Family Aetideidae Giesbrecht, 1892
Morphology:
Female: Total length 1.19-9.20 mm. Cephalothorax 2-8 (more often 3-4) times longer than abdomen. Cephalon and Th1, as well as Th4-Th5 partially or completely separated, or fused. Rostrum present or absent, if present may be 2-pointed, one-pointed, conic or vestigial in the form of semicircle plate. Head with crest, or crest absent, some Gaetanus species with frontal spine in the anterior part of head. Th5 posterior corners symmetrical or asymmetrical, rounded or pointed, may be extended into spines /or spikes/ of various size and configuration; or in lobes of various shape. Genital segment symmetrical or asymmetrical, may be barrel-like, or of other configuration, often with projections at both sides, or at one side (dorsal view), sometimes with 1-2 spines, ventral swelling may be very, or not very large. Abdomen comprises 4 free segments, Abd1-Abd3 often supplied with transverse row of spinules along posterior border. Caudal rami with 4 apical setae, 1 internal (ventrally) and 1 short external one. A1 23-24-segmented, of various length: may be shorter than cephalothorax, more often longer, or may reach the end of caudal rami, sometimes twice as long as body. A2 with Re being 1.2-2.0 times longer then Ri, but sometimes Re as long as Ri, or shorter than Ri. A2 coxopodite with 1 (Azygokeras with 2) seta, basipodite with 2 (Euchirella with 1) setae, Ri1 A2 with 1-2 setae, rarely (Pseudeuchaeta ) setae absent. Ri2 A2 internal lobe with 7-8 terminal setae, rarely there are 6-7 setae (in Euchirella may be another number of setae: 1-2, 4-8); external lobe of Ri2 A2 with 6 (7) terminal setae and 1 posterior (Euchirella and Paracomantenna may have another number of setae). Re1 A2 lacking seta, or with 1-2 setae, Re1 and Re2 completely, or not completely fused (Euchirella ), or sometimes Re2 and Re3 completely, or partly fused (Comantenna , Mesocomantenna ); Re2 with 1-3 setae, or they are absent (Chiridiella , Comantenna , Euchirella ), Re3-Re6 with 1 long seta each, Re7 with 1 medial (rarely absent) and 3 terminal setae (rarely there is one terminal seta in Mesocomantenna ). Comantenna and Mesocomantenna with atypically short Re7, shorter than 2 previous segments together. Re7 is much longer in all other genera. Md palp base with 2-3 setae, sometimes setae absent, or there is 1 seta, Ri1 Md lacking setae, or there are 1-3 setae, Ri2 Md with 9 terminal and 1-2 posterior setae, sometimes this number is different, (some species of Aetideopsis , Bradyetes , Bradyidius , Chiridius , Euchirella , and in Chiridiella , Comantenna , Crassantenna , Lutamator , Mesocomantenna , Pseudeuchaeta , Paracomantenna ). Mx1 gnathobase with 9 terminal setae, some of them more sclerotized and claw-like, and 1 shorter, 4 (rarely 3) setae on the posterior surface, sometimes number of posterior setae is less (Chiridiella , Azygokeras , etc.). Mx1 second internal lobe with 3-5, or 2 (some species of Pseudeuchaeta ) setae, sometimes this lobe reduced, or with 1 seta (some species of Chiridiella ), third internal lobe of Mx1 with 3-4 setae (5 in some species of Chirundinella , Bradyidius , or 2 in Comantenna , Crassantenna , Lutamator , or 1-2 in some species of Euchirella , Chiridiella ); protopodite near Ri base with 3-5 setae, Ri with 14-16, or rarely less number: 3- 5, or 7 (Chiridiella ), 10 or 11 (Paivella ) and 3-5 (Euchirella ), in most genera with 11 setae at Re, rarely there are 8 or 10 (some species of Chiridiella , Euchirella , in genera Aetideopsis , Bradyetes , Bradyidius , Chiridius , Chirundinella , Jaschnovia ; if Chiridiella species have Re, number of seta may be less), Mx1 external lobe with 7 long and 2 short setae. Usually Mx2 with 5 well developed endites (sometimes with sixth endite Jaschnovia , Senecella and some species of Aetideopsis ), Ri with 6 long setae, there may be additional small setae. Mx2 1-5 endites with 2 long setae and one short seta covered with fan-arranged hairs; often one of 2 long setae at the fifth endite, and sometimes 1 seta at the fourth endite is thickened (sometimes also shortened) and transformed into claw-like spine, sixth endite (if exists) bears 1 long seta. Two aetideid genera have Mx2 strongly deviating from typical of the family: in Pseudeuchaeta setae at the 4 - 5th endites and in distal part of Ri are more sclerotized and sabre-like and in Chiridiella Mx2 is varying from typical of Aetideidae to highly modified. There are small spines at external surfaces of Mx2 endites, modified in Paracomantenna and Mesocomantenna into large strongly sclerotized spines, sometimes conjoined at the base. Mxp usually with protopodite with 1 proximal seta (sometimes absent), then groups of 2, 3 (medial) and 3 (distal) setae (from proximal to distal), sometimes there is a digital appendage of variable configuration near base of setae of distal group, some Gaetanus species have a lateral blade at Mxp protopodite. Ri1 Mxp normally 1.5-2.0 times longer than protopodite (in Aetideus these segments of nearly equal length). Distal part of Ri much shorter than Ri1 Mxp. Normally Re P1 3-segmented, rarely 1-segmented (Chiridiella ) or 2-segmented (some species of Gaetanus , Euchirella ). Re1 P1 may be supplied with external spine, or it is absent, following segments always with 1 external spine each. At the anterior surface of P1 basipodite near the base of 1-segmented Ri P1 there is a long, curved seta covered with small hairs. Nearly always Ri P1 external lobe well developed, with small spinules apically, rarely there are hairs. Ri2 P2 2-segmented, all other rami of swimming legs 3-segmented (in some Aetideopsis species with 2-segmented Re P2, Chiridiella may have another segmentation of swimming legs). Sometimes there are spinules at posterior surfaces of Ri and Re, that may be larger on lateral surfaces of coxopodite and basipodite. Sometimes (if exists) there is a row of small spinules on anterior surface of Re2 P2 at the base of second external spine. In the majority of genera P4 coxopodite without spines, but sometimes with: 2 parallel transverse rows of 4-6 spines (upper row - at the level of internal seta - Paivella ); or "bush"- like spines near the base of internal seta (Gaetanus , Pseudochirella ), or spines arranged in the same place as mentioned above, but less in number (from 1 to 5, or from 8 to 13 -Euchirella ), sometimes there are only few small spinules (some species of Aetideus , Undeuchaeta ). Terminal Re3 P2-P4 spines serrated externally, the number of spinules varies from 20 to 90. Aetideidae are characterized by lacking P5 in females, but one Comantenna species has weak P5, vestigial P5 is found in some specimens of Sursamucro , and Aetideopsis .
Male: Total length 1.19-8.80 mm. Cephalothorax 2.4-4.0 times longer than abdomen. Cephalon and Th1 fused, Th4-Th5 often fused, sometimes not completely (Aetideopsis , Azygokeras ). Rostrum bifurcate, or one-pointed, or quite absent. Crest present or absent. Th5 posterior corners symmetrical, rarely somewhat asymmetrical (some Pseudochirella and Undeuchaeta species), rounded, of triangular shape, extended into spines, sometimes carry spines (Gaetanus , Pseudochirella pacifica ). Abdomen of 5 free segments, genital opening on the left, Abd 5 sharply reduced. Usually A1 23-24-segmented, but sometimes 20-21-segmented (Aetideus ). Male of Azygokeras has geniculated right A1 of 21 segments: its 6 distal segments relatively enlarged, turned into circle and supplied with setae transformed into strong, short spines, filamentous in their top. All other genera of Aetideidae have no morphologically transformed A1, but may have the variable number of segments in left and right A1. There are aesthetascs on joints of A1 in the majority of species. Length of A1 less than in females of corresponding genus. A2 of the same structure as in female, but the number of setae at Re1, Re2 and Ri may be less, setae of Md palp partially reduced, Md gnathobase vestigial. Mx1 and Mx2 very reduced, especially the last one. Mxp poorly equipped, less than in female of the corresponding genus. Segments of P1-P4 more pronounced than in females of the corresponding genus (i.e. if female has indistinct division, the male has complete division). Re P1 setation as in females, but sometimes external spines reduced, occasionally absent. Spines at P4 coxopodite absent. There may be right and left P5, sometimes there is only left one (Aetideus ); P5 biramous, or uniramous. Usually biramous P5 with 3-segmented left and 2-segmented right Re (as an exception the latter may be 3-segmented in Azygokeras , Chiridiella and Pseudeuchaeta ). Both left and right Ri one-segmented. Left Ri 2-segmented in Bradyetes matthei and Comantenna brevicornis .
Remarks. P5 of Aetideidae males sometimes are characterized as legs of "simple" or "complex" structure. P5 of "simple" structure with P5 segments close to cylindrical shape, lacking specialized structures (protuberances, projections, extrusions, teeth, grooves, etc.). But even when configuration of P5 is simple, segments may be swelled at one side, or extended, etc. Therefore it is very difficult to give strict definition to these subdivisions. Males of some genera may have much specialized P5: with right Re2 and Ri P5 elongate and pointed in distal parts, forming "tongs" and with left Re2 and Re3 P5 of pincer structure (some of Euchirella species), or left Re3 P5 of 2 lobes and left Ri of very complicated form with deep grooves and projections (Batheuchaeta ), or left Re2 P5 with teeth and often projection (Pseudochirella ), etc.
Type genus: Aetideus Brady, 1883.
There are 26 genera in Aetideidae. Wilsonidius Tanaka, 1969 is as synonym of Chirundina Giesbrecht (Markhaseva, 1996). Gaidiopsis is not included in the present work due to poor description and loss of the type material. Pseudotharybis T. Scott. 1909 is included by Bradford and Jillett (1980) into Aetideidae, however this genus occupies intermediate position between Aetideidae and Tharybidae and needs further study; the same may refer to Valdiviella which is sometimes included into Aetideidae or into Euchaetidae and for which Zvereva (1975) suggested a new family.