Cerithidea rhizophorarum A. Adams, 1855

Reid, David G., 2014, The genus Cerithidea Swainson, 1840 (Gastropoda: Potamididae) in the Indo-West Pacific region, Zootaxa 3775 (1), pp. 1-65 : 50-52

Cerithidea rhizophorarum A. Adams, 1855

( Figures 14 B, 15A–I)

Cerithidea rhizophorarum A. Adams, 1855: 85 –86

( Cagayan, province of Misamis, Mindanao [Cagayan de Oro, Mindanao, Philippines]; 3 syntypes NHMUK 1996432/4–6, Fig. 15A ,

seen; Higo et al. 2001: 29, fig.). Sowerby, 1866: sp. 13, pl. 2, fig. 13a, b (as rhizoperarum; as rhizoporarum in text of pl. 3 and index). Tapparone-Canefri, 1874: 142 –143, pl. 1, fig. 14 (as rhizosperarum). Hidalgo, 1904 –1905: 203–204. Dautzenberg & Fischer, 1905: 134 –135 (in part, includes C. moerchii ; as rhizoporarum). Springsteen & Leobrera, 1986: 64, pl. 14, fig. 15. Higo et al., 2001: 29, fig. Reid et al., 2013: fig. 2 (map).

Cerithium rhizophorarum — Sowerby, 1855: 886, pl. 186, fig. 273.

Potamides (Cerithidea) rhizophorarum — Tryon, 1887: 162, pl. 33, fig. 67 (in part, includes C. quoyii ; as rhizoporarum). von Martens, 1897a: 189.

Cerithium (Cerithidea) rhizophorarum — Kobelt, 1890a: 53 –54, pl. 11, figs 3, 4 ( Cecalupo 2005: pl. 31, fig. 13).

Cerithidea (Cerithidea) rhizophorarum — Cecalupo, 2005: 316, pl. 31, fig. 3. Cecalupo, 2006: 136, 234 (in part, includes C. decollata , C. moerchii , C. weyersi ).

Cerithium (Cerithidea) freytagi Kobelt, 1893: 152 –154, pl. 29, figs 1, 2 ( Philippines; types not found; Cecalupo 2005: pl. 31, fig. 3).

Cerithidea rhizophorarum var. freytagi — Dautzenberg & Fischer, 1905: 135 (in part, includes C. moerchii ; as freitagi).

Taxonomic history. The name ‘ C. rhizophorarum ’ has been widely applied to C. moerchii in Japan, Korea, China and Vietnam (see synonymy of the latter). However, C. rhizophorarum was originally described from the Philippines and is morphologically distinct, as recently noted by Reid et al. (2013). Higo et al. (2001) noted that the status of the possible syntypes of C. rhizophorarum (NHMUK 1996432) was undetermined. This registration number includes nine specimens, three in each of three lots. In one of these lots there is an original label with the locality ‘Cagayan, Philippines’, and a label ‘ C. rhizophorarum A. Ad. ’ in the hand of A. Adams himself, so the three shells in this lot are identified as unequivocal syntypes (NHMUK 1996432/4–6) and the other six have no type status. Apart from refiguring of type specimens ( Higo et al. 2001; Cecalupo 2005), only one original figure of this species has been published in more than a century ( Springsteen & Leobrera 1986).

The identity of Cerithidea similis , described by A. Adams (1855) from the Philippines, is unknown, but some aspects of the description match the present species (see Excluded and Doubtful Species, above).

Diagnosis. Shell: periphery rounded, spire whorls only slightly rounded; elongated-pupoidal outline; aperture slightly thickened and flared, sinuous apertural margin; 18–32 rounded axial ribs on penultimate whorl, ribs usually weak or absent after ventrolateral varix; ventrolateral varix a wide rib at 170–270°; 0–7 varices on spire; 5– 6 spiral cords above periphery; brown, paler at shoulder. Philippines.

Material examined. 18 lots.

Shell ( Fig. 15A–I ): H = 18.0– 36.1 mm. Shape elongated-pupoidal (H/B = 2.14–2.66; SH = 3.0–3.52); decollate, 6–7 whorls remaining; spire whorls slightly rounded, suture sometimes indistinct; spire profile convex, final whorl constricted so adults have pupoidal outline; 0–7 thick pale varices on spire; periphery rounded; moderate thickness. Adult lip slightly thickened and flared; apertural margin sinuous in side view; weak anterior projection adjacent to canal. Sculpture on spire of straight to slightly opisthocline axial ribs, becoming slightly curved (opisthocyrt) on later whorls, ribs low, rounded, interspaces equal to width of ribs, 18–32 ribs on penultimate whorl, ribs weak or absent after ventrolateral varix; spiral sculpture of 5 strong, flattened, primary cords on spire whorls, of which anterior cord is usually divided on later whorls to give 6 cords above periphery, posterior cord adjacent to suture is strongest and bears small nodules (corresponding to, or up to twice as numerous as axial ribs); spiral cords cross relatively weaker axial ribs; base with 8–10 flattened cords or ridges. Ventrolateral varix a wide rib at 170–270°; 0–7 wide varices on spire. Surface with fine spiral microstriae on periostracum; surface dull when worn. Colour: white, fawn or pale brown, often with paler zone across 2–3 posterior cords; spiral grooves darker brown, varices white; aperture pale brown.

Animal: unknown.

Range ( Fig. 14 B): Philippines: Subic Bay, Luzon ( USNM 593859); Mactan I., Cebu ( USNM 862804); Panabutan Bay, Mindanao ( USNM 862797); Cagayan de Oro, Mindanao ( NHMUK 1996432); Nabas, Panay (S. Tracey); Palawan ( Springsteen & Leobrera 1986).

According to Springsteen & Leobrera (1986: 64) this species occurs “throughout the Philippines ”. Sowerby (1866) gave ‘Borneo and the Philippines’ as the distribution, but occurrence in Borneo has not been verified and is considered unlikely in view of the many reliable records of other Cerithidea species from the island. Kobelt’s (1890a) record from northern Australia is incorrect.

Habitat and ecology. On sandy mud near the estuary of a small drainage stream from a mangrove area at Nabas, Panay (S. Tracey, pers. comm.).

Remarks. Until very recently ( Reid et al. 2013), ‘ C. rhizophorarum ’ has been well known as an oriental species found from northern Honshu, throughout the coast of China and to Vietnam. However, the type locality of A. Adams’ species is Mindanao in the Philippines and it would be unusual for a predominantly warm-temperate oriental species to extend its range across the South China Sea to the tropical Philippines. Close comparison of shells revealed differences, which persuaded Reid et al. (2013) to treat the form from the Philippines as a distinct species, C. rhizophorarum s. s., while the mainland species was identified as C. moerchii . The differences are subtle. Cerithidea rhizophorarum has a pupoidal outline (i.e. convex spire profile), the whorls are nearly flat, the axial ribs are fine and numerous, and the colour is pale with broad light brown zones (without dark, narrow bands) ( Fig. 15A–I ). Cerithidea moerchii has a straight spire, more rounded whorls, often shows darker coloration and sometimes has rugose axial ribs ( Fig. 15 J–AA). Significantly, the shells of C. moerchii from the Ryukyu Islands and Taiwan, which from their geographical proximity could be expected to be most similar if all were conspecific, are in fact the most distinct from C. rhizophorarum in the Philippines (the shells from Ryukyus and Taiwan are small and rugose, Fig. 15 U–AA; see Remarks on C. moerchii ). So far, no molecular samples have been available to test this hypothesis, but it is predicted that C. rhizophorarum and C. moerchii will prove to be distinct sister species.

The intertidal shells of the Philippines are rather well known, so it is surprising that the presence there of C. rhizophorarum has been mentioned in the literature only once in the past century, when Springsteen & Leobrera (1986: 64) reported that it occurred “throughout the Philippines ”. The species was not included in the family account by Lozouet (2008) in the comprehensive Philippine Marine Mollusks and was not found by Lozouet & Plaziat (2008) in Bohol. There are, however, 15 lots from the Philippines in USNM, mostly collected by P. Bartsch in the early twentieth century. Two of these lots consist of> 100 specimens and one of these was from Batangas Market, Luzon (USNM 243643), suggesting that the snails had been collected for food. A few specimens were found in Panay in 1979 by S. Tracey (pers. comm.). The conservation status of this species could be a matter of concern.

Figures

FIGURE 14. A. Distribution of Cerithidea tonkiniana (squares). B. Distribution of C. rhizophorarum (triangles) and of C. moerchii (circles). Solid symbols, specimens examined; open symbols, literature records: A, Thach (2007); B, Ma (2004); C, Noseworthy et al. (2007); D, Lee & Chao (2004); E, Hong et al. (2010); F, Springsteen & Leobrera (1986).

FIGURE 15. A – I, Cerithidea rhizophorarum. J – AA, C. moerchii. A, C. rhizophorarum A. Adams, 1855, syntype, Cagayan de Oro, Mindanao, Philippines (NHMUK 1996432 / 4). B, no locality (NHMUK 1996432 / 7; not a syntype of C. rhizophorarum). C – H, Guijulngan, Negros Oriental, Philippines (USNM 232846; E – H views of same specimen). I, Batangas, Luzon, Philippines (USNM 243643). J, Tai Mei Tuk, Tolo Harbour, Hong Kong (NHMUK 20130263). K – N, Shiu Hau, Tong Fuk Min Wan, Lantau I., Hong Kong (NHMUK 20130264); L, M views of same specimen). O, P, Yoshida R., Oiehama, Kasaoka City, Hiroshima Pref., Japan (NHMUK 20130265). Q, Kushida R., Matsunase, Mie Pref., Japan (NHMUK 20130266). R, Yonekura, Kiire-nukumi-cho, Kagoshima City, Kagoshima Pref., Japan (NHMUK 20130267). S, Tsuyazaki, Fukuoka Pref., Japan (NHMUK 20130268). T, Hikawa R., Kumamoto Pref., Japan (NHMUK 20130269). U, Cerithium moerchii A. Adams in G. B. Sowerby II, 1855, syntype, no locality (NHMUK 20060321). V, Funaura Bay, Iriomote I., Ryukyu Is, Japan (NHMUK 20130270). W – Y, Ura, Tatsugou-cho, Amami Is, Kagoshima Pref., Japan (NHMUK 20130271; X, Y views of same specimen). Z, AA, Tamshui R., Bali, Taiwan (NHMUK 20070387).