Megalomma, Johansson, 1925

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 : 13-14

Key to American species of Megalomma

1 Radiolar eyes present only in dorsalmost radioles........................................................... 2

- Radiolar eyes not only in dorsalmost radioles............................................................... 5

2(1) Dorsal collar margins fused to faecal groove ( Fig. 1A ); anterior peristomial ring not exposed ( Fig. 17A, D )...................................................................................... M. modestum ( de Quatrefages, 1866)

- Dorsal collar margins not fused to faecal groove ( Figs 1D , 22E ); anterior peristomial ring exposed ( Figs 1D , 3A , 12A , 22E ). ................................................................................................... 3

3(2) Ventral shield of collar divided transversally in two parts ( Fig. 23D, G ); with caruncle ( Fig. 23H )...................................................................................................... M. pigmentum Reish, 1963

- Ventral shield of collar entire ( Fig. 5C ); caruncle absent....................................................... 4

4(3) Anterior peristomial ring exposed dorsally ( Figs 3A , 5A ); ventral basal flanges absent; inferior thoracic chaetae type B ( Fig. 5G ).......................................................................... M. bioculatum ( Ehlers, 1887)

- Anterior peristomial ring exposed dorsally and laterally ( Figs 12A–C , 13A–B, D ); ventral basal flanges present ( Fig. 13D ); inferior thoracic chaetae type C ( Fig. 1G )............................................ M. gesae Knight-Jones, 1997

5(1) Eyes distributed only in 2–7 pairs of radioles............................................................... 6

- Eyes distributed in most radioles........................................................................ 8

6(5) Spiraled eyes ( Figs 24G–I , 25F–H ); dorsal collar margins rounded posteriorly, showing the anterior peristomial ring partially ( Fig. 24B )................................................................... M. splendidum ( Moore, 1905)

- Spherical eyes ( Figs 7G–H , 11E–F )...................................................................... 7

7(6) Dorsal lappets present ( Fig. 11A ); eyes in seven pairs of radioles (dorsalmost and lateral radioles) ( Fig. 7G–H ).................................................................................... M. fauchaldi Giangrande et al. 2007

- Dorsal lappets absent ( Fig. 7C ); eyes in two pairs of radioles (dorsalmost and fifth dorsal radioles); with a glandular ring on chaetiger 3 ( Fig. 7C )........................................................ M. coloratum ( Chamberlin, 1919)

8(5) Dorsal margins of collar not fused to faecal groove ( Fig. 1D ); anterior peristomial ring exposed dorsally; ocular spots in ventralmost radioles ( Fig. 26G )............................................................. M. georgiense n. sp.

- Dorsal margin of collar fused to faecal groove ( Figs 1A , 16A ); anterior peristomial ring not exposed.................... 9

9(8) With dorsal lappets ( Fig. 21A ); inferior thoracic chaetae type A ( Fig. 1E ).................................................................................................. M. perkinsi Tovar-Hernández and Salazar-Vallejo, 2006

- Dorsal lappets absent ( Fig. 16A ); inferior thoracic chaetae types B ( Fig. 1F ) or C ( Fig. 1G )......................... 10

10(9) With caruncle; interramal eyespots present in thorax and abdomen; inferior thoracic chaetae type B................... 11

- Caruncle absent; interramal eyespots absent; inferior thoracic chaetae type C..................................... 12

11(10) Dorsal collar margins rounded posteriorly, showing partially the anterior peristomial ring.................................................................................. M. carunculata Tovar-Hernández and Salazar-Vallejo, 2008

- Dorsal collar margins level, covering the anterior peristomial ring ( Fig. 16A )................ M. lobiferum ( Ehlers, 1887)

12(10) Thoracic tori contacting ventral shields ( Fig. 19C ); ventral sacs and dorsal pockets present ( Fig. 19B )................................................................................................... M. pacifici ( Grube, 1859)

- Thoracic tori separated from ventral shields ( Figs 4B , 14C )................................................... 13

13(12) Radioles and anterior thorax with scattered dark spots ( Fig. 14C, E–F ); ventral sacs absent....... M. heterops Perkins, 1984

- Radioles and anterior thorax without scattered dark spots; ventral sacs present ( Fig. 4D ).. M. circumspectum ( Moore, 1923)

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 3. Megalomma bioculatum (Ehlers, 1887). A) Thorax, dorsal view; B) same, ventral view; C) dorsalmost radiolar eye. A–C) Specimen from Florida, MCZ, 47066. Abbreviation: apr anterior peristomial ring. Scale bars: A–B) 1 mm; C) 0.3 mm.

FIGURE 4. Megalomma circumspectum (Moore, 1923). A) Thorax, dorsal view; B) same, ventral view; C) same, lateral view; D) ventral sacs as indicated with arrows, branchial crown removed; E) posterior end; F) eyes from dorsal radioles; G) dorsalmost radiolar eye; H) eye from 2nd dorsal radiole; I) eye from a lateral radiole; J) ventralmost ocular spot. A–J) Specimens from La Paz, México, ECOSUR. Scale bars: A–C, E) 1 mm; D) 0.5 mm; F) 2 mm; G–J) 0.3 mm.

FIGURE 5. Megalomma bioculatum (Ehlers, 1887) and M. claparedei (Gravier, 1908). A, I) Thorax, dorsal views; B–C, H) thorax, ventral views; D, P) thoracic uncini; E–F, N) companion chaetae; G) inferior thoracic chaeta type B; J) dorsalmost radiolar eye; K) abdominal uncinus; L) superior thoracic narrowly hooded chaeta; M) abdominal broadly hooded chaeta; O) inferior thoracic chaeta type B. A–G) Megalomma bioculatum; H–P) Megalomma claparedei. A) Specimen from Florida, MCZ, 47066; B–G) modified from Perkins, 1984; H–I) syntype from Djibouti, MNHN 559; J–P) modified from Gravier, 1908. Abbreviations: apr anterior peristomial ring; dl dorsal lip; dp dorsal pockets; vsc ventral shield of collar. Scale bars: A) 1 mm; H–I) 0.5 mm; B–G, J–P) not scaled.

FIGURE 7. Megalomma coloratum (Chamberlin, 1919). A) Body, lateral view; B) thorax, lateral view; C) glandular ridge on chaetiger 3 as indicated with arrow; D) thorax, ventral view; E) branchial crown and thorax, dorsal view; F) ventralmost radiole; G) dorsalmost radiolar eye; H) eye from 5th dorsal radiole; I) abdominal tori; J–L) pygidiums. A–L) Specimens from Mazatlán, México, ECOSUR. Scale bars: A, E) 10 mm; B–D) 3 mm; F–H) 0.3 mm; I–L) 3 mm.

FIGURE 11. Megalomma fauchaldi Giangrande et al. 2007. A) Thorax, dorsal view; B) same, lateral view; C) same, ventral view; D) dorsalmost radiolar eye; E–G) eyes from lateral radioles. A–G) Specimen from Galeta Reef, Panama, USNM, 066403. Abbreviations: dlc dorsal lappets. Scale bars: A–C) 0.5 mm, D–G) 0.3 mm.

FIGURE 12. Megalomma gesae Knight-Jones, 1997. A) Collar and keel as indicated with arrow; B) thorax, dorsolateral view; C) ventral sacs as indicated with arrow; D) dorsalmost radiolar eye; E) posterior abdomen and pygidium. A–E) Specimen from Balboa, Panama, ECOSUR. Abbreviations: apr anterior peristomial ring. Scale bars: A–C, E) 1 mm; D) 0.3 mm.

FIGURE 13. Selected structures of Megalomma species. A, D, G, R) Thorax, lateral views; B, F, O–P) thorax, dorsal views; C, H, Q) thorax, ventral views; E) dorsalmost radiolar eye; I, K) eyes from ventral radioles; J) eye from lateral radiole; L) thoracic uncinus; M) abdominal uncinus; N) companion chaetae. A–E) Megalomma gesae Knight-Jones, 1997; F–N) Megalomma heterops Perkins, 1984; O–R) Megalomma lanigera (Grube, 1846). A–E) Paratype from El Salvador, ZMH, 15245; F–N) modified from Perkins, 1984; O–R) specimens from Naples, MCZ, 1517. Abbreviations: apr anterior peristomial ring; vs ventral sacs; vbf ventral basal flange. Scale bars: A–D) 0.5 mm; E) 0.25 mm; F–N) not scaled; O–P) 2 mm.

FIGURE 14. Megalomma heterops Perkins, 1984. A) Tube from posterior abdomen; B, E–F) thorax, dorsal view; C) same, ventral view; D) same, lateral view; G) dorsal lip; H) dorsalmost radiolar eye; I) eye from a dorsal radiole; J–K) eyes from lateral radioles; K) eye from a ventral radiole. A, D) holotype from Florida, USNM, 54721; B–C, E–H) paratype from Florida, USNM, 67953; I–L) specimen from Cozumel, México, ECOSUR. Abbreviations: dl dorsal lip; vsc ventral shield of collar. Scale bars: A) 1 mm; B–G) 0.5 mm; H) 0.2 mm; I–L) 0.3 mm.

FIGURE 16. Megalomma lobiferum (Ehlers, 1887). A) Thorax, dorsal view; B) same, ventral view; C) same, lateral view; D) collar, dorsal view; E) dorsalmost radiolar eye; F) eye from a lateral radiole; G) eye from a ventral radiole; H) thoracic noto- and neurochaetae. A–B) Specimen from Florida, USNM, 67959; C–H) specimen from Isla Contoy, México, ECOSUR. Scale bars: A–D) 1 mm; E–G) 0.3 mm; H) 0.5 mm.

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 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 21. Megalomma perkinsi Tovar-Hernández and Salazar-Vallejo, 2006. A) Thorax, dorsal view; B) same, lateral view; C) same, ventral view; D) dorsal lips; E) dorsalmost radiolar eye; F) eye from a lateral radiole; G) eye from a ventral radiole. A–G) Holotype from North Carolina, USNM, 53976. Abbreviations: dl dorsal lip; vl ventral lip. Scale bars: A–C) 1 mm; D) 0.5 mm; E–G) 0.3 mm.

FIGURE 22. Megalomma pigmentum Reish, 1963. A) Anterior end, dorsal view; B) same, ventral view; C) same, lateral view; D) tube; E) collar, dorsal view; F) same, ventral view; G) same, lateral view; H) dorsalmost radiolar eye; I) lateral radiole; J–K) posterior abdomen. A–K) Specimens from Bahia San Quintín, México, ECOSUR. Ventral flanges in B–C, F as indicated with arrows. Scale bars: A–D) 1 mm, E–G, J–K) 0.5 mm, H–I) 0.2 mm.

FIGURE 23. Megalomma pigmentum Reish, 1963. A, H) Thorax, dorsal views; B) thorax, lateral view; C–D, G) thorax, ventral views; E) dorsal and ventral lips; F) dorsalmost radiolar eye; I) thoracic uncini and companion chaeta; J) spermatozoon; K) abdominal uncinus; L) inferior thoracic chaetae type C; M–N) superior narrowly hooded thoracic chaetae; O) last abdominal chaetiger, nephridia and sperm tissue in grey. A–O) Specimens from San Quintín, México. Abbreviations: apr anterior peristomial ring, ca caruncle, dl dorsal lip, fl flange, vl ventral lip, vs ventral sacs, vsc ventral shield of collar. Scale bars: A–D, G–H: 1 mm; E: 0.5 mm; F: 0.25 mm; I, K–O: 40 µm; J: not scaled.

FIGURE 24. Megalomma splendidum (Moore, 1905). A) Body, anterior end, ventro-lateral view; B) anterior end, dorsal view; C) same, lateral view; D) collar, ventral view showing the parallel lamellae as indicated with arrows; E) thoracic torus and chaetigers; F) thoracic chaetigers; G–H) eyes from dorsalmost radioles; I) eye from 2nd dorsalmost radiole; J) abdominal chaetiger. A–J) Specimens from British Columbia, Canada, LACM, 003466. Abbreviation: apr anterior peristomial ring. Scale bars: A–B) 2 mm; C–F) 1 mm; G–J) 0.5 mm.

FIGURE 25. Megalomma splendidum (Moore, 1905). A–B) Thorax, lateral views; C) thorax, dorsal view; D) thorax, ventral view; E) dorsal and ventral lips; F–H) eyes from dorsal radioles; I) thoracic uncini and companion chaeta; J) spermatozoon; K) abdominal uncinus. A–K) Specimens from British Columbia, Canada, LACM, 003466. Abbreviations: dl dorsal lip; vl ventral lip. Scale bars: A–C) 2 mm; D–E) 1 mm; F–H) 0.5 mm; I, K) 40 µm; J) not scaled.

FIGURE 26. Megalomma georgiense n. sp. A) Thorax, dorsal view; B–C) same, ventral views; D) dorsalmost radiolar eye; F) eye and spot of a lateral radiole; G) eye and spot of a ventral radiole; H) thoracic paleate chaetae; I) thoracic narrowly hooded chaetae; J) abdominal parapodium; K) thoracic uncini; L) abdominal uncini. A–B, D–L) Holotype from Georgia, USNM, 061328; C) paratype, USNM, 061328. Scale bars: A–C) 1 mm; D–F) 0.3 mm; H–L) 0.02 mm.