Research Article |
Corresponding author: Eijiroh Nishi ( enishi@ynu.ac.jp ) Academic editor: Christopher Glasby
© 2017 Eijiroh Nishi, João Gil, Katsuhiko Tanaka, Elena K. Kupriyanova.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Nishi E, Gil J, Tanaka K, Kupriyanova EK (2017) Notaulax yamasui sp. n. (Annelida, Sabellidae) from Okinawa and Ogasawara, Japan, with notes on its ecology. ZooKeys 660: 1-16. https://doi.org/10.3897/zookeys.660.11228
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The polychaete Notaulax yamasui sp. n. (Sabellidae) is described from Okinawa and Ogasawara, south Japan, where it was found living embedded in a dead skeleton of the coral Porites sp. The new species is characterized by the presence of a pigmented sub-distal swelling on the tips of the crown radioles, a unique feature among species of the genus. Besides, its collar chaetae have an L-shape orientation, and the dorsal basal flanges of the branchial lobes are long and have a dorsal joint.
Boring species, coral reef, new species description, Polychaeta , taxonomy, worms
A revision of the Japanese sabellid polychaetes belonging to the genera Megalomma Johansson, 1925, Notaulax Tauber, 1879, Parasabella Bush, 1905 and Sabella Linnaeus, 1767, is in progress. In the course of this revision, several Japanese collections are being revised for specimens belonging to these genera. As a result, two specimens belonging to the same species showed radioles with sub-distal swellings, like those found in Sabella discifera Grube, 1874 and in Bispira brunnea (Treadwell, 1917), as reported by Tovar-Hernández and Pineda-Vera (2008). These swellings can be pigmented, in which case they superficially resemble the compound eyes of Megalomma and Stylomma Knight-Jones, 1997. Other main features of the specimens include the long flanged radiolar lobes (similar to those in Notaulax, Stylomma, and Anamobaea Krøyer, 1856), and simple radiolar eyes (like those in Notaulax, Anamobaea, and Hypsicomus Grube, 1870). All these genera were revised or described by
The specimens collected at Okinawa and Ogasawara (south-western Japan) were studied using both light and scanning electron microscopy (SEM) for their external morphology, and through histological cross sections at different levels of the radioles for the internal anatomy of the radioles and their sub-distal swellings. As a result, the specimens were determined to belong to an unknown species of Notaulax, which is described below as a new taxon.
The specimens were collected together with the surrounding coral at shallow water by hand, using chisels to break pieces of the coral, and fixed in the laboratory with a 10% seawater-buffered formalin solution. Some parapodia were removed from the body and prepared for microscopy observations. For light microscopy observations the parapodia were placed on a microscope slide, covered with a cover slip, and gentle pressure was applied in order to observe the chaetae and uncini. Histological sections were made from radioles embedded in paraffin, cut on a microtome, and stained with Sudan Black B. For SEM observations, the parapodia were run through a series of increasing concentrations of ethanol (80, 90, 95, 99 and 100%), air-dried, coated with palladium and platinum, and viewed in a Hitachi S-800 SEM. The holotype and paratype were deposited in the Coastal Branch of Natural History Museum and Institute, Chiba at Katsuura, Chiba, Japan (catalogue code,
Holotype:
Megalomma sp.,
Pigmented sub-distal swelling on tips of crown radioles; collar chaetal row in L-shape orientation; dorsal basal flanges of radiolar lobes long and with a dorsal joint.
Tube dark brown, thin and membranous. Body and radiolar crown pale in preserved specimens, except for light brown collar and for two (upper and lower) brown bands on distal free region of radioles (Fig.
Body of holotype 40 mm long (excluding crown) for 130 chaetigers (including thorax and abdomen); thorax 4 mm long and 2.0-2.5 mm wide, excluding chaetae; radiolar crown 6 mm long, radiolar lobes 1 mm long. Paratype similar in size, body 6 mm long (posterior portion of abdomen missing) for 32 chaetigers, thorax 3 mm long and 1.5 mm wide, excluding chaetae; radiolar crown 7 mm long, radiolar lobes 1.5 mm long.
Notaulax yamasui sp. n.: A holotype, dorsal view B ventral view of thorax C latero-dorsal view of left side of thorax D dorsal view of first chaetiger and radiolar base E distal side view of radiole F middle region of radiole showing a row of simple radiolar eyes G lateral close up view of tip of radiole, with pigmented sub-distal swelling H basal part of radiole showing paired longitudinal flanges (f) I schematic ventral view of interior of crown showing dorsal lip (dl), ventral lip (vl), ventral flange of radiolar base margin (vf) J posterior abdomen and pygidium, showing eye-spots K schematic arrangement of collar chaetae, right side L schematic arrangement of thoracic chaetae from second chaetiger, black spots representing superior chaetae, white circles representing inferior chaetae M anterior abdominal segment, left side view N schematic arrangement of neuropodial abdominal chaetae O cross-section of radiole, middle region P base of radioles and inter-radiolar membrane. Abbreviations: df, dorsal basal flange; dl, dorsal lip; f, longitudinal flange; j, junction of dorsal basal flange; vf, ventral flange; vl, ventral lip; w, inter-radiolar membrane. Scale bars 1 mm (A, B, C), 0.5 mm (D, J), 0.25 mm (E, F, H, K, P), 0.1 mm (G, I, L, M, N, O).
Crown with 16 pairs of radioles, joined by inter-radiolar membrane (Fig.
Thorax with eight chaetigers; posterior peristomial ring collar entire, without dorsal or ventral slits, well separated from peristomium, with straight brown line above ventral glandular shield (Fig.
Collar chaetae spine-like, each with knee wider than shaft (Figs
Notaulax yamasui sp. n. Chaetae of thorax (A–E) and abdomen (G, H) drawn from SEM micrographs, and uncini (F, I), drawn under a dissecting light microscope. A–B collar chaetae C superior thoracic chaeta D inferior thoracic chaeta E companion chaeta, dorsal view F thoracic uncini G inferior abdominal chaeta, anterior abdominal chaetiger H inferior abdominal chaeta, posterior abdominal chaetiger I abdominal uncini. Scale bars 20 µm (A–C), 50μm (D), and 30μm (E–I).
Notaulax yamasui sp. n. SEM micrographs of chaetae and uncini. A collar chaetae B 3rd left notopodial thoracic fascicle C detail of B, showing superior chaetae D uncini and companion chaetae, 3rd thoracic neuropodial torus E inferior abdominal spatulate chaetae showing distal mucros from 7th fascicle of abdomen, lateral view F abdominal uncini. Scale bars 30μm (A), 60μm (B), 40μm (C), 30μm (D, E), 12μm (F).
Notaulax yamasui sp. n. is known to live in the subtidal zone, embedded in dead coral masses of Porites sp.
The new species is named after Dr. Terufumi Yamasu, Emeritus Professor of the University of the Ryukyus, Japan, for his great contribution to the development of the Okinawan marine biology.
Under the stereo-microscope the radiolar sub-distal swellings of Notaulax yamasui sp. n., pigmented in the holotype, superficially resemble the typical radiolar compound eyes of the genera Megalomma and Stylomma, while other characters are typical of other sabellid genera lacking such eyes: the linear collar chaetae fascicles of Notaulax, Panousea Rullier and Amoureux, 1970, or Panoumethus Fitzhugh, 2002; the loosely aligned simple radiolar eyes of Hypsicomus, Notaulax, and Anamobaea; the long radiolar lobes of Stylomma, Notaulax, and Anamobaea. From these, Panousea and Panoumethus were ruled out from the beginning due to the presence of thoracic acicular uncini.
The fan-worm eyes and other photoreceptors are summarized in
Notaulax yamasui sp. n. (A, B) and Megalomma sp. (C, D), SEM micrographs of anterior and middle parts of radiole and distal tip with a distal swelling in N. yamasui sp. n. and with a compound eye in Megalomma sp. A close-up view of a sub-distal radiolar swelling B middle part of radiole showing pinnules and dorsal flange C compound eye on radiole D close-up view of surface of compound eye. Scale bars 75 µm (A), 200 µm (B), 300 µm (C), and 30 µm (D).
The internal morphology of both structures in Megalomma sp. and N. yamasui sp. n. compared through histological cross-sections showed ultrastructural differences: Megalomma sp. presents lenticular photoreceptor units (Fig.
Notaulax yamasui sp. n. (A–E) and Megalomma sp. (F, G), internal structure of radiole. Notaulax yamasui sp. n. A radiole tip, lateral view B, C internal structure of proximal region of radiole D, E, internal structure of sub-distal swelling. Megalomma sp. F, G internal structure of compound eye F radiole with compound eye, lateral view G internal structure of compound eye, with many individual photoreceptor units (pu) B–E and G are drawn from sliced sections of eyes and radioles. Abbreviations: sc, skeletal cells; pu, photoreceptor unit. Scale bars 100μm (A), 200μm (B–E), 300μm (F), 20μm (G).
The remaining three genera (Notaulax, Anamobaea, and Hypsicomus) belong to a well-defined group inside the Sabellidae (
Finally, other characters typical for the genus Notaulax and also present in the new species, such as long flanged radiolar lobes, gave further support to its identification as a member of the genus. The genera Hypsicomus and Notaulax were partially revised by
Among the members of the genus Notaulax (see
The entire posterior peristomial ring collar is also an uncommon feature among Notaulax species, being described only in two other species: Notaulax pyrrhogaster (Grube, 1878) from Philippine Islands, and N. alticollis (Grube, 1868) from the Red Sea. Like in these two species, N. yamasui sp. n. also shows the ventral margin of the collar more or less extended forward, forming a triangular lobe. However, neither of those two species has radiolar distal swellings, nor the collar chaetae in an L-shaped arrangement. Besides, N. pyrrhogaster does not show simple radiolar eyes (likely not faded by alcohol, as according to
The two types of Notaulax yamasui sp. n. were found living embedded in dead masses of coral Porites sp. Boring by worms in coral reefs is a common and very well-known phenomenon described as early as in 1902 by
Boring by worms plays an important role in the bio-erosion of coral reefs, but much less so than grazing by echinoids and fish, with boring polychaete species belonging to several families (the most important being Eunicidae, Lumbrineridae, Dorvilleidae, Oenonidae, Spionidae, Cirratulidae, and Sabellidae) and also Sipuncula (
Many (if not all) Sabellidaesensu Kupriyanova and Rouse, 2008 secrete mucus tubes by ventral sacs, general body walls, ventral gland shields, and parapodial glands, and at least in five genera (Sabella, Myxicola Koch in Renier, 1847, Pseudopotamilla Bush, 1905, Perkinsiana Knight-Jones, 1983, and Sabellastarte Krøyer, 1856) the tubes are made of acid mucopolysaccharide-protein complexes (Chungtai and Knight-Jones 1988,
Similarly, larvae of Notaulax species settle on dead corals, probably benefiting from the rugose surface for protection, while burrowing holes into the dead coral mass. A transverse section of a Notaulax sp. burrow in a Porites sp. coral is represented in
Many sabellids are known to live in hard carbonate substrates and some of them have been described as having their tubes embedded into substrates such as rocks (Sabellastarte magnifica (Shaw, 1800); Pseudopotamilla reniformis (Bruguière, 1789); Parasabella saxicola (Grube, 1861), as Demonax brachychona (Claparède, 1870); Potamethus mucronatus (Moore, 1923)), concretions of coralline algae (Demonax langerhansi Knight-Jones, 1983), shells or limestone (Perkinsiana rubra (Langerhans, 1880)), abalone shells (Terebrasabella heterouncinata Fitzhugh and Rouse, 1999) or shells of freshwater mollusks (genus Caobangia) (
At least seven species of Notaulax live embedded in dead corals (see below), and the same is true for one undescribed Megalomma species (
Scleractinian corals seem to constitute the preferred habitat of the genus Notaulax. From the 20 described species of Notaulax valid according to
The latitudinal distribution of Notaulax fits almost perfectly the global carbonate production, especially as aragonite (
We are grateful to late Professor Emeritus Terufumi Yamasu, University of the Ryukyus, for his support during the study of Okinawan polychaetes. We would like to thank Dr. María Ana Tovar-Hernández and an anonymous reviewer for their criticism and suggestions of useful references that significantly improved the contents and the format of our paper.