Hiona (Hionarion) pilsbryi Baker 1940

Figures 33H, 38C, 39F

Material examined. Hawaii: BPBM 206801 & 20701 (one specimen dissected), Kipu, Kauai, valley directly back of stables, 14 Mar. 1910, M.C. Cooke.

Description. External morphology: Shell not examined. Animal pale brown. Right mantle lap moderately long, narrow, finger-shaped, left mantle lap absent, mantle laps uniform in colour. Mantle lobes small. Sole of foot tripartite; caudal apparatus formed from curled up sole (Muratov’s 1999 helicarionid type); caudal horn overhangs foot slightly; caudal foss vertical slit in tail.

Mantle cavity (Figure 38C): As for family. Pigmentation and mantle gland absent.

Digestive system: Oesophageal crop absent.

Genital system (Figures 33H, 39F): As for family. Oviduct non-glandular, containing three embryos. Postuterine oviduct very long, internal longitudinal pilasters absent. Bursa copulatrix inserted on penis, very short, shorter than free oviduct; duct of bursa copulatrix wide, not distinguishable from bursa copulatrix, internally smooth. Penis moderately long; epiphallus enters penis through simple pore; penis internally smooth, one longitudinal penis pilaster present, penial diverticulum absent. Penial sheath present, enclosing coiled penis and epiphallus; penis retractor muscle attached to junction of penis and epiphallus. Epiphallus shorter than penis, simple internally. Epiphallic retractor caecum absent; Flagellum and lime-sac absent. Spermatophore not present in dissected specimens.

Radula: Not examined.

Remarks. The shell, anatomy and radula of this species were figured by Baker (1940). Ten subgenera of Hiona were accepted by Baker (1940); eight of these were used by Schileyko (2002a). Hionarion contains only two species, both from the Hawaiian Island of Kauai (Schileyko 2002a).

In the phylogenetic analysis Hiona pilsbryi grouped with other Microcystinae from Vanuatu, Norfolk Island and Lord Howe Island (Figures 1–3). In the molecular phylogenetic analysis of Wade et al. (2006), Hiona sp. was the only microcystid and grouped with Louisia and Euconulus (Euconulinae) (Figure 44B).