Tenagodus barbadensis, Bieler, 2004

Bieler, Rüdiger, 2004, Sanitation with sponge and plunger: western Atlantic slit-wormsnails (Mollusca: Caenogastropoda: Siliquariidae), Zoological Journal of the Linnean Society 140 (3), pp. 307-333 : 321-322

TENAGODUS BARBADENSIS SP. NOV.

Type material: Holotype ( Fig. 6 ): 35.8 mm overall shell length, 3.6 mm inner apertural diameter, about 7 teleoconch whorls, FMNH 301239 . Paratypes (ranging in overall length 13.8–48.9 mm): 15 shells, 15 fragments (incl. SEM specimens, Figs 14 , 23-25 ), FMNH 301290 ; 10 shells, HBOM 065 : 00000; 10 shells, AMNH 308079 . Type locality: off Speightstown , Barbados (13∞14.82¢N, 59∞39.82¢W), 101 m; collected by suction device, submersible Johnson-Sea-Link II, dive 1732, with R/ V Seward Johnson; previously embedded in unidentified sponge (not Spongosorites ) .

Description

Shell (teleoconch) ( Figs 6 , 14 ). Very loosely coiled, with most known specimens between 20 and 45 mm in total length and with inner apertural diameter of 3– 4 mm (4.6 mm in largest fragment collected). Juvenile shells with little sculpture except growth marks, but developing numerous fine spiral striae of increasing strength on subsequent whorls; after 5–6 whorls only some of these striae developing into 4–6 rows of spines, the others continuing as finer riblets interspersed between them. Spines strongest on underside of coils, and nearly absent in what would be the umbilicus in a regularly coiled shell. Spines curved and fluted tube-like, with open side facing aperture. Earliest whorls often internally closed off by concave calcareous septa ( Fig. 14 ). Early part of open shell slit (corresponding to region of posterior mantle cavity in the living animal) narrowed by lateral ingrowths, but not forming series of regular, complete holes ( Fig. 6 ); the most recent (body whorl) slit barely restricted, with undulating to near-even margins ( Fig. 6 ). Slit of earlier whorls (corresponding to region of digestive gland and gonad) filled-in with shell material. Fresh specimens with glossy shell surface. Shell light tan, often blotchily darker on earlier whorls.

Protoconch ( Figs 23–25 ; n = 2 for measurements). Fragile and readily decollating (only 2 retrieved), 303– 337 Mm high and 298–320 Mm wide, most of its bulk represented by a large embryonic shell ( PC-I) 228– 235 Mm in diameter; larval shell ( PC-II) of only 1/3 whorl. Sculpture consisting of very small pustules on upper part of whorl, followed below by finely granulated spiral striae (which appear as rows of fused pustules); aperture strongly sinuous, deeply embayed on upper whorl surface at point of contact with teleoconch slit area. Embryonic shell whitish brown, larval shell light tan.

Operculum and anatomy: unknown.

Habits and habitat

Only known from single locality, as empty shells embedded in situ in unidentified sponge (not Spongosorites ), from 101 m depth.

Geographical distribution

Only known from off Barbados.

Comparison

The teleoconch morphology is very similar to that of T. squamatus , with rows of fluted shell spines. From the limited material at hand it appears that T. barbadensis has more and better-defined spiral striae between the spine-bearing ribs than T. squamatus . Its shell slit does not show the regular pattern of restriction to well-defined holes as present in comparatively smooth-shelled T. modestus . It remains to be seen whether the collected specimens of T. barbadensis are fully grown or whether this species also reaches much larger shell sizes. The key characters that set this new species apart are in the protoconch. Its sculpture is much finer, with less distinction of the area of pustules and the rows of striae than seen in the two other western Atlantic species (compare Figs 19, 22, 24 ). As in the latter, the protoconch is roughly as wide as it is tall, but it shows different allometry. The embryonic shell is much larger (in fact, it is larger than the entire protoconch of T. modestus ), and there is a much shorter section of the larval shell ( PC-II): T. modestus grows an entire whorl following the embryonic shell, T. squamatus about one-and-a-quarter, but T. barbadensis develops only a third of a whorl (compare Figs 20, 22, 25 ). Note that eroded teleoconch fragments of this species are hardly distinguishable from those of T. squamatus and collections might contain shells of both under the latter name.

Figures

Figures 1–6. Figs 1, 2, Tenagodus modestus, shell. 1: Florida Keys, 56 m, FMNH 296716; greatest length = 48 mm. 2: lectotype of Siliquaria modesta Dall, 1889, Cuba, MCZ 341075; greatest length = 22.8 mm. Figures 3–5, Tenagodus squamatus, shell. 3: Venezuela, Golfo Triste, 46–55 m, FMNH 296706; greatest length = 165 mm. 4: Bermuda, 110 m, FMNH 296697; greatest dimension (diameter of spiral) = 46.6 mm. 5: lectotype of Tenagodus anguillae Mörch 1861, Anguilla; ZMK; greatest length = 11.6 mm. Fig. 6, Tenagodus barbadensis sp. nov., shell; Barbados, 69 m, FMNH 301239; greatest length = 35.8 mm.

Figures 7–14. Figs 7-9, Tenagodus modestus, teleoconch detail (Florida Keys, FMNH 296716). 7: transition from shell covering posterior organs (shell slit filled) to posterior mantle cavity region (shell slit narrowed to series of holes). 8: detail of Fig. 7; note regular, layered restrictions. 9: late shell; slit unrestricted. Figs 10–13, Tenagodus squamatus, teleoconch detail (Bahamas, FMNH 296709). 10: transition from shell covering posterior organs (shell slit filled) to posterior mantle cavity region (shell slit open). 11, 12: detail of Fig. 10; note incomplete restrictions when compared to Fig. 8. Fig. 13: adult sculpture; note fluted hollow spines. Fig. 14, Tenagodus barbadensis sp. nov., teleoconch detail (FMNH 301290); early whorls opened to display internal septation by calcareous plugs. All SEM. Scale bars = 300 Mm (Figs 8, 11, 12) and 1 mm (all others).

Figures 15–25. Figs 15-21, Tenagodus modestus, protoconch (Florida Keys, FMNH 296716). 15, 16: side aspects. 17: basal aspect with larval shell umbilicus. 18: apical aspect, showing smooth embryonic shell and sculptured larval shell. 19, 20: oblique aspects of protoconch. 21: detail of sculpture, pustules and striae (embryonic shell on the left). Fig. 22, Tenagodus squamatus, protoconch (courtesy J. Leal). Figs 23–25, Tenagodus barbadensis sp. nov., protoconch (FMNH 301290). 23: detail of sculpture, pustules and striae (embryonic shell on the left). 24: side aspect showing large embryonic shell. 25: apical aspect, showing smooth embryonic shell and comparatively small larval shell. All SEM. Arrows marking simple apertural margin of embryonic shell (PC-I) and sinuous apertural margin of larval shell (PC-II). Scale bars = 20 Mm (Fig. 20), 80 Mm (Figs 22, 24, 25), and 40 Mm (all others).