Scaphander meridionalis Siegwald, Pastorino, Oskars & Malaquias, 2020

Scaphander meridionalis Siegwald, Pastorino, Oskars & Malaquias, 2020 View in CoL

( Figs 15 View Figure 15 , 26 View Figure 26 , 27 View Figure 27 ; Table 2)

Scaphander meridionalis Siegwald, Pastorino, Oskars & Malaquias, 2020 .

Taxonomic history: This was, until the present work, the most recent species described of the genus Scaphander and was, up to now, cited in the literature only in the original description ( Siegwald et al. 2020).

Type material: Scaphander meridionalis Siegwald, Pastorino, Oskars & Malaquias, 2020 — Argentina: Argentine Sea, off Mar del Plata (38°04’38.76”S, 53°34’46.32”W to 38°01’35.16”S, 53°39’58.32”W), holotype, dissected and sequenced, MACNIn 42431 , H = 26.5 mm GoogleMaps ; one paratype, dissected and sequenced, ZMBN 127881 , H = 24.3 mm ; four paratypes, one dissected and sequenced, one sequenced, ZMBN 127882 , H = 17.8, rest of shells greatly damaged; one paratype, MACNIn 42432 , shell damaged .

Other material examined: Australia: Tasmania, Freycinet Commonwealth Marine Reserve , one spc., dissected and sequenced, AM C.590963, H = 24 mm; six spcs and four sh., AM C.482170, H = 14–32 mm; one spc., sequenced, AM C.519366, H = 23 mm; Bass Strait, one spc., dissected and sequenced, AM C.594398, H = 25 mm; one spc., sequenced, AM C.594399, H = 27 mm; 14 spcs, AM C.590964, H = 15.5–25 mm ; Victoria, East Gippsland Commonwealth Marine Reserve , four spcs, AM C.590960, H = 18–25 mm; one spc., dissected and sequenced, AM C.590967 , H = 27 mm ; New South Wales, Hunter Commonwealth Marine Reserve, one spc., sequenced, AM C.482252, H = 14 mm; Jervis Commonwealth Marine Reserve , one spc., dissected and sequenced, AM C.590966, H = 20 mm; three spcs, AM C.590958, H = 21–25 mm .

Diagnosis: Shell ovoid to sub-rectangular, white. Spiral sculpture composed of rows of large polygonal punctations. Spire small, flat or slightly raised, partly separated from body whorl by suture widening into groove along parietal wall. Outer lip rounded posteriorly, forming a shoulder inserted below, level, or above apex. Rachidian teeth subquadrate. Prostate cylindrical, separated from penial chamber by thin prostatic duct. Penial papilla bulbous to elongate, covered with warts and wrinkles.

Shell ( Fig. 26 View Figure 26 ): Maximum H observed = 31 mm. Shell ovoid to sub-rectangular. Aperture wide, as long as shell, narrowing posteriorly. Small flat or partly raised spire made of three to four whorls. Deep suture partly separating spire from body whorl, widening into a protruding groove along the upper part (one-quarter) of the parietal wall. Posterior edge of outer lip joining body whorl in a rounded shoulder, sometimes protruding beyond apex. Parietal wall covered with thick, smooth white callus. Spiral sculpture composed of punctuated striations. Punctations large, sub-rectangular. Thin, translucent periostracum. Shell white.

Radula ( Fig. 27A–C View Figure 27 ): Radular formula 17 × 1.1.1 (H = 24.3 mm). Lateral teeth curved, with weak denticulation on inner edge. Rachidian teeth sub-quadrate, slightly wider on one end, with pointed cusps.

Digestive tract ( Fig. 27D, E View Figure 27 ): Salivary glands long, surface uneven. Paired gizzard plates sub-rectangular.

Male reproductive system ( Fig. 27F, G View Figure 27 ): Penial chamber cylindrical, lined with soft longitudinal ridges. Muscular penial papilla, bulbous to elongate, covered in warts and wrinkles. Penial chamber separated from prostate by thin prostatic duct. Prostate cylindrical, rounded at end.

Ecology: Found between 2338 and 2952 m depth. Feeds on foraminifera, smaller bivalves, gastropods, and tubicolous polychaetes ( Siegwald et al. 2020; present study).

Distribution ( Fig. 15 View Figure 15 ): Argentina in the Southwestern Atlantic Ocean ( Siegwald et al. 2020) and Southeastern Australia between New South Wales, Tasmania, and Victoria (present study).

Remarks: The shell of S. meridionalis is similar to the ones of S. grandis from the Northern Pacific Ocean and the Atlantic species S. imperceptus . However, the spire groove is remarkably less prominent in the latter. Furthermore, S. meridionalis is molecularly distinct from S. grandis (COI uncorrected p -distances estimated at 5.02%–7.09% between these species). It was not possible to extract DNA successfully from the available samples of S. imperceptus , but according to its original description by Bouchet (1975), S. imperceptus has a bifid penis, which is lacking in S. meridionalis .

Scaphander meridionalis View in CoL is also a rare case of a benthic gastropod with Pacific–Atlantic distribution ( Zaharias et al. 2020, Siegwald et al. 2022). It has so far been recorded only from Argentina and Australia, and such striking wide disjunct distribution suggests possible undersampling across the southern regions of the Indo-West Pacific Ocean, but also certainly high dispersal capabilities likely to be related to a planktotrophic development. An alternative hypothesis is a human-mediated introduction.

Several specimens from Australia were hosting specimens of parasitic pycnogonids in their mantle cavity. Only the legs of the pycnogonids were protruding from the Scaphander View in CoL shell, and their proboscis and chelifores were piercing into the gut of the snails. Some snails were found hosting up to 12 pycnogonid individuals. This is similar to what was observed for Ascorhynchus endoparasiticus Arnaud, 1978 found in Scaphander punctostriatus (Arnaud 1978) . The pycnogonid specimens found in S. meridionalis View in CoL also seem to belong to Ascorhynchus.