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The tricky business of identifying invertebrates

Identifying invertebrates is challenging. For many taxa you require specialised knowledge and for this reason many taxonomists focus on only a few groups. Moreover, speciment preparation may be required, for example clearing the body so that transmission microscopes can reveal structures in or on the body cuticle, for example the presence of pores, setae, or organs such as the post-antennal organ in Collembola. 

Many species have been missidentified in the Svalbard literature leading to confusion in which species are actually present (see Coulson et al. 2014 for a summary) and an updated species inventory is underway. 

Moveover, changes in taxonomy mean that species may be transferred between genera and even families resulting in more confusion, particularly in older reference works. Finally some species described from Svalbard during the early half and the 1900’s have not since been recovered and type material may be lost meaning confirmation of these species is currently not possible. 

Keys to the invertebrates focussing on the mites and the insects are currently under preparation and are being used, and tested, with AB-206 and 201. Excellent keys for the Collembola (The Collembola of Fennoscandia and Denmark, Arne Fjellberg) already exist.

The following text is taken from Gwiazdowicz & Teodorowicz 2017 and is the recognised description of H. coulsoni and the characters used to distinguish this species from other species of Halolaelaps. This indicates the skill and knowledge often required to identify microarthropods to species and why many taxonomists specialise in one or two groups.

Professor Dariusz Gwiazdowicz is one of several taxonomists working to reassess the invertebrate fauna of Svalbard, in this case the gamasid (Mesostigmata) fauna.


Halolaelaps coulsoni n. sp.

Zoobank: A137B515-F6D2-4DCF-8AB7-1B325D60923B

Specimens examined—Holotype. Female. Spitsbergen, Pyramiden (78°40’N, 016°27’E), kittiwake nest detritus, July 16 2012, coll. S.J. Coulson and D.J. Gwiazdowicz; Paratypes: in the same location and date as holotype, two deutonymphs, coll. S.J. Coulson and D.J. Gwiazdowicz; three females, one deutonymph, four males in the same location, September 13 2012, coll. S.J. Coulson and A. Sjöblom.

Female (n=4), idiosoma oval, 690 – 730 m in length and 430 – 450 m in width. Dorsal idiosoma — On dorsal side two shields of irregular edges – podonotal length 280 – 310 and width 340 – 380 m and opisthonotal (280 – 310 [1] 300 – 340 m) (Fig. 1A). Podonotal shield bearing 22 – 23 pairs of simple setae (6 per row “j”, “z” and “s”, and 4 or 5 setae in row “r”). Accordingly opisthonotal shield – usually with 14 pairs of simple setae. The total number of setae on both shields varies and this fact has been underlined in the section “Morphological variation”. Lengths of setae on podonotal shield also vary, for example, that of “j” row are median in length (25 – 28 m), while posterior setae in rows “z” and “s” (z5, z6, s5, s6) are noticeably longer (47 – 50 m). The shortest are z1 (7 – 11 m). Fine areolate ornamentation covers the shield in the area between “j” and “z” rows. Opisthonotal shield with a characteristic irregular incision in the middle (45 – 55 m), starting from the anterior edge and running between setae J1-J1 and J2-J2. Similar to setae on podonotum, setae on opisthonotum differ in length e.g. J1-J3 are shorter (34 – 38 m), slightly longer are J5, Z1, Z2 (41 – 45 m), and the longest are Z4, S4 (57 – 58 m). The anterior part of the shield between setae J1, Z1, S1 and J2, Z2, S2 is covered with delicate areolate ornamentation. Ventral idiosoma — Tritosternum with elongate trapezoidal base (25 – 28 m) and fine lightly pilose laciniae (42 – 47 m) (Fig. 2A, NOTE: FIGURES NOT PRESENTED HERE. REFER TO GWIAZDOWICZ & TEODOWROWICZ 2017 ). A pair of lightly sclerotized pre-sternal plates fused with sternal shield.

Sternal shield rectangular (105 – 115 [1] 80 – 90 m) with three pairs of simple setae st1-st3 (21 – 25 m) and two pairs of pores (Fig. 1B). Pair of setae st4 (29 – 32 m) on soft integument. Epigynial shield peculiar (105 – 115 [1] 70 – 75 m); epigynial setae on the edges of a shield, simple (30 – 32 m); beneath  epigynial (genital) shield, between setae JV1 a ZV1 lies a pair of narrow platelets (18 – 21m). Three pairs of free narrow in shape endopodal plates present between coxae I/II, II/III and the largest between III/IV. Peritreme 260 – 280 m long mounted on a broad peritrematal shield. Stigma on the horizontal line of coxae IV. Posteriorly to peritrematal shield lie two pairs of oval metapodal plates, a bigger outer platelets (21 – 25 [1] 10 – 12) m and smaller inner platelets of 13 – 15 [1] 5 – 6 m. Anal shield oval in shape (125 – 135 [1] 112 – 115 m) with three typical circum-anal setae (45 – 48 m). Between genital and anal shield are 8 – 9 pairs of simple setae (33 – 40 m). Gnathosoma — Corniculi short and robust, internal malae short, smooth. Palp coxal setae short (21 – 23 m), internal posterior setae h3 longer (30 – 32 m), external posterior setae h2 shorter (13 – 15 m) and rostral setae h1 longer (28 – 31 m). Hypostome with 8 transverse rows of denticles (8 – 15 denticles per row), denticles in each row irregular in size, and spacing (Fig. 2D). Tectum rounded with multiple small denticles (Fig. 2C). Chelicera with first and second segments slender, elongate (38 – 40 m); fixed digit with two triangular distal teeth, pilus dentilis short, spine-like, dorsal cheliceral seta thick, prostrate. Movable digit slender (37 – 41 m), with three distal triangular teeth (Fig. 2B). Palps 80 – 85 mlong (Fig. 2E, F, G), palp apotele three-tined. Legs — Variable in length, pretarsi equipped with claws and rounded pulvilli: I – 420 – 440 m, II – 340 – 360 m, III – 350 – 370 m, IV – 430 – 450 m. Chaetotaxy of legs is peculiar for genus Halolaelaps: leg I (coxa 2, trochanter 6, femur 13, genu 12, tibia 11), leg II (2, 5, 11, 10, 10), leg III (2, 5, 6, 9, 8), leg IV (1, 5, 6, 9, 8) (Fig. 3A, B, C, D).

Characteristics to distinguish Halolaelaps coulsoni sp. nov. (mesostigmatid mite) (Gwiazdowicz & Teodorowicz 2017) illustrating the complexity of species determination.
Example identification characters used to determine Willemia similis Mills 1934 illustrating the challenges. 
© Ávila-Jiménez, M.L
Example identification characters used to determine Ceratophysella longispina (Tullberg 1876)
© Ávila-Jiménez, M.L
The type locality for H. coulsoni. Nest debris and kittiwake guano under the abandoned buildings in Pyramiden. Here shown collecting this debris for later examination by Dariusz Gwiazdowicz and Ewa Teodorowicz.
Photo Steve Coulson
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