Ontogeny of South African intertidal oribatid mite species (Acari, Oribatida, Ameronothroidea) and supplements to adult morphology

Information about larva and nymphal stages as well as additional descriptions of adults of four littoral species of the families Fortuyniidae, Selenoribatidae and Podacaridae found around the coast of South Africa are provided. Juveniles of Fortuynia elamellata micromorpha are well in accordance with the morphology of other known juveniles of Fortuynia, but the larva of the former shows distinctly barbed rostral setae, a trait which lacks in all the other species. Adults of the South African Selenoribates divergens are similar in morphology to the Egyptian specimens, except for the presence of small rostral humps, anterior notogastral tubercles and the position of lyrifissure ih. These differences are presently considered to be only geographic variation. Juveniles of Sel. divergens can be easily distinguished from juveniles of other known Selenoribates species by the presence of a spinose clavate bothridial seta and branched notogastral setae in deutoand tritonymph. Due to the loss of type specimens of Schusteria ugraseni, a neotype was designated. The juveniles of this species are very similar to those of Schusteria littorea and Schusteria melanomerus, but differ in amongst others the anoadanal and leg setation. Adults of Halozetes capensis show strong variation in the length of dorsal setae and juveniles of this species differ significantly from others in the number of prodorsal and gastronotic porose sclerites. Finally, a table is provided listing all ameronothroid species with known juvenile stages.


Introduction
The marine intertidal oribatid mites of the superfamily Ameronothroidea are air-breathing animals living on the edge of the constant fluctuating cycle of low tide and high tide, of submersion and emersion and variable temperatures. Consequently, they have adapted to this environment in their morphology, behavior, reproduction, respiration and physiology (Bücking et al. 1998; Pfingstl 2013a, 2017. Ameronothroid mites live in the littoral zone in algae mats, rock crevices, on boulders, in barnacles and tubeworms, and man-made structures (Marshall and Pugh 2002; Pfingstl 2013a, 2017 or in estuaries and mangrove forests . They feed mainly on algae, but also on lichens and cyanobacteria (Luxton 1966; Pugh and King 1985; Bücking et al. 1998; Pfingstl 2013a.
Ameronothroidea consists of four families namely, Ameronothridae, which occurs in the northern polar and cold temperate regions, the Podacaridae of the southern polar and cold Material and methods

Sample collection
This study forms part of a larger study in which samples were taken at different locations along the coastline of South Africa (Pfingstl et al. 2021a). Fresh specimens for this study originated from Sheffield Beach, Umkomaas, Umdloti, St. Lucia (all KwaZulu-Natal), East London (Eastern Cape) and Nature's Valley (Western Cape) sampled in 2019 and 2020. In addition, previous collected specimens of F. e. micromorpha (collected in 1998-1999) and H. capensis (2000), housed at the National Museum, Bloemfontein, were used (these included holotypes, paratypes and juveniles). Localities and sample details are given in the respective species descriptions under: Material examined. Samples (app. 10 cm 3 ) of littoral algae, barnacle and mussel shells were scraped off rocks with a knife or a small shovel and then put in Berlese-Tullgren funnels for 12 to 24 hours to extract mites. Most mites extract within 24 hours from these rather small samples with rare occurrences after this extraction time. Specimens were collected alive in small plastic containers with plaster of Paris, sorted with a fine brush and preserved in ethanol (100%) for morphological investigation. Juveniles were assigned to a specific species only if adults of a single species were contained in the respective sample. Specimens are stored in the Acarology collection of the National Museum, Bloemfontein, South Africa (abbreviated as NMB) and in the collection of the Senckenberg Museum für Naturkunde Görlitz.

Preparation and visual documentation
Specimens were mounted in lactic acid on temporary cavity slides for measurement and illustration. Body length was measured in lateral view, from the tip of the rostrum to the posterior edge of the notogaster. Notogastral width refers to the maximum width in dorsal view. Lengths of body setae were measured in the aspect they could be best observed. All body measurements are presented in micrometers. In most instances the range of sizes are given, but for body measurements the range is given followed by the mean in brackets. Drawings were made with a camera lucida using a Nikon transmission light microscope "Nikon Eclipse 50i″. Drawings were made with software CorelDraw 2021. For photographic documentation, specimens were air-dried and photographed with a Keyence VHX-5000 digital microscope using automated image stacking.
Morphological terminology used in this paper follows Grandjean (1966Grandjean ( , 1968 and Norton and Behan-Pelletier (2009) ; Norton (1977) for setal nomenclature; Norton and Franklin (2018) for notation of epimeral setae (e.g. Remark 15, setae are named according to their relative position and not to their ontogenetic appearance).
Lateral aspect ( Figure 1C): PdI round, small; cuticular canals of van der Hammen's organ present, canal ce very short, reaching posterior border of bothridium, canal ci absent.

Juvenile stages
Common features -apheredermous; dark brown in colour, integument plicate and soft except for the more sclerotised centrodorsal plate, median posterior of centrodorsal plate with a less sclerotised area forming a narrow inverted ′v′ (except in larva where the plate is uniform in sclerotisation); body finely granulate, with more distinct granulation around insertions of dorsal gastronotal setae and in furrows and acetabular regions, granulation on prodorsum more distinct in the larva and deutonymph; prodorsum triangular, hysterosoma oval in dorsal view; rostrum broadly rounded; le setiform, short, smooth, in represented by alveoli; bothridia small, cup-like, bs with short stalk and smooth head clavate in lateral view, globose in dorsal view; ventral side with specific pattern of folds i.e., folds between epimeres 2 and 3, anterior and posterior of  genital area and lateral to anal orifice, with pores within these folds leading into tracheal tubes; legs monodactylous with large hook like claws, with small teeth dorsally; porose areas on legs as in adults; for leg setation and solenidia see Table 1.

Remarks
The original description of the adult by Marshall and Pugh (2002) provides good morphological information and the drawings are detailed, but there are no drawings of the lateral side of the body or the legs. Also, canal ce is present, but ci is absent, whereas the authors stated both are absent. The adults of the other locations match the adults of Park Rynie of the original description.
The morphology of most Fortuynia juveniles is similar in habitus and development of setation, except for the juveniles of F. arabica and F. taiwanica (Bayartogtokh et al. 2009), which may be attributed to several factors (see Pfingstl et al. 2021b). For the other 10 species, the main differences lie in the length and morphology of setae (Pfingstl and Schuster 2012a) and other minor characteristics such as ontogeny of certain leg setae, especially on the femora. One characteristic of the larva of F. elamellata micromorpha that is distinctly different is the strongly barbed rostral setae. The juveniles of F. elamellata elamellata are not very well described (Luxton 1967), but in general terms, besides the larger sizes they seem to be similar to F. elamellata micromorpha. The only difference is in the placement of the lamellar setae in the larva which is very close together in the nominate species and further from each other in the subspecies. However, only one badly damaged larva specimen was used for the description of F. elamellata elamellata.  Integument ( Figure 5): brown in colour, antero-medial notogaster with lighter area, ventrally area posterior to genital plates darker than anterior to this area, genital and anal plates same colour as this posterior area, trochanters III and IV of legs darker than rest of legs; body densely granulate, larger granules irregularly sparsely distributed, denser bigger granules in acetabular region, legs with small dense granules.

Juvenile stages
Common features -apheredermous; light brown in colour, integument strongly plicate and soft, except for the more sclerotised centrodorsal plate; body finely granulate (less distinct in larva), with more distinct granulation in the acetabular regions; prodorsum triangular, hysterosoma oval in dorsal view; rostrum with weak lateral humps and rounded apex; le, ro setiform, short, smooth, simple; in and ex very short; bothridia small, cup-like, bs with medium stalk and clavate spinose head; plicate centrodorsal shield bearing central dorsal setae, da, dm, dp on small apophyses; no cupules discernable; folds lateral to anal orifice; epimeral seta 1b very long; legs monodactylous with hook like claws, small tooth proximo-ventrally on each claw; leg porose areas not visible; for leg setation and solenidia see Table 2.

Remarks
The original description of this species with material from Egypt provides very good morphological information and drawings of all aspects including the legs (Pfingstl 2015c). The South African specimens are similar in morphology to the Egyptian specimens, except for the presence of small lateral humps on the rostrum, the small tubercle antero-laterally on the notogaster and lyrifissure ih not located on the lateroventral border of the notogaster. Considering the large geographic distance between Egypt and South Africa, there is a possibility that these differences are indicative of a closely related but genetically distinct new species. However, the differences are very subtle and could also be a result of geographic variation. Without genetic Table 2 Selenoribates divergens Pfingstl, 2015. Chaetome and solenidia from larva to adult. First development of setae and their homologies indicated by letters. () pairs of setae, -no change with regard to preceding stage.
The protonymph and tritonymph of S. divergens and S. quasimodo differ most noticeably by the number of gastronotal setae and many more gastronotal folds in the latter. The nymphs of S. divergens have 15 pairs of setae, whereas the protonymph of S. quasimodo has 24 pairs and the tritonymph 44 pairs stemming from a multiplication of certain setae. Furthermore, the setae in the tritonymph of S. divergens are branched, while the setae in S. quasimodo are setiform, with setae da, dm, dp thickened and serrated. Setae ex is minute in S. divergens and vestigial in S. quasimodo. There is only one difference on the leg setae in the number of setae on Fe II (S. divergens proto-and tritonymph: 3 setae, S. quasimodo protonymph: 2, tritonymph: 4). Other characteristics, which also differ in the adults, are the form of the bothridial setae (S. divergens head clavate, spinose, S. quasimodo flagelliform) and the number of adanal setae (S. divergens three pairs, S. quasimodo two pairs).
In general, the deuto-and tritonymph of S. divergens and S. mediterraneus look similar in habitus and gastronotal folds. An obvious difference is that S. divergens has branched gastronotal setae with setae da, dm, dp slightly thickened while S. mediterraneus has setiform setae and all setae are thin. There are differences on the leg setae in the number of setae on Fe I and II (S. divergens: 3 setae, S. mediterraneus: 4). Other characteristics, which also differ in the adults, is the form of the bothridial setae (S. divergens: head clavate, spinose, S. mediterraneus: spatuliform) and the number of adanal setae (S. divergens: three pairs, S. mediterraneus: two pairs).
Integument (Figures 8 and 9): brown in colour, antero-medial notogaster with lighter area, ventrally the area posterior to genital plates darker than the anterior area, genital and anal plates dark with small foveolae; legs lighter brown, except trochanter III and IV dark brown; femora distally with faint striae; body distinctly granulate with large granules interspersed with small granules, larger granules on PdI.
Legs (Figures 9A-D): monodactylous, hooked claw with small tooth proximo-ventrally; most setae barbed, except thickened blunt antiaxial lateral seta on genua I-IV; Fe I, II with only three setae (as in S. littorea), on tarsi seta u′ longer than u″; for setation and solenidia see Table  3.

Neotype designation
The holotype and paratype of S. ugraseni have been lost (Marshall, personal communication) and therefore a neotype should be selected. There is no material available from the type locality (Park Rynie). The specimens used here originate from Sheffield Beach (app. 116 km from Park Rynie) and Winterstrand (app. 612 km from Park Rynie). Due to the closer proximity, we selected a neotype from Sheffield Beach (NMB 4717.2.1) and five neo-paratypes from Sheffield Beach (NMB 4717.2.2) and four neo-paratypes from Winterstrand (NMB 4707.1.1) stored in the Acarology collection of NMB. Additional specimens will be stored in the Senckenberg Natural History Museum, Görlitz, Germany.

Remarks
The original description of Marshall and Pugh (2000) provides good morphological information and drawings of all aspects of the body, but not the legs. The adult specimens from Sheffield and Winterstrand match the description of the specimens from Park Rynie of the original description.
In general appearance the juveniles of S. ugraseni are very similar to those of the other two species of which juvenile stages are known: S. littorea Grandjean, 1968 (all stages) and S. melanomerus Marshall & Pugh, 2000 (protonymph) (Grandjean 1968; Pfingstl 2016. They have the same appearance and specific patterns of lateral and ventral folds. The protonymph of S. ugraseni differs from S. melanomerus in the presence of short ex (vestigial in S. melanomerus), two pairs of white spots on the anal valves (vs absent) and setae l′ on Fe I and II (vs absent).
A distinct difference between the adults of S. ugraseni and S. littorea is the number of anal and adanal setae with two pairs of anal and two pairs of adanal setae in the former, but one pair of anal and two pairs of adanal setae in the latter species. This trait is also different in the juveniles of these two species: the deuto-and tritonymph of S. ugraseni with two pairs of adanal setae and S. littorea with one pair, deutonymph and tritonymph of S. ugraseni with two pairs of anal (vestigial in deutonymph) while S. littorea has one pair in deuto-and tritonymph (also vestigial in deutonymph); the anal valves of the protonymph of S. ugraseni has two pairs of white spots, but they are absent in S. littorea. There is also a difference in the leg setae with seta l″ on Ti II present in the deuto-and tritonymphs, while it is only appearing in the adult of

S. littorea.
Another difference is the presence in S. ugraseni of a short ex seta in larva, protoand deutonymphs and alveolus in tritonymph and adult, while a short ex seta is present in all stages of S. littorea and in the adult.
Integument ( Figure 12): dark brown in colour; leg tarsi, tibiae lighter brown; dorsal side distinctly granulate with various sized granules, on prodorsum granules medially from anterior to posterior along hour-glass shape of ro, le and in, ventrally small area of granules between leg I and II, remainder of ventral side without granulation, legs with granules of various sizes; chelicera punctate.

Juvenile stages
Common features -apheredermous; dark brown in colour, integument strongly plicate and soft, body distinctly granulate; three oval sclerites in posterior region of prodorsum, three pairs of sclerites on notogaster laterally between setal rows of l-series and d-series, anterior pair irregular in shape, others rounded or oval; prodorsum triangular, hysterosoma oval in dorsal view; rostrum rounded; ro short, le of medium length, in very long, all three setae roughened, ex very short, smooth; bothridia small; gastronotal setae thickened, setiform, smooth or slightly roughened; no cupules discernible; folds lateral to anal opening; epimeral region with folds; legs monodactylous; leg porose areas visible; for setation and solenidia see Table 4.

Remarks
The original description by Coetzee and Marshall (2003) of H. capensis provides very good morphological information and drawings of all aspects including legs. The adults from Nature's Valley of our samples do not differ from those of Kommetjie. The variation in the length of dorsal setae, even within a population, is noteworthy.