Siratus lamyi, Merle & Garrigues, 2008

Merle, Didier & Garrigues, Bernard, 2008, New muricid species (Mollusca, Gastropoda) from French Guiana, Zoosystema 30 (2), pp. 517-526 : 518-524

Siratus lamyi n. sp.

( Figs 1 A-C, E-G; 2A; 4A, B)

TYPE MATERIAL. — French Guiana. Continental shelf, Holotype ( Figs 1 A-C; 4B), length: 40.2 mm ( MNHN); 1 paratype ( Figs 1 E-G; 2A; 4A), length: 25.1 mm ( MNHN).

TYPE LOCALITY. — N French Guiana (70-80 m).

ETYMOLOGY. — Named in honour of Dominique Lamy.

OTHER MATERIAL EXAMINED. — N French Guiana. VI.2003, 7 specimens (coll. Lamy). — VI.2003, 2 specimens (coll. B. Garrigues).

Surinam. X.2003, 2 specimens (coll. Lamy).

DESCRIPTION OF THE HOLOTYPE

Paucispiral protoconch: 1.25 whorls and high of 0.75 mm ( Fig. 2A ). Surface covered by numerous granules. Subfusiform teleoconch of 40.2 mm in length, of 16.4 mm in width. Spire slightly elongated, high, with 7 subcarinate whorls. Last whorl (7th whorl) of 73.1% of total length of teleoconch. Apical angle of 55°. Spiral sculpture with fine primary cords in the intervarical spaces becoming larger on the varices. First and 2nd whorls: presence of primary cords P1, P2 and P3. Third whorl: appearance of primary cord IP and secondary cord adis on the sutural ramp. Fourth whorl: appearance of secondary cords abis, s1 and s3. Fifth and 6th whorls: appearance of secondary cords s2 and occasionally P4. Seventh and last whorl showing the primary cords IP (sutural ramp), P1 to P6 (convex part of the whorl), and ADP, MP, ABP, EAB 1 (siphonal canal); secondary cords (adis, abis, s1-s6, ads and ms). P2 slightly atrophied. P6 and s6 more strongly developed

E-G than P5 and ADP. MP more strongly developed than ADP and ABP. Axial sculpture with 9 protovarices on 1st whorl and 11 on the 2nd whorl. On 3rd whorl, appearance of 3 major varices and 8 intervarical ribs (2 to 3 between each major varix). On 4th whorl, 9 intervarical ribs (3 between each major varix). On the 5th, 12 intervarical ribs (4 between each major varix). On the 6th whorls, 20 intervarical ribs (5 to 10 between each major varix). On the 7th whorl, 22 intervarical ribs (6 to 10 between each major varix). Intervarical ribs decreasing in height after the 6th whorl. P1 spine short, occurring between the 2nd and the 5th whorls. P6 and s6 spines, short, open and joined by short foliation of the varices. MP spines short, open. Other spines not developed on the last whorl. Intervarical nodules more developed on P2 and P3 on the 1st whorls, but with similar development in height on the last whorls. Microsculpture with fine growth laminae, always erected and particularly expressed on the last 2 whorls. Oval and large aperture of 37% of the diameter and of 87.3% of length of the body whorl (including the siphonal canal). Columellar lip with 2 weak, low knobs abapically. Rim partially erect, adherent adapically. Small and poorly defined anal notch. Parietal callus poorly developed. Inner denticles not visible on outer lip (covered by shelly material). Denticles at the edge of the outer lip (= crenulations) present between the major cords (primary and dominant secondary cords). Siphonal canal up to 69.3% of the aperture length and slightly dorsally recurved. Shell rosy-brown with dark brown lines between P1 and P3 and P6 and s6. Operculum with apical nucleus. Animal and radula unknown.

INTRASPECIFIC VARIATION

The number of protovarices (axial ridges occurring before the distinction between true varices and intervarical ribs) varies from 9 to 16 on the 1st whorl and from 11 to 14 on the 2nd whorl ( Fig. 3 ). The varices appear between the 2nd and the 11113rd whorls. They are marked by short spines on P1. The number of intervarical ribs ( NIR) varies from 6 to 8 on the 3rd whorl, from 7 to 11 on the 4th whorl, from 8 to 19 on the 5th whorl, from 9 to 20 on the 6th whorl and from 16 to 27 on the 7th. Then, an increase of the number of intervarical ribs is observed from the 5th whorl on ( Fig. 3 ). Following this increase, the relief of the intervarical ribs decreases. Another decrease of the sculptural expression during the growth corresponds to the progressive disappearance of the P1 spine on the last 2 whorls of the oldest specimens. Then, the paratype, which seems younger (length: 25.1 mm) than the holotype (length: 40.2 mm), does not bear a total disappearance of P1 spine on its last whorl. This progressive disappearance corresponds to the recording of other disappearances of spines during the ontogeny. Indeed, the studied series of

TAR

NIR growth shows the disappearance of the spines of P3, P4 and P5, present in some young specimens, but lacking in the adults.

INTERSPECIFIC COMPARISONS

Siratus lamyi n. sp. may be compared to two recent species, S. consuela (Verrill, 1950) and S. coltrorum (Vokes, 1990) reported from the northern part of Brazil ( Vokes 1990a, b).

Siratus consuela

Siratus consuela is distinguishable by its protoconch of 2.5 whorls and a well-marked sinusigeral lamella and a small basal cord ( Fig. 2C ). Regarding the axial sculpture, the total number of intervarical ribs ( NIR) on the last 4 whorls of S. consuela (5th, 6th, 7th and 8th whorls) stabilizes between 5 and 9 per whorl (5th: 5-9; 6th: 6-9; 7th: 6-9; 8th: 8), but increases in the oldest specimens of S. lamyi n. sp. ( Fig. 3 ). This stabilization had earlier been observed in S. consuela ( Merle et al. 2001) , but was based on a smaller number of specimens. The stabilized number of intervarical ribs in S. consuela is probably due to their type of growth, because they remain well-developed during ontogeny. Intervarical ribs are reduced in thickness and more numerous in S. lamyi n. sp. Siratus lamyi n. sp. and S. consuela tend to lose their cord spines (P1 to P5) on the last whorls. However, the cords P6 and s6 of S. lamyi n. sp. ( Fig. 4A, B ) are hypermorphic and connected by a beginning of foliation, while s6 remains poorly developed in S. consuela ( Fig. 5C, D ). Siratus lamyi n. sp. is also characterized by its axial microsculpture, formed of a dense network of small and erected growth laminae that are lacking in S. consuela . Other characters, such as columellar ornamentation with more tubercles and a greater size in S. consuela , distinguish the species, even though they may have a great intraspecific variability.

Siratus coltrorum

Siratus coltrorum ( Fig. 2B ) has a protoconch of 1.25 whorls, which is very similar to that of S. lamyi n. sp. Regarding the axial sculpture, the total NIR on the last 4 whorls of S. coltrorum (5th, 6th, 7th and 8th whorls) varies from to 9 to 14 (5th: 9-11; 6th: 10-13; 7th: 10-12; 8th: 12-14), while it varies from 8 to 27 (5th: 8-19; 6th: 9-20; 7th: 16-27) in S. lamyi n. sp. ( Fig. 3 ). Then, Siratus lamyi n. sp. differs by a higher number of intervarices at the end of its growth. Siratus coltrorum and S. lamyi n. sp. share a well-developed P6 ( Fig. 5A, B ), but the secondary cord s6 of S. coltrorum is not hypermorphic as in S. lamyi n. sp. Siratus lamyi n. sp. is also characterized by its axial microsculpture, formed of a dense network of small and erected growth laminae, lacking in S. coltrorum . In conclusion three characters distinguish S. lamyi n. sp. from S. coltrorum :

– higher number of intervarical ribs on the last 2 whorls;

– hypermorphic cord s6;

– dense and erected growth laminae.

The geographic range of S. lamyi n. sp. extends from Surinam to French Guiana, while that of S. coltrorum extends from Rio Grande del Norte to Salvador de Bahia ( Fig. 6 ).

GENERIC DISCUSSION

Vokes (1965, 1990a, b), Houart (1999, 2000) and Merle et al. (2001) previously regarded Siratus to be a subgenus of Chicoreus Montfort, 1810 (type species: Murex ramosus Linnaeus, 1758 , by original designation), while Vokesimurex Petuch, 1994 (type species: Haustellum (Vokesimurex) messorius (Sowerby, 1841)) was accorded generic status. However, the sculptural patterns of Siratus and Vokesimurex are closely related. They share the atrophy of P2 and P4 when the cord spines are developed, narrow spines without secondary ornamentation, poorly developed tertiary cords, columellar tubercles, internal denticules on the apertural lip, crenulations forming secondary denticles on the posterior part of the apertural lip, a narrow and elongated siphonal canal and they lack labral spine. These characters easily distinguish Vokesimurex and Siratus from the type species of Chicoreus (see Merle 2001, 2004;

-50

0

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Merle et al. 2001) and are sufficient to exclude Siratus species from the genus Chicoreus .

Figures

FIG. 1. — Teleoconchs: A-C, Siratus lamyi n. sp., French Guiana, holotype (MHNH); D, S. coltrorum (Vokes, 1990), Brazil (Garrigues coll.); E-G, S. lamyi n. sp., French Guiana, paratype (MNHN); H, S. consuela (Verrill, 1950), Brazil (Garrigues coll.). Scale bar: 10 mm.

FIG. 2. — Protoconchs: A, Siratus lamyi n. sp., N French Guiana, paratype (MNHN); B, S. coltrorum (Vokes, 1990), Brazil (Garrigues coll.); C, S. consuela (Verrill, 1950), Guadeloupe (Garrigues coll.). Scale bar: 1 mm.

FIG. 3. — Evolution of the TAR and the NIR during the ontogeny of Siratus lamyi n. sp., S. coltrorum (Vokes, 1990) and S. consuela (Verrill, 1950). For each species, the mean is used.

FIG. 4. — Spiral sculpture (apertural view) of Siratus lamyi n. sp., French Guiana: A, paratype (MNHN); B, holotype (MNHN). Scale bars: 5 mm.

FIG. 5. — Spiral sculpture:A, B, Siratus coltrorum (Vokes, 1990); A, young specimen,Brazil (Garrigues coll.); B, adult specimen, Brazil (Garrigues coll.); C, D, S. consuela (Verrill, 1950); C, Guadeloupe (Garrigues coll.); D, adult specimen, Brazil (Garrigues coll.). Scale bars: 5 mm.

FIG. 6. — Geographic range of Siratus lamyi n. sp. (▲) and S. coltrorum (Volkes, 1990) (●).