Metaxia excelsa Faber & Moolenbeek, 1991

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 : 7-10

Metaxia excelsa Faber & Moolenbeek, 1991

Figs 2A , 3

Material examined

BRAZIL • [2, 1 d] specs; Fernando de Noronha Archipelago , canal between islands Ressureta and Rata; 03°48′55″ S, 32°23′31″ W; 12 m depth; 10 Aug. 2012; G.H. Pereira Filho leg.; MZSP 122353 .

Description of basic anatomy

OPERCULUM. Elliptical, thin, semi-transparent, membranous, nucleus and number of whorls not discernible; diameter of operculum exceeds diameter of opercular pouch in 17%.

JAW. Wing-shaped; outer side with scales usually rectangular/squared, sometimes rhombus-shaped or even oblong-lanceolate; some scales covered by micro-pores up to 270 nm in diameter; rectangular scales 10.5–15.4 µm long, 4.8–7.7 µm wide, ratio length/width 1.8–2.9, rhombus-shaped scales 17.9– 24.5 µm long, 5.9–10.0 µm wide, ratio length/width 2.4–3.1, oblong-lanceolate scales 14.6–16.5 µm long, 4.0–5.0 µm wide, ratio length/width 2.9–3.6.

RADULA. Formula 4-1-1-1-4; central tooth with four to five elongated and claw-like cusps, median cusp present or not but always thinner, with the basal plate of tooth assuming a concave format (i.e., outer cusps in an upper position than median one), outer cusps usually distinctly oriented outwards and reaching slightly larger dimensions (equal or up to 1.2× more elongated) than inner cusps; lateral teeth with four elongated claw-like cusps, basal plate of tooth slightly concave (not as much as central tooth), all cusps approximately with the same length, but cusp 1 considerably broader and sometimes slightly shorter than remaining cusps; marginal teeth gradually diminishing in size outwards; M1 and M2 with four cusps very similar to lateral teeth, with all cusps similar in length or width; M3 with three similar, moderately elongated, pointed and claw-like cusps; M4 small, with three curved and pointed cusps, median one 1.2 to 1.6 times more elongated than remaining cusps; central tooth 6.4–9.2 µm wide, lateral teeth 7.1–9.9 µm wide, M1 5.8–8.7 µm wide, M2 4.1–6.7 µm wide, M3 3.2–4.4 µm wide, M4 2.3–3.1 µm wide.

Remarks

The radula of M. excelsa shares several features with that of M. exaltata (Powell, 1930) ( Marshall 1977) , such as the general tooth morphology and the gradual decrease of size towards the outermost marginal teeth, confirming their affinity at genus-level. The distinction lies in the number of marginal teeth (only four in M. excelsa , but nine or ten in M. exaltata ), the median cusp of the central tooth (apparently more reduced or vestigial in M. exaltata ) and the number of cusps in the outermost marginal teeth (three in M4 of M. excelsa , two in M9 or M10 of M. exaltata ). The radula of M. metaxa described by Bouchet (1985) shows slight differences compared to M. excelsa , like a central tooth with four cusps (instead of five in M. excelsa ), lateral teeth and M1-M2 with five cusps (four in M. excelsa ) and the presence of five marginal teeth (four in M. excelsa ). Radulae of both species are similar in general tooth morphology, with claw-like cusps, and in the number of cusps of the outermost marginal teeth (i.e., three cusps). The tooth morphology of M. excelsa is also quite similar to the two unnamed species from the southwestern Pacific studied by Nützel (1998), especially to Metaxia sp. 1, albeit these two species have six and five marginal teeth (but four in M. excelsa ). The predominance of rectangular scales in the jaw of Metaxia sp. 1 looks identical to the observed in M. excelsa ( Fig. 3B ).

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. 3. Metaxia excelsa Faber & Moolenbeek, 1991. A–G. MZSP 122353. A. External morphology. B–C. Jaw, outer side. D–G. Radula. Scale bars: A = 1 mm; B = 50 µm; C = 2 µm; D–F = 10 µm; G = 5 µm.