on abdominal segment VIII, 13 pairs on the siphon (pecten plate in anophelines) and spiracular apparatus (derived from embryonic abdominal segments VIII and IX) and five pairs on abdominal segment X. The terminology for these setae consists of an Arabic number for each indicating its presumed primitive sequential relationship in the Culicidae in which seta 1 is closest to the dorsal longitudinal midline with the higher numbered setae following progressively around the side to the ventral longitudinal midline, connected by a hyphen with a capitalised Roman numeral indicating the abdominal segment on which the seta occurs.

Abdominal segments I to VII  A maximum of 12 pairs of setae are found on abdominal segment I, with setae 0, 8 and 14 presumed to be those which are absent. A maximum of 15 pairs of setae are found on each of abdominal segments II through VII. The sequential Arabic numerals applied to the setae of abdominal segments I through VII are believed to indicate serial homologies down the row of segments, ontogenetic homologies between the larval stages, as well as with the pupa, and phylogenetic homologies throughout the Culicidae. Typically on these abdominal segments, setae 0 to 5 are dorsal, 6 to 9 lateral and 10 to 14 ventral. Serial homologies for setae 0 to 5 are most clearly apparent on abdominal segment I and for setae 6 to 14 on abdominal segment II. On these segments the setae designated are typically present in a consecutive numerical sequence or in departures from this that can be more or less readily determined. In determining serial homologies, similarities in setal branching and development should be noted, as well as relative position. Difficult setae can sometimes be named through a process of elimination.

Abdominal segment VIII  Of the seven pairs of setae that occur on this segment, the minute setae 0 and 14 are treated as homologues of those similarly designated on abdominal segments II to VII. The numerical designations applied from dorsal to ventral to the other five pairs of setae are arbitrary and do not imply homologies with setae of the segments anterior and posterior to segment VIII.

Siphon and spiracular apparatus  The siphon (pecten plate in anophelines) and spiracular apparatus possess 13 pairs of setae of uniform occurrence. Additional setae occur in sabethines but since they do not occur in other taxa they are regarded as being adventitious and are therefore not included in the standard setal nomenclature. The setae on these structures are numbered from proximal to distal. No homologies are implied with setae borne elsewhere on the abdomen. The terminology consists of an Arabic number for each seta connected by a hyphen with the capital letter “S”. The structures referred to above are comprised of parts of embryonic abdominal segments VIII and IX.

Abdominal segment X  Four pairs of setae are of uniform occurrence on this segment. No homologies with other abdominal setae are implied by the numbers assigned to these setae.

Pupae

This section contains a comprehensive treatment of the specific terminology applied to the structures that comprise the external skeleton of mosquito pupae. Extensive anatomical changes take place within the pupa, and the adult emerges by a splitting of the dorsal surface of the cephalothorax. The pupal-adult apolysis occurs shortly after the larval-pupal ecdysis. Hence, there is a very short exposed pupal period followed by a very long pharate adult phase. Hence, most of the conventional "pupal stage" is an adult, not a pupa, enclosed by the remains of the pupal cuticle. Consequently, much of the terminology applied to pupal structures is the same as that applied to adult mosquitoes. A more detailed explanation is provided under the definition of "pupa". Borkent (2012) proposed different terms (not accepted here) for some of the structures defined below based on comparative study of the families of Culicomorpha.

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Pupal chaetotaxy

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Background  The components of the pupal chaetotaxy are homologous phylogenetically, ontogenetically and in part serially. The discovery (Belkin, 1960, 1962) that the developing pupal setae are connected by sensory neurons to their homologues in the fourth-instar larva established beyond doubt the ontogenetic homology of the setae. Presently, the fate in the pupa of many larval setae is unknown. It would seem possible that their vestiges, although not producing setae, are at least present in the pupa as cells comparable to those normally occurring at the base of a seta, and techniques might subsequently be developed that would permit their recognition.

In the period since names were first applied to most of the pupal setae (Macfie, 1920), numerous naming systems and modifications have been proposed. This process culminated in a nomenclature (Belkin, 1962) that is both soundly based and convenient to use. Although most pupal setae can be named by the presently used terminology, there are situations where two or three setae are grouped in such a way as sometimes to make a choice of which is which a purely arbitrary decision. The setal definitions presented herein are based on the interpretations of Belkin (1962) and numerous later publications. Borkent (2012) proposed a different setal nomenclature based on comparative study of the families of Culicomorpha, but it is not accepted as a replacement for the traditional nomenclature used by culicid taxonomists.

The setal definitions all begin with the word seta and are arranged numerically for each body area. The small square inserted between the word seta and the setal number should be ignored. It functions to enable links to pupal rather than larval setae with the same alphanumeric designators.

One hundred and nineteen (119) pairs of setae are found on mosquito pupae. The setae are distributed as follows.

Cephalothorax  Fifteen pairs of setae occur on the cephalothorax, three on the lateralia of the head, four on the prothorax, two on the mesothorax and usually three, sometimes four, five or six on the metathorax. The setae of this area are designated with a number connected by a hyphen to the suffix “CT”.

Abdomen  A total of 104 pairs of setae are found on the pupal abdomen, including the paddles. The numbers applied to the abdominal setae indicate homologies with larval abdominal setae as established by Belkin (1952), unless otherwise stated. Individual setae, as in the case of larval abdominal setae, are denoted by a number followed with a hyphen and a Roman numeral to indicate the abdominal segment involved. Paddle setae are denoted by a number followed by a hyphen and the abbreviation "Pa".

Vestiture

The vestiture (general surface covering) of mosquitoes is comprised of two types of cuticular projections: setae (singular seta), which are articulated processes arising from a basal alveolus, and spicules, which are non-articulated continuous outgrowths of the cuticle. Flattened setae with longitudinal ridges that arise from minute alveoli are known as scales. Ordinary setae are innervated sensory organs (mechanical receptors) borne in various locations on all body areas of adults, larvae and pupae. Scales form the principal body covering (ornamentation and coloration) of adult mosquitoes.

The terminology applicable to the vestiture of mosquitoes consists of names applied to the fundamental types of cuticular projections and descriptors (adjectival names) that characterise their common structural forms. The latter are listed as italicised adjectival names under each of the fundamental types of cuticular projections defined herein.

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Morphometry

This section contains descriptive terms for measurements, ratios and indices that characterise the size and dimensions of various external structures of adults, eggs, larvae and pupae. These terms are not included in other sections of the glossary because they are not terms for anatomical structures per se.

Terms contained in this section can be accessed by clicking on the name of a section below or by returning to the side bar and clicking on the + that precedes the name of a section. Terms are defined on individual pages. A click on the term will open the page. The basic set of headings available for each page is explained in the Overview. As in other sections of the glossary, the abbreviation of the term that denotes a structure is encircled in red on the accompanying illustration(s).

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith