Visayaseguenzia compsa

Visayaseguenzia compsa (Melvill, 1904)

Fig. 20

Basilissa (Ancistrobasis) compsa Melvill, 1904: 160, pl. 10 fig. 4.

Type loc.: Gulf of Oman, 24°58′ N, 56°54′ E, depth 156 fathoms [285 m].

Visayaseguenzia compsa – Herbert 2015: 35, figs 3i–j, 4m.

WALTERS SHOAL – slopes • 1 empty shell; stn DW4877; 33°10′ S, 43°49′ E; depth 217–256 m; 1 May 2017; MNHN • 14 empty shells; stn DW4879; 33°17′ S, 43°52′ E; depth 288–300 m; 1 May 2017; MNHN • 60+ specimens, some living; stn DW4880; 33°17′ S, 43°51′ E; depth 275–318 m; 1 May 2017; MNHN • 80+ empty shells; stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; MNHN • 7 empty shells; stn DW4885; 33°17′ S, 43°55′ E; depth 272–380 m; 3 May 2017; MNHN • 60+ empty shells; stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN • 19 empty shells; stn DW4887; 33°17′ S, 43°57′ E; depth 599–640 m; 3 May 2017; MNHN • 36 empty shells; stn DW4890; 33°09′ S, 43°59′ E; depth 492–588 m; 4 May 2017; MNHN • 1 empty shell; stn DW4892; 33°12′ S, 44°01′ E; depth 624–646 m; 4 May 2017; MNHN • 80+ empty shells; stn DW4893; 33°16′ S, 43°58′ E; depth 623–629 m; 4 May 2017; MNHN • 11 empty shells; stn DW4897; 33°09′ S, 43°59′ E; depth 490–584 m; 5 May 2017; MNHN • 1 empty shell; stn DW4899; 33°09′ S, 44°02′ E; depth 707– 720 m; 6 May 2017; MNHN • 1 empty shell; stn DW4900; 33°10′ S, 44°01′ E; depth 660–670 m; 6 May 2017; MNHN • 1 empty shell; stn CP4902; 33°08′ S, 44°02′ E; depth 700–711 m; 7 May 2017; MNHN.

Western Indian Ocean, from the Gulf of Oman to north-eastern South Africa; also on the slopes of Walters Shoal, at depths of 256–707 m (live-taken material 275–318 m); dredged on coarse sandy substrata.

The abundant material from Walters Shoal of this species is somewhat variable in shell height, strength of sculpture and the relative width of the umbilicus. It is extremely similar to material dredged off northern South Africa that I have referred to Visayaseguenzia compsa (Herbert 2015), originally described from the Gulf of Oman. In South African material the labral projection is more elongate in fully mature specimens and, in the single live-collected specimen of V. compsa from Walters Shoal, the protoconch and first teleoconch whorl are orange-brown and the following two spire whorls have a faint lime-green wash that appears to originate from the underlying dried viscera. This has not been seen in South African specimens, the apex of which is uniformly whitish in live-collected specimens. This spire coloration of live-collected material from Walters Shoal is not evident in empty shells. South African material also occurs in somewhat shallower water (mostly <100 m) than the samples from Walters Shoal, but the depth at which the holotype was dredged in the Gulf of Oman falls within the depth range of the records from Walters Shoal.

Visayaseguenzia compsa closely resembles V. cumingi Poppe, Tagaro & Dekker, 2006 from the Philippines, as well as unidentified material from the Ogasawara Islands (Hasegawa 2018). All are very similar in shape and sculpture, and such differences as may be evident between individuals from these different localities are small and difficult to evaluate, given the distances involved. Resolution of these issues will require more detailed morphological study including additional topotypic samples of V. compsa, as well as molecular data.

Visayaseguenzia is clearly closely related to Calliobasis Marshall, 1991 and the differences between them are essentially a matter of degree. They are unusual amongst seguenziids in that fresh shells exhibit a distinct colour pattern, usually of pale yellowish-green to brown blotches or axial bands. Marshall (1991) reported that the radula of Calliobasis differed from that of other seguenziids in having latero-marginal plates. To date, no information is available concerning the radula of Visayaseguenzia. The crisply granular microsculpture of V. compsa (Fig. 20F) is similar to that illustrated for Calliobasis by Marshall (1991), as is the morphology of the protoconch and the early teleoconch sculpture (Fig. 20G).