Review Article |
Corresponding author: Nataliya Yu. Dnestrovskaya ( ndnestro@mail.ru ) Academic editor: Christopher Glasby
© 2017 Inna L. Alalykina, Nataliya Yu. Dnestrovskaya, Igor A. Jirkov.
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:
Alalykina IL, Dnestrovskaya NY, Jirkov IA (2017) Identification key to Nephtyidae (Annelida) of the Sea of Okhotsk. ZooKeys 684: 1-18. https://doi.org/10.3897/zookeys.684.12180
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Currently, 15 species of Nephtyidae (Annelida) are known from the Sea of Okhotsk (north-western Pacific). A new user-friendly identification key is presented with a brief description for each species. The taxonomic positions of three closely related species, Nephtys brachycephala Moore, 1903, N. schmitti Hartman, 1938 and N. paradoxa Malm, 1874, are revised. The distributions of two species, Nephtys discors Ehlers, 1968 and N. assignis Hartman, 1950, are discussed.
Aglaophamus , Micronephthys , Nephtys , Polychaeta , north-western Pacific
Nephtyids are benthic polychaetes occurring worldwide from the intertidal to abyssal depths and mainly inhabiting soft sediments. Most of them are actively burrowing carnivores, although several species may be subsurface deposit feeders (
The family Nephtyidae includes approximately 140 species (Read and Fauchald 2017). More than 90 species occur in Pacific waters (
At present, 15 species of Nephtyidae are known from the Sea of Okhotsk. Thirteen of them belong to the most diverse genus Nephtys: N. assignis Hartman, 1950, N. brachycephala Moore, 1903, N. caeca (Fabricius, 1780), N. californiensis Hartman, 1938, N. ciliata, N. longosetosa Örsted, 1842, N. neopolybranchia Imajima and Takeda, 1987, N. paradoxa Malm, 1874, N. pente Rainer, 1984, N. punctata Hartman, 1938, N. rickettsi Hartman, 1938, N. sachalinensis Alalykina and Dnestrovskaya, 2015 and N. schmitti Hartman, 1938; one species belongs to Aglaophamus: A. malmgreni (Théel, 1879); and one to Micronephthys: M. minuta (Théel, 1879) (
Herein, an illustrated key is provided to identify species known from the Sea of Okhotsk. This key is based mainly on external morphological characters. In brief species descriptions characters of the pharynx are also included, which are easily visible by dissection and highlighted by staining. This review facilitates the creation of a valid checklist of Nephtyidae species for this region.
Nephtyids are rather similar in their gross morphology and often difficult to distinguish. The main taxonomic characters are the position of the first branchiae, their shape and the number of branchiferous chaetigers, parapodial features (shape and size of acicular lobes, pre- and postacicular lobes, characters of chaetae) and pharynx structure.
The parapodia are biramous. Both noto- and neuropodia consist of acicular, pre- and postacicular lobes, and dorsal (notopodial) and ventral (neuropodial) cirri. The acicular lobes are supported by one acicula and may be conical, rounded or bilobed (Fig.
The pharynx is a large eversible muscular proboscis, covered with soft papillae located in different areas that can be seen when everted (Fig.
The prostomium is subquadrangular to subpentagonal (shape depends on whether the proboscis is everted or not). A pair of conical antennae is present in the anterior corners of the prostomium (absent in Inermonephtys). A pair of palps is inserted ventrolaterally (may be bifid in Micronephthys). A pair of nuchal organs is located dorsolaterally on the posterior margin of the prostomium (Fig.
The morphological details of the parapodia can usually be seen under the stereomicroscope without preparing slides. All parapodia are shown in anterior view. Pharynx dissection is not always necessary but may be useful to confirm identifications. It is important to mention that not all characters are developed in juveniles, and it is not always possible to identify fragmented animals without specialized training.
Each species of Nephtys is here provided with a brief description and distribution. All figures are original except for that of N. brachycephala (after
No key is complete and perfect. The key given below should be used with caution and collated with descriptions of the species concerned. If you have any difficulties, do not hesitate to contact us by e-mail or by other means.
1. Nephtys brachycephala Moore, 1903 was originally described from Sagami Bay and recorded only a few times subsequently from the northern part of the Sea of Japan (
Nephtys schmitti Hartman, 1938 from Alaska was also synonymized with N. paradoxa by
All three closely related species N. brachycephala, N. schmitti and N. paradoxa, have foliaceous branchiae and similar parapodial features. However, in contrast to N. paradoxa, the two other species (N. brachycephala and N. schmitti) have leaf-like branchiae with a thick tapering midrib that runs through its centre. Our examination of material from the Arctic, North Atlantic and north-western Pacific (497 specimens) has indicated that the foliaceous branchiae of N. paradoxa specimens lack the tapering midrib.
Furthermore, we examined the type material of both N. brachycephala (
2. Nephtys discors Ehlers, 1868 was originally described from Maine, USA and its distribution appears to be restricted to the north-western Atlantic. Specimens of N. discors from the west coast of Kamchatka (Sea of Okhotsk) (
Nevertheless, both species remain valid. Nephtys assignis is a Pacific species with the initially minute branchiae increasing in size through segments 12–20; it has a proximally smooth pharynx and posterior parapodia with well-developed branchiae. Nephtys discors is a West Atlantic species with the branchiae best developed on the anterior third of the body and rudimentary in the posterior half; the pharynx is covered with proximal warts.
1 | 3–9 branchiferous chaetigers in worms longer than 3 mm; no more than 34 chaetigers. Up to 16 mm long (usually shorter) | Micronephthys minuta |
(Key figure |
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– | Usually several tens of chaetigers with branchiae; up to 100 chaetigers or more and may be over 200 mm long in adults (in juveniles number of chaetigers may be low, but just before the pygidium there is a growing zone with numerous developing chaetigers) | 2 |
2(1) | Branchiae of median parapodia curved inward | Aglaophamus malmgreni |
(Key figure |
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– | (Key figure |
Nephtys...3 |
3(2) | (Key figure |
4 |
– | (Key figure |
10 |
4(3) | Branchiae from C3 or C4 | 5 |
– | Branchiae from C5 or posteriorly | 6 |
5(5) | In median parapodia, acicular lobes bilobed; dorsal and ventral parapodial cirri of C1 (arrow) long; subsequent chaetigers with short dorsal and ventral cirri; in median and posterior chaetigers cirri long again | N. californiensis |
(Key figure |
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– | Acicular lobes rounded-conical or conical throughout; dorsal and ventral parapodial cirri short throughout | N. neopolybranchia |
(Key figure |
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6(4) | (Key figure |
7 |
– | (Key figure |
9 |
7(6) | (Key figure |
8 |
– | Foliaceous branchiae without a tapering midrib and lateral wings, their thickness not varying from the centre to the edges | N. paradoxa |
(Key figure |
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8(7) | Branchiae from C7 or C8; thin lateral wings of well-developed branchiae reaching to approx. half way along midrib or slightly higher, absent exactly from C36 | N. schmitti |
(Key figure |
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– | Branchiae from C4 or C5; thin lateral wings of well-developed branchiae reach almost to the distal end of the midrib except for a slightly projecting tip | N. brachycephala |
(Key figure |
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9(6) | Branchiae from C5 or C6, they continue to C75–C85 as structures longer than dorsal cirri; dorsal cirri of median chaetigers short, broadly triangular | N. pente |
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– | Branchiae from C8–C12 (rarely from C7), they continue as structures longer than dorsal cirri to C45–C55; dorsal cirri of median chaetigers long and cirriform | N. ciliata |
(Key figure |
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10(3) | Neuropodial postacicular lobes of median chaetigers with distinct indentation on the ventral side (arrow); branchiae from C3 to near posterior end (rarely from C4 – usually in small worms) | N. longosetosa |
(Key figure |
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– | (Key figure |
11 |
11(10) | (Key figure |
12 |
– | (Key figure |
13 |
12(11) | Branchiae from C6; rounded interramal parts of acicular lobes enlarged in anterior and median chaetigers | N. rickettsi |
(Key figure |
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– | Branchiae from C4; rounded interramal parts of acicular lobes greatly enlarged up to posterior end | N. sachalinensis |
(Key figure |
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13(11) | (Key figure 28) Branchiae from C7–C9; neuropodial postacicular lobes of median chaetigers distinctly longer than notopodial | N. punctata |
(Key figure |
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– | (Key figure |
14 |
14(13) | Branchiae from C4 (rarely from C5); in median chaetigers notopodial postacicular lobes obliquely oval, neuropodial postacicular lobes distinctly triangular with pointed (in juveniles) or rounded tips | N. caeca |
(Key figure |
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– | Branchiae from C6; both noto- and neuropodial postacicular lobes wide, rounded | N. assignis |
(Key figure |
Aglaophamus Kinberg, 1865
Aglaophamus malmgreni (Théel, 1879)
Micronephthys Friedrich, 1939
Micronephthys minuta (Théel, 1879)
Nephtys Cuvier, 1817
Nephtys assignis Hartman, 1950
Nephtys brachycephala Moore, 1903
Nephtys caeca (Fabricius, 1780)
Nephtys californiensis Hartman, 1938
Nephtys ciliata (Müller, 1789)
Nephtys longosetosa Örsted, 1842
Nephtys neopolybranchia Imajima & Takeda, 1987
Nephtys paradoxa Malm, 1874
Nephtys pente Rainer, 1984
Nephtys punctata Hartman, 1938
Nephtys rickettsi Hartman, 1938
Nephtys sachalinensis Alalykina & Dnestrovskaya, 2015
Nephtys schmitti Hartman, 1938
The authors are very grateful to Dr. M. Siddall (