Aetideus Brady, 1883
Taxonomic description:
Female: Total length 1.40-2.50 mm. Cephalothorax 2.8-4.7 times longer than abdomen. Cephalon and Th1, as well as Th4-Th5 fused. Sometimes there is crest in the anterior part of cephalothorax. Rostrum bifurcate, rami widely arranged, usually strongly sclerotized, some species have undivided massive rostral base. Body surface often with "dotted" structure. Th5 posterior corners symmetrical, rarely rounded, usually prolonged into points /spikes/, extending the last third of genital segment or exceeding it, Th5 may be transformed into wing-like protrusions pointed at tops, reaching Abd2-Abd3. Genital segment symmetrical, its length 1.1-1.2 times more than width. Spermatheca clearly visible and of characteristic shape in many species: of two parts: ventral oval and rounded dorsal connected by curved channel of various length and width. Caudal rami 2.0-3.3 longer than wide. A1 24-segmented, equal in langth to cephalothorax or body and even overreaching body by two last segments. Re A2 slightly longer than Ri, coxopodite with 1 seta, basipodite with 2, Ri1 A2 with 14-15 setae (8 at internal and sometimes there is 1 dorsal seta, and 6-7 at external lobe). Re1 A2 lacking seta, Re2 A2 with 3 setae, Re3-Re6 each with 1 seta, Re7 with 1 medial and 3 terminal setae. Md palp base with 2 setae, Ri1 Md with 2 setae, Ri2 Md with 9-10 terminal setae arranged in row and 1 (rarely 2) dorsal setae; each segment of Re2-Re4 with 1 long terminal seta and 2 terminal setae at Re4. Mx1 gnathobase with 9 claw-like terminal and 4 thin surface dorsal setae, second and third internal lobes with 3 and 4 setae correspondingly, protopodite near Ri base with 4 setae, Ri with 12-14 (Park (1968) notes 15) setae, Re with 11, external lobe with 9 (7+2) setae. Mx2 typical of Aetideidae, fourth and fifth endites with 1 seta thicker than others that transformed into claw-like spine. Setation of protopodite and Ri1 Mxp typical of Aetideidae (protopodite with 1 proximal seta and 3 groups of 2, 3 and 3 setae correspondingly from proximal to distal part of segment), Ri1 Mxp with 3 medial setae. Mxp less developed than in other Aetideidae, Ri1 Mxp sometimes slightly longer than protopodite. P1 with 3-segmented Re and one-segmented Ri, Ri external lobe with apical spinules; Re1 P1 lacking spine, Re2 with short spine usually not reaching the middle of Re3. P2 with one- or incompletely 2-segmented Ri and 3-segmented Re. P3-P4 with 3-segmented rami, majority of Aetideus species with few tiny spines near the base of internal seta at P4 coxopodite, or they are absent.
Male: Total length 1.22-2.10 mm. Cephalothorax 2.7-3.8 times longer than abdomen. Cephalon and Th1, as well as Th4-Th5 fused. Rostrum and crest absent. Th5 posterior corners elongated into points /spikes/, reaching posterior border of Abd1, or slightly exceeding it (Th5 of A. arcuatus rounded). Caudal rami 1.64-3.70 times longer than wide. A1 20-21-segmented, equal in length or slightly longer than cephalothorax. Oral limbs in comparison with that in female less developed. Setae at gnathobase and second internal lobe of Mx1 may be absent (in A. acutus after Park, 1974); number of setae on other segments of Mx1 may be less than that in female, thus Re Mx1 of A. acutus , A. arcuatus and A. mexicanus bear 10 setae. P1-P4 like that in female. P5 uniramous, of simple structure, only left leg present, 5-segmented, elongated, sometimes equal to abdomen in length.
Remarks. Aetideus united with Euaetideus Sars, 1925 (Bradford, 1971a) on the base of similarity in external morphology and oral parts structure. Bradford also supposed that Snelliaetideus Vervoort, 1949 should to be united with Aetideus. Afterwards Roe found male of Snelliaetideus arcuatus Vervoort, 1949 to be the same structure as typical of Aetideus males and thereby confirmed Bradford's conclusion about identity of these genera (Roe, 1975). Paivella is very close to Aetideus. Type species of the latter genus P. inaciae Vervoort, 1965 closely conforms to Aetideus diagnosis in females, but male differs in presence of both right and left P5 legs and of rostrum.
Type species: Aetideus armatus Brady 1883 = Pseudocalanus armatus Boeck, 1872, by monotypy.
The genus Aetideus includes 11 species. All species except A. australis (Vervoort, 1957), most records of wich are from subantarctic waters, are included in this work.
Aetideus acutus Farran, 1929
Aetideus arcuatus (Vervoort, 1949)
Aetideus armatus (Boeck, 1872)
Aetideus bradyi A. Scott 1909 (male unknown)
Aetideus divergens Bradford, 1971
Aetideus giesbrechti Cleve, 1904
Aetideus mexicanus Park, 1974
Aetideus pacificus Brodsky, 1950
Aetideus pseudarmatus Bradford, 1971 (male unknown)
Aetideus truncatus Bradford, 1971