Monophorus olivaceus (Dall, 1889)

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 : 24-30

Monophorus olivaceus (Dall, 1889)

Figs 2F , 14–18

Material examined

BRAZIL – Bahia State • [3, 1 d] specs; Salvador ; 13°00´31″ S, 38°22´38″ W; 6 m depth; 16 Feb. 2016; M.R. Fernandes leg.; MNRJ 35075 . – Espírito Santo State • [1, d] spec.; Ilha Escalvada, Guarapari ; 15 Feb. 2014; W. Vieira leg.; MNRJ 34028 • [1] spec.; exit of Guarapari Canal, Guarapari ; Apr. 1992; J. Coltro leg.; MZSP 78376 . – Rio de Janeiro State • [3] specs; Campos Basin ; 22°42´S, 40°40´W; 2006; MNRJ 18741 • [1] spec.; Arraial do Cabo ; 25–30 m depth; Aug. 2003; P. Gonçalves leg.; MZSP 133322 • [2, 2 d] specs; Enseada do Cardeiro, Arraial do Cabo ; 6 m depth; 12 Sep. 2015; M. R. Fernandes and L.S. Souza leg.; MNRJ 34615 • [1, d] spec.; Ilhas Maricás, Maricá ; 23°00´S, 42°55´W, 8 m depth; 12 Feb. 2015; M. R. Fernandes and L.S. Souza leg.; MNRJ 34240 .

Description of basic anatomy

EXTERNAL MORPHOLOGY. Body mainly cream-white, roof of mantle cavity with distinct brown or red spiral patches (occasionally with discrete lilac patches and small white dots), extending up to one whorl; pedal slit covering about 75% of foot length.

OPERCULUM. Rounded, flat, moderately thin but rigid, semi-transparent, poorly distinct whorls, nucleus subcentral or even slightly eccentric, dislocated 27% to 30% from center toward margin.

JAW. Wing-shaped; outer side with scales rectangular/squared, rectangular-bilobed, bone-shaped, hexagonal, acute-lanceolate, X-shaped, puzzle-shaped or irregular; scales with micro-pores up to 400 nm in diameter, concentrated in the posterior region (close to the radula), abruptly disappearing in the anterior region; inner side with scales moderately lanceolate, hexagonal/gem-like or rhombus-shaped, surface smooth; scales of outer side 10.1–14.7 µm long, 6.2–7.0 µm wide, ratio length/width 1.4–2.3 (rectangular/squared), 12.9–15.4 µm long, 2.6–4.1 µm wide, ratio length/width 2.6–2.7 (rectangularbilobed), 15.2–15.5 µm long, 4.7–5.9 µm wide, ratio length/width 3.8–5.8 (bone-shaped), 16.3–19.8 µm long, 6.9–10.4 µm wide, ratio length/width 1.7–2.4 (hexagonal scales), 18.3–19.0 µm long, 5.9–6.7 µm wide, ratio length/width 2.7–3.2 (acute-lanceolate), 12.4–14.1 µm long, 2.7–4.0 µm wide, ratio length/ width 3.1–5.3 (puzzle-shaped); scales of inner side 17.8–19.4 µm long, 5.7–6.4 µm wide, ratio length/ width 2.9–3.4 (lanceolate), 13.7–18.7 µm long, 6.2–7.8 µm wide, ratio length/width 1.9–2.6 (hexagonal), 11.3–13.2 µm long, 5.7–6.6 µm wide, ratio length/width 1.9–2.2 (rhombus-shaped).

RADULA. Up to 43 teeth per row, but formula hardly defined owing to dozens of teeth very similar and close to each other (especially in median portion of rows), in addition to frequent bilateral asymmetry; undifferentiated teeth, comb-like and usually having five to six cusps (outer cusps, 1 and 5/6, often reduced in size), but even up to seven cusps; outer marginal teeth somewhat head-fork shaped or clawlike with two to four irregular cusps (inner cusps can be more elongated, and some cusps may be fingerlike with a rounded end) to comb-like with five cusps (i.e., when typical outer marginal teeth are not developed); teeth with five cusps 3.5–4.6 µm wide, teeth with six cusps 4.3–4.5 µm wide, teeth with seven cusps 4.6–5.1 µm wide, outer marginal teeth with three cusps 1.7–2.7 µm wide, outer marginal teeth with four cusps 2.0– 3.1 µm wide.

Remarks

Monophorus is often associated with species showing an intense red coloration in the anterior body (e.g., Bouchet & Guillemot 1978: fig. 3). Agreeing with Rolán & Fernández-Garcés (1994), who studied specimens from Cuba, M. olivaceus differs from other congeneric species by not having a red coloration, although the roof of the mantle cavity can present such feature in some cases ( Fig. 14C ). The lack of a vivid red pigmentation may be merely associated with feeding on sponges different from the usual ones for the genus, possibly not having any major phylogenetic significance, or this coloration severely vanishes soon after the storage in ethanol (see remarks on N. verbernei (Moolenbeek & Faber, 1989)) , in this case pending further photographs of live specimens.

The operculum of M. olivaceus is herein illustrated for the first time ( Fig. 14 E–F). The simple morphology of the operculum is similar to that described for the genus (e.g., Marshall 1983; Fernandes & Rolán 1988; Romani 2015), although with an expanded last whorl owing to a proportionally larger shell and aperture of M. olivaceus compared to congeneric species.

The radula of M. olivaceus has by far the highest number of teeth per row in the genus, with up to 43. Monophorus perversus (Linnaeus, 1758) has the second highest number of teeth per row, i.e., 29 ( Bouchet 1985), whereas the smallest number of teeth per row in Monophorus is 11, observed in a species from Chile (Fernandes & Araya in prep.).

The single radular preparation of M. olivaceus from Cuba ( Rolán & Fernández-Garcés 1994) masked some important features of this species. For example, these authors found only teeth with five cusps and a total number of 33 teeth per row, instead of teeth with two to seven cusps and up to 43 teeth per row in the present study. This highlights the importance of illustrating more than one radula per species when dealing with triphorids, especially in cases of abnormal local bilateral asymmetry ( Marshall 1983), which is the case of M. olivaceus . As understood from Marshall (1983), the abnormal local bilateral asymmetry occurs when any significant discrepancy is observed between the two sides (left or right of central tooth) of the same radula, e.g., in tooth shape, number of cusps or relative cusp size. This process was firstly observed for the western Pacific species M. angasi (Crosse & P. Fischer, 1865) in Marshall (1983) .

The most similar radula to M. olivaceus is that of the eastern Atlantic population of M. erythrosoma ( Bouchet & Guillemot, 1978) , with undifferentiated teeth bearing three to six cusps ( Bouchet & Guillemot 1978). The Mediterranean population of M. erythrosoma has a remarkably different radula ( Bouchet 1985) than the eastern Atlantic population, with differentiated tooth morphology (especially the central tooth) and more marginal teeth, demanding investigation of intraspecific variation vs the existence of cryptic but distinct species. Another case is that of M. perversus , which presents two radular types in the same Mediterranean population, probably reflecting a considerable intraspecific variation. They are distinguished by the morphology of central, lateral and M1 teeth, and one type ( Bouchet 1985: figs 5, 7) is somewhat similar to M. olivaceus .

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. 14. Monophorus olivaceus (Dall, 1889). A–C, E–F. MNRJ 34615. D. MNRJ 34028. A–C. External morphology. D. Jaw (gold) and radula (white). E–F. Operculum. Scale bars: A–C = 1 mm; D = 500 µm; E–F = 250 µm.

Fig. 15. Monophorus olivaceus (Dall, 1889). A–B, F. MNRJ 34240. C–E. MNRJ 35075. A–F. Jaw, outer (A–B) and inner (C–F) sides. Scale bars: A = 50 µm; B = 2 µm; C, F = 10 µm; D–E = 5 µm.

Fig. 16. Monophorus olivaceus (Dall, 1889). A–H. MNRJ 34028, jaw (outer side). Scale bars: A = 50 µm; B–C, F–H = 10 µm; D–E = 1 µm.

Fig. 17. Monophorus olivaceus (Dall, 1889), radula. A. MNRJ 35075. B–F. MNRJ 34240. Scale bars: A, D = 10 µm; B–C, E–F = 5 µm.

Fig. 18. Monophorus olivaceus (Dall, 1889), radula. A–B. MNRJ 35075. C–F. MNRJ 34028. Scale bars: A, E = 10 µm; B = 2 µm; C = 20 µm; D, F = 5 µm.