Metaxia rugulosa (C.B. Adams, 1850)

Fernandes, Maurício Romulo & Pimenta, Alexandre Dias, 2019, Basic anatomy of species of Triphoridae (Gastropoda, Triphoroidea) from Brazil, European Journal of Taxonomy 517, pp. 1-60 : 10-12

Metaxia rugulosa (C.B. Adams, 1850)

Figs 2B , 4

Material examined

BAHAMAS • [2, 1 d] specs; Abaco; 0.2 m depth; 11 Jul. 1994; C. Redfern leg.; BMSM 56034 .

Description of basic anatomy

OPERCULUM. Elliptical, thin, semi-transparent, membranous, paucispiral, ~2.25 whorls, nucleus considerably eccentric, dislocated 47% from center towards margin; diameter of operculum exceeds diameter of opercular pouch in 10%.

JAW. Wing-shaped; outer side with scales rectangular or rhombus-shaped, some of them covered by micro-pores up to 330 nm in diameter; rectangular scales 13.4–25.2 µm long, 5.0– 11.1 µm wide, ratio length/width 2.3–3.1, rhombus-shaped scales 19.8–22.2 µm long, 6.8–9.4 µm wide, ratio length/ width 2.3–3.2.

RADULA. Formula 3-1-1-1-3; central tooth with four main cusps, triangular and curved (claw-like), outer cusps slightly broader and occupying an upper position in relation to inner ones, in addition to a fifth, median and thin cusp up to 60% the length of remaining cusps; lateral teeth with four cusps, of which 1, 3 and 4 are claw-like and cusp 2 is vestigial or very reduced (up to 56% the length of remaining cusps); M1 with three to four cusps, cusps 1 and 4 slightly broader, cusp 2 often considerably reduced but even reaching the same length of remaining cusps; M2 with three to four small cusps; M3 very reduced, usually with three small cusps; central tooth 7.7–8.7 µm wide, lateral teeth 6.7–7.4 µm wide, M1 5.4–7.6 µm wide, M2 4.0–5.0 µm wide, developed M3 2.1–3.0 µm wide.

Remarks

The white color of the soft parts of M. rugulosa was illustrated by Redfern (2013), and the specimen herein figured was poorly preserved inside the shell, giving a false aspect of cream color to the external morphology ( Fig. 4 A–B). The operculum of M. rugulosa resembles that of M. exaltata , despite

the former showing a shorter whorl expansion ( Fig. 4B ) instead of the wide whorl expansion of the latter and its consequent more eccentric nucleus ( Marshall 1977).

Metaxia rugulosa has a paucispiral protoconch with a few spiral threads in the embryonic whorl, and has a radula ( Fig. 4 E–I) with tooth morphology similar to that of species with a multispiral protoconch with several spiral threads in the embryonic whorl, e.g., M. excelsa , M. exaltata and the type species M. metaxa . A remarkable aspect of the radula of M. rugulosa is the reduced number of marginal teeth (three), which is followed by M. excelsa (four), M. metaxa and Nützel’s Metaxia sp. 2 (five), Nützel’s Metaxia sp. 1 (six) and M. exaltata (nine or ten). The increment of teeth at the margins of the radular ribbon was indicated by Marshall (1977) for M. exaltata , and could be the reason for the deviation of this genus from the taenioglossate radula (with two marginal teeth) typical of Cerithiopsidae .

Figures

Fig. 2. Specimens studied. A. Metaxia excelsa Faber & Moolenbeek, 1991 (MZSP 122353). B. Metaxia rugulosa (C.B. Adams, 1850) (BMSM 56034). C. Cosmotriphora melanura (C.B. Adams, 1850) (MNRJ 33980). D. Iniforis pseudothomae Rolán & Fernández-Garcés, 1993 (MZSP 100957). E. Latitriphora albida (A. Adams, 1854) (BMSM 55442). F. Monophorus olivaceus (Dall, 1889) (MNRJ 34615). G. Nanaphora verbernei (Moolenbeek & Faber, 1989) (MZSP 85022). H. Nototriphora decorata (C.B. Adams, 1850) (MNRJ 28941). I. Sagenotriphora osclausum (Rolán & Fernández-Garcés, 1995) (MNRJ 35061). J. Similiphora intermedia (C.B. Adams, 1850) (MNRJ 29763). K. Strobiligera gaesona (Dall, 1927) (MZSP 53685). L. “Inella” harryleei Rolán & Fernández-Garcés, 2008 (FLMNH 450495). Scale bars: 1 mm.

Fig. 4. Metaxia rugulosa (C.B. Adams, 1850). A–I. BMSM 56034. A–B. External morphology. C–D. Jaw, outer side. E–I. Radula. Scale bars: A–B = 1 mm; C = 20 µm; D = 2 µm; E–G = 10 µm; H–I = 5 µm.