New taxa of quill mites (Acariformes: Syringophilidae) parasitising aquatic birds of the Faroe Islands

The paper presents descriptions of new taxa and new records of quill mites of the family Syringophilidae Lavoipierre, 1953 (Acari: Prostigmata: Cheyletoidea) parasitising aquatic birds in the Faroe Islands, Denmark. Sulisyringophilus jenskjeldi n. gen., n. sp., is described from the northern gannet, Morus bassanus (Linnaeus) (Suliformes: Sulidae). The new genus, Sulisyringophilus, is new genus differs from the morphologically similar genus Procellariisyringophilus Schmidt and Skoracki, 2007 by the presence of lateral hypostomal teeth and leg setae vsII in females, the features which are absent in the latter. A new species Charadriphilus lymnocryptes n. sp. is described from the jack snipe, Lymnocryptes minimus (Brünnich) (Charadriiformes: Scolopacidae). Additionally, two rarely recorded species, Niglarobia ereuneti Kethley, 1970, and Creagonycha lara Kethley, 1970, are reported from two charadriiform hosts: the semipalmated sandpiper, Calidris pusilla (Linnaeus) and the black-legged kittiwake, Rissa tridactyla (Linnaeus), respectively.


Introduction
Research on parasites associated with vertebrate hosts on islands and archipelagos is of particular interest, as it plays a crucial role in understanding parasitic behavior and ecosystem development in relatively isolated conditions.Among the specialised parasites associated with birds, the quill mites of the family Syringophilidae (Acariformes: Prostigmata: Cheyletoidea) are distinguished by their high morphological specialisation.These mites inhabit exclusively the internal cavities of feather quills, carrying out their entire lifecycle within this unique microhabitat, including feeding and reproduction.The family Syringophilidae represents the most taxonomically diverse group among quill-inhabiting mites, occupying a wide range of habitats in the plumage of their hosts (Kethley, 1970;Skoracki, 2011).Despite their diversity, the taxonomic system of syringophilid mites remains unsatisfactorily developed.Currently, the family comprises approximately 400 described species, and its representatives have been recorded from hosts representing 27 bird orders (Zmudzinski et al., 2023).
The Faroe Islands, an archipelago in the North Atlantic Ocean, consist of 18 volcanic islands.Their unique geological features and geographical location make them a significant habitat for a wide array of seabirds and waders, which either breed on or regularly visit the islands.A comprehensive survey has documented a total of 355 bird species on the Faroe Abstract The paper presents descriptions of new taxa and new records of quill mites of the family Syringophilidae Lavoipierre, 1953 (Acari: Prostigmata: Cheyletoidea) parasitising aquatic birds in the Faroe Islands, Denmark.Sulisyringophilus jenskjeldi n. gen., n. sp., is described from the northern gannet, Morus bassanus (Linnaeus) (Suliformes: Sulidae).The new genus, Sulisyringophilus, is new genus differs from the morphologically similar genus Procellariisyringophilus Schmidt and Skoracki, 2007 by the presence of lateral hypostomal teeth and leg setae vsII in females, the features which are absent in the latter.A new species Charadriphilus lymnocryptes n. sp. is described from the jack snipe, Lymnocryptes minimus (Brünnich) (Charadriiformes: Scolopacidae).Additionally, two rarely recorded species, Niglarobia ereuneti Kethley, 1970, andCreagonycha lara Kethley, 1970, are reported from two charadriiform hosts: the semipalmated sandpiper, Calidris pusilla (Linnaeus) and the black-legged kittiwake, Rissa tridactyla (Linnaeus), respectively.

Materials and methods
The birds were collected by Jens-Kjeld Jensen (Nólsoy, Faroe Islands, Denmark) over the period from 1996 to 2024 and were preserved in his private freezer until examination.Their causes of death varied, including natural causes, traffic accidents, predation by feral cats, or hunting.For each bird studied, the majority of the flight, tail, and covert feathers were meticulously removed and examined for the presence of quill mites.Additionally, 10-20 contour feathers from the chest and ventral areas were carefully extracted and analysed.An overview of examined bird species is presented in Table 1.
Mites found in infested feathers were meticulously removed using fine-pointed tweezers.These specimens underwent a clearing and softening process by being immersed in Nesbitt's solution at ambient temperature for 24 to 36 hours (Skoracki, 2011).Subsequently, mites were transferred to 70% ethanol for a brief period of approximately 10 minutes and then mounted on microscopic slides using Hoyer's medium, following the established protocol by Krantz and Walter (2009).The mite specimens were examined using a ZEISS Axioscope light microscope equipped with differential interference contrast (DIC) optics.Illustrations were made using a camera lucida attachment.All measurements are given in micrometres, with the dimension ranges of paratypes presented in parentheses, following the measurements of the holotype.The idiosomal setation nomenclature aligns with Grandjean's (1939) system as modified for Prostigmata by Kethley (1990), and the leg chaetotaxy follows Grandjean's (1944) classification.All other morphological terminology follows Kethley (1970) and Skoracki (2011).
Specimen depositories are cited using the following abbreviations: AMU, A. Mickiewicz University, Department of Animal Morphology, Poznan, Poland; NHMD, Natural History Museum of Denmark, Copenhagen, Denmark.
Male.Characteristics as in female except: total body length 660; lateral hypostomal teeth absent; posterior margin of stylophore without projection; all setae on propodonotum smooth; setal pattern of propodonotal region arranged 3-2-1; propodonotal shield bearing bases of setae vi, ve, si and c1; Etymology: The name refers to the order name of the host -Suliformes, and Syringophilus -type genus of the family Syringophilidae.

Remarks
This new genus is morphologically close to the monotypic genus Procellariisyringophilus Schmidt and Skoracki, 2007.In females of both genera, the movable chericeral digits are edentate; the peritremes are M-shaped; the stylophore is constricted posteriorly; idiosomal setae are stout and strongly ornamented; the hysteronotal shield is absent; the pygidial shield is present; the genital setal series is represented by 1 pair of setae; the pseudanal setal series with 2 pairs of setae, and the coxal apodemes I are weakly divergent.Sulisyringophilus differs from Procellariisyringophilus in the following features: in females of Sulisyringophilus, the lateral hypostomal teeth and leg setae vsII are present.In females of Procellariisyringophilus, the lateral hypostomal teeth and leg setae vsII are absent.Furthermore, the new genus can be easily distinguished from Stibarokris Kethley, 1970, which females also possess strongly ornamented idiosomal setae and lateral hypostomal teeth, by the presence of only 1 pair of genital setae (vs. 2 pairs in Stibarokris).
Site in host: Quills of contour feathers.
Type material deposition: Female holotype and most paratypes will be deposited in the AMU, except four female paratypes in the NHMD.
Site in host: Quills of secondaries.
Type material deposition: Holotype and most paratypes will be deposited in the AMU, except 5 female and 2 male paratypes in the NHMD.

Remarks
Charadriphilus lymnocryptes n. sp. is morphologically similar to Ch. ludmilae Bochkov and Chystiakov, 2001 found on the Eurasian woodcock Scolopax rusticola Linnaeus (Scolopacidae) from Russia (Bochkov and Chystiakov 2001).In females of both species, setae si are distinctly longer than vi; each medial branch of the peritremes has 3 or 4 chambers, the propodonotal shield is concave on the anterior margin; all coxal fields are apunctate, and fan-like setae of legs III and IV have 6-8 tines.This new species differs from Ch. ludmilae in the following features: in females of Ch. lymnocryptes, the infracapitulum is apunctate; each lateral branch of the peritremes has 9 chambers, and the lengths of setae ve and si are 35-45 and 70-75, respectively.In females of Ch. ludmilae, the infracapitulum is densely punctate; each lateral branch of the peritremes has 14-15 chambers, and the lengths of setae ve and si are 65 and 130, respectively.
Material examined: 18 females and 5 males from quills of contour feathers from Calidris maritima (Charadriiformes: Scolopacidae), Nólsoy, Faroe Islands, 27 May 1996, mites collected by Simon Haarder, bird obtained by Jens-Kjeld Jensen -all specimens are deposited in the AMU, except 8 females and 3 males in the MNHD. 10 females and 2 males from quills of upper wing coverts from same host species; Nólsoy, Faroe Islands, 15 April 1996 -all specimens are deposited in the MNHD.
Material examined: 11 females and 1 male from quills of secondaries from Rissa tridactyla (Charadriiformes: Laridae), Nólsoy, Faroe Islands, 28 December 2007, mites collected by Simon Haarder, bird obtained by Jens-Kjeld Jensen.All specimens are deposited in the AMU, except 4 females in the MNHD.

Prevalence
A total of 31 species and 75 specimens of aquatic birds from the Faroe Islands were investigated for quill mites during this study (Table 1).Generally, only a few specimens of each bird species were examined for quill mites.Quill mites were found on five bird specimens (6%), a finding consistent with reports indicating a generally low prevalence of quill mites in avian wild populations (e.g.Skoracki et al., 2010;Skoracki, 2011).However, aquatic birds have received very little attention regarding the prevalence and intensity of quill mite infestations.Both examined specimens of the purple sandpiper (Calidris maritima) were infested by the quill mite Niglarobia ereuneti Kethley, 1970, albeit in two different microhabitats, whereas only one specimen of the northern gannet (Morus bassanus) was sampled for quill mites.Quill mites were recovered from one specimen of the jack snipe (Lymnocryptes minimus), out of three examined.Only one of the black-legged kittiwake (Rissa tridactyla) was found to harbour quill mites.This specimen was caught in December 2007, while the remaining kittiwakes in this study were obtained in July 2014 (1 specimen) and January 2024 (18 specimens).Further examination of additional bird specimens is imperative to attain a comprehensive understanding of the actual occurrence status of these underexplored mites on aquatic avifauna.Finally, future investigations could focus on elucidating the relationships between the presence of quill mites and seasonal fluctuations, as well as the health status, age, and sex of the host avian species.

Table 1
Examined bird species from the Faroe Islands and their quill mites