Lohmannella njoerdri, Bartsch, 2020

Bartsch, Ilse, 2020, Lohmannella (Acari, Halacaridae) from a cold-water coral reef off Norway, description of two new and a list of North Atlantic species, Zootaxa 4722 (3), pp. 277-286 : 278-280

Lohmannella njoerdri spec. nov.

( Figs 1–16 )

Material examined. Holotype male, ZMH-A0002058, Sula Ridge, 64°05’N, 8°02’E, 285 m, 31 July 1999, POSEIDON Cruise 254, submersible dive JAGO 22 J1-10; coll. W. Michaelis and T. Pape.

Additional material. One female, one larva which both are expected to belong to Lohmannella njoerdri, Sula Ridge , 64°05’N, 8°02’E, 285 m, 31 July 1999, POSEIDON Cruise 254; coll. W. Michaelis and T. Pape .

Diagnosis. Length of male 310 µm. Surface of plates without marked ornamentation.AD hexagonal, major part of PD rectangular. OC with two corneae. Length to width of AD and PD about 1:1.2 and 1:0.8, respectively. Length AD:PD 0.6:1. Gland pores vestigial. Opposing margins of AE and GA truncate. GA with two pairs of outlying and further 45 pgs close around GF. Length of gnathosoma 0.6 times that of idiosoma. Rostrum longer than gnathosomal base. P-2 5.8 times longer than wide. All legs shorter than idiosoma. Tibiae I to IV with 6, 3, 1, 3 bipectinate ventral setae. Tarsi I to IV with 4, 4, 4, 3 dorsal setae and 2, 1, 2, 1 bipectinate ventral setae. Claws slender.

Description. Idiosomal length of holotype male 310 µm, its width 230 µm. Surface of dorsal and ventral plates densely covered by minute papillae, else no marked ornamentation or porose areolae present. AD hexagonal, length 105 µm, width 127 µm, L:W about 1:1.2. Anterior and posterior margin truncate, lateral margins arched, AD widest about mid-way between anterior and posterior margin. OC rhomboidal, lateral and medial margins parallel; length 77 µm, width 47 µm. Each OC with two corneae. Length of PD 165 µm, width 134 µm, L:W equalling 1:0.8; anterior margin of PD truncate, lateral margins mostly parallel. Posterior margin slightly protruding ( Fig. 1 ). Length AD:PD 1:1.6. All gland pores vestigial. Pair of ds-1 60 µm long, situated at 0.3 in relation to length of AD. Pairs of ds-2, ds-3 and ds-4 short, about 8 µm long, arising within striated integument, short ds-5 on PD at 0.5, ds-6 on anal cone.

Length of AE 112 µm, width 218 µm. Plate with three pairs of ventral and one pair of marginal setae. Marginal setae shorter than ventral setae. Length of PE 150 µm. Each plate with one dorsal and one marginal seta anterior to insertion of leg III and three ventral setae. Length of GA 158 µm, width 118 µm. Anterior part of plate almost rectangular and its anterior margin truncate ( Fig. 2 ). Length of GF 40 µm, width 26 µm, distance from anterior margin of GF to that of GA about twice length of GF. Forty-five pgs close around GO, another two pairs outlying. Genital sclerites with four pairs of short, furcate sgs ( Figs 3 and 4 ). Spermatopositor, 63 µm in length and 66 µm in width, extending beyond GF; anterior and posterior arms at about the level of anterior margin of GF.

Length of gnathosoma 182 µm or 0.6 times of idiosomal length. Length of rostrum 105 µm, basal and apical maxillary setae at 0.6 and 0.9 of length of rostrum ( Fig. 5 ). Length of palps 130 µm. Length of P-2 98 µm; P-2 5.8 times longer than wide. P-4 slightly shorter than P-1 and about ¼ of length of P-2. P-3 with spiniform process (but no spine). P-4 with one spur-like and three slender setae, two of the latter at almost the same level; apically with dorsolateral solenidion ( Figs 6 and 7 ); P-4 ending with a 5 µm-long blunt, apically delicately dentate spine (claw).

Legs shorter than idiosoma, segments almost cylindrical. Length ratios idiosoma:leg I and leg IV about 1:0.7 and 1:0.8. Tibiae of legs I to IV shorter than these legs telofemora. Tarsi I and II slightly shorter ( Figs 8 and 9 ) and tarsi III and IV distinctly longer than the legs telofemora ( Figs 10 and 11 ). Chaetotaxy of legs I to IV (apical eupathidia and pas of tarsi omitted): leg I, 1, 3, 6–7, 8–7, 10–11, 6; leg II, 1, 3, 6, 7, 9, 5; leg III, 1, 3, 4, 4, 7, 6; leg IV, 1, 3, 4, 4, 6, 4. Genu I to IV with 3–4, 1, 0, 1 bipectinate ventral setae, tibiae I to IV with 6, 3, 1, 3 such ventral setae. Tarsi I to IV with 4, 4, 4, 3 dorsal setae and 2, 1, 2, 1 bipectinate ventral setae. Solenidion on tarsus I 11 µm long and in dorsolateral position ( Fig. 12 ), that on tarsus II 9 µm long and in dorsomedial position ( Fig. 13 ). Tarsi I and II apically each with two ventral eupathidia, doubled lateral and single medial pas. Lateral pas on tip of tarsus III a single, medial pas a doubled seta. Tarsus IV with pair of short, bristle-like pas. Tarsi III and IV without ventral eupathidia ( Figs 14 and 15 ). Paired claws on tarsi remarkably slender, claws I almost 10 times longer than wide, length 25 µm, width slightly less than 3 µm wide; claws with very delicate accessory process.

A sample held remnants of a female (obviously dead prior preservation), its gnathosoma, all claws and major parts of the leg segments as well as almost half of PD and GA are lacking. Though a reliable identification is not possible that mite is expected to be the female of L. njoerdri . Length of idiosoma about 314 µm. Shape of AD, OC and PD the same as in the male, each OC with two corneae; surface of plates delicately papillate. Anterior and middle part of GA rectangular but anteriorly with rounded corners ( Fig. 16 ). One half of GA (posterior most part lacking) with 8 pgs. Genital sclerite with four slender sgs. Internal genital acetabula small, situated as shown in Fig. 16.

A larva in the sample, which also may belong to Lohmannella njoerdri , has an idiosomal length of 179 µm. The PD of the larva is longitudinally divided.

Etymology. The species is dedicated to Njoerdr (Njörðr) who in the Nordic mythology is a god of the sea and oceans with the ability to calm the sea. Lohmannella njoerdri is expected to live in an area sheltered from strong currents or wave actions.

Remarks. Now 10 records of marine Lohmannella species are known from the north-eastern Atlantic and its adjacent basins (freshwater species excluded), namely L. falcata ( Hodge, 1863) , L. kervillei ( Trouessart, 1894) , L. multisetosa Bartsch, 1986 , L. norvegica Viets, 1927 , L. nudipes Bartsch, 1977 , L. reducta Bartsch, 1986 , L. rustica Bartsch, 1977 , L. steueri Viets, 1940 , L. subfalcata Bartsch, 2003 , and L. njoerdri . The description of another species will follow.

At a first glance, the just mentioned 10 species are rather similar in size and general outline of the idiosoma and gnathosoma and shape of the plates. If experienced, L. njoerdri is quickly distinguished from the other species because of the unusual slender claws.

Other differences are: Lohmannella falcata has four dorsal setae on tarsus IV, L. njoerdri three; L. kervillei and L. norvegica have a compact gnathosoma, rostrum and palps are shorter than the gnathosomal base; in L. multisetosa the ventral margin of P-2 is distinctly convex, in L. njoerdri it is straight, furthermore, the female of L. multisetosa has numerous pgs and enlarged genital acetabula, whereas, if the female described above belongs to L. njoerdri , the genital acetabula as well as the number of pgs are small; L. nudipes is characterized by the absence of bipectinate setae on its tarsi; L. reducta and L. steueri bear four and five bipectinate ventral setae on tibiae I, respectively, and L. rustica a single bipectinate ventral seta on tarsus I, whereas L. njoerdri has six bipectinate ventral setae on tibia I and two on tarsus I; L. subfalcata is characterized by its short PD which is only slightly longer than the AD, length AD:PD equalling 0.8:1 but in L. njoerdri 0.6:1.

Biology. The claws on the tarsi of L. njoerdri are long and more slender than in the majority of Lohmannella species. Slender claws are generally expected to be correlated with a life in a soft surface ooze. An example, Halacarus longiunguis Police, 1909 has very slender claws on the tarsi of the walking legs II, III and IV. The species has been collected only twice, namely in the Golfo di Napoli ( Italy) and the Golfe du Lion ( France), both times taken at about 100 m depth with a sledge meant for studies of the hyperbenthos/plankton ( Police 1909; Bartsch 2007b). Due to the long claws, the mite is expected to find several stepping points which prevent it from sinking into deeper sediment layers ( Bartsch 2007b). In contrast to Halacarus longiunguis , the legs of Lohmannella njoerdri are short, not meant to raise the mite above the ground. The mode of life of L. njoerdri is not known.

Figures

FIGURES 1–9. Lohmannella njoerdri nov. spec., male, 1, idiosoma, dorsal; 2, idiosoma, ventral; 3, genital area and spematopositor; 4, two of posterior subgenital setae; 5, gnathosoma, lateral; 6, apical part of palp, lateral; 7, apical part of palp, medial; 8, leg I, medial; 9, leg II, medial. (sgs, subgenital setae) (Scale bars in Figs 1–3, 5–9 = 50 µm, in Fig. 4 = 10 µm)

FIGURES 10–16. Lohmannella njoerdri nov. spec., 10, leg III, medial, male; 11, leg IV, medial, male; 12, tarsus I, lateral, male (medial setae in broken line, medial claw omitted); 13, tarsus II, medial, male (lateral setae in broken line, lateral claw omitted); 14, tarsus III, lateral, male (medial parambulacral setae and claw omitted); 15, tip of tarsus IV, lateral, male (medial parambulacral seta and claw omitted); 16, part of genitoanal plate, female (broken line indicates rupture in plate). (Scale bar = 50 µm)