Aviassiminea, Fukuda & Ponder, 2003

Fukuda, Hiroshi & Ponder, Winston F., 2003, Australian freshwater assimineids, with a synopsis of the Recent genus-group taxa of the Assimineidae (Mollusca: Caenogastropoda: Rissooidea), Journal of Natural History 37 (16), pp. 1977-2032 : 1978-1980

Aviassiminea n. gen.

Derivation: avius —Latin—out of the way, remote, solitary. Assiminea —like the genus Assiminea . Refers to the lack of closely related taxa.

Type species: Aviassiminea palitans n. gen. and sp.

Diagnosis

Shell ovate–conic, narrowly perforate, reddish-brown, lacking prominent sculpture on teleoconch whorls. Pallial cavity with three to five rudimentary gill filaments consisting of only gf1 (note: the left hand edge of the gill filament referred to as gf1 by Davis et al. (1992), while the right hand edge is gf2; thus a complete filament is gf1+gf2). Central radular teeth quadrangular, elongated, with two to three pairs of basal cusps and long, triangular basal projection; outer marginal radular teeth with recurved outer edge distally. Penis with numerous, fine wrinkles, long distal filament and flat, thin, semi-circular appendage on right edge behind distal papilla. Renal oviduct with two to three loops; seminal receptacle small, brownish, elongate– ovate, usually lying between bursa copulatrix and renal oviduct loops. Right pleural and supraoesophageal ganglia separated by long pleuro-supraoesophageal connective; left pleural ganglion completely fused with suboesophageal ganglion.

Remarks

Aviassiminea has two to three pairs of basal cusps on the central radular teeth and lacks cephalic tentacles. This combination of characters is known in six genera of the Assimineidae listed in the Appendix under Group 1 (=subfamily Assimineinae ). Amongst them, the only genus having a clearly umbilicate shell is Austropilula Thiele, 1927 , a brackish-water genus found in tropical southeast Asia. Austropilula has a very depressed shell that is easily distinguishable from all other assimineid genera. Other assimineid taxa with umbilicate shells are mostly seen in Groups 2 and 3 (including a part of the subfamily Omphalotropidinae ) (see Appendix).

In addition to the above, one of us (H.F. unpublished observations) has examined the reproductive systems of the type species of Assiminea Fleming, 1828 , Angustassiminea Habe, 1943 and Pseudomphala Heude, 1882 . We consider that most of the species that have been described anatomically (see below) do not belong to Assiminea sensu stricto because they each have several important differences from A. grayana (see Appendix).

Aviassiminea is distinguishable from all the anatomically known genera in several characters. In the previously reported genera of Group 1 (see Appendix), the penes are usually slender, long and almost simple (except for a row of small papillae in Assiminea s.s.). In contrast, the penis of Aviassiminea has wrinkles on the external surface, a semi-circular flat appendage and a terminal papilla. In Aviassiminea , the renal oviduct loops two or three times just before entering the albumen gland and the ovate, brownish seminal receptacle lies between the bursa copulatrix and the oviduct loops. In Assiminea , Angustassiminea and Pseudomphala, the oviduct coils only once and the seminal receptacles of the latter genera are long, slender with different coloration (black in Assiminea and colourless in Angustassiminea and Pseudomphala ). The seminal receptacle in these latter assimineids usually lies on the left side of the bursal duct and extend dorsally between the posterior end of the albumen gland and the anterior end of the bursa copulatrix.

Because of the scarcity of anatomical studies we cannot compare the anatomical characters exhibited by Aviassiminea with most of the other genera in Group 1 (see Appendix). Of those described, the type species of Assiminea , Assiminea grayana Fleming, 1828 , is one of the best known. Studies on this species include the radula (Thiele, 1927), the reproductive system (Krull, 1935; Fretter and Patil, 1961), the central nervous system (Krull, 1935), the osmoregulatory system (Little and Andrews, 1977; Little, 1981; Andrews, 1981), chromosomes (Butot and Kiauta, 1966; Kiauta and Butot, 1967), larval morphology, oviposition and seasonality (Sander, 1950, 1952; Sander and Sibrecht, 1967) and population structure (Fortuin et al., 1981). However, other organ systems have not been described in detail. Abbott (1958) described the basic anatomy of some ‘ Assiminea ’ species of the Philippines. Graham (1939) provided a few notes on the alimentary system of an unidentified species of Assiminea . Marcus and Marcus (1965) described in detail the anatomy of ‘ A. ’ succinea vina from Brazil, while Fowler (1980) reported on the reproductive system of ‘ Assiminea ’ californica (Tryon, 1865) . Hershler (1987) examined the anatomy of ‘ A. ’ infima Berry, 1947 from Death Valley, USA.

The unusual condition of the tentacular nerve seen in Aviassiminea is a probable synapomorphy of the Assimineinae (see Appendix).

Aviassiminea is contrasted with the superficially similar Austroassiminea below.