Hybochelus fossulatulus: 6-15 mm

Hybochelus fossulatulus: Japan-Philippines

The juvenile specimens from the Gulf of Thailand are characterized by 1) turbiniform, low-spired shell not exceeding 3 mm in height, 2) inflated body whorl, 3) narrow umbilicus, 4) aperture large and subcircular, 5) outer lip thin, serrate and with internal spiral grooves, 6) columella simple, slightly arched and 7) sculpture of strong spiral cords and finer collabral ribs forming nodules on crossing the spirals; 3 spirals are noted on the earliest whorls; the body whorl bears 8 main spirals and weaker ones in the intervening spaces; the most abapical main spiral bounds the umbilicus.

The main characteristics of this species are:
♦ height up to 16 mm, width up to 20 mm;
♦ first whorl with axial threads; P3 almost immediately, P2 almost simultaneously, PI later;
♦ S1 at or after beginning of second whorl, as strong and other cords at end of whorl; axial threads as thick as cords, giving a regular reticulate pattern;
♦ at third whorl, P4 merging from suture; one additional thinner Ti cord appearing between each existing spiral cord, also between suture and P1 and under P4 on the last whorl, giving an amount of 11 spiral cords on the last whorl;
♦ base with 5 main spiral cords, the most internal one bordering the umbilicus; additional thin spiral cords possibly between the most external main cords; space between internal cords deeply excavated;
♦ large, deep, funnel shaped umbilicus, with perspective to apex;
♦ arcuate columella without tooth; no denticles in the aperture.

I follow here Herbert (1996) who considers that Hybochelus fossulatulus (Souverbie in Souverbie & Montrouzier, 1875) is a synonym of Hybochelus
cancellatus (Krauss, 1848). It can be only noted that, on the New Caledonian species, SI appears apparently earlier than on Australian H. cancellatus samples I have examined.

DISTRIBUTION AND HABITAT. Hybochelus cancellatus is reported to range in the Indo-West Pacific; in the latter ocean, it is distributed from Australia to Hong Kong and Japan. It dwells on intertidal and shallow subtidal gravelly bottoms. Previous records in western Thai waters were from reef flats (TANTANASIRIWONG, 1978).
FOSSIL RECORDS. Holocene of Eniwetok.