Herpetopoma Pilsbry, 1890

Herbert, D. G., 2012, A revision of the Chilodontidae (Gastropoda: Vetigastropoda: Seguenzioidea) of southern Africa and the south-western Indian Ocean, African Invertebrates 53 (2), pp. 381-381 : 427

Genus Herpetopoma Pilsbry, 1890

Huttonia: Kirk 1882: 282 [non Pickard-Cambridge, 1880 ( Araneae ) nec Marshall, 1896 (Diptera)]. Type species: Euchelus bellus Hutton, 1873 , by subsequent designation (Pilsbry 1890 in 1889–90: 429).

Herpetopoma: Pilsbry 1890 in 1889–90: 430, 445. Type species: Euchelus scabriusculus Adams & Angas in Angas, 1867, by original designation.

The type species of Herpetopoma , Euchelus scabriusculus Adams &Angas in Angas, 1867, from southern and south-eastern Australia, is a small gemmate species with a simple, open umbilicus bordered by a strongly beaded spiral cord. The columella is likewise relatively simple with a single well-developed tooth at its base. Another well-developed tooth is situated on the basal lip, close to its junction with the columella, the space between these teeth forming a deep U-shaped notch. The inner margin of the outer lip is set with numerous small, ridge-like denticles and the operculum is openly multispiral, with a broad growing margin ( Fig. 4H ).

Herpetopoma has frequently been treated as a subgenus of Euchelus , but like most more recent authors, I consider it to represent a distinct radiation and to be worthy of recognition at generic level. Species of Euchelus s.s. are generally larger and have an operculum with fewer, more rapidly expanding whorls (see above).Although they may have a single simple tooth/denticle at the base of the columella, they mostly lack the characteristic pattern of two teeth at the junction of the columella and basal lips, separated by a U-shaped notch, which is typical of Herpetopoma . Other taxa (e.g. Ascetostoma , Clypeostoma and Danilia ) that exhibit this last feature have additional characters, which set them apart from Herpetopoma .

However, even when recognised as a genus itself, Herpetopoma , may prove to be a composite taxon, given the diversity of shell form evident in the species assigned to it. I have reasonable confidence that H. instrictum , H. seychellarum , H. serratocinctum and H. stictum are correctly placed in this genus and refer them to Herpetopoma sensu stricto. However, I am less certain about H. helix , H.? naokoae and H. xeniolum and thus consider them Herpetopoma sensu lato. The protoconch is more exsert and evidently less strongly sculptured, the juvenile microsculpture sometimes granular rather than vermiform and, at least in H. helix , the operculum is tightly multispiral throughout.

No well preserved alcohol material is available for any of the local species of Herpetopoma and thus details of the external anatomy are not available. However, I have been able to extract a radula from H. helix as well as from dried specimens of the type species loaned from the Australian Museum, Sydney. Details of the latter are given below.

Radula ( Fig. 22 ): Formula ∞+(3–4)+1+(3–4)+∞; ca 55 transverse rows of teeth; transition from lateral to marginal series relatively clear. Rachidian with broad, trigonal cusp and well-developed hood; cusp with strong transverse ridge at its base, this generally concave due to medial indentation near cusp base; cutting edge coarsely dentate, central denticle largest, lanceolate, with 2–4 smaller denticles on each side. Lateral teeth progressively decreasing in size from first to last, but not markedly so; one specimen with 3 pairs of laterals per row, another with four; cusp elongate-trigonal to spathulate, bearing coarse lateral denticles on both margins (3–6). Marginals longer and more slender than laterals, but relatively shorter than in other genera; inner marginals distinctive in having a slender, recurved cusp with a few short, barb-like denticles near the tip on inner margin and a series of much longer, close-set, curved denticles on outer margin, the central part of the cusp appearing as a rib-like structure from which the two series of denticles project ( Fig. 22C ); remaining marginals with smaller, ladle-shaped cusps with a finely pectinate margin, the outermost one with a somewhat enlarged cusp ( Fig. 22D ).

Figures

Fig. 4. Operculum morphology in the Chilodontidae: (A) Littorina littorea (Linnaeus, 1758), Cancale, Brittany,France,max.diameter 10.2mm (NMSA G778);(B) Euchelus asper (Gmelin,1791),Bombay, India,max.diameter 9.0 mm (NMSA J8066);(C) Granata sulcifera, Mtwalume,KZN, max.diameter 3.58 mm (NMSA V3927); (D) Clypeostoma salpinx, off Whale Rock, Eastern Cape, max. diameter 2.59 mm (NMSA C9502); (E) Danilia textilis, max. diameter 2.97 mm (holotype, NMSA E7756/ T2595); (F) Ascetostoma providentiae, off Boteler Point, KZN, max. diameter 2.52mm (NMSA S4904); (G) Herpetopoma (s.s.) instrictum, Low Isles, GreatBarrier Reef, Queensland,max.diameter 3.17 mm (AMS C.304699); (H) H. (s.s.) scabriusculum, Bradleys Head, Sydney Harbour,Australia, max. diameter 1.78 mm (AMS C.30695); (I) H. (s.l.) helix, off Umzinto, KZN, max. diameter 1.01 mm (NMSA D5427); (J) Vaceuchelus cretaceus, SE of Kosi Bay, KZN, max. diameter 2.52 mm (paratype, NMSA S4006/T2638); (K) V. natalensis, off Umzinto, KZN, max. diameter 0.99mm (NMSA D5428); (L) V.semilugubris, Réunion, max. diameter 1.28 mm (M.Jay coll’n MNHN); (M) Perrinia angulifera, off Boteler Point, KZN, max. diameter 4.44 mm (NMSA D9209); (N) P.konos, off Port Grosvenor, Eastern Cape, max. diameter 1.23 mm (NMSA E177); (O) P.stellata, Kosi Bay main coral reef, KZN, max. diameter 1.14 mm (NMSA S1985).

Fig. 22. Herpetopoma scabriusculum (Adams & Angas in Angas, 1867), radula: (A) half-row, specimen with only 3 pairs of lateral teeth, bar = 50 µm; (B) rachidian and lateral teeth, specimen with 4 pairs of laterals, bar = 15 µm; (C) inner marginal teeth with sparsely barbed inner margin and coarsely pectinate outer margin, bar = 15 µm; (D) radula margin showing finely pectinate cusps of outer marginals and broad cusp of the outermost one, bar = 20 µm. All AMS C304695, Bradleys Head, Sydney Harbour, NSW,Australia.