Onuphis eremita Audouin & Milne Edwards, 1833 Emended

Arias, Andrés & Paxton, Hannelore, 2014, Hidden diversity within the polychaete Onuphis eremita sensu lato (Annelida: Onuphidae) — redescription of O. eremita Audouin & Milne-Edwards, 1833 and reinstatement of Onuphis pancerii Claparède, 1868, Zootaxa 3861 (2), pp. 145-169 : 148-158

Onuphis eremita Audouin & Milne Edwards, 1833 Emended

Figures 1–8 ; Tables 1–3

Onuphis eremita Audouin & Milne Edwards, 1833: 226 ; Redondo & San Martín, 1997: 227. Onuphis falesia Castelli, 1982: 45 , fig. 1–11 (Gulf of Follonica, Italy).

? Onuphis eremita oculata — Çinar, 2009: 2297 –2299, fig. 4 ( Turkey). Not Hartman, 1951.

Material examined. Neotype: La Rochelle ( France, eastern Atlantic), 46°09’N, 01°09’W – 46°09’N, 01°10’W, intertidal sands, coll. 28 Sep 2011 ( MNHN TYPE 1555); Paraneotypes: La Rochelle ( France, eastern Atlantic), 46°09’N, 01°09’W – 46°09’N, 01°10’W, intertidal sands, coll. 28 Sep 2011, 2 specimens ( MNCN 16.01/15343, MNCN 16.01/15344), 10 specimens coated with gold ( MNCN 16.01/15345), 2 specimens (AM W46618, AM W46619), 2 specimens ( BMNH 2014.39–40); Non-type specimens: Cap Ferret, Arcachon Bay, France, eastern Atlantic, intertidal sands, coll. 26 Sep 2011, 4 specimens ( MNCN 16.01/15346); Off shore between Vidio Cape and Peñas Cape, Cantabrian Sea, Spain, 15–32 m, 1998, 2 specimens ( MNCN 16.01/3966, MNCN 16.01/3971); Mazarrón beach, SE. Spain, western Mediterranean, intertidal sands, coll. 20 Mar 2012, 5 specimens (AM W46795 ); Denia, Alicante, E. Spain, western Mediterranean, intertidal, 0 1 Dec 1997, 1 specimen ( MNCN 16.01/ 4345); Off shore between San Antonio cape and Valencia harbour, E. Spain, western Mediterranean, 3–30 m, 93 specimens ( MNCN 16.01/1805, MNCN 16.01/1812, MNCN 16.01/1863– MNCN 16.01/1868, MNCN 16.01/ 1870– MNCN 16.01/1872, MNCN 16.01/1875– MNCN 16.01/1877, MNCN 16.01/1875– MNCN 16.01/1892, MNCN 16.01/1986, MNCN 16.01/2411– MNCN 16.01/2414, MNCN 16.01/2416, MNCN 16.01/2419, MNCN 16.01/2431, MNCN 16.01/2440, MNCN 16.01/2443, MNCN 16.01/2445, MNCN 16.01/2663, MNCN 16.01/ 2664, MNCN 16.01/2669, MNCN 16.01/2670, MNCN 16.01/2673, MNCN 16.01/2674); Sagunto Port, Valencia, E. Spain, western Mediterranean, 2–15 m, 4 specimens ( MNCN 16.01/5969– MNCN 16.01/5972); Off shore between Sagunto Port and Castellón harbour, E. Spain, western Mediterranean, 3–30 m, 10 specimens ( MNCN 16.01/5976, MNCN 16.01/5994, MNCN 16.01/6016, MNCN 16.01/6028, MNCN 16.01/6035, MNCN 16.01/ 6043, MNCN 16.01/6048); Off shore between Olympic Port of Barcelona and Mataró, NE. Spain, western Mediterranean, 5–25 m, 1 Jan 2000, 2 specimens ( MNCN 16.01/7819, MNCN 16.01/7830); St. Julians Bay, Malta, central Mediterranean, intertidal sands, coll. 6 Apr 2012, 2 specimens ( MNCN 16.01/15347).

Diagnosis. Based on specimens wider than 0.5 mm at chaetiger 10 excluding parapodia. Prostomium anteriorly extended, one pair of small eyespots present at anterolateral end of prostomium. Palps reaching chaetiger 2–4, lateral antennae reaching chaetiger 7–14 and median antenna chaetiger 4–7. Ceratophores long and strongly ringed, palpal ceratophores with 16–20 rings, lateral antennae with 19–22 and median antenna with 13–19 rings. Subulate ventral cirri in first five to six chaetigers; distinct subulate postchaetal lobes in first 10–17 chaetigers. Small interramal papilla present at base of dorsal cirrus in chaetigers 4(5)–9. Strongly tridentate pseudocompound long and short appendaged hooks in first three chaetigers. Subacicular hooks from chaetiger 10. Flat, distally oblique pectinate chaetae with 10–13 teeth. Single branchial filaments from chaetiger 1 to 20–26, thereafter number increasing rapidly to maximum of three to five. Colour pattern consisting of two rows of brownish patches on dorsal anterior end or brown transverse stripes when lateral patches coalesce medially. Tube thin-walled and covered with sand grains.

Description. Wide size range available (0.3–2.0 mm wide at chaetiger 10), but majority of specimens slender and medium sized, 54–98 mm long, 1.3–1.8 mm wide (170–196 chaetigers); maximum length 100 mm (200 chaetigers); maximum width 2.0 mm without parapodia. Various colour morphs, most with variation ( Fig. 1 A–D). Most common morph ( Fig. 1 A, C): brown pigment forming 4–6 circular spots on underside of ceratophores of antennae and palps; brown band on peristomium; chaetigers 1–2(3) with two pairs of dorsal lateral brown spots, continuing on anterior chaetigers but coalescing medially into two parallel bands and disappearing by chaetiger 25–30; lateral patches at bases of anterior parapodia starting at chaetiger 3–4, sometimes large enough to be visible ventrally. Other morphs with anterior chaetigers (1–25) with two pairs of dorsal lateral brown spots without coalescing medially ( Fig. 1 E).

Prostomium subtriangular with pair of conical frontal lips ( Fig. 1 F). Small pair of cup shaped eyespots present, situated close to bases of lateral antennae ( Figs 1 F, 2B). Palps reaching chaetiger 2–4 with 15–19 basal rings and longer distal one. Lateral antennae reaching chaetiger 7–14 with 18–21 basal rings, median antenna reaching chaetiger 4–7 with 12–18 basal rings, all three antennae with longer distal ring ( Fig. 3 A). Styles with irregular longitudinal rows of sensory buds ( Fig. 3 E); sensory buds flat, pores of serous glands forming semicircles ( Fig. 3 F). Nuchal grooves ( Fig. 3 D) straight with narrow middorsal separation. Peristomial cirri inserted distally on peristomium slightly lateral to lateral antennae, longer than length of peristomium, not exceeding anterior margin of prostomium ( Fig. 3 A).

Anterior chaetigers (1–3) slighty longer than those following ( Figs 1 A–E, 3A–C). First three pairs of parapodia modified, not enlarged, directed slightly anterolaterally, with low prechaetal fold, triangular prechaetal lobe and spindle-shaped postchaetal lobe, longer than base of parapodium; digitate dorsal cirrus about as long as postchaetal lobe and ventral cirrus longer than postchaetal lobe ( Figs 3 G, 4A). Subulate ventral cirri in first five to six chaetigers and pad-like thereafter ( Fig. 3 B, C). Postchaetal lobe as distinct subulate lobe in first 10–17 chaetigers, becoming smaller and conical in shape thereafter. Small interramal papilla present at base of dorsal cirrus in chaetigers 4(5)–9, sometimes reduced to a small bump on chaetiger 10 ( Fig. 3 H, I).

Branchiae as single filament from first chaetiger to chaetiger 20–25 ( Fig. 4 A), then number of filaments increasing rapidly to maximum of three to five in pectinate arrangement over chaetiger 35–50 ( Fig. 4 B, C); by chaetiger 50–60 diminishing in number and getting smaller and being simple again in posterior chaetigers.

Aciculae yellowish with pointed tips, usually three per parapodium. Hooded pseudocompound hooks in first three chaetigers. First three parapodia ( Figs 4 A, 5A) with following chaetal complement going from superior to inferior part of chaetal fan: one to two simple chaetae, two pectinate chaetae flat and slightly oblique with 10–13 long teeth ( Fig. 5 D, E), three protruding distal tips of aciculae ( Fig. 5 A, E), two to three slender long-appendaged strongly tridentate pseudocompound hooks ( Fig. 5 C), two to three more robust short-appendaged strongly tridentate pseudocompound hooks ( Fig. 5 B). Pseudocompound hooks replaced by limbate chaetae from chaetiger 4 ( Fig. 5 E). Hooded bidentate subacicular hooks from chaetiger 10 ( Fig. 5 F). Pygidium with four anal cirri, ventral twice as long as dorsal ones. Mandibles ( Fig. 4 E) with white calcified cutting plates and slender shafts. Maxillae ( Fig. 4 D) weakly sclerotised; maxillary formula: Mx I = 1 + 1, Mx II = 7 + 7, Mx III = 8 + 0, Mx IV = 6 + 10, Mx V = 1 + 1, Mx VI absent. Tube cylindrical in shape, parchment-like and externally covered with sand-grains ( Fig. 1 G, H).

Variation. Some variation was noted in the specimens examined ( Table 1 ). This information was based upon a large amount of material examined from the Atlantic Ocean and the Mediterranean Sea (150 specimens). Onuphis eremita does not display a high degree of variability with respect to its prostomial appendages, parapodial structures and chaetae. Most variation is size-related, as the maximal number of ceratophoral rings of antennae ( Fig. 6 A) or the maximal number of branchial filaments ( Fig. 6 B). In onuphids, the first appearance of subacicular hooks is usually positively correlated to the size of the worms, in smaller specimens the subacicular hooks start more anteriorly ( Paxton 1986, 1996). However, in O. eremita the stabilisation of this character seems to occur early in juvenile development, since in all examined specimens larger than 0.3 mm (width of 10th chaetiger) the appearance of subacicular hooks occurred invariably on chaetiger 10 ( Fig. 6 C). The number of anterior chaetigers with subulate ventral cirri varies from five to six. Specimens with five and six subulate ventral cirri occur together in samples from the same collection and from the same size-ranges. For example, of 93 specimens from the Mediterranean samples collected from subtidal sediments between San Antonio Cape and Valencia harbour, about 26% presented subulate ventral cirri on anterior five chaetigers and the other 74% on anterior six chaetigers. In Atlantic samples of O. eremita the percentages of specimens with five and six chaetigers with subulate ventral cirri were 15.38% and 84.62% respectively (N = 26). The number of chaetigers with subulate ventral cirri have been considered in previous reports of the species as an invariant character ( Fauchald 1982), most likely due to the lower number of specimens examined. The first chaetiger with one branchial filament ranges from 21–26 and does not appear to be size-related either ( Fig. 6 D).

The presence/absence of eyespots on the prostomium was used as a diagnostic character in discriminating species and subspecies within O. eremita , such as O. eremita oculata Hartman, 1951 ( Hartman 1951; Castelli 1982; Cinar 2009). Based on the original description and the large number of specimens herein examined, we can conclude that O. eremita has invariably a pair of eyespots on its prostomium, even the larger specimens. The examination of several specimens apparently without eyespots ( Fig. 2 A) under the confocal technique revealed that they actually possess a pair of eyespots, being detected by the presence of melanin pigment of its cups ( Fig. 2 B).

This technique also showed that the amount of the melanin pigment of the eyespot cup from larger specimens was lower than that of the smallest ones. However, this character is of little use in field identification or in routine evaluation of preserved animals. The eyespots cannot be easily observed most likely due to the following reasons: 1) in large animals the cuticle becomes thickened and the amount of melanin of the eyespot cap is lower than in smaller ones, hindering their observation, remaining invisible without using the confocal technique; 2) in preserved specimens of all sizes, the cuticle of the worm has often lifted off and the eyespot has become internalised.

Taxonomic remarks. Castelli (1982) described Onuphis falesia from the Gulf of Follonica (Tyrrhenian Sea, Italy). This author pointed out that O. falesia “is remarkably like O. eremita (which was collected in the same habitat)”, however he considered that the two species differed in the maximal number of branchial filaments (five to seven in O. eremita and two in O. falesia ), the range of chaetigers with one branchial filament (chaetiger 1 to 10– 20 in O. eremita and chaetiger 1 to 20– 25 in O. falesia ) and the ornamentation of the tube (small stones and shell fragments absent in O. eremita and present in O. falesia ). The maximal number of branchial filaments is a size-related character and Castelli’s specimens were small (20–25 mm length), accounting for the low number of branchial filaments. On the basis of the original description of O. eremita and the new type material here designated, the first chaetiger with more than one branchial filament ranges from 21–26, not from 10–20 as Castelli considered. Therefore, the range indicated for O. falesia is consistent with the range of variation of O. eremita . Types of O. falesia were not available for examination. However, after careful perusal of the original description and contrasting it with O. eremita features, we found no significant differences justifying O. falesia as a distinct species. Therefore, we think it most likely that O. falesia represents juvenile O. eremita and is a junior synonym of the latter species.

Çinar (2009) reported Onuphis eremita oculata from the coasts of Turkey (eastern Mediterranean basin). On the basis that his specimens had a small pair of eyes on the prostomium which he considered as a diagnostic feature of the Caribbean subspecies, he concluded that it was an alien species. Subsequently this presumed alien subspecies was included in various catalogues and reports on Mediterranean alien species (e.g. Zenetos et al. 2010; Çinar & Dagli 2012; Çinar 2013). Since the original description of O. eremita indicates the presence of eyespots, as well as that they are present in the neotype and most of the studied specimens, it is very likely that the subspecies reported by Çinar (2009) is actually O. eremita and hence a native species.

Onuphis eremita was previously reported from the Canary Islands ( Herrando-Pérez et al. 2001) but Canarian specimens were re-examined by Núñez in October 2013, revealing that they are a different Onuphis -like species and constitute most likely an undescribed species (J. Núñez, pers. com. to A.A.).

Neotype and paraneotypes. The original type locality of O. eremita was given as the sandy shore of La Rochelle ( France); however, the exact location was not specified. The new type material was selected from specimens collected from the intertidal sands (at low water mark) between the Port Neuf cove and La Concurrence beach 46°09’N, 01°09’W – 46°09’N, 01°10’W (La Rochelle, Atlantic coast of France).

Neotype ( Fig. 1 A), almost complete specimen with 170 chaetigers, 82 mm long, 1.4 mm wide (at chaetiger 10, without parapodia). Paraneotypes all incomplete, ranging from 4.1 to 98 mm in length (30–94 chaetigers) and from 0.5 to 2 mm in width. Neotype specimen with most common colour pattern ( Fig. 1 A). With a pair of eyespots situated on anterior part of prostomium. Palps reaching chaetiger 2 with 20 rings. Lateral antennae reaching chaetiger 11–12 with 22 rings and median antenna reaching chaetiger 4 with 18 rings. Chaetigers 1–3 slighty longer than those following. Subulate ventral cirri in first six chaetigers. Postchaetal lobe as distinct subulate lobe in first 12–13 chaetigers. Small interramal papilla present at base of dorsal cirrus in chaetigers 4–9, reduced to a small bump on chaetiger 10. Branchiae as single filament from first chaetiger to chaetiger 21–22 (with asymmetry between right and left parapodia), then reaching a maximal number of five filaments. Hooded pseudocompound strongly tridentate hooks in first three chaetigers. Hooded bidentate subacicular hooks from chaetiger 10.

Justification for the neotype. A neotype is needed for O. eremita , the type species of the genus since the original description of the species is brief and rather incomplete and no type material appears to be extant ( Fauchald 1982; T. Meziane (MNHN), pers. com. to H.P.). This has resulted in the species being variably defined by different authors and reported from many different localities and habitats around the world. The confusion over the identity of this species has hindered description and correct identification of related species over the last century. A redescription will constitute a baseline from which the numerous O. eremita like species reported worldwide can be contrasted with the type species and the assumed cosmopolitanism of the species can be assessed. Furthermore, by defining the type species, the cornerstone for a future revision of the Onuphis species complex is established.

Reproductive biology. Onuphis eremita is poorly known biologically. However, among the specimens from the Mediterranean, collected during spring months (from March to June), we found several individuals bearing eggs inside the coelomic cavity ( Fig. 7 B, C) which in some cases were protruding through openings of the body wall. As typical in Onuphinae , two strings of nurse cells were found attached to immature oocytes ( Fig. 7 C). Coelomic eggs ranged from 58 to 205 Μm in size (C = 143.83; SD = 40.50; N = 30); extracoelomic eggs varied from 122 to 216 Μm in diameter (X = 193.66; SD = 21.06; N = 30). No brooded eggs or embryos were found inside the dissected tubes or attached to them.

The spermatozoon of O. eremita has a more or less depressed subspherical nucleus, a cone-like acrosome and a long flagellum ( Fig. 7 D–I). The mean length of the head ( Fig. 7 F), from the acrosome tip to the posterior midpiece, is 2.26 Μm (SD = 0.14; N = 30). The spermatozoon is surrounded by the plasmalemma, which appears crenulated in the acrosomal and nuclear regions, and becomes smooth at the mitochondrial and flagellar regions ( Fig. 7 F–I). The acrosomal vesicle is conical in shape and radially symmetrical ( Fig. 7 F, G) with a small button-like structure present anteriorly on the acrosome tip ( Fig. 7 G). The middle piece consists of four to five almost spherical mitochondria ( Fig. 7 H–I). A ring is present around the initial portion of flagellum ( Fig. 7 H). The external morphology of the spermatozoon of O. eremita is consistent with a typical ect-aquasperm type ( Jamieson & Rouse 1989) due to its short, rounded head with a conical acrosome, four to six mitochondria and long tail.

Distribution, habitat and faunal associates. Onuphis eremita sensu lato has been recorded worldwide. However, O. eremita sensu stricto, as redefined on the basis of the neotype, is here restricted to the eastern Atlantic (Bay of Biscay) and western and central Mediterranean ( Fig. 8 ) where the species is most likely widely distributed.

Onuphis eremita occurs in sandy bottoms from the low water mark to ca. 30 m depth and is commonly affiliated with the classical biocoenosis of well sorted fine sands (SFBC) as defined by Pérès & Picard (1964). In its type locality this species is reported from an intertidal-shallow subtidal fine to medium sand community dominated by balthic tellins, Macoma balthica (Linnaeus) , and cockles, Cerastoderma edule (Linnaeus) . Along the Atlantic coasts of France, this species was found together with other onuphids of the genus Diopatra Audouin & Milne- Edwards, 1833. In La Rochelle O. eremita co-inhabits with D. biscayensis Fauchald et al., 2012 and in Arcachon Bay, with D. biscayensis and D. neapolitana Delle Chiaje, 1841 . That association seems to occur also in Mediterranean populations, where O. eremita was reported along with another Diopatra species, D. micrura Pires et al., 2010 (Redondo & San Martín 1997; Arias & Paxton 2013).

Ectosymbiotic microorganisms were found on the surface of the anterior parapodia of O. eremita . These epibionts were identified as peritrich ciliates belonging to the genus Epistylis Ehrenberg , characterised by forming colonies utilising its noncontractile and longer peduncle or stalk for attachment to the substrate ( Fig. 6 A). The symbiotic association “onuphid-peritrich” was previously reported for D. marocensis Paxton et al., 1995 from Villaviciosa estuary, northern Spain ( Arias et al. 2010).

Figures

FIGURE 1. Onuphis eremita. Neotype A (MNHN TYPE 1555), Paraneotypes C – E (MNCN 16.01 / 15343 - MNCN 16.01 / 15345), specimen from western Mediterranean B (AM W 46795). Photomicrographs. A – E, anterior end, dorsal view; F, detailed view of prostomium and peristomium, arrows point to little eyespots; G, whole specimen within its tube; H, anterior portion of tubes in nature.

FIGURE 2. Onuphis eremita. Photomicrographs. A, detailed view of prostomium of a specimen without externally visible eyespots; B, detailed view of prostomium of same specimen under Confocal microscopy, arrows point to little eyespots.

FIGURE 3. Onuphis eremita. Paraneotypes A – I (MNCN 16.01 / 15345). Scanning electron micrographs. A, anterior end, dorsal view; B, anterior end, ventral view of specimen with six chaetigers with subulate ventral cirri; C, anterior end, ventral view of specimen with five chaetigers with subulate ventral cirri; D, detailed view of nuchal groove; E, detailed view of style of antenna; F, detailed view of a sensory bud of antenna; G, parapodium chaetiger 1, anteroventral view; H, parapodium chaetiger 4, dorsal view, arrow points to interramal papilla; I, detailed view of chaetigers 6 to 8, ventral view; b, branchia; ch, chaetiger; dc, dorsal cirrus; gp, glandular pad, p, interramal papilla; pol, postchaetal lobe; prl, prechaetal lobe; sb, sensory bud; vc, ventral cirrus.

FIGURE 4. Onuphis eremita. Paraneotype (MNCN 16.01 / 15344). Line drawings. A, parapodium chaetiger 1, anterior view; B, parapodium chaetiger 23, anterior view; C, parapodium chaetiger 62; D, maxillae; E, mandibles.

FIGURE 5. Onuphis eremita. Paraneotypes (MNCN 16.01 / 15345). Scanning electron micrographs. A, pseudocompound hooks and aciculae, chaetiger 1; B, detailed view of short appendaged tridentate pseudocompound hook, chaetiger 2, arrow points to pseudocompound fracture; C, detailed view of long appendaged pseudocompound hook, chaetiger 1, arrow points to pseudocompound fracture; D, pectinate chaeta, chaetiger 10; E, detailed view of chaetae, chaetiger 4; F, subacicular hooks, chaetiger 10; a, acicula; l, limbate chaeta; la, long appendaged pseudocompound hook; pc, pectinate chaeta; sa, short appendaged pseudocompound hook.

FIGURE 6. Graphs illustrating size-related features in Onuphis eremita. A, relationship between body width of specimens and number of ceratophoral rings on antenna (N = 30); B, relationship between body width of specimens and maximal number of branchial filaments (N = 30); C, relationship between body width of specimens and origin of subacicular hooks (N = 30); D, relationship between body width of specimens and origin of multifilamentous branchia (N = 30).

FIGURE 7. Onuphis eremita. Scanning electron micrographs. A, detailed view of the ectosymbiont peritrich Epistylis sp. on anterior parapodia; B, intracoelomic developing oocytes; C, detailed view of immature oocyte with nurse cells attached; D – E, spermatozoa protruding from openings of the body wall; F, detailed view of spermatozoon, lateral view; G, detailed view of spermatozoon, frontal view. H – I, detailed view of spermatozoon, posterior view; a, acrosome; c, corona of cilia; f, flagellum; m, mitochondria; n, nucleus; nc, nurse cells; o, oocyte; p, peduncle; r, ring.

FIGURE 8. Distribution map of confirmed occurrences of Onuphis eremita and Onuphis pancerii. Squares, O. eremita localities; circles, O. pancerii localities.

Tables

TABLE 1. Statistics of variable features of Onuphis eremita

Character	Range	Mean	SD	N
Lateral antennae to chaetiger	7–14	11.63	1.04	50
Median antenna to chaetiger	4–7	5.76	0.96	50
No. of ceratophoral rings of antennae	13–22	19.60	1.68	50
No. of chaetigers with subulate VC	5–6	-	-	50
No. of chaetigers with subulate PCL	10–17	14.36	1.81	50
First chaetiger with interramal papillae	4–5	-	-	50
Last chaetiger with interramal papillae	9	invariant	-	50
Single branchial filaments from chaetiger	1	invariant	-	50
Two or more branchial filaments from chaetiger	21–26	23.63	1.36	50
Maximal no. of branchial filaments	3–5	4.26	0.62	50
No. of chaetigers with PCHs	3	invariant	-	50
Tip of PCH	tridentate	invariant	-	50
No. of teeth of pectinate chaeta	10–13	11.43	0.88	50
Origin of SAH (chaetiger no.)	10	invariant	-	50

No., number; PCH, pseudocompound hook; PCL, postchaetal lobe; SAH, subacicular hook; VC, ventral cirrus.