Microparmarion exquadratus Schilthuizen et al., 2019

Schilthuizen, Menno, Clavera, Anna Pazos, Khoo, Min Sheng, Bondar, Carin A., Elder, Charles H. S., Bouma, Aglaia M., Eddington, Taly D., Reisinger, Christian, Cosentino, Emanuela, Rossato, Marzia & Delledonne, Massimo, 2019, Bringing the lab to the field: a new lowland Microparmarion semi-slug (Gastropoda: Ariophantidae) described and DNA-barcoded in the forest, Journal of Molluscan Studies 85, pp. 35-40 : 36-38

Microparmarion exquadratus Schilthuizen et al. , new species

( Figs 2–4 )

Types: Holotype: adult in 70% ethanol ( SP13559 ). Paratypes: 1 subadult ( SP13551 ), dissected and subsampled for DNA, in 70% ethanol; 3 subadults ( SP13552–SP13554 ) in 100% ethanol, subsampled for DNA; 4 adults ( SP13555–SP13557 , SP13561 ) in 70% ethanol; 1 adult SP13560 dissected, in 70% ethanol. All material from vicinity of park headquarters, Tawau Hills Park , Sabah, Malaysia, 4°23.959 ′ N, 117°53.358 ′ E; 240 m asl, collected at night, 6–7 March 2018; leg. taxon expedition participants.

ƶoobank registration: http://zoobank.org/B64843A4-7A74-4D07- AD96-96C160E6D80B

Etymology: The name was chosen at a naming and voting session during the taxon expedition and refers to the ‘squad’ of participants that jointly sampled this species during night-time walks in the forest. The taxonomic authority for this species is attributed to all authors of this paper. Following Article 51 C of the Code ( ICZN, 1999), the species can be referred to as Microparmarion exquadratus Schilthuizen et al., 2018 , provided the full citation of this publication appears in the bibliography or elsewhere in the referring work.

Diagnosis: Among Microparmarion species of Borneo, M. ex quadratus is characterized by small size (less than half the size of M. pollonerai and M. simrothi ), three dark longitudinal stripes on head (shared with M. simrothi , but lacking in M. pollonerai and M. litteratus), dark dorsal stripe on tail, kink in dart sac (shared with M. pollonerai ) and reduced receptaculum.

Description: Exterior in adult, preserved specimens ( Fig. 2A–D ): Body length 18–21 mm. Shell 8.5–9 mm long, 5 mm wide. Body dull, greyish pink, 3 black dorsal longitudinal stripes, separated by 2 white stripes starting immediately caudal of black eye tentacles and ending ventrally of frontal edge of mantle. Lateral black stripes are half breadth of dorsal stripe. Mantle may also be dull greyish pink, with dark grey mottling. Keeled tail approximately one-third total body length (5–6 mm in adults), with 1 black dorsal stripe. Margin of foot has vertical, dark grey striated pattern. Sole of foot off-white. Tail with caudal horn, not very prominent. Shell semi-transparent, smooth, thin, pale yellow, with faint trace of spiral on right side, approximately 2 whorls. Genital opening visible on right side as short vertical slit. Dark pattern on mantle of 2, nearly continuous lines encircling shell, which are separated by pale greyish-pink ridge with about 10 dark spots.

Live specimens ( Fig. 2E–J ): Colour dull orange with deep brown pattern. Mantle lobes meet along curved suture, bulging to left, lying left of midline of body. Shell lobes with slight granulation. Frontal part of mantle with slight longitudinal ridges. Caudal horn triangular, slightly longer than wide, pointing caudally. Eye tentacles, when fully extended, as long as shell.

Genitalia ( Figs 3 , 4 ): Atrium wide. Penis doubly folded into Z-shape, proximally narrow (one-quarter width of atrium), gradually doubling in width, then narrowing to original width distally. Penis sharply folding back on itself as a very narrow tube until half length of proximal part of penis, then folding, broadening, eventually tapering into vas deferens. When following the vas deferens from where it departs from penis, it remains detached from free oviduct until level with middle of dart sac. Vagina short, receptaculum reduced, externally invisible, only discernible after clearing in clove oil. Free oviduct irregularly looped and coiled. Dart sac long, equivalent to combined length of vagina and free oviduct, doubly folded into a Z-shape. Basal portion of dart sac is narrow, containing the dart; middle portion half as long as basal portion, externally somewhat granulate; distal portion inflated, sausage-shaped, 3 times as long as wide, flattened on one side. Dart straight, with gently tapering point, possibly with several low, longitudinal flanges; crown twice as wide as dart.

DNA barcode: We obtained 3 sequences for the COI DNAbarcoding region. These sequences were identical, with the following exceptions when compared with the generated consensus (i.e. the most frequent nucleotide at each position among the three sequences). The sequence for SP13554 lacked a TA dinucleotide at the 5’ end, which might be an artefact; we have replaced these nucleotides by unknown bases in the BOLD sequence. The sequence for SP13553 had an A instead of G at position 268, a T instead of C at position 628, and a C instead of T at position 637. The three sequences form a well-supported clade in the tree ( Fig. 5 ), which is clearly separated (by>10% sequence divergence) from all other Microparmarion COI sequences available (all from Sabah as well). Sequences for M. litteratus were not available. Microparmarion exquadratus has been assigned BIN ADM3588.

Distribution: So far only known from lowland dipterocarp forest around the headquarters of Tawau Hills Park (c. 240 m asl). It is surprising to find a Microparmarion at such a low elevation, since the genus is normally found in montane forest—it is therefore also not sympatric with any other known Microparmarion species. There is a slight possibility that the population is nonindigenous to the lowlands, since the park’ s botanical garden (stocked with plants from elsewhere in the park, including the highlands) is nearby. The semi-slug may thus have been introduced from a higherelevation habitat in the surrounding area. However, we failed to find the species on nearby Mount Lucia (1,300 m asl) and we also did not find it in the botanic garden itself, so we tentatively conclude that it is indigenous and possibly widespread throughout Tawau Hills Park. To confirm this, nocturnal sampling will have to be carried out in other parts of the park.

Remarks: In colour pattern, M. exquadratus is somewhat similar to a Microparmarion species found at an elevation of 1,200 m asl in Long Pa Sia, southwestern Sabah, and also to a species photographed (but not collected) at 1,000 m asl in Penrissen, Sarawak ( Schilthuizen, 2017). However, it is unlikely to be conspecific with either, because it differs in colour pattern (the Penrissen specimen has two, rather than three, head stripes, and the Long Pa Sia specimen lacks the black markings on the mantle lobes) and is larger in size. For the time being, therefore, we consider the M. exquadratus to be restricted to Tawau Hills Park. Our phylogenetic reconstruction ( Fig. 5 ), although primarily intended to assess the genetic distinctness of the new species, also suggests that the genus Microparmarion consists of multiple clades that are not fully congruent with named species. We therefore recommend that the genus be subjected to a formal revision.

We must also stress that our work was conducted under several limitations and constraints. It was part of a full 10-day field course schedule, carried out by untrained citizen scientists in a field station with limited equipment and erratic electricity supply. Specimens could not be exported. Consequently, the extent of our work is less than is customary for descriptions of new semi-slug species: we sequenced only three individuals and dissected only one. Also, all individuals were obtained from a very small geographic area. Nonetheless, the genetic and morphological features are suffi- cient to recognize the species unambiguously.

Figures

Figure 2. External morphology of (presumably) adult Microparmarion exquadratus n. sp. A preserved individual (syntype SP.13561) showing left lateral (A), right lateral (B), ventral (C) and dorsal (D) views. Six of the syntypes (E–J) in living state as photographed in the field in Tawau Hills Park, Sabah.

Figure 3. Genital system of Microparmarion exquadratus n. sp. (syntype SP13560).

Figure 4. Dart sac of Microparmarion exquadratus n. sp. (syntype SP13560), cleared with clove oil and showing dart (shaded) in position.

Figure 5. Phylogenetic reconstruction for Bornean Microparmarion based on COI barcode locus, with Parmarion as outgroup. Numbers on nodes are Bayesian posterior probabilities. Registration numbers in parentheses: RMNH, Naturalis Biodiversity Center, Leiden, The Netherlands; SP, Sabah Parks collection; FJ481180 is a GenBank accession number. Scale bar indicates substitutions per site.