Arion intermedius

Arion intermedius View in CoL

We collected eight specimens. They were adult and about 20 mm long, up to 23 mm when fully extended. The general appearance when alive was of a pale-yellowish or light-greyish body with faint lateral bands and dark head and tentacles ( Figs 1 View Figure 1 , 2 View Figure 2 ). All specimens exhibited the diagnostic prickly appearance generated by the pointed tubercles, although some individuals more so than others. Most also showed one or more tiny black dots above the foot fringe near the head (another character known only in this species), but these were not apparent in two of the living specimens. The mucus was yellow and dense.

Preserved specimens were light-yellowish or cream with smooth (i.e. not prickly) skin ( Fig. 3A View Figure 3 ). Lateral bands were generally more visible on preserved individuals than on living specimens. Dark dots above the anterior foot fringe were also apparent in most preserved specimens, although they could be faint or even absent ( Fig. 3B View Figure 3 ). For anatomical confirmation of identity, it was already informative that fully developed genitalia were found in animals of this size, ruling out most other Arion species, which mature at a larger size. Other distinctive anatomical characters were the large and round bursa copulatrix with a short, thick peduncle, and the short and tubular oviductus ( Fig. 3C–E View Figure 3 ).

In Hungary we collected A. intermedius specimens in October and they laid eggs at the beginning of November. The eggs were 2–3 mm in diameter, white, and were laid in clutches typically of about 10 eggs ( Fig. 4A View Figure 4 ). Freshly hatched specimens were about 3 mm long. Hatchlings and juveniles were similar in external appearance to adults, and the prickly appearance was visible from hatching ( Fig. 4B View Figure 4 ) .

The only known locality of A. intermedius in Hungary remains the Kámoni Arborétum, Szombathely ( Fig. 5A View Figure 5 ), outside but close to the part open to the public. We found the slugs at three locations within 50 m of each other on both sides of the Gyöngyös stream, which originates over the border in Austria. The slugs were found under the bark of decaying logs amongst deep leaf litter in woodland of mainly Alnus glutinosa and Acer platanoides ( Fig. 6A View Figure 6 ).

The partial-COI sequences of two individuals from this locality were identical. The most similar haplotype in GenBank differs by just one nucleotide and had been found in A. intermedius from two distant sites in the eastern USA (GenBank EU382743.1 and MG813885.1).