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1 Acarologia A quarterly journal of acarology, since 1959 Publishing on all aspects of the Acari All information: acarologia@supagro.inra.fr Acarologia is proudly non-profit, with no page charges and free open access Please help us maintain this system by encouraging your institutes to subscribe to the print version of the journal and by sending us your high quality research on the Acari. Subscriptions: Year 2018 (Volume 58): Previous volumes ( ): 250 / year (4 issues) Acarologia, CBGP, CS 30016, MONTFERRIER-sur-LEZ Cedex, France The digitalization of Acarologia papers prior to 2000 was supported by Agropolis Fondation under the reference ID through the «Investissements d avenir» programme (Labex Agro: ANR-10-LABX ) Acarologia is under free license and distributed under the terms of the Creative Commons-BY-NC-ND which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

2 ON THE OCCURRENCE OF CLAPARÈDE ORGANS IN THE HALACARIDAE (ACARI : ACTINEDIDA) 1 BY G. W. KRANTZ Oregon State University, Corvallis INTRODUCTION The organs of Claparède, or urstigmata, have been described as typical larval and prelarval structures in many acariform taxa (GRANDJEAN, 1938, 1946, 1949; LIONS, 1973 ; CoINEAU, 1974). Claparède organs vary greatly in size and shape, but are always found in the region of coxae I-II. GRANDJEAN (1946) suggested that the organs are homologous with the" lateral organs" of other arachnids, and that they may represent the endites of legs I or II in acariform mites. He further observed that their presence in larvae heralded the appearance of genital papillae in subsequent stages. Conversely, he found that the absence of Claparède organs in larval forms indicated (with exceptions in the Acaridida) that genital papillae also would be absent. Examination of these structures led Grandjean to suggest that the organs of Claparède and the genital papillae are homeotypic, noting the parallelism in structure and degree of their development. For example, the organs are large mobile appendages in the oribatid genus Epilohmannia Berlese, and the postlarval genital papillae are similarly extravagant (GRANDJEAN, 1946). Conversely, extreme regression in Claparède organ development in genera such as Caecitlits Dufour, Cyta von Heyden, Cunaxa von Heyden and H aplochthonius Willmann is mirrored in papillar regression. Complete loss of Claparède organs and parallel loss of genital papillae occurs in several acariform families (e.g. Tetranychidae, Cheyletidae and Tarsonemidae). An apparent exception to the correlation in development of the organs of Claparède and the genital papillae has been implied in the actinedid marine mite family Halacaridae. Genital papillae occur throughout the family (NEWELL, 1947), but Claparède organs have never been reported. Recent examination of halacarid larvae of the genus Thalassarachna Packard, however, revealed that Claparède organs are present in the larvae of T. rhaphidochela Krantz, an inhabitant of mussel beds on the Oregon coast (KRANTZ, 1973). They also were found in an undescribed species of the genus Agaue Lohmann from the same area. The descriptions which follow are based on study of specimens under phase contrast at magnifications of up to 4, ooox. 1. Technical Paper No. 4136, Oregon Agricultural Experiment Station. Acarologia, t. XIX, fasc. 1, 1977.

3 -- (>3 - MüRPHOLOGY The organs of Claparèdc in T. rlwj)hùlochela arc totally intcrnal and lack the protective scale typical of othcr groups (GRA:\'DJEA?-1, 1955). Each organ consists of a sclerotized ring and a membranous tubular canal which opens at the ventral invaginated juncture of coxal fields I-II, laterad of both th ~ primary ani s ~condary epimeral porcs of shicld AE. Its position relative to coxal fidjs and epimeral pores, and its abs.-ncc in nymphal and adult stadia of the species observed, vcrifi.'s its identity as a Claparède organ. 4 FIGURES 1-4 : Thalassarachna rhaphidochela Krantz Posterior portion of shield AE. 1) Larva (v = organ of Claparède) ; 2) Protonymph ; 3 Adult female; 4) Larval pore complex, showing position of organ of Claparède (<Ji = epimeral and sternal pores; v = organ of Claparède, vs = shaft, vr = ring). FIGURE 5 : Agaue sp: (Oregon, USA) Shield AE of larva (v = organ of Claparède}. The Claparède organ and associated epimeral pores of T. rhaphidochela are illustrated in Fig. 4. The shaft of the organ (vs) is indistinctly annulate, and is broader at its juncture with the basal ring (vr) than at its mouth ~ The secondary epimeral pores (~II) are weakly developed both in the larva and in succeeding stages. The primary pore (~I) is a distinctive structure even

4 in the larval stage, as are the more medial sternal pores (~III). Figs. r-3 show the progressive development of the epimeral pores and setaè-lhrough the life stadia of T. rhaphidochela, and loss of the organs of Claparède following the larval molt. The relative positions of pores and setae remain constant from stage to stage throughout ontogeny. As in other halacarids, setae ae 2 aµpear only after the larval molt (Fig. 2). t - -,1 tf... f;~ r~g J~~l~ ~ :l~.i. î 25µ 1 î 25µ l 12 pg~\j"\t ~ î 25µ l FIGURES 6-7 : Thalassarachna psammophila Krantz Larva. 6) Lateral portion of shield AE (~1 = primary epimeral pore) ; 7) Enlargement of ~I. FIGURES 8-12 : Actacarus illustrans Newell. 8) Lateral portion of shield AE of larva (v? =? organ of Claparède); g) Enlargement of organ of Claparède; IO) Lateral portion of shield AE of protonymph; II) Enlargement of mediolateral pores of shield AE, protonymph; 12) Genitoanal region of protonymph, showing genital papillae (pg). Utilizing T. rhaphidochela as a basic form, other species of Halacaridae were examined and pore homologies established between species. Included in these comparative studies were members of the genera Rhombognathus Trouessart, Isobactrus Newell, Agaue Lohmann, Actacarus Schulze, Agauopsis Viets, and Copidognathus Trouessart. Two additional species of Thalassarachna also were examined. Clarapède organs were identifi.ed with certainty only in one other halacarid - an undescribed member of the genus Agaue (Fig. 5) which, like T. rhaphidochela, is an intertidal mussel bed inhabitant. In some of the species examined, the primary epimeral

5 pore was found to be strongly developed in the larval stage and, in certain cases where pores ~II are absent in the larva (e.g. Actacarus illustrans Newell and Thalassarachna psammophila Krantz), ~I could possibly be identified as a Claparède organ. The location of ~I in T. psammophila in relation to the lateral invagination between coxal fields I-II, and its position relative to ae 3 (Fig. 6), would make its identification as a Claparède organ questionable. The reappearance of ~I in protonymphal and subsequent stages removes any doubts as to its true identity. The situation is less clear in regard to A. illustrans. Here the larval structure is similar to the " typical" halacarid Claparède organ (Figs. 8, 9) and resembles the genital papillae of subsequent stages (Fig. 12). However, the postlarval stadia possess two subsurface pore-like entities near the juncture of coxal fields I-II, the more lateral of wich could be a homolog of the larval organ (Figs. ro, rr). Aside from location, there is little similarity between the larval and postlarval structures. Further study of additional material utilizing scanning and sectioning techniques may help establish whether homologies exist between these two entities. DISCUSSION The form of the Claparède organ in T. rhaphidochela and in Agaite sp. is strongly reminiscent of that seen in the prelarva of Pilogalumna allifera (Oudemans) (GRANDJEAN, 1962). The organ is vestigal and entirely internal in all three species, consisting only of a shaft and basal ring. The prelarval Claparède organs of other Oribatida (LIONS, 1973) are similarly reduced, although larval organs in more primitive forms may be extremely large and complex (e.g. Epilohmannia). The organs of Claparède thus far identified in the Halacaridae, therefore, are equivalent in their level of development to that observed in the prelarvae of other acariform groups. While the presence of Claparède organs generally is a generic or suprageneric characteristic in the Acariformes, it is reduced to a species trait in the Halacaridae. Its absence in most of the species studied, and its reduction in complexity, suggests that the halacarid Claparède organ is a relict structure which has been retained only incidentally. Unlike other acariform groups lacking the organ, however, halacarids do posses genital papillae, which are considered to be Claparède organ homeotypes. The loss of Claparède organsin most of the taxa studied, and the retention of papillae in succeeding stages, indicates that the function of these entities continues to be essential only in the postlarval stadia. It is tempting to conclude that the combination of organ loss (or inhibition) and papillar retention is related in some way to the acquisition of a marine habitat. Yet a similar trend is evident in some terrestrial groups, among them Bdelloidea (GRANDJEAN, 1938, 1946). Here the organs may be greatly reduced (Cyta von Heyden, Trachymolgus Berlese) or absent (Cunaxa?capreolus (Berl.), Oregon, USA), while weakly developed but distinct papillae generally are present. The loss of Claparède organs in the preponderance of halacarid genera may reprensent a final stage in the suppression of these structures in the bdelloid-halacaroid evolutionary line. ABSTRACT Organs of Claparède were identified in representatives of two of seven genera of Halacaridae examined - Thalassarachna and Agaue. The organ is vestigal, attaining the level of development seen in prelarvae of other acariform groups. Acarologia, t. XIX, fasc. r, 1977.

6 RÉSUMÉ Les organes de Claparède ont été identifiés chez des représentants de deux genres d'ralacaridae exanùnés - Thalassarachna et Agaue. L'organe est un vestige, atteignant le niveau du développement des prélarves d'autre groupes ne dépassant pas le niveau structural de ceux des prélarves d'autres Acariens. LITERATURE CITED COINEAU (Y.), Éléments pour une monographie morphologique, écologique et biologique des Caeculidae (Acariens). - Mém. Mus. Nat. d'ristoire nat., n. série A (Zool.) 81 : l vr. GRANDJEAN (F.), Observations sur les Bdelles (Acariens). - Ann. Soc. ent. France, 107 : l -24. GRANDJEAN (F.), Au sujet de l'organe de Claparède, des eupathidies multiple et des taenidies mandibulaires chez les Acariens actinochitineux. - Arch. Sei. phys. natur. Genève, 28 (5) : GRANDJEAN (F.), Remarques sur l'évolution numérique des papilles génitales et de l'organe de Claparède chez les Rydracariens. - Bull. Mus. Rist. nat. Paris, 2e série, 21 (1) : GRANDJEAN (F.), L'organe de Claparède et son écaille chez Damaeus omtstits Koch. - Bull. Mus. Rist. nat., Paris, 2e série, 27 (4) : GRANDJEAN (F.), Prélarves d'oribates. - Acarologia, 4 (3) : KRANTZ (G. W.), Four new predatory species of Ralacaridae (Acari: Prostigmata) from Oregon, with remarks on their distribution in the intertidal mussel habitat (Pelecypoda : Mytilidae). - Ann. Ent. Soc. Amer. 66 (5) : LIONS (J.-C.), Quelques prélarves nouvelles d'oribates. - Acarologia, 15 (2) : NEWELL (I. M.), A systematic and ecological study of the Ralacaridae of eastern North America. - Bull. Bingham Oceanogr. Coll., 10 (3) : l-232. Paru en Septembre I977