Megalomma modestum ( de Quatrefages, 1866 )

Tovar-Hernández, María Ana & Carrera-Parra, Luis F., 2011, Megalomma Johansson, 1925 (Polychaeta: Sabellidae) from America and other world-wide localities, and phylogenetic relationships within the genus 2861, Zootaxa 2861 (1), pp. 1-71 : 41-42

Megalomma modestum ( de Quatrefages, 1866)

Figures 17A–F , 18A, D, G–H

Sabella modesta de Quatrefages, 1866: 451–452 , pl. 15, fig. 2, 22.

Potamilla anophthalma Hartmann-Schröder, 1960: 41–43 , Figs 89–91 fide Knight-Jones, 1997: 314.

Megalomma modestum .— Knight-Jones, 1997: 314, Fig. 1F–L .

Type material examined. [ MNHN] 163, three incomplete syntypes of Sabella modesta de Quatrefages, 1866 , Peru, Lima, South America. [ MCZ] 2171, holotype of Potamilla clara Chamberlin, 1919 (now synonym of M. coloratum ) California, Laguna Beach, low tide, Coll. W. A. Hilton, complete but broken in anterior abdomen. [ ZMH] 15435, holotype complete and one incomplete paratype (only crown and anterior thorax) of Potamilla anophthalma Hartmann-Schröder, 1960 , Bei Ancas, Peru, September 13, 1950, Coll. Koepcke.

Additional material examined. [ ECOSUR] México, Oaxaca, La Ventosa , May 21, 2000, Colls SISV & JRBZ (3 specs) . Panamá, Balboa, Club de Yates , Coll. SISV , June 01, 2002 (3 specs); May 30, 2002 (1 spec.). [ USNM] 24484 , Ecuador, South side of Santa Elena # 7, Point Ecuador, September 17, 1926 (1 spec.). [ USNM] 41513 , Perú, Mancora , June 14, 1960, Coll. Klawe (3 specs) .

Diagnosis. Eyes only in dorsalmost radioles (spherical); dorsal margins of collar fused to faecal groove; thoracic chaetae Type A; abdominal chaetae narrowly hooded.

Description. Branchial crown as long as thorax with 11–21 pairs of radioles. One syntype (MNHN 163) with brown radiolar bands along entire crown. Outer surfaces of radioles quadrangular basally, rounded distally. Subdistal compound eyes spherical, present only in dorsalmost radioles ( Figs 17F , 18H ). All radiolar tips short. Dorsal collar margins square, fused to faecal groove, forming broad gap ( Figs 17A, D , 18D ). Dorsal lappets absent. Dorsal pockets well developed ( Figs 17A, D , 18D ). Ventral lappets rounded, not overlapped ( Figs 17B, E , 18A ). Anterior peristomial ring not exposed. Lateral collar margins covering bases of radioles ( Fig. 17C ). Dorsal lips erect, triangular about one-quarter the length of branchial crown, with mid-rib. Three–4 short, dorsal pinnular appendages united by membrane. Ventral lips short, broadly rounded ( Fig. 18G ). Caruncle and keel absent. Ventral sacs absent. Specimens fairly medium-size and plump. Total thorax-abdomen length 12–23 mm, maximum width 1.5– 4 mm throughout most of thorax. Seven thoracic chaetigers. Thoracic tori longest on chaetiger 2. Tori in chaetigers 2–3 occupy the entire distance between notopodia and ventral shield margins, contacting shields ( Fig. 17B, E ). Length of thoracic torus in other thoracic segments slightly shorter than those in chaetigers 2–3, but also contacting shields. Inferior thoracic chaetae Type A. Thoracic uncini with crest surmounted by 8–10 rows of numerous minute teeth, handles 2x length of main fang. Companion chaetae with teardrop-shaped membranes. Abdomen with 42–54 chaetigers. Abdominal chaetae narrowly hooded; chaetae in posterior row longer than those in anterior row. Abdominal uncini with crest surmounted by 8–10 rows of numerous minute teeth. Pygidium rounded. Tubes covered with fine sand.

Remarks. de Quatrefages (1866) described M. modestum (as Sabella ) from Lima, Peru. Knight-Jones (1997) synonymized M. clara ( Chamberlin, 1919) , a species described from Laguna Beach, California and M. anophthalma ( Hartmann-Schröder, 1960) , a species described from Lima with M. modestum . During this study, revision of types reveals that M. clara ( Fig. 18C, E, I ) is a synonym of M. coloratum , not M. modestum (see remarks section for M. coloratum ). Thus, only M. anophthalma ( Fig. 18B, F, J ) is a synonym of M. modestum . In Megalomma , four species share the presence of eyes only in the dorsalmost radioles: M. bioculatum , M. gesae , M. kaikourense , M. modestum and M. pigmentum . Among these, M. modestum is unique in having the anterior peristomial ring not exposed beyond collar (exposed in some degree in the other four species).

Figures

FIGURE 1. Variations on dorsal margins of collar and inferior thoracic chaetae in Megalomma. A–C) Margins fused to faecal groove; D) margins not fused to faecal groove; E) chaeta type A; F) chaeta type B; G) chaeta type C. A–D) Schematized; E–G) modified from Fitzhugh (1989). Abbreviations: dlc dorsal lappets; fg faecal groove. The partial exposition of the anterior peristomial ring is marked in gray.

FIGURE 17. Megalomma modestum (de Quatrefages, 1866). A, D) Thorax, dorsal views; B, E) thorax, ventral views; C) thorax, lateral view; F) dorsalmost radiolar eye. A–C, F) Specimen from Balboa, Panamá, ECOSUR; D–E) syntype from Perú, MNHN, 163. Scale bars: A–E) 1 mm; F) 0.3 mm.

FIGURE 18. Selected structures of Megalomma species. A–B) Thorax, ventral views; C) thorax, lateral view; D–F, K, T) thorax, dorsal views; G) dorsal lips; H–J) dorsalmost radiolar eyes; L–M) superior narrowly hooded thoracic chaetae; N) companion chaeta; O) inferior thoracic chaetae type C; P) abdominal uncinus; Q) thoracic uncinus; R) narrowly hooded abdominal chaeta. A, D, G–H) Megalomma modestum (de Quatrefages, 1866); B, F, J) Potamilla anophthalma Hartmann-Schröder, 1960; C, E, I) Potamilla clara Chamberlin, 1919; K–R) Megalomma mushaense (Gravier, 1908a). A, D, G–H) Syntype from Perú, MNHN, 163; B, F, J) holotype from Perú, ZMH, 15435; C, E, I) holotype from California, MCZ, 2171; K–R) modified from Gravier, 1908a. Abbreviation: dl dorsal lip. Scale bars: A–B, D–F: 1 mm; C: 2 mm; G–J: 0.25 mm; K–R: not scaled.