Notomastus sp. (NHM_162)

Wiklund, Helena, Neal, Lenka, Glover, Adrian G., Drennan, Regan, Muriel Rabone, & Dahlgren, Thomas G., 2019, Abyssal fauna of polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean: Annelida: Capitellidae, Opheliidae, Scalibregmatidae, and Travisiidae, ZooKeys 883, pp. 1-82 : 1

Notomastus sp. (NHM_162) Fig. 3 A–I

Material examined.

NHM_162 NHMUK ANEA 2019.7100, coll. 13 Oct. 2013, 13°57.794N, 116°34.093W, 4084 m http://data.nhm.ac.uk/object/f34e2921-7b6d-4c14-b217-690d9315f073; NHM_915B NHMUK ANEA 2019.7101, coll. 23 Feb. 2015, 12°34.28N, 116°36.63W, 4198 m http://data.nhm.ac.uk/object/98291a2a-c89a-4f62-bde5-91171368c749; NHM_1025D NHMUK ANEA 2019.7102, coll. 24 Feb. 2015, 12°08.02N, 117°17.52W, 4122 m http://data.nhm.ac.uk/object/3e34e783-a51b-4a84-bc2e-6a19bac82b4e; NHM_1200 NHMUK ANEA 2019.7103 coll. 27 Feb. 2015, 12°00.567N, 117°10.687W, 4144 m http://data.nhm.ac.uk/object/2612dd53-cce5-47b9-aeed-c321bda6c3d8; NHM_1948J NHMUK ANEA 2019.7104, coll. 13 Mar. 2015, 12°02.49N, 117°13.03W, 4094 m http://data.nhm.ac.uk/object/24374a21-17b6-4de5-8436-18c160aa5c8d.

Description.

All specimens short anterior fragments, posteriorly incomplete with thorax only or thorax and 2-5 abdominal segments only. Small species, 2-4 mm long and 0.3-0.8 mm wide for 11-16 chaetigers. Preserved specimens creamy white in ethanol; live specimens white to light brown semi-opaque/translucent. Epithelium of peristomium and first two chaetigers smooth or at best weakly annulated, on chaetigers 3-11 epithelium tessellated, distinctly bi-annulated ( Fig. 3 A–D ).

Prostomium low, rounded mound ( Fig. 3D ). Eyespots not observed. Nuchal organs inconspicuous. Peristomium as a broad, non-tessellated, achateous ring.

Thorax with 11 chaetigers, first with notochaetae only. All thoracic chaetae long, slender, bilimbate capillaries ( Fig. 3G ). Genital pores and lateral organs not observed under light microscopy. Transition between thorax and abdomen marked abruptly by the segment size, neuropodia development and chaetal type.

Abdominal segments with hooded hooks only in both rami. Noto- and neuropodia free laterally, notopodia widely separated dorsally. Abdominal notopodia coalesce into lobe, which protrudes from dorsum ( Fig. 3E ). Superior edges of the neuropodia taper to broadly rounded lobes ( Fig. 3F, G ). All abdominal chaetae hooded hooks, about 45 per ramus ( Fig. 3H ). All hooded hooks similar in shape on noto- and neuropodia; hooks with long shaft, with swelling at mid-point; with a main fang and rows of small teeth. The rest of the body unknown.

Methyl green stain.

Anterior fragment with 13 chaetigers staining more or less uniformly; more pronounced in chaetigers 6-11 ( Fig. 3I ).

Genetic data.

GenBank MN217417-MN217421 for 16S, MN217497 for 18S. COI was unsuccessful for this species, no identical matches on GenBank for 16S or 18S. In our phylogenetic tree Notomastus sp. (NHM_162) is sister to Notomastus latericeus M. Sars, 1851, but the genus Notomastus is not monophyletic in our tree ( Fig. 4 ).

Remarks.

This species is consistent with the genus Notomastus in possessing 11 chaetigers with notochaetae only, followed by abdominal chaetigers with hooded hooks only. As the specimens are poorly preserved with the thorax only or with 2-5 abdominal segments observed, this species cannot be meaningfully compared with other known species in this genus and is therefore not formally described.

Ecology.

Found in the eastern polymetallic nodule province of the CCZ.

Figures

Figure 3. Notomastus sp. NHM _ 162. A Lab image, whole specimen (specimen NHM _ 162) B Live image, whole specimen (specimen NHM _ 162) C Lab image, biannulated chaetigers (specimen NHM _ 162) D Lab image, prostomium (specimen NHM _ 162, pr = prostomium) E Lab image, whole specimen, dorsal (specimen NHM _ 915 B, no = notopodial lobe, nu = neuropodial lobe) F Lab image, whole specimen, ventral (specimen NHM _ 915 B, nu = neuropodial lobe) G Lab image, thoracic chaetae, (specimen NHM _ 162) H Lab image, thoracic hooks (specimen NHM _ 162) I Lab image, whole specimen (specimen NHM _ 162, methyl green stain). Scale bars: 1 mm (A, E, F, I); 50 μm (G, H).

Figure 4. Phylogenetic analysis of Capitellidae. 50 % majority rule tree from the Bayesian analyses using 18 S and 16 S, with posterior probability values on nodes. Twenty-four taxa from GenBank were included, and Echiura was chosen as outgroup following the annelid phylogeny of Weigert and Bleidorn (2016).