Megalomma pacifici ( Grube, 1859 )

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 : 44

Megalomma pacifici ( Grube, 1859)

Figures 19A–K , 20A–J

Sabella pacifici Grube, 1859: 9 .

Pseudopotamilla panamica Chamberlin, 1919: 268–269 , Pl. 3, Fig. 8 fide Knight-Jones, 1997: 314.

Megalomma pacifici .— Knight-Jones, 1997: 316, Figs 1A–E .

Type material examined. [ ZMUC] POL–1985, holotype incomplete (lacking posterior abdomen) of Sabella pacifici Grube, 1859 , Punta Arenas, Costa Rica. [ MCZ] 72, holotype complete (but broken in two parts) of Pseudopotamilla panamica Chamberlin, 1919 , Panama, Coll. A. Agassiz with the following note in label: “In 1937 species identified by Hartman as M. vesiculosum (Montagu) , reported in the Bull MCZ Vol. LXIII, No 6: 268–69”.

Additional material examined. [Harlan Dean, personal collection] Costa Rica, Bahía Salinas, Coll. Dean, H., on rocky intertidal (1 female). Playa Panamá, Papaguayo, Colls Dean, H. & J. A. Vargas, August 1999, rocky intertidal (1 spec.) . [ ZMUC] POL–1986, Costa Rica, Punta Arenas , Realejo, September 1845, Legit Orsted (1 female) . [ USNM] Acc. 292580, Panama, Shore of Perico Island, Sta. 252–1, lower part of sand beach, soft mud, hard sand/shell, January 25, 1978, Coll. Jones, M. L. (1 spec.) . [ ECOSUR] OH-P0282 , Guerrero , Acapulco, Hornos beach, 16° 51’ 6.4’’ N, 99° 54’ 1’’ W, April 20, 2008, Colls SISV & LFCP, in sponge (1 spec) . [ ECOSUR] OH-P0284 , Oaxaca , Pueto Angel, Panteon Beach, 15° 39’ 51.7’’ N 96° 29’ 44.8’’ W, April 16, 2008, Colls SISV & LFCP, in sabellariid reef (1spec) . [ ECOSUR] OH-P0285 , Guerrero , Acapulco, Hornos beach, 16° 51’ 6.4’’ N, 99° 54’ 1’’ W, April 19, 2008, Colls SISV & LFCP, in oyster Spondylus calcifer (1 spec) . [ ECOSUR] OH-P0287 , Oaxaca , Pueto Angel, Panteon Beach, 15° 39’ 51.7’’ N, 96° 29’ 44.8’’ W, April 16, 2008, Colls SISV & LFCP, in sabellariid reef (1 spec.) . [ ECOSUR] OH-P0289 , Guerrero , Acapulco, Hornos beach, 16° 51’ 6.4’’ N, 99° 54’ 1’’ W, April 19, 2008, Colls SISV & LFCP, in oyster Spondylus calcifer (1 spec.) .

Diagnosis. Eyes in most radioles (spherical); ocular spots in ventralmost radioles; dorsal margins of collar fused to faecal groove; thoracic chaetae Type C; abdominal chaetae broadly hooded.

Description. Branchial crown longer than thorax with 24 radiolar pairs (12–20). Branchial crown with orange bands along entire length (brown in old preserved material). Outer surfaces of radioles quadrangular basally, rounded distally. Sub-distal compound eyes present in most radioles. Dorsalmost pair of radioles with large, spherical and short tips ( Figs 19D , 20J ). Lateral and ventral radioles with spherical eyes decreasing their size towards ventral radioles ( Fig. 19E–F ). Ventralmost radioles with ocular spots and long tips ( Fig. 19G ). Dorsal collar margins rounded posteriorly, fused to faecal groove, forming broad gap ( Figs 20B, H , 19A–B ). Dorsal lappets absent. Dorsal pockets well developed ( Figs 19A–B , 20B, H ). Ventral lappets triangular, not overlapping ( Figs 19C , 20C, F ). Anterior peristomial ring exposed dorsally between dorsal pockets. Lateral margins of collar covering basal union of radioles ( Figs 19B–C ). Dorsal lips erect, triangular about one-quarter length of branchial crown, with midrib and dorsal pinnular appendages. Ventral lips short, broadly rounded. Ventral sacs present. Caruncle and keel absent. Total thorax-abdomen length 34 (19–34) mm, maximum width 5 (2) mm throughout most of thorax. Seven thoracic chaetigers (7). Dorsal thorax dark, except for faecal groove. Lateral margin of ventral thoracic shields brown colored. Ventral shields orange. Thoracic tori longest on chaetigers 2–3. Tori in chaetigers 2–3 occupy the entire distance between notopodia and ventral shield margins ( Figs 19C , 20D–E ), contacting shields. Inferior thoracic chaetae Type C ( Fig. 19H ). Thoracic uncini with crest surmounted by 8–10 rows of numerous minute teeth, handles 2x length of main fang ( Fig. 19I ). Companion chaetae with teardrop-shaped membranes ( Fig. 19I ). Abdomen with 40 chaetigers (42–65). Abdominal chaetae broadly hooded ( Fig. 19K ); chaetae in posterior row longer than those in anterior row. Abdominal uncini with main fang surmounted by 8–10 rows of numerous minute teeth ( Fig. 19J ). Pygidium trilobed with three groups of 4–5 red pygidial eyespots, unequal in size ( Fig. 20I ). Abdominal posterior of holotype regenerating ( Fig. 20G ). Tube attached to large basal stone and composed by shell fragments, echinoderm spines and coralline sand ( Fig. 20A ).

Remarks. Megalomma pacifici , M. circumspectum and M. georgiense n. sp., share the presence of ocular spots in ventralmost radioles. In M. georgiense n. sp., the dorsal collar margins are not fused to faecal groove (fused in M. pacifici and M. circumspectum ). Megalomma pacifici differs from M. circumspectum by having the anterior peristomial ring exposed between dorsal pockets (not exposed in M. circumspectum ) and the thoracic tori longest in chaetigers 2–3 and in contact with ventral shields (same length in all segments and separate from ventral shields in M. circumspectum ).

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 8. Scanning electronic micrographs of body and caruncle. A) Lateral view of Megalomma coloratum (Chamberlin, 1919) from Mazatlán, México, ECOSUR; B–C) lateral and dorsal views of caruncle of Megalomma lobiferum (Ehlers, 1887) from Ria Lagartos, México, ECOSUR. Scale bars: A) 1 mm, B–C) 0.2 mm.

FIGURE 19. Megalomma pacifici (Grube, 1859). A–B) Thorax, dorsal views; C) thorax, ventral view; D) dorsalmost radiolar eye; E) eye from 5th dorsal radiole; F) eye from a lateral radiole; G) ventralmost radiolar eye; H) thoracic chaetae; I) thoracic uncini and companion chaetae; J) abdominal uncini; K) abdominal chaetae. A–K) Specimen from Costa Rica, ECOSUR. Scale bars: A–C) 2 mm; D–G) 0.25 mm; H) 50 µm; I–J) 10 µm; K) 40 µm.

FIGURE 20. Selected structures of Megalomma pacifici (Grube, 1859). A) Tube; B) thorax, dorsal view; C, F) thorax, ventral views; D–E) thorax, lateral views; G) posterior abdomen; H) collar dorsal view; I) pygidium; J) dorsalmost radiolar eye. A–D, I–J) Megalomma pacifici (Grube, 1859); E–H) Pseudopotamilla panamica Chamberlin, 1919, MCZ, 72. A–D, J) Holotype from Costa Rica, ZMUC POL 1985; E–H) holotype from Panama, MCZ, 72; I) specimen from Costa Rica, ECOSUR. Scale bars: A: 5 mm; B–D: 3 mm; E–H: 2 mm; I–J: 0.25 mm.