Figure 1.
Variation of head appendages (antennae, palps) and eyes in representatives of Eunicida. Living specimens (A–D,F–H), fixated specimens (E). (A) Paucibranchia bellii, dorsal view. Five head appendages—one median antenna (ma), one pair of lateral antennae (la) and one pair of palps (pa) are present. One pair of small red-pigmented eyes (ey) is located at the lateral basis of the lateral antennae. (B) Lysidice unicornis, lateral view. One median antenna (ma) and one pair of red-pigmented eyes (ey) are located on the prostomium. (C) Lysidice ninetta, dorsal view. Three head appendages are present (1 ma,1 pair of la) and one pair of relatively big red-pigmented eyes is located on the ventral basis of the lateral antennae. (D) Leodice torquata, dorsal view. Five head appendages are present (1 ma, 1 pair of la, 1 pair of pa). One pair of blackish-purple eyes (ey) is located on the ventral basis of the lateral antennae. (E) Hyalinoecia tubicola, lateral view. Five relatively long head appendages are present (1 ma, 1 pair of la, 1 pair of pa). One pair of black-pigmented eyes (ey) is located at the basis of the lateral antennae. The specimen was already fixed when the picture was taken—deviation in colouration of the specimen is possible. (F) Dorvillea spec., dorsal view. Four relatively long head appendages are present (1 pair of la, 1 pair of pa). Two pairs of red-pigmented eyes (ey) are located on the posterior edge of the prostomium. (G) Arabella iricolor, dorsal view. Head appendages are lacking, but two pairs of black-pigmented eyes (ey) are present on the prostomium. (H) Scoletoma tetraura, dorsal view. Lacks head appendages as well as eyes. ey = eye, la = lateral antenna, ma = median antenna, pa = palp, pe = peristomium, pr = prostomium.
Figure 1.
Variation of head appendages (antennae, palps) and eyes in representatives of Eunicida. Living specimens (A–D,F–H), fixated specimens (E). (A) Paucibranchia bellii, dorsal view. Five head appendages—one median antenna (ma), one pair of lateral antennae (la) and one pair of palps (pa) are present. One pair of small red-pigmented eyes (ey) is located at the lateral basis of the lateral antennae. (B) Lysidice unicornis, lateral view. One median antenna (ma) and one pair of red-pigmented eyes (ey) are located on the prostomium. (C) Lysidice ninetta, dorsal view. Three head appendages are present (1 ma,1 pair of la) and one pair of relatively big red-pigmented eyes is located on the ventral basis of the lateral antennae. (D) Leodice torquata, dorsal view. Five head appendages are present (1 ma, 1 pair of la, 1 pair of pa). One pair of blackish-purple eyes (ey) is located on the ventral basis of the lateral antennae. (E) Hyalinoecia tubicola, lateral view. Five relatively long head appendages are present (1 ma, 1 pair of la, 1 pair of pa). One pair of black-pigmented eyes (ey) is located at the basis of the lateral antennae. The specimen was already fixed when the picture was taken—deviation in colouration of the specimen is possible. (F) Dorvillea spec., dorsal view. Four relatively long head appendages are present (1 pair of la, 1 pair of pa). Two pairs of red-pigmented eyes (ey) are located on the posterior edge of the prostomium. (G) Arabella iricolor, dorsal view. Head appendages are lacking, but two pairs of black-pigmented eyes (ey) are present on the prostomium. (H) Scoletoma tetraura, dorsal view. Lacks head appendages as well as eyes. ey = eye, la = lateral antenna, ma = median antenna, pa = palp, pe = peristomium, pr = prostomium.
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Figure 2.
Components and topology of the cns in Eunicida. The 3D reconstructions and volume renderings are based on µCT scans (A–F), cLSM scans of sagittal sections (G,H). (A) Leodice torquata, dorsal view. (B) L. torquata, lateral view. (C) Lysidice ninetta, dorsal view. (D) L. ninetta, lateral view. (E) Hyalinoecia tubicola, dorsal view. (F) H. tubicola, lateral view. (G) Scoletoma tetraura, lateral view. A fine net of frontal nerves (fn) originating from the brain neuropil innervates the anterior part of the prostomium. The dorsal and the ventral brain neuropil (dnp, vnp) can be distinguished. Nuchal organ nerves (non) originate from the posterior-most part of the dorsal brain neuropil (dnp) and innervate the nuchal organ (indicated by green arrowhead). (H) S. tetraura, lateral view. From the ventral brain neuropil, the oesophageal nerves (on) originate at height of the mouth opening (purple arrowhead). br: brain; ca: caudal; cc: circumoesophageal connective; cns: central nervous system; dnp: dorsal brain neuropil; ey: eye; fn: frontal nerves; fr: frontal; jn: jaw nerves; ma: median antenna; mo: mouth opening; no: nuchal organ; non: nuchal organ nerve; on: oesophageal nerves; pe: peristomium; pr: prostomium; vnc: ventral nerve chord; vnp: ventral brain neuropil; green arrow: nuchal cavity; pink arrow: mouth opening.
Figure 2.
Components and topology of the cns in Eunicida. The 3D reconstructions and volume renderings are based on µCT scans (A–F), cLSM scans of sagittal sections (G,H). (A) Leodice torquata, dorsal view. (B) L. torquata, lateral view. (C) Lysidice ninetta, dorsal view. (D) L. ninetta, lateral view. (E) Hyalinoecia tubicola, dorsal view. (F) H. tubicola, lateral view. (G) Scoletoma tetraura, lateral view. A fine net of frontal nerves (fn) originating from the brain neuropil innervates the anterior part of the prostomium. The dorsal and the ventral brain neuropil (dnp, vnp) can be distinguished. Nuchal organ nerves (non) originate from the posterior-most part of the dorsal brain neuropil (dnp) and innervate the nuchal organ (indicated by green arrowhead). (H) S. tetraura, lateral view. From the ventral brain neuropil, the oesophageal nerves (on) originate at height of the mouth opening (purple arrowhead). br: brain; ca: caudal; cc: circumoesophageal connective; cns: central nervous system; dnp: dorsal brain neuropil; ey: eye; fn: frontal nerves; fr: frontal; jn: jaw nerves; ma: median antenna; mo: mouth opening; no: nuchal organ; non: nuchal organ nerve; on: oesophageal nerves; pe: peristomium; pr: prostomium; vnc: ventral nerve chord; vnp: ventral brain neuropil; green arrow: nuchal cavity; pink arrow: mouth opening.
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Figure 3.
General brain anatomy. Histological cross sections (5 µm, AZAN) of Leodice torquata (A,B) and Arabella iricolor (F,G). Three-dimensional reconstructions based on histological serial sections of Lysidice ninetta (C–E) and A. iricolor (H–J). at: association tract; atmla: association tracts of the median and the lateral antennae; bc: buccal cavity; ca: caudal; cc: circumoesophageal connective; d: dorsal; dcvr: dorsal commissure of the ventral root of the circumoesophageal connective; dn: dorsal nerves; dnp: dorsal brain neuropil; drcc: dorsal root of the circumoesophageal connective; ey: eye; fr: frontal; ic: intracerebral commissure; if: intermediate filaments; jn: jaw nerves; lan: lateral antenna nerve; man: median antenna nerve; no: nuchal organ; oc: optical commissure; oegc: connective of the oesophageal ganglion; oen: oesophageal nerves; on: optical nerve; stn: stomatogastric nerves v: ventral; vcvr: ventral commissure of the ventral root of the circumoesophageal connective; vnp: ventral brain neuropil; vrcc: ventral root of the circumoesophageal connective.
Figure 3.
General brain anatomy. Histological cross sections (5 µm, AZAN) of Leodice torquata (A,B) and Arabella iricolor (F,G). Three-dimensional reconstructions based on histological serial sections of Lysidice ninetta (C–E) and A. iricolor (H–J). at: association tract; atmla: association tracts of the median and the lateral antennae; bc: buccal cavity; ca: caudal; cc: circumoesophageal connective; d: dorsal; dcvr: dorsal commissure of the ventral root of the circumoesophageal connective; dn: dorsal nerves; dnp: dorsal brain neuropil; drcc: dorsal root of the circumoesophageal connective; ey: eye; fr: frontal; ic: intracerebral commissure; if: intermediate filaments; jn: jaw nerves; lan: lateral antenna nerve; man: median antenna nerve; no: nuchal organ; oc: optical commissure; oegc: connective of the oesophageal ganglion; oen: oesophageal nerves; on: optical nerve; stn: stomatogastric nerves v: ventral; vcvr: ventral commissure of the ventral root of the circumoesophageal connective; vnp: ventral brain neuropil; vrcc: ventral root of the circumoesophageal connective.
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Figure 4.
Lateral brain neuropils in Arabella iricolor (Oenonidae) and Scoletoma tetraura (Lumbrineridae). Histological cross sections (5 µm, AZAN) (A,C,D). Three-dimensional reconstructions based on histological serial sections (B,E). (A) The lateral brain neuropil (lnp) is surrounded by a dense layer of somata of type 1 neurons (S1) and intermediate filaments (if) of glia cells in A. iricolor. (B) 3D reconstruction of the lnp and the tract (tlnp) connecting both neuropils in the brain (np) in A. iricolor. The dorsal nerves (dn) root partially in the tlnp. Frontal view. (C) The dn root in the tlnp and the dorsal brain neuropil (dnp) in A. iricolor. The tract is surrounded by intermediate filaments (if) of glia cells. (D) A dense layer of somata of type 1 neurons (S1) surround the lnp in S. tetraura. (E) A 3D reconstruction of the lnp and the tlnp connecting both neuropils in the brain (np) of S. tetraura. Frontal view. d: dorsal; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dn: dorsal nerves; dnp: dorsal brain neuropil; if: intermediate filaments; lnp: lateral brain neuropil; np: neuropil; S1: somata of type 1 neurons; tlnp: tract of the lateral brain neuropils; v: ventral; vnp: ventral brain neuropil.
Figure 4.
Lateral brain neuropils in Arabella iricolor (Oenonidae) and Scoletoma tetraura (Lumbrineridae). Histological cross sections (5 µm, AZAN) (A,C,D). Three-dimensional reconstructions based on histological serial sections (B,E). (A) The lateral brain neuropil (lnp) is surrounded by a dense layer of somata of type 1 neurons (S1) and intermediate filaments (if) of glia cells in A. iricolor. (B) 3D reconstruction of the lnp and the tract (tlnp) connecting both neuropils in the brain (np) in A. iricolor. The dorsal nerves (dn) root partially in the tlnp. Frontal view. (C) The dn root in the tlnp and the dorsal brain neuropil (dnp) in A. iricolor. The tract is surrounded by intermediate filaments (if) of glia cells. (D) A dense layer of somata of type 1 neurons (S1) surround the lnp in S. tetraura. (E) A 3D reconstruction of the lnp and the tlnp connecting both neuropils in the brain (np) of S. tetraura. Frontal view. d: dorsal; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dn: dorsal nerves; dnp: dorsal brain neuropil; if: intermediate filaments; lnp: lateral brain neuropil; np: neuropil; S1: somata of type 1 neurons; tlnp: tract of the lateral brain neuropils; v: ventral; vnp: ventral brain neuropil.
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Figure 5.
Brain neuropil and different types of neuronal somata. Ultra-thin cross sections (70 nm) of Paucibranchia bellii (A,B) and histological cross sections (5 µm, AZAN) of Scoletoma tetraura (C–F). (A) Distribution of different types of somata (S1, S2, S3) around the brain neuropil (np). (B) Somata of type 1 neurons (S1). (C) Somata of type 2 neurons (S2). (D) Somata of type 3 neurons (S3) with prominent nucleoli (nuc) in the nucleus. © The brain neuropil (np) consists of neurites (nt) of different sizes and orientations. Processes of glial cells (pgc) surround the central neuropil (np) creating a layer between the central neuropil (np) and the neuronal somata (so). Nuclei of the glial cells (ngc) are brick-shaped and processes of the glial cells (pgc) can be distinguished. Neuronal somata (so) are interconnected by desmosomes (ds). (F) Dense (dcv) and lucent core vesicles (lcv) are present in the brain containing neurotransmitters. dcv: dense core vesicles; ds: desmosomes; gc: glia cells; if: intermediate filaments; lcv: lucent core vesicles; ngc: nucleus of glia cell; np: neuropil; nt: neurite; nu: nucleus; nuc: nucleolus; pgc: processes of glia cell; S1: somata of type 1 neurons; S2: somata of type 2 neurons; S3: somata of type 3 neurons; so: somata.
Figure 5.
Brain neuropil and different types of neuronal somata. Ultra-thin cross sections (70 nm) of Paucibranchia bellii (A,B) and histological cross sections (5 µm, AZAN) of Scoletoma tetraura (C–F). (A) Distribution of different types of somata (S1, S2, S3) around the brain neuropil (np). (B) Somata of type 1 neurons (S1). (C) Somata of type 2 neurons (S2). (D) Somata of type 3 neurons (S3) with prominent nucleoli (nuc) in the nucleus. © The brain neuropil (np) consists of neurites (nt) of different sizes and orientations. Processes of glial cells (pgc) surround the central neuropil (np) creating a layer between the central neuropil (np) and the neuronal somata (so). Nuclei of the glial cells (ngc) are brick-shaped and processes of the glial cells (pgc) can be distinguished. Neuronal somata (so) are interconnected by desmosomes (ds). (F) Dense (dcv) and lucent core vesicles (lcv) are present in the brain containing neurotransmitters. dcv: dense core vesicles; ds: desmosomes; gc: glia cells; if: intermediate filaments; lcv: lucent core vesicles; ngc: nucleus of glia cell; np: neuropil; nt: neurite; nu: nucleus; nuc: nucleolus; pgc: processes of glia cell; S1: somata of type 1 neurons; S2: somata of type 2 neurons; S3: somata of type 3 neurons; so: somata.
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Figure 6.
Generalized schemes of the innervation patterns of species bearing different numbers of antennae, palps, and eyes and conditions in species lacking these sensory organs. The asterisk (*) in picture D indicates the inclusion of data from Zanol [
20]. (
A) Innervation patterns found in Eunicidae and Onuphidae bearing 5 head appendages (
Pauchibranchia bellii,
Marphysa spec.,
Leodice torquata,
Hyalinoecia tubicola). (
B) Innervation patterns found in
Lysidine ninetta (3 head appendages). (
C) Innervation patterns of
Nematonereis unicornis (1 head appendage). (
D) Innervation patterns of
Dorvillea spec. (4 head appendages). (
E) Innervation patterns of
Arabella iricolor (lacking head appendages, but possessing two pairs of eyes). (
F) Conditions found in
Scoletoma tetraura and
Scoletoma fragilis (lacking head appnendages and eyes). aoc: anterior optical commissure; atla: association tract of the lateral antennae; atma: association tract of the median antenna; bln: buccal lip nerve; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dn: dorsal nerve; e: eye; ic: intracerebral cavity; lan: lateral antenna nerve; lnp: lateral neuropil; lnpc: lateral neuropil commissure; lnpc1: first commissure of the lateral neuropils; lnpc2: second commissure of the lateral neuropils; man: median antenna nerve; np: brain neuropil; oc: optical commissure; pn: palp nerve; pnr: palp nerve root; poc: posterior optical commissure.
Figure 6.
Generalized schemes of the innervation patterns of species bearing different numbers of antennae, palps, and eyes and conditions in species lacking these sensory organs. The asterisk (*) in picture D indicates the inclusion of data from Zanol [
20]. (
A) Innervation patterns found in Eunicidae and Onuphidae bearing 5 head appendages (
Pauchibranchia bellii,
Marphysa spec.,
Leodice torquata,
Hyalinoecia tubicola). (
B) Innervation patterns found in
Lysidine ninetta (3 head appendages). (
C) Innervation patterns of
Nematonereis unicornis (1 head appendage). (
D) Innervation patterns of
Dorvillea spec. (4 head appendages). (
E) Innervation patterns of
Arabella iricolor (lacking head appendages, but possessing two pairs of eyes). (
F) Conditions found in
Scoletoma tetraura and
Scoletoma fragilis (lacking head appnendages and eyes). aoc: anterior optical commissure; atla: association tract of the lateral antennae; atma: association tract of the median antenna; bln: buccal lip nerve; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dn: dorsal nerve; e: eye; ic: intracerebral cavity; lan: lateral antenna nerve; lnp: lateral neuropil; lnpc: lateral neuropil commissure; lnpc1: first commissure of the lateral neuropils; lnpc2: second commissure of the lateral neuropils; man: median antenna nerve; np: brain neuropil; oc: optical commissure; pn: palp nerve; pnr: palp nerve root; poc: posterior optical commissure.
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Figure 7.
Schematic drawings of association tracts and nerve roots (light grey, reddish) of species bearing five head appendages based on a serial histological cross section of the dorsal brain neuropil (dark grey). (A) Eunicidae (Marphysa spec., Paucibranchia bellii and Leodice torquata). (B) Onuphidae (Hyalinoecia tubicola). atla: association tract of the lateral antenna; atla1: first association tract of the lateral antenna; atla2: second association tract of the lateral antenna; atma: association tract of the median antenna; atmla: association tract of the median and the lateral antennae; cas: commissure of the association system; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dfm: dorsal fibril mass; dnp: dorsal brain neuropil; drcc: dorsal root of the circumoesophageal connective; lan: lateral antenna nerve; lanr: nerve root of the lateral antenna; latla: lateral association tract of the lateral antenna; latla1: lateral root of the first association tract of the lateral antenna; latla2: lateral root of the second association tract of the lateral antenna; llanr: lateral root of the lateral antenna nerve; man: median antenna nerve; matla: median association tract of the lateral antenna; matla1: median root of the first association tract of the lateral antenna; matla2: median root of the second association tract of the lateral antenna; manr1: first root of the median antenna nerve; manr2: second root of the median antenna nerve; manr3: third root of the median antenna nerve; mlanr: median root of the lateral antenna nerve; mlanr2: second median root of the lateral antenna nerve; mlanr3: third median root of the lateral antenna nerve; pn: palp nerve; pnr1: first root of the palp nerve; pnr2: second root of the palp nerve; pnr3: third root of the palp nerve.
Figure 7.
Schematic drawings of association tracts and nerve roots (light grey, reddish) of species bearing five head appendages based on a serial histological cross section of the dorsal brain neuropil (dark grey). (A) Eunicidae (Marphysa spec., Paucibranchia bellii and Leodice torquata). (B) Onuphidae (Hyalinoecia tubicola). atla: association tract of the lateral antenna; atla1: first association tract of the lateral antenna; atla2: second association tract of the lateral antenna; atma: association tract of the median antenna; atmla: association tract of the median and the lateral antennae; cas: commissure of the association system; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dfm: dorsal fibril mass; dnp: dorsal brain neuropil; drcc: dorsal root of the circumoesophageal connective; lan: lateral antenna nerve; lanr: nerve root of the lateral antenna; latla: lateral association tract of the lateral antenna; latla1: lateral root of the first association tract of the lateral antenna; latla2: lateral root of the second association tract of the lateral antenna; llanr: lateral root of the lateral antenna nerve; man: median antenna nerve; matla: median association tract of the lateral antenna; matla1: median root of the first association tract of the lateral antenna; matla2: median root of the second association tract of the lateral antenna; manr1: first root of the median antenna nerve; manr2: second root of the median antenna nerve; manr3: third root of the median antenna nerve; mlanr: median root of the lateral antenna nerve; mlanr2: second median root of the lateral antenna nerve; mlanr3: third median root of the lateral antenna nerve; pn: palp nerve; pnr1: first root of the palp nerve; pnr2: second root of the palp nerve; pnr3: third root of the palp nerve.
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Figure 8.
Association tracts of Pauchibranchia bellii, Marphysa spec., Leodice torquata and dorsal nerves of Arabella iricolor. Histological cross sections (5 µm), silver staining (A–C,E,G), AZAN staining (F). Three-dimensional reconstructions based on histological serial sections (D). Pictures (B,C,E,G) show association tracts in a consecutive anterior-posterior course. (A) Marphysa spec. The nerves of the median and the lateral antenna (man, lan) root in the dorsal commissure of the dorsal root of the circumoesophageal connective (dcdr) and the respective association tracts (atma, atla). The association tract of the median antenna (atma) proceeds in a ventral direction through the dorsal brain neuropil (dnp). The association tract of the lateral antenna (atla) runs diagonally through the dorsal brain neuropil. (B) Leodice torquata. The association tracts of the lateral antennae (atla) fuse with the association tracts of the median antenna (atma) in the ventral part of the dorsal brain neuropil (dnp). (C) L. torquata. The association tracts of both lateral antenna (atla) fuse in the ventral brain neuropil creating a ventral commissure (vc). (D) Paucibranchia bellii, frontal view. The association tracts of the median antenna (atma) and the lateral antennae (atla) fuse in two association tracts (atmla). The association tracts of the median and the lateral antennae (atmla) proceed in the anterior direction through the dorsal brain neuropil. (E) L. torquata. Both nerves of the median antenna (man) fuse in one association tract (atma). (F) Arabella iricolor. A pair of dorsal nerves (dn) originates from the dorsal brain neuropil (dnp) in a topologically similar position as the median antenna nerves of antennae-bearing species. (G) L. torquata. The association tract of the median antenna (atma) splits into two tracts, which will fuse with the respective association tracts of the lateral antenna (atla) creating the association tracts of the median and the lateral antennae (atmla). atla: association tract of the lateral antenna; atma: association tract of the median antenna; atmla: association tract of the median and the lateral antennae; d: dorsal; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dn: dorsal nerves; dnp: dorsal brain neuropil; ey: eye; la: lateral antenna; lan: lateral antenna nerve; ma: median antenna; man: median antenna nerve; np: neuropil; on: optical nerve; pn: palp nerve; vc: ventral commissure; v: ventral.
Figure 8.
Association tracts of Pauchibranchia bellii, Marphysa spec., Leodice torquata and dorsal nerves of Arabella iricolor. Histological cross sections (5 µm), silver staining (A–C,E,G), AZAN staining (F). Three-dimensional reconstructions based on histological serial sections (D). Pictures (B,C,E,G) show association tracts in a consecutive anterior-posterior course. (A) Marphysa spec. The nerves of the median and the lateral antenna (man, lan) root in the dorsal commissure of the dorsal root of the circumoesophageal connective (dcdr) and the respective association tracts (atma, atla). The association tract of the median antenna (atma) proceeds in a ventral direction through the dorsal brain neuropil (dnp). The association tract of the lateral antenna (atla) runs diagonally through the dorsal brain neuropil. (B) Leodice torquata. The association tracts of the lateral antennae (atla) fuse with the association tracts of the median antenna (atma) in the ventral part of the dorsal brain neuropil (dnp). (C) L. torquata. The association tracts of both lateral antenna (atla) fuse in the ventral brain neuropil creating a ventral commissure (vc). (D) Paucibranchia bellii, frontal view. The association tracts of the median antenna (atma) and the lateral antennae (atla) fuse in two association tracts (atmla). The association tracts of the median and the lateral antennae (atmla) proceed in the anterior direction through the dorsal brain neuropil. (E) L. torquata. Both nerves of the median antenna (man) fuse in one association tract (atma). (F) Arabella iricolor. A pair of dorsal nerves (dn) originates from the dorsal brain neuropil (dnp) in a topologically similar position as the median antenna nerves of antennae-bearing species. (G) L. torquata. The association tract of the median antenna (atma) splits into two tracts, which will fuse with the respective association tracts of the lateral antenna (atla) creating the association tracts of the median and the lateral antennae (atmla). atla: association tract of the lateral antenna; atma: association tract of the median antenna; atmla: association tract of the median and the lateral antennae; d: dorsal; dcdr: dorsal commissure of the dorsal root of the circumoesophageal connective; dn: dorsal nerves; dnp: dorsal brain neuropil; ey: eye; la: lateral antenna; lan: lateral antenna nerve; ma: median antenna; man: median antenna nerve; np: neuropil; on: optical nerve; pn: palp nerve; vc: ventral commissure; v: ventral.
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Figure 9.
Inner morphology and innervation of antennae and palps. Histological cross sections (5 µm) stained in AZAN (A,E–H) or silver (C,D). Horizontal section (5 µm, AZAN) (B). (A) Leodice torquata (lateral antenna). Antennae as well as palps possess one main nerve, which consists of medially located longitudinal nerve fibres (ln) and surrounding circular nerve fibres (cn). Both types of nerve fibres possess nuclei of glia cells (gcn). (B) Leodice torquata (palp). Longitudinal nerve fibres (ln) and circular nerve fibres (cn) proceed nearly until the tip of the respective head appendage. (C) Marphysa spec.: The main nerve of the median antenna and the lateral antenna splits at height of the coelomic cavity (co) into two main roots (median antenna: 2x manr1; lateral antenna: mlanr1, llanr), respectively. Each main nerve root runs alongside the antenna coelom (palp coelom) (co) towards the brain (np). Prior to entering the brain, the main nerve roots split into several minor nerve roots (e.g., manr2, manr3, atma), some of which originate from the dcdr or proceed as association tracts (e.g., atma) through the dorsal brain neuropil. Each antenna or palp coelom (co) contains musculature (mu). (D) Marphysa spec.: The palp nerve (pn) proceeds along the dorsally located side of the palp coelom (co) and splits into minor nerve roots prior to entering the brain (np). (E) Palp nerve roots exemplified for Leodice torquata. The palp nerve (pn) passes the palp coelom (co) and splits at least into three minor palp nerve roots (pnr) before entering the brain. The two more dorsally located palp nerve roots originate from the dorsal brain neuropil (dnp), and the more ventrally located palp nerve root originates from the ventral brain neuropil (vnp). (F,G) In Dorvillea spec. each palp is innervated by two palp nerves (dpn, vnp). The more dorsally located palp nerve (dpn) originates from the dorsal brain neuropil (dnp), and the more ventrally located palp nerve (vpn) originates from the ventral brain neuropil (vnp). Both nerves proceed together with the coelomic cavity (co) and musculature (mu) through the palp. (H) Separation of palps into palpophore (pp) and palpostyle (ps) exemplified for Hyalinoecia tubicola. The palp is composed of an annulated basal palpophore (pp) and a distal palpostyle (ps). One palp nerve (pn) innervates the palp. atma = association tract of the median antenna, ca = caudal, cn = circular nerve fibres, co = coelom, cu = cuticle, d = dorsal, dcdr = dorsal commissure of the dorsal root of the circumoesophageal connective, dfm = dorsal fibril mass, dnp = dorsal brain neuropil, dpn = dorsal palp nerve, ep = epidermis, ey = eye, fr = frontal, gcn = nuclei of glia cells, la = lateral antenna, lan = lateral antenna nerve, llanr = lateral root of the lateral antenna nerve, ln = longitudinal nerve fibres, ma = median antenna, manr1 = first root of the median antenna nerve, manr2 = second root of the median antenna nerve, manr3 = third root of the median antenna nerve, mlanr1 = median root of the lateral antenna nerve, mu = musculature, np = neuropil, p = palp, pn = palp nerve, pnr = roots of palp nerve, pp = palpophore, ps = palpostyle, S3 = somata of class 3 neurons, sc = stomatogastric cavity, so = somata, v = ventral, vnp = ventral brain neuropil, vpn = ventral palp nerve.
Figure 9.
Inner morphology and innervation of antennae and palps. Histological cross sections (5 µm) stained in AZAN (A,E–H) or silver (C,D). Horizontal section (5 µm, AZAN) (B). (A) Leodice torquata (lateral antenna). Antennae as well as palps possess one main nerve, which consists of medially located longitudinal nerve fibres (ln) and surrounding circular nerve fibres (cn). Both types of nerve fibres possess nuclei of glia cells (gcn). (B) Leodice torquata (palp). Longitudinal nerve fibres (ln) and circular nerve fibres (cn) proceed nearly until the tip of the respective head appendage. (C) Marphysa spec.: The main nerve of the median antenna and the lateral antenna splits at height of the coelomic cavity (co) into two main roots (median antenna: 2x manr1; lateral antenna: mlanr1, llanr), respectively. Each main nerve root runs alongside the antenna coelom (palp coelom) (co) towards the brain (np). Prior to entering the brain, the main nerve roots split into several minor nerve roots (e.g., manr2, manr3, atma), some of which originate from the dcdr or proceed as association tracts (e.g., atma) through the dorsal brain neuropil. Each antenna or palp coelom (co) contains musculature (mu). (D) Marphysa spec.: The palp nerve (pn) proceeds along the dorsally located side of the palp coelom (co) and splits into minor nerve roots prior to entering the brain (np). (E) Palp nerve roots exemplified for Leodice torquata. The palp nerve (pn) passes the palp coelom (co) and splits at least into three minor palp nerve roots (pnr) before entering the brain. The two more dorsally located palp nerve roots originate from the dorsal brain neuropil (dnp), and the more ventrally located palp nerve root originates from the ventral brain neuropil (vnp). (F,G) In Dorvillea spec. each palp is innervated by two palp nerves (dpn, vnp). The more dorsally located palp nerve (dpn) originates from the dorsal brain neuropil (dnp), and the more ventrally located palp nerve (vpn) originates from the ventral brain neuropil (vnp). Both nerves proceed together with the coelomic cavity (co) and musculature (mu) through the palp. (H) Separation of palps into palpophore (pp) and palpostyle (ps) exemplified for Hyalinoecia tubicola. The palp is composed of an annulated basal palpophore (pp) and a distal palpostyle (ps). One palp nerve (pn) innervates the palp. atma = association tract of the median antenna, ca = caudal, cn = circular nerve fibres, co = coelom, cu = cuticle, d = dorsal, dcdr = dorsal commissure of the dorsal root of the circumoesophageal connective, dfm = dorsal fibril mass, dnp = dorsal brain neuropil, dpn = dorsal palp nerve, ep = epidermis, ey = eye, fr = frontal, gcn = nuclei of glia cells, la = lateral antenna, lan = lateral antenna nerve, llanr = lateral root of the lateral antenna nerve, ln = longitudinal nerve fibres, ma = median antenna, manr1 = first root of the median antenna nerve, manr2 = second root of the median antenna nerve, manr3 = third root of the median antenna nerve, mlanr1 = median root of the lateral antenna nerve, mu = musculature, np = neuropil, p = palp, pn = palp nerve, pnr = roots of palp nerve, pp = palpophore, ps = palpostyle, S3 = somata of class 3 neurons, sc = stomatogastric cavity, so = somata, v = ventral, vnp = ventral brain neuropil, vpn = ventral palp nerve.
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Figure 10.
Anatomy and innervation of buccal lips. Ventral view of the prostomium (A,B). Histological cross sections (5 µm, AZAN) (D,E). (A) Paired buccal lips (bl) of Leodice torquata. (B) In Hyalinoecia tubicola two pairs of buccal lips are present—one pair of dorsal buccal lips (dbl) and one pair of ventral buccal lips. Additionally, one pair of accessory buccal lips (abl) are present. (C) In Arabella iricolor buccal lips are absent. (D,E) Innervation of buccal lips (bl) in L. torquata. Buccal lips (bl) are innervated by nerves (bln) originating from the ventral brain neuropil (vnp). The nerves run along the cavity of the buccal lip (blc). abl = accessory buccal lips, bl = buccal lip, blc = coelomic cavity of the buccal lip, bln = buccal lip nerve, dbl = dorsal buccal lip, dnp = dorsal brain neuropil, mo = mouth opening, vbl = ventral buccal lip, vnp = ventral brain neuropil.
Figure 10.
Anatomy and innervation of buccal lips. Ventral view of the prostomium (A,B). Histological cross sections (5 µm, AZAN) (D,E). (A) Paired buccal lips (bl) of Leodice torquata. (B) In Hyalinoecia tubicola two pairs of buccal lips are present—one pair of dorsal buccal lips (dbl) and one pair of ventral buccal lips. Additionally, one pair of accessory buccal lips (abl) are present. (C) In Arabella iricolor buccal lips are absent. (D,E) Innervation of buccal lips (bl) in L. torquata. Buccal lips (bl) are innervated by nerves (bln) originating from the ventral brain neuropil (vnp). The nerves run along the cavity of the buccal lip (blc). abl = accessory buccal lips, bl = buccal lip, blc = coelomic cavity of the buccal lip, bln = buccal lip nerve, dbl = dorsal buccal lip, dnp = dorsal brain neuropil, mo = mouth opening, vbl = ventral buccal lip, vnp = ventral brain neuropil.
Figure 11.
Anatomy and innervation of the eyes. Histological cross sections (5 µm), AZAN staining (A,B), silver staining (C), 3D reconstructions (D,E). (A) Paucibranchia bellii. The eye is composed of a lens-like structure (lls) in the inner, covered by a layer of sensory microvilli (smv), pigmented supportive cells (psc), and photoreceptor cells (prc). Unpigmented sensory cells (usc) and microvilli (mv) cover the lens-like structure as the uppermost layer. The eye is situated basally to the epidermis (ep). A cuticular channel (cuc) can be identified projecting from the cuticle (cu) into the eye. The eye is innervated by an optical nerve (on) originating from the brain (np). The optical nerve (oc) splits next to the eye into minor nerves. (B) Arabella iricolor. Two pairs of eyes are present, the ventral one being bigger than the dorsal one. Both eye pairs are innervated by one optical nerve (on), respectively. (C,D) Lysidice ninetta. In the brain (np), the optical nerves are connected by an optical commissure (oc). (E) Arabella iricolor. Two optical commissures can be differentiated in the brain (np)—an anterior optical commissure (aoc) connects the optical nerves of the more ventrally located pair of eyes and a posterior optical commissure (poc) connects the optical nerves of the more dorsally located pair of eyes. ae = additional eye, aoc = anterior optical commissure, cu = cuticle, cuc = cuticular channel, dn = dorsal nerve, ep = epidermis, ey = eye, lan = lateral antenna nerve, lls = lens-like structure, man = median antenna nerve, mv = microvilli, no = nuchal organ, np = neuropil, on = optical nerve, poc = posterior optical commissure, prc = photoreceptor cell, psc = pigmented sensory cell, smv = sensory microvilli, usc = unpigmented sensory cells.
Figure 11.
Anatomy and innervation of the eyes. Histological cross sections (5 µm), AZAN staining (A,B), silver staining (C), 3D reconstructions (D,E). (A) Paucibranchia bellii. The eye is composed of a lens-like structure (lls) in the inner, covered by a layer of sensory microvilli (smv), pigmented supportive cells (psc), and photoreceptor cells (prc). Unpigmented sensory cells (usc) and microvilli (mv) cover the lens-like structure as the uppermost layer. The eye is situated basally to the epidermis (ep). A cuticular channel (cuc) can be identified projecting from the cuticle (cu) into the eye. The eye is innervated by an optical nerve (on) originating from the brain (np). The optical nerve (oc) splits next to the eye into minor nerves. (B) Arabella iricolor. Two pairs of eyes are present, the ventral one being bigger than the dorsal one. Both eye pairs are innervated by one optical nerve (on), respectively. (C,D) Lysidice ninetta. In the brain (np), the optical nerves are connected by an optical commissure (oc). (E) Arabella iricolor. Two optical commissures can be differentiated in the brain (np)—an anterior optical commissure (aoc) connects the optical nerves of the more ventrally located pair of eyes and a posterior optical commissure (poc) connects the optical nerves of the more dorsally located pair of eyes. ae = additional eye, aoc = anterior optical commissure, cu = cuticle, cuc = cuticular channel, dn = dorsal nerve, ep = epidermis, ey = eye, lan = lateral antenna nerve, lls = lens-like structure, man = median antenna nerve, mv = microvilli, no = nuchal organ, np = neuropil, on = optical nerve, poc = posterior optical commissure, prc = photoreceptor cell, psc = pigmented sensory cell, smv = sensory microvilli, usc = unpigmented sensory cells.
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Figure 12.
Nuchal organs. Histological cross sections (5 µm) stained in AZAN (A–G) and immunohistochemically stained section (60 µm) (H). Schematic drawings (I–M), 3D reconstructions based on histological sections (N–P). (A) Paucibranchia bellii, unpaired, arc-shaped nuchal organ. (B) Lysidice ninetta, unpaired, arc-shaped nuchal organ. (C) Hyalinoecia tubicola, unpaired, arc-shaped nuchal organ. (D) Dorvillea spec., paired nuchal organs. (E) Arabella iricolor, paired, branched nuchal organ. (F) Scoletoma tetraura, unpaired, x-shaped nuchal organ. (G) L. ninetta, nuchal organ nerves (non) emanating from the brain (np) and innervating the nuchal organ. (H,I) Unpaired, arc-shaped nuchal organ in Eunicidae and Onuphidae. (J) Paired nuchal organ of Dorvillea spec. (K) Paired, branched nuchal organ of Oenonidae. (L) Unpaired, branched nuchal organ of Lumbrineridae. (M) Topology of the paired, branched nuchal organ in A. iricolor, lateral view. The nuchal organ (no) is located dorsally to dorsal brain neuropil (dnp) and is innervated by nerves (non) emanating from the posterior part of the brain. (N) Topology of the paired, branched nuchal organ in A. iricolor, dorsal view. (O) Topology of the unpaired, branched nuchal organ in S. tetraura, lateral view. The nuchal organ (no) is located dorsally to the posterior part of the dorsal brain neuropil (dnp). White arrow = cilia. ca = caudal, cu = cuticle, cp = ciliary patch, d = dorsal, dnp = dorsal brain neuropil, ey = eye, fr = frontal, m = musculature, nc = nuchal cavity, no = nuchal organ, non = nuchal organ nerve, np = neuropil, v = ventral.
Figure 12.
Nuchal organs. Histological cross sections (5 µm) stained in AZAN (A–G) and immunohistochemically stained section (60 µm) (H). Schematic drawings (I–M), 3D reconstructions based on histological sections (N–P). (A) Paucibranchia bellii, unpaired, arc-shaped nuchal organ. (B) Lysidice ninetta, unpaired, arc-shaped nuchal organ. (C) Hyalinoecia tubicola, unpaired, arc-shaped nuchal organ. (D) Dorvillea spec., paired nuchal organs. (E) Arabella iricolor, paired, branched nuchal organ. (F) Scoletoma tetraura, unpaired, x-shaped nuchal organ. (G) L. ninetta, nuchal organ nerves (non) emanating from the brain (np) and innervating the nuchal organ. (H,I) Unpaired, arc-shaped nuchal organ in Eunicidae and Onuphidae. (J) Paired nuchal organ of Dorvillea spec. (K) Paired, branched nuchal organ of Oenonidae. (L) Unpaired, branched nuchal organ of Lumbrineridae. (M) Topology of the paired, branched nuchal organ in A. iricolor, lateral view. The nuchal organ (no) is located dorsally to dorsal brain neuropil (dnp) and is innervated by nerves (non) emanating from the posterior part of the brain. (N) Topology of the paired, branched nuchal organ in A. iricolor, dorsal view. (O) Topology of the unpaired, branched nuchal organ in S. tetraura, lateral view. The nuchal organ (no) is located dorsally to the posterior part of the dorsal brain neuropil (dnp). White arrow = cilia. ca = caudal, cu = cuticle, cp = ciliary patch, d = dorsal, dnp = dorsal brain neuropil, ey = eye, fr = frontal, m = musculature, nc = nuchal cavity, no = nuchal organ, non = nuchal organ nerve, np = neuropil, v = ventral.
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Figure 13.
Characters mapped on the latest phylogenetic tree of Eunicidae (Tilic et al. [
2]). Dotted lines indicate unresolved phylogenetic positions: either Dorvilleidae and Histriobdellidae are a clade and sister group to the remaining Eunicidae, or Histriobdellidae is a sister taxon to all remaining Eunicidae. Numbers code for characters listed in the character matrix (see
Table 2).
Figure 13.
Characters mapped on the latest phylogenetic tree of Eunicidae (Tilic et al. [
2]). Dotted lines indicate unresolved phylogenetic positions: either Dorvilleidae and Histriobdellidae are a clade and sister group to the remaining Eunicidae, or Histriobdellidae is a sister taxon to all remaining Eunicidae. Numbers code for characters listed in the character matrix (see
Table 2).
Table 1.
Number of sensory prostomial structures (antennae, palps, buccal lips, eyes and nuchal organ) in the examined Eunicida.
Table 1.
Number of sensory prostomial structures (antennae, palps, buccal lips, eyes and nuchal organ) in the examined Eunicida.
Species | Median Antenna | Lateral Antennae | Palps | Buccal Lips | Eyes | Nuchal Organ |
---|
Pauchibranchia bellii | 1 | 2 | 2 | 2 | 2 | unpaired, arc-shaped |
Marphysa spec. | 1 | 2 | 2 | 2 | 2 | unpaired, arc-shaped |
Lysidice unicornis | 1 | 0 | 0 | 2 | 2 | unpaired, arc-shaped |
Lysidine ninetta | 1 | 2 | 0 | 2 | 2 | unpaired, arc-shaped |
Leodice torquata | 1 | 2 | 2 | 2 | 2 | unpaired, arc-shaped |
Hyalinoecia tubicola | 1 | 2 | 2 | 2 | 2 | unpaired, arc-shaped |
Dorvillea spec. | 0 | 2 | 2 | 0 | 4 | paired, simple |
Arabella iricolor | 0 | 0 | 0 | 0 | 4 (5) | paired, branched |
Scoletoma tetraura | 0 | 0 | 0 | 0 | 0 | unpaired, x-shaped |
Scoletoma fragilis | 0 | 0 | 0 | 0 | 0 | unpaired, x-shaped |
Histriobdella homari | 1 | 2 | 2 | 0? | 0? | “oval, very small pits” |
Table 2.
Character matrix. Depicted is the distribution of characters among the six studied families of Eunicida. The presence of a character is indicated by “+”, while its absence (or reduction) is marked with “-”. abl: accessory buccal lips, at: association tracts, dbl: dorsal buccal lips, ey: eye, la: lateral antenna, lo: lateral organ, ma: median antenna, no: nuchal organ, pa: palp, pr: prostomium, vbl: ventral buccal lips.
Table 2.
Character matrix. Depicted is the distribution of characters among the six studied families of Eunicida. The presence of a character is indicated by “+”, while its absence (or reduction) is marked with “-”. abl: accessory buccal lips, at: association tracts, dbl: dorsal buccal lips, ey: eye, la: lateral antenna, lo: lateral organ, ma: median antenna, no: nuchal organ, pa: palp, pr: prostomium, vbl: ventral buccal lips.
Tree Code | Character | Lumbrineridae | Oenonidae | Onuphidae | Eunicidae | Dorvilleidae | Histriobdellidae |
---|
1 | ma | - | - | + | + | - | + |
2 | la | - | - | + | + | + | + |
3 | pa | - | - | + | + | + | + |
4 | vbl | - | - | + | + | - | - |
5 | dbl | - | - | + | - | - | - |
6 | abl | - | - | + | - | - | - |
7 | ey | - | + 2 pairs | + 1 pair | + 1 pair | + 2 pairs | - |
8 | no | + | + | + | + | + 2 pairs | + |
9 | shape no | unpaired, x-shaped | paired, branched | unpaired, arc-shaped | unpaired, arc-shaped | paired, simple | paired, simple |
10 | lo | + | + | + | + | + | + |
11 | at | - | - | + | + | - | ? |
12 | shape pr | elongated, tapered | elongated, tapered | roundish | roundish | roundish | roundish |