Redescription of Tubulanus mawsoni (Wheeler 1940) comb. nov. (Palaeonemertea: Tubulanidae) from the Bellingshausen Sea (Antarctica)

Figures & data

Figure 1 Position of station 5 during Bentart-03 survey, where Tubulanus mawsoni (Wheeler, 1940) comb. nov. was found.

Figure 2 Tubulanus mawsoni (Wheeler, 1940) comb. nov.A, Immature female specimen after fixation in Bouin's fluid. B, Detail of the head in ventral view. HE, head; MO, mouth; PP, proboscis pore. Scale bars: 1 mm.

Figure 3 Tubulanus mawsoni (Wheeler, 1940) comb. nov.A, Transverse section at the proboscis pore showing the dorsoventral fibres in cerebral lacunae. B, Transverse section through the posterior rhynchodaeal region showing the glandular cells shared by the epidermis and the rhynchodaeal epithelia. C, Transverse section through the cerebral region at level of the proboscis insertion. D, Transverse section through the rhynchodaeal region showing the connection between rhynchodaeal and epidermal serous glands (arrowhead). E, Transverse section through the buccal region; note two different types of epidermal glands. F, Transverse section through the foregut region, at what would be the level of the fixation band. G, Transverse section through the anterior buccal region showing the buccal nerve. H, Transverse section through the foregut region showing the muscular plate (MP). I, Transverse section through the intestinal region, arrowhead points to the dorsal muscle cross. J, Transverse section through the intestinal region, arrowhead points to the ventral muscle cross. BM, basal membrane; BN, buccal nerve; BS, blue-staining mucous cell; CL, cephalic blood lacuna; CN, cephalic neural layer; DG, dorsal ventral ganglion; CP, connective tissue processes; EP, epidermis; IC, body-wall inner longitudinal muscle layer; IC, body-wall inner circular muscle layer; LB, longitudinal muscles below horizontal transverse muscles; LM, body wall longitudinal muscle layer; LN, lateral nerve cord; MC, mucous cell; OC, body wall outer longitudinal muscle layer; PS, pink-stained serous glandular cell; PN, proboscis nerve; PP, proboscis pore; PR, proboscis; RC, rhynchocoel; RD, rhynchodaeum; RS, deep red-staining cell; UD, upper mid-dorsal nerve; VG, ventral cerebral ganglion; WE, weak red-staining cell. Scale bars: 100 µm.

Figure 4 Tubulanus mawsoni (Wheeler, 1940) comb. nov.A, Transverse section through the proboscis. B, Transverse section through the mouth showing the buccal chamber. C, Transverse section through the anterior foregut region. D, Transverse section through the posterior foregut region. E, Transverse section through the intestinal region. F, Transverse section through the foregut region showing the arrangement of the nephridial ducts and the lateral blood vessel. G, Transverse section through the foregut region, showing an excretory collecting tubule (EX). EP, epidermis; FG, foregut; IN, intestine; LM, body-wall longitudinal muscle layer; LN, lateral nerve cord; LV, lateral blood vessel; MO, mouth; NE, nephridial duct; OC, body-wall outer circular muscle layer; PE, proboscis outer glandular epithelium; PC, proboscis outer circular muscle layer; PL, proboscis inner longitudinal muscle layer; PR, proboscis; RC, rhynchocoel. Scale bars: 100 µm.

Figure 5 Tubulanus mawsoni (Wheeler, 1940) comb. nov.A, Transverse section through the posterior portion of the brain showing the connection between the ventral cerebral commissure and the proboscis nerve. B, Transverse section through the lateral nerve cord showing its position between the outer circular muscle layer and the basal membrane; black arrowhead points to a neurochord. C, Transverse section through the upper mid-dorsal nerve; white arrowhead points to the basal membrane; black arrowhead points to the inner neurilemma. D, Transverse section through the posterior portion of the dorsal cerebral commissure showing the junction with the upper mid-dorsal nerve. E, Transverse section through the cerebral sensory organ pit (CP). F, Transverse section through the intestinal region in the mature male. G, Transverse section through the intestinal region in the immature female. BM, basal membrane; CL, cephalic blood lacuna; EP, epidermis; IC, body-wall inner longitudinal muscle layer; IN, intestine; LN, lateral nerve cord; LM, body-wall longitudinal muscle layer; LV, lateral blood vessel; PN, proboscis nerve; PR, proboscis; OC, body wall outer longitudinal muscle layer; OV, ovum; RM, retractor muscle; RS, deep red-staining cell; TE, testis; UD, upper mid-dorsal nerve; VG, ventral cerebral ganglion. Scale bars: 100 µm.

Character matrix for Tubulanus mawsoni (Wheeler, 1940) comb. nov. Character states and code from Sundberg et al. (2009).

Character	Character state	Code	Figure
1. Biology	Free-living	0
2. Habitat	Marine	0
3. Benthic divisions	Sublittoral	2
4. Pelagic divisions	N/A	N/A
5. Substrate	Mud	0
6. Behaviour	Not observed	–
External morphology
7. Cephalic furrows	Two pairs	2	2B
8. Distribution of anterior cephalic furrows	Ventral	0	2B
9. Shape of anterior (dorsal) cephalic furrows	N/A	N/A
10. Shape of posterior (dorsal) cephalic furrows	N/A	N/A
11. Head demarcated from body	Head not wider than trunk	2	2A, B
12. Position of cephalic furrows	N/A	N/A
13. Shape of head/cephalic lobe	Rounded	0	2B
14. Head viewed laterally	Without extensions	0	2A
15. Shape of posterior tip	Pointed	0	2A
16. Eyes	Absent	0	2A
17. Eye morphology	N/A	N/A
18. Relative eye size	N/A	N/A
19. Eye distinctiveness	N/A	N/A
20. Eye position relative to brain lobes	N/A	N/A
21. Colour pattern	Absent	0
22. Primary dorsal body colour	Pink	7
23. Body colour hue/tint	Light	2
24. Internal organs visible through dorsal epidermis	Not observed	–
25. Lateral margins	Appear paler than dorsal body surface	0
26. Distribution of bristles/cirri	Not seen	0
Body wall
27. Epidermis non-cellular inclusions	Absent	0
28. Epidermis of anterior body	Without intra-epithelial muscle network	0
29. Ratio of thickness of epidermis/lateral body diameter in brain region	>0.1	1	3C
30. Dermis	Forming a distinct zone between epidermis and circular muscle layer	0	3F
31. Thickness of dermis	Less than half epidermal height	0	3F
32. Muscle processes from dermis into epidermis	Absent	0	3D
33. Muscle layers	Outer circular, middle longitudinal and inner circular muscle layer	2	3J, 4C, D, 5G
34. Muscle crosses between body wall circular muscle layers	Both dorsal and ventral muscle crosses	2	3I, J
35. Body wall longitudinal muscle layer just behind brain	N/A	N/A
36. Precerebral septum	N/A	N/A
37. Central (medial) muscle plate	Between foregut and rhynchocoel	1	3H
38. Parenchyma	Barely distinguishable other than as a membrane enclosing various body organ systems	0
39. Muscles fibre in mouth/foregut region	Present	1	3G
Proboscis apparatus
40. Proboscis pore	Subterminal, ventral	1	2B, 3A
41. Mouth and proboscis pore connection	Open separately	0	2B, 3A, 4B
42. Gland cells of rhynchodaeum	Present	1	3A, B, D
43. Rhynchocoel musculature	Circular muscles only	1	3C, 5A, G
44. Rhynchocoel musculature in posterior end	Approximately as anterior part	0	4E
45. Rhynchocoel length	Extending to or almost to posterior region of body	2	5G
46. Rhynchocoelic caeca	Absent	0
47. Size of posterior third of proboscis region	Small, less than 50% of body diameter in retracted position	0	4E, 5G
48. Musculature of proboscis (everted state)	Outer circular and inner longitudinal muscle layer	0	4A
49. Musculature of posterior proboscis region (everted state)	Outer circular and inner longitudinal muscle layer	2	4E
50. Epithelium of anterior proboscis region when everted	Developed into barbs/pseudocnids (secretory products of the epithelium)	2
51. Number of proboscis nerves	2	1
52. Proboscis nerve arrangement	Peripheral neural sheath absent or indistinct	0
53. Secondary proboscis nerves	N/A
54. Proboscis armature	Absent	0
55. Number of accessory stylet pouches	N/A	N/A
56. Number of stylets in each accessory stylet pouch	N/A	N/A
57. Stylet basis/stylet ratio	N/A	N/A
58. Stylet shaft	N/A	N/A
59. Shape of stylet basis	N/A	N/A
60. Median waist of stylet basis	N/A	N/A
61. Proboscis used for locomotion	Unknown	0
Alimentary system
62. Position of mouth	Just behind the brain	2
63. Oesophagus	Absent	0
64. Oesophagus epithelium	N/A	N/A
65. Stomach	Not regionally differentiated	0
66. Stomach connection with intestine	N/A	N/A
67. Length of pyloric canal	N/A	N/A
68. Intestinal caecum	Absent	0
69. Anterior pouches of intestinal caecum	N/A	N/A
70. Lateral diverticula of intestinal caecum	N/A	N/A
71. Intestinal diverticula	Absent	0
Circulatory system
72. Cephalic vasculature	Forming a blood lacuna in front of cerebral ganglion	3	3A, B
73. Vascular plugs	N/A	N/A
74. Rhynchocoelic villus	Absent	0
75. Position of lateral blood vessels	Outside inner circular body wall muscle layer	2	4F, G, 5G
76. Mid-dorsal blood vessel	Absent	0
77. Length of mid-dorsal blood vessels	N/A	N/A
78. Extravascular pouches/valves	Absent	0
79. Pseudometameric transverse connectives linking mid-dorsal and lateral blood vessels in intestinal region	N/A	N/A
80. Vascular plexus in foregut region	Absent	0
Nervous system
81. Location of cerebral ganglia and lateral nerve cords	Cerebral ganglia and lateral nerve cords situated between epidermal basement membrane and outer circular body wall muscle layer	1	3C, F, 5A, B, C, D
82. Number of dorsal cerebral commissures	One	1
83. Distinct outer neurilemma of cerebral ganglion	Absent	0
84. Inner neurilemma of cerebral ganglion	Present	1	5A
85. Statocysts in brain tissue	Absent	0
86. Lateral nerve cords	N/A	N/A
87. Accessory lateral nerve	N/A	N/A
88. Four large nerves in head region	Absent	0
89. Number of dorsal nerves	Both upper and lower dorsal nerves	2
90. Posterior junction of lateral nerve cords	Not observed	–
91. Neurochord cell in brain	Absent	0
92. Neurochords in lateral nerve cords	Present	1	5B
93. Myofibrillae in lateral nerve cords	Absent	0
94. Position of myofibrillae in lateral nerve cords	N/A	N/A
95. Buccal nerves	Paired	1	3G
Excretory system
96. Excretory system	Present	1	4F, G
97. Extent of system	Confined to foregut region of body	0
98. Excretory canal	Canal outside inner circular muscle	1	4F
99. Nephridial gland	Present	1
100. Flame cells	N/A	N/A
101. Glandular components in excretory tubules	Present	1
102. Number of nephridiopores	Limited to one or two on each side of body	0	4G
103. Position of nephridiopores	Region of excretory system	2	4G
Reproductive system
104. Nature of sexes	Separate sexes	0	5F, G
105. Gonad arrangement in heterogamous taxa	In lateral rows/groups diverticula absent	3	5F, G
106. Gonad arrangement in hermaphroditic taxa	N/A	N/A
107. Testes	Simple	0	5F
108. Sexual colour dimorphism	Absent	0
109. Gonoduct position	Not observed	–
110. Nature of reproduction	Not observed	–
Sensory organs
111. Apical organ	Absent	0
112. Typical cephalic gland	Absent	0
113. Cephalic gland type	N/A	N/A
114. Opening of cephalic glands	N/A	N/A
115. Position of cerebral sensory organs in relation to brain	Behind brain	4
116. Position of cerebral sensory organs in relation to epidermis	Ciliated pits or ciliated canals in epidermis	0	5E
117. Size of cerebral sensory organs	Less than half size of brain lobes	0	5E
118. Ciliated cerebral canal	N/A	N/A
119. Side organs	Absent	0
120. Sensory pits in head region	Absent	0

Notes: N/A, no applicable character.

Wheeler JFG 1940. Nemerteans of Kerguelen and the southern ocean. B. A. N. Z. Antarctic Research Expedition Report, Series B 4: 233–256.

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Sundberg P, Chernyshev AV, Kajihara H, Kanneby T, Strand M 2009. Character-matrix based descriptions of two new nemertean (Nemertea) species. Zoological Journal of the Linnean Society 157: 264–294. 10.1111/j.1096-3642.2008.00514.x

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