Laspionchis bourkei Dayrat & Goulding

Dayrat, Benoit, Goulding, Tricia C., Khalil, Munawar, Comendador, Joseph, Xuan, Qu ảng Ngo, Tan, Siong Kiat & Tan, Shau Hwai, 2019, A new genus of air-breathing marine slugs from South-East Asia (Gastropoda, Pulmonata, Onchidiidae), ZooKeys 877, pp. 31-80 : 53-59

Laspionchis bourkei Dayrat & Goulding sp. nov. Figs 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29

Holotype.

AUSTRALIA • holotype, designated here, 23/18 mm [1657 H]; Northern Territory, Darwin; 12°33.228'S, 130°52.580'E; 14 Aug. 2012; B Dayrat and party leg.; st 61, on the right side of the road just before bridge to Channel Island, Avicennia mangrove with sandy mud; NTM P.57615.

Additional material examined.

See below for each subspecies.

Distribution

( Fig. 7 ). Australia (Northern Territory) for L. bourkei bourkei . Indonesia (Ambon) for L. bourkei lateriensis . Indonesia (Sulawesi, Sumatra), Malaysia (Peninsular Malaysia), Singapore, Philippines (Bohol), and Vietnam for L. bourkei matangensis .

Habitat

( Figs 17 , 26 ). Laspionchis bourkei is found on mud, hard or soft, in open or dense mangrove forests. It can be locally common across its entire distribution.

Etymology.

Laspionchis bourkei is dedicated to Adam Bourke, from Darwin, Northern Territory, Australia, a very knowledgeable mangrove expert and great naturalist, who generously accompanied us in the field around Darwin and showed us good collecting sites.

Diagnosis

(Table 3 ). Externally, Laspionchis bourkei cannot be distinguished from L. boucheti . Internally, however, the long retractor muscle of the penis inserts at the posterior end of the visceral cavity in L. boucheti while the retractor muscle is short (and inserting in the first third of the visceral cavity) in L. bourkei bourkei and vestigial or absent in L. bourkei lateriensis and L. bourkei matangensis . Also, additional, distal, retractor muscle fibers are present in L. boucheti but absent in L. bourkei .

Color and morphology of live animals

( Figs 18 , 27 ). Live slugs are covered with mud and their dorsal color can hardly be seen. The background of the dorsal notum is brown, light to dark, homogenous or mottled with darker or lighter areas. The color of the foot is a mix of gray (light or dark) and yellow, as is the color of the hyponotum. The color of the ventral surface (foot and hyponotum) can change rapidly, especially when slugs are disturbed. The ocular tentacles are brown (variable from light to dark) and short (a few millimeters). The number of papillae with dorsal eyes is variable (between five and ten, on average) and they mostly are on the central part of the notum.

Digestive system

( Figs 19 , 20 , 25 ). Examples of radular formulae are in Table 4 . Radulae measure up to 2.9 mm in length (see below for each subspecies). The intestine is long, narrow, and the intestinal loops are exactly between types I and II, i.e., with a transitional loop on average oriented at 6 o’clock, acknowledging minor individual variation ( Figs 1 , 19 ).

Reproductive system

( Fig. 21 ). There is a narrow receptaculum seminis (caecum) along the hermaphroditic duct. The large, ovate-spherical spermatheca connects to the oviduct through a narrow and short duct. The oviduct is straight, slightly larger than the deferent duct or of a similar diameter.

Copulatory apparatus

( Figs 22 - 24 , 28 , 29 ). The length of the flagellum of the accessory penial gland varies among individuals but it is always heavily coiled. The hollow spine of the penial gland is narrow, straight, elongated. Its base is conical. Its length varies from 0.35 mm to 1 mm (see below for each subspecies). The penial sheath is narrow and short. The penial sheath protects the penis for its entire length. The beginning of the retractor muscle marks the separation between the penial sheath (and the penis inside) and the deferent duct. The retractor muscle is short (as long as the penial sheath) and inserting in the first third of the visceral cavity, vestigial (and free with no attachment), or absent (see below for each subspecies). There is no additional, distal, retractor muscle fibers. The deferent duct is highly convoluted. Inside the penial sheath, the penis is a narrow, thin, elongated, hollow tube, with numerous and densely-arranged (next to each other) hooks in its distal part. Penial hooks are pointed and measure from 15 to 45 μm (see below for each subspecies). When the penis is retracted inside the penial sheath, the hooks are inside the tube-like penis; during copulation, the penis is everted like a glove and the hooks are then on the outside.

Remarks.

A new species name is needed because no existing name applies to the species described here, based on the examination of all the type specimens available in the Onchidiidae , a careful study of all the original descriptions, and our ongoing taxonomic revision of each genus of the family ( Dayrat et al. 2016, 2017, 2018, 2019; Dayrat and Goulding 2017; Goulding et al. 2018a, b, c).

Laspionchis bourkei is divided in three distinct units of which the reciprocal monophyly is highly-supported in both mitochondrial and nuclear analyses (except for L. bourkei matangensis , unresolved using nuclear data). The fact that the three units within L. bourkei are distinct taxa means that they should be recognized and named. Even though we could have ranked them as species, we decided to rank them as sub-species for three main reasons.

(1) The three units within L. bourkei are cryptic externally and internally. Some minor anatomical differences seem to exist but which can hardly be used for identification (Table 3 ).

(2) Ranking the three units within L. bourkei as subspecies rather than species is more in agreement with the genetic distances observed between L. boucheti and L. bourkei . Indeed, the distance gap between L. boucheti and L. bourkei is between 2.5% and 7.5%, while the distance gap between the three L. bourkei units is between 2.5% and 3.9%, clearly suggesting that the three L. bourkei units are much less divergent (their COI sequences) than L. boucheti and L. bourkei , supporting their ranking as subspecies. Distance values should not necessarily be compared from one genus to another, but they can be compared between very closely related species.

(3) As of today, the three units within L. bourkei are allopatric which means that a doubt remains as to whether the three units are reproductively isolated or not. Overall, the three units within L. bourkei probably are relatively young taxa which diverged recently, explaining that they are cryptic internally and that their COI sequences are less divergent than the COI sequences between L. boucheti and L. bourkei .

Figures

Figure 1. Intestinal loops, dorsal view A, B Type I C, D Type II E-H Between types I and II. Small black arrows show the direction of the intestinal transport. The clockwise loop is in blue. The counterclockwise loop is in yellow. The transitional loop (between clockwise and counterclockwise loops) is in green. Red arrows indicate the orientation of the transitional loop. A Type I, with a transitional loop oriented at 3 o'clock, redrawn from Plate (1893: pl. 8, fig. 29) B Type I, with a transitional loop oriented at 3 o'clock, Wallaconchis sinanui (from Goulding et al. 2018: fig. 8 D) C Type II, with a transitional loop oriented at 9 o'clock, redrawn from Plate (1893: pl. 8, fig. 31) D Type II, with a transitional loop oriented at 9 o'clock, Paromoionchis tumidus (from Dayrat et al. 2019: fig. 12 A) E Between types I and II, with a descending transitional loop at 7 o'clock, holotype, Laspionchis boucheti, Australia, Northern Territory, [1688 H] (NTM P. 57614) F Between types I and II, with a descending transitional loop at 6 o'clock, L. boucheti, Australia, Northern Territory, [1681] (NTM P. 57612) G Between types I and II, with a descending transitional loop at 6 o'clock, L. boucheti, Vietnam, [5610] (ITBZC IM 00017) H Between types I and II, with a descending transitional loop at 5 o'clock, L. boucheti, Australia, Queensland, [2612] (MTQ). Scale bars: 1 mm (B), 2 mm (D, E), 5 mm (F-H).

Figure 7. Geographical distribution of the two species of Laspionchis. Distinct colors are used for each subspecies of L. bourkei. The colors used are the same as those used in the phylogenetic trees (Figs 2 - 5). Colored areas correspond to hypothetical geographical ranges based on known records.

Figure 17. Habitats, Laspionchis bourkei A-D L. bourkei bourkei Australia, Northern Territory E L. bourkei lateriensis, Indonesia, Ambon. A Avicennia on sandy mud (st 61, type locality) B same as A C large Sonneratia alba, open forest, soft mud by shore (st 62) D Sonneratia, Rhizophora, and Ceriops mangrove (st 66) E mudflat beside a mangrove and a creek (st 128, type locality).

Figure 18. Live animals, Laspionchis bourkei A-D, G, H L. bourkei bourkei Australia, Northern Territory E, F, I L. bourkei lateriensis, Indonesia, Ambon. A Dorsal view, 20 mm long [1618] (NTM P. 57617) B dorsal view, 21 mm long [1656] (NTM P. 57617) C holotype, dorsal view, 23 mm long [1657 H] (NTM P. 57615) D dorsal view, 19 mm long [1673] (NTM P. 57618) E dorsal view, 12 mm long [2743] (UMIZ 00116) F dorsal view, 17 mm long [2753] (UMIZ 00116) G ventral view, 19 mm long [1659] (NTM P. 57618) H ventral view, 23 mm long [1617] (NTM P. 57617) I ventral view, same as E.

Figure 19. Digestive system, dorsal view, Laspionchis bourkei A-C L. bourkei bourkei, Australia, Northern Territory D Holotype, L. bourkei lateriensis, Indonesia, Ambon E, F L. bourkei matangensis, Peninsular Malaysia. A [1673] (NTM P. 57618) B [1666] (NTM P. 57618) C [1693] (NTM P. 57619) D [6064 H] (UMIZ 00115) E [5959] (USMMC 00056) F holotype, [5958 H] (USMMC 00055). Scale bars: 2 mm (A, C-E), 2.5 mm (B), 1 mm (F). Abbreviations: ddg dorsal digestive gland i intestine pdg posterior digestive gland r rectum st stomach.

Figure 20. Radula, Laspionchis bourkei A, B L. bourkei matangensis, Peninsular Malaysia [5965] (USMMC 00056) C-F Holotype, L. bourkei bourkei, Australia, Northern Territory [1657 H] (NTM P. 57615). A Rachidian and innermost lateral teeth B lateral teeth C rachidian and lateral teeth D rachidian and innermost lateral teeth E lateral teeth F outermost lateral teeth. Scale bars: 10 μm (A, D, F), 30 μm (B), 100 μm (C), 80 μm (E).

Figure 21. Posterior, hermaphroditic (female) reproductive system, Laspionchis bourkei. A Holotype, L. bourkei bourkei, Australia, Northern Territory, [1657 H] (NTM P. 57615) B holotype, L. bourkei lateriensis, Indonesia, Ambon, [6064 H] (UMIZ 00115) C holotype, L. bourkei matangensis, Peninsular Malaysia, [5958 H] (USMMC 00055). Scale bars: 2 mm (A), 1 mm (B, C). Abbreviations: dd deferent duct fgm female gland mass hg hermaphroditic gland ov oviduct rs receptaculum seminis sp spermatheca.

Figure 22. Anterior, male, copulatory apparatus, Laspionchis bourkei. A Holotype, L. bourkei bourkei, Australia, Northern Territory, [1657 H] (NTM P. 57615) B holotype, L. bourkei lateriensis, Indonesia, Ambon, [6064 H] (UMIZ 00115) C holotype, L. bourkei matangensis, Peninsular Malaysia, [5958 H] (USMMC 00055). Scale bars: 1 mm (A), 2 mm (B), 0.5 mm (C). Abbreviations: ag accessory penial gland dd deferent duct ms muscular sac ps penial sheath rm retractor muscle v vestibule.

Figure 23. Penial hooks, Laspionchis bourkei A-D Holotype, L. bourkei lateriensis, Indonesia, Ambon [6064 H] (UMIZ 00115) E, F L. bourkei bourkei, Australia, Northern Territory [1692] (NTM P. 57619). Scale bars: 40 μm (A, E), 20 μm (B), 5 μm (C, D), 4 μm (F).

Figure 24. Spine of the accessory penial gland, Laspionchis bourkei A-D, F L. bourkei bourkei, Australia, Northern Territory E, G L. bourkei lateriensis, Indonesia, Ambon. A Holotype, [1657 H] (NTM P. 57615) B [1666] (NTM P. 57618) C [1692] (NTM P. 57619) D [1673] (NTM P. 57618) E holotype, [6064 H] (UMIZ 00115) F same as A G same as E. Scale bars: 100 μm (A-E), 10 μm (F, G).

Figure 25. Radula, Laspionchis bourkei lateriensis, Indonesia, Ambon A-D holotype [6064 H] (UMIZ 00115) E, F [6063] (UMIZ 00116). A Rachidian and innermost lateral teeth B rachidian and innermost lateral teeth C lateral teeth D lateral teeth E lateral teeth (inferior view) F outermost lateral teeth. Scale bars: 10 μm (A, F), 20 μm (B, C), 30 μm (D), 8 μm (E). Abbreviations: bls basal lateral spine hlt hook of a lateral tooth.

Figure 26. Habitats, Laspionchis bourkei matangensis. A, B Peninsular Malaysia, Matang, old and open Rhizophora forest of with hard and soft mud, many creeks, and many old logs (st 256, type locality) C Singapore, mud outside mangrove on sun-exposed mudflat (st 7) D Philippines, narrow mangrove on the edge of fish ponds, tall Rhizophora and Avicennia trees, many old logs (st 194) E Indonesia, Sumatra, soft but solid mud, big Avicennia, a few logs, some Nypa on margin, little open space (st 76) F Vietnam, open Avicennia and Rhizophora mangrove with hard mud by a small road and deep mud near water (st 221).

Figure 27. Live specimens, Laspionchis bourkei matangensis. A Dorsal view, 13 mm long [1785], Indonesia, Sumatra (UMIZ 00113) B dorsal view, 10 mm long [1784], Indonesia, Sumatra (UMIZ 00113) C dorsal view, 11 mm long [1783], Indonesia, Sumatra (UMIZ 00113) D dorsal view, 15 mm long [5961], Peninsular Malaysia, Matang (USMMC 00056) E dorsal view, 25 mm long [3343], Philippines, Bohol (PNM 041254) F holotype, dorsal view, 15 mm long [5958 H], Peninsular Malaysia, Matang (USMMC 00055) G ventral view, 13 mm long [5963], Peninsular Malaysia, Matang (USMMC 00056) H ventral view, 8 mm long [5965], Peninsular Malaysia, Matang (USMMC 00056) I ventral view, same as E.

Figure 28. Penial hooks, Laspionchis bourkei matangensis, Peninsular Malaysia A, B Holotype [5958 H] (USMMC 00055) C-E [5959] (USMMC 00056) F [5960] (USMMC 00056). Scale bars: 10 μm (A, C), 3 μm (B), 4 μm (D), 5 μm (E), 20 μm (F).

Figure 29. Spine of the accessory penial gland, Laspionchis bourkei matangensis. A Holotype, Peninsular Malaysia, [5958 H] (USMMC 00055) B Peninsular Malaysia, [5959] (USMMC 00056) C Philippines, [3343] (PNM 041254) D Peninsular Malaysia, [5960] (USMMC 00056) E same as A F same as B. Scale bars: 100 μm (A-C), 50 μm (D), 5 μm (E, F).