Teratothyadidae K. Viets 1929
Creators: name: Gerecke, Reinhard
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Trombidiformes
Teratothyadidae

description: Family Teratothyadidae K. Viets, 1929  A high number of representatives of this family were identified from the material collected in Madagascar, but it is too early to say if a particular adaptive radiation took place on the island. As many of the recorded populations inhabit inconspicuous, small springs and rivulets, it is possible that teratothyadids are generally understudied in all parts of their distribution area. In the following, a general morphological outline valid for all representatives of the family is given (for the structures described, compare Figs 23–29):  
 The idiosoma maximum width is reached in general in the posterior part; anterior edges with strongly projecting anterolateral “shoulders”, posteriorly, anterior to II-L insertions, followed by a narrowing of the idiosoma, frontal margin convex or projecting in an obtuse angle. In the arrangement of dorsal and posteroventral muscle attachment plates and the formation of the genital field, members of this family resemble hydryphantids. However, similarity is restricted to plesiomorphies, and the combination of four character states is rather distinct in comparison to hydryphantids: (1) conspicuous idiosoma sclerotization consisting of stellate structures–with increasing age these filled by coarsely porose secondary sclerotization to form large reticulate plates around muscle attachments and glandularia, and fringes around coxae, occasionally also genital plates; (2) if the genital field is triacetabulate, at least one acetabulum lies on the genital plate; (3) chelicera with an extremely elongate, blade-like straight claw; (4) palp not chelate–P-4 without a dorsodistal extension flanking the dorsal margin of P-5 (in exceptional cases, auch an extension may be developed as a socket of a seta: Fig. 24 b). At the present state of systematics, this set of character states is distinctive for the family. However, the compared family Hydryphantidae is probably paraphyletic, combining numerous diverging evolutionary lines (Dabert et al. 2015), and including taxa resembling Teratothyadidae in character state (1) (Thyopsis Piersig, 1899) or (3) (Neocalonyx Walter, 1919). A P-2 with two strong pinnate distoventral setae is found strikingly similar in Hydrodromidae and the subfamily Diplodontinae of Hydryphantidae; a chelicera similar in proportions, with an extremely elongated blade-like claw in some species of the hydryphantine genus Hydryphantes. A better understanding of the relationships between hydryphantoid families–also Rhynchohydracaridae fit character state (1), as well as between genera and subgenera of Teratothyadidae, can be expected from studies on larval morphology and molecular biology.   
 As in the hydryphantine genus Thyopsis, with increasing age of the mite, muscle insertion sclerites grow below the integument. Except for the central point from where a muscular apodeme originates or a glandular platelet is situated, the whole plate surface is covered by the same (in most cases papillose) membrane that extends over the whole body except for the coxal and genital area. Integument structure is often difficult to observe due to a dense cover of fine material (including diatoms and fungal mycelia) extending all over the body. Subcuticular idiosoma sclerotization is formed by star-shaped primary sclerites radially extending from ring sclerites surrounding glandularia and excretory pore. Like the fabric of an umbrella, a net of finer sclerites expands between the primary sclerite bars. A similarly structured pattern of secondary sclerites surrounds the lateral eye capsules, coxae and an unpaired sclerite located in the centre of the coxal area. The coxae themselves bear fine round pores, tips of Cx-1 are strongly projecting over the frontal margin, here and along medial margins covered with short, curved setae; similar setae at tips of the remaining coxae and scattered over their surface.   
In shape and extension of idiosoma sclerites, a probably age-dependent variability is possible: Idiosoma sclerites of juveniles have rather large pores in low numbers, appearing reticulate, while in old specimens, dorsomedial plates, as well as medial parts of dorsolateral plates, display a finer porosity. However, the final stage of plate growth obviously differs species-specifically, in some cases with dorsomedial plates bearing up to 20 pores along a transverse transect, in other cases less than 10. Often, coxal plates of old specimens develop fringes of heavy secondary sclerotization with localized pores distant from each other, leaving extended areas with a smooth surface.  
Except for presence/absence of the genital skeleton (plesiotypical morphology as found in Hydryphantoidea, no species-specific modifications in morphology is observed, for a figure see K.O. Viets & Böttger 1974) and generally minor differences in dimensions (males being smaller than females, but with a wide overlap), no sexual dimorphism is known in teratothyadids. Genital flaps are always finely porose, with about 20 setae (longer and dense at anterior and posterior edges, finer and regularly-arranged along central medial margin), and a group of longer, posteriorlydirected setae at the posteriomedial tips (their base often covered by posterior acetabula and therefore difficult to observe).  
In the course of this study, particular attention was paid to legs, documenting a wide intraspecific variability of segment proportions. The results given in the single species descriptions indicate that these measurements are of restricted value for species definition. In addition to stronger setae located dorsodistally on I-IV-L-2 and around distal margins of segments of I-II-L-3–4 and III-IV-L-3–5, all leg segments are covered with characteristic, basally inflated setae. These setae form a dense, fur-like cover on segments 3-5, but are more scattered and restricted to the distal part on terminal segments. In all investigated species, II-L exceeds in total L III-L – I-L is the shortest, IV-L the longest leg. Leg claws have on the inner side basally a more or less projecting basal claw blade, distally followed by a comb of 15–18 denticles arranged in a line smoothly switching to the lateral surface distomedial surface, on the outer side a clawlet slightly set off.  
A particular feature is the unusually-shaped, slender teratothyadid chelicera, with an extremely long, straight claw forming an acute angle with its extended proximal part (L/H ratio always> 5.0, basal segment/claw <1.5, often <1.0). It must be underlined that a fine dorsal extension of the basal segment, flanking the basal part of the claw, in our basal segment/claw L calculations is not considered. As this extension is often nearly invisible, and the optical impact of the basal segment/claw proportion is governed by the point of the proximal claw end, I decided to give two basal segment measurements (proximal L, total L) and to use the (distinctly lower) basal L value for calculations. In this way, total chelicera L can be calculated as [proximal basal segment L & claw L].  
Important species-specific differences are frequently found in the genital field (number, shape and arrangement of acetabula), and gnathosoma and palps (from stout to more or less slender). In contrast, the palp setation is rather conservative, as follows: P-1, 1 (rarely 2) dorsal; P-2, 4–5 dorsal, two strong and pinnate distoventral; P-3, 4–5 dorsal; P-4 one slender, sharply pointed distal and several fine, hair-like (one proximal, three distal).  
Teratothyadidae are reported from the Old World tropics only (continental Africa and SE Asia). Here, the family is recorded for the first time from Madagascar. The life cycle is not known for any species.
description: Published as part of Gerecke, Reinhard, 2020, The early derivative water mites (Acari: Hydrachnidia, superfamilies Eylaoidea, Hydrachnoidea and Hydryphantoidea) of Madagascar, pp. 1-77 in Zootaxa 4727 (1) on pages 44-45, DOI: 10.11646/zootaxa.4727.1.1, http://zenodo.org/record/3613302