Fastosarion longimentula sp. nov.

Figs. 18, 19G, 27

Etymology

From longus (Latin, meaning long) and mentula (Latin, meaning penis), referring to the very long penis; noun in apposition.

Material examined

Types: Holotype: QM MO85838 (Dan Dan Scrub, c. 30 km SW Calliope, 24° 10' S, 151° 5' E, coll. 27 Jun 1898, J. Stanisic, D. Potter, J. Chaseling).

Paratypes: QM MO 23355 (same data as holotype).

Non-type material: See table 1.

Diagnosis

External morphology: Shell (fig. 19G) medium-sized (12.6–15.2 mm), golden, 3.0 whorls, flattened, last whorl very large. Body 30 mm long, colour (in ethanol) beige with a grey tail and neck, mantle lobes large, mottled grey; shell lappets moderately large, joined by narrow collar, right lobe rounded, left pointed; lappets smooth, without warts or pustules. Tail weakly keeled, slime network prominent.

Genital anatomy: Genitalia (fig. 27) with medium length vagina; bursa copulatrix of moderate length, duct broad, bursa elongate. Penis long, cylindrical, muscular, same diameter as epiphallus, inner penial wall sculptured with transverse, chevron-shaped ridges; 50% of penis contained in thin penial tunica. Penis longer than epiphallus; epiphallus enters penis through a simple pore; epiphallus 2 much longer than epiphallus 1; epiphallic caecum of moderate length; flagellum moderately short, slender.

Remarks This species (referred to above as ‘ Helicarionidae sp. Taroom’) contains two populations originally identified as candidate taxa through curatorial work, Helicarionidae SQ 10 from Dan Dan NP and BL5 to the west in Expedition NP near Taroom. Both populations are found in semi-evergreen vine thicket. The two sequenced specimens, one from each population, differ by around 3% in both COI and 16S and it is possible that they represent separate species. The Taroom specimen was reproductively immature; however, despite this, the morpho-anatomical features were in agreement apart from a slight difference in the proportion of penis and epiphallus length (possibly due to immaturity) and a slightly more protruding protoconch in the Taroom specimen. Therefore, in the absence of further evidence, we retain both populations in Fastosarion longimentula (fig. 18).

Fastosarion longimentula is sympatric with F. rowani and F. alyssa in Dan Dan NP, but can be distinguished from the former species by its more flattened shell with a larger aperture, its more distinct slime network and by the lack of black pustules on the shell lappets, and from the latter species by its larger size. Both species also have a very different genital anatomy.