Meiodorvillea minuta (Hartman, 1965)

Bonaldo, Rafael de Oliveira, Steiner, Tatiana Menchini & Amaral, Antônia Cecília Zacagnini, 2022, Revision of Meiodorvillea Jumars, 1974 (Annelida: Dorvilleidae) including descriptions of three new species from the Southwestern Atlantic Ocean, PLoS ONE (e 0264081) 1974 (3), pp. 1-27 : 4-11

Meiodorvillea minuta (Hartman, 1965)

( Figs 1–6 , Table 1 )

Protodorvillea minuta Hartman, 1965 [ 13]: 125–127, plate 23

Meiodorvillea minuta –Jumars, 1974 [ 17]: 119–120, Fig 9

Type locality. Block Canyon , New England ( USA), upper continental slope, 39˚58’24"N, 70˚40’18"W, 300 m depth.

Type material examined. Neotype: LACM-AHF Poly 12561 39˚58’24"N 70˚ 40’18"W, 300 m, very fine sand, 28 Aug 1962 . Paratypes: LACM-AHF Poly 692 (6 specimens) 39˚58’24"N 70˚40’18"W, 300 m, very fine sand, 28 Aug 1962. (m = meters depth).

Other material examined. State of North Carolina – USNM 1008896 (8 specimens) 34˚ 15’2.16"N 75˚43’40.08"W, 1,019 m, mud, 27 Mar 1984. State of Espírito Santo – ZUEC-POL 21403 (1 spec) 21˚11’12.228"S 40˚12’51.745"W, 683 m, 04 Feb 2009; ZUEC-POL 21404 (1 spec) 20˚36’1.61"S 39˚51’39.15"W, 1,003 m, mud, 18 Jun 2013; ZUEC-POL 21392 (1 spec) 21˚ 11’3.022"S 40˚12’19.168"W, 790.2 m, 05 Jul 2008. State of Rio de Janeiro – ZUEC-POL 21393 (1 spec) 21˚47’26.324"S 40˚2’13.825"W, 730.5 m, 28 Jun 2008; ZUEC-POL 21394 (1 spec) 22˚ 36’25.559"S 40˚22’28.988"W, 698.1 m, 29 Jan 2009; ZUEC-POL 21395 (1 spec) 22˚36’27.781"S 40˚22’30.727"W, 695.4 m, 29 Jan 2009; ZUEC-POL 21396 (1 spec) 21˚41’11.649"S 40˚ 2’20.690"W, 699.4 m, 07 Jul 2008; ZUEC-POL 21397 (1 spec) 22˚19’2.381"S 40˚5’27.062"W, 383.8 m, 30 Jan 2009; ZUEC-POL 21398 (1 spec) 22˚33’35.143"S 40˚26’37.449"W, 401 m, 31 Jan 2009; ZUEC-POL 21399 (1 spec) 23˚39’21.880"S 41˚18’33.045"W, 692.7 m, 28 Jan 2009; ZUEC-POL 21400 (1 spec) 23˚37’58.489"S 41˚19’41.504"W, 400.5 m, 01 Feb 2009; ZUEC-POL 21401 (4 spec) 21˚56’11.912"S 39˚57’45.190"W, 705.2 m, 28 May 2008; ZUEC-POL 21402 (3 spec) 22˚19’10.211"S 40˚5’42.884"W, 400 m, 10 Feb 2009. (m = meters depth).

SEM material. State of Espírito Santo – ZUEC-POL 21405 (2 spec): 19˚37’45.14"S 39˚ 3’58.75"W, 1,050 m, mud, 25 Jun 2013 and 20˚14’17.95"S 39˚48’34.35"W, 395 m, mud, 19 Jun 2013. (m = meters depth)

Diagnosis. One pair of antennae and one pair of palps. Dorsal cirrus papilliform from chaetigers 2 to 5–9. Ventral cirrus papilliform, absent in the first chaetiger. Chaetae capillary, furcate asymmetrical, dorsalmost compound spiniger or falciger, median and ventralmost falcigers, and cultriform occasionally in last chaetigers in some specimens, replacing the ventralmost compound. Two pairs of pygidial cirri.

Designation of neotype. Hartman [ 13] listed the material examined of M. minuta as ‘Records: C 1 (3); S1 3 (11, TYPE); S1 4 (6); D 1 (4)’, mentioning off New England as the type locality, but not designating holotype and paratypes. Jumars [ 17] mentioned and re-examined the holotype, without clarifying the exact type locality.

The catalog of the Polychaete Collection of the Natural History Museum of Los Angeles County (NHMLAC) has registered the holotype, examined by Jumars [ 17], in the lot LACM-AHF Poly 0691 and seven paratypes in LACM-AHF Poly 0692. Both lots were assigned later the Hartman’s [ 13] publication, the holotype by assistants of Olga Hartman and paratypes by Kristian Fauchald (Leslie Harris, NHMLAC, pers com.), at the time a graduate student, but who has become one of the greatest 20th century polychaetologists. Although Jumars [ 17] examined and described the holotype, the vial was empty, so that the holotype is missing.

Both R/V Atlantis Expedition Gay Head ( Bermuda Transect)’s data [ 13] and the NHMLAC’s catalog show that the type locality of M. minuta is the Station Sl 3 (letter ‘l’, instead number ‘1’), meaning Station Slope 3 (east of upper end of Block Canyon, in New England upper continental slope), at 39˚58’24"N, 70˚40’18"W, 300 meters deep, collected at 28 August 1962. Thus, in accordance with ICZN’s Articles 75.1 and 75.3.1 [ 28], we designate the neotype LACM-AHF Poly 12561, selected from the paratypes of LACM-AHF Poly 0692, clarifying the type locality of M. minuta .

In the same way, considering Articles 75.3.2 and 75.3.3 of the ICZN [ 28], the neotype is named to ensure morphological data sufficient for recognition of the species, clarifying the correct presence and distribution of dorsal and ventral cirri, not clearly described by Hartman [ 13] and Jumars [ 17]. Likewise, M. minuta represents the species type of the genus, requiring the correct registration of its morphological characters.

Redescription of neotype. Complete specimen, 43 chaetigers, 2.5 mm long, median region 0.25 mm wide, excluding parapodia; body width almost uniform, anterior and posterior regions slightly narrower ( Fig 1A ). Color in ethanol pale yellow.

Prostomium pear-shaped, as long as wide, anterior half depressed, posterior half globular, as long as the first two segments ( Fig 1A–1C ). Eyes absent. One pair of clavate antennae inserted dorsolaterally on middle posterior half of prostomium, 2/3 of prostomium length. One pair of small and clavate palps inserted laterally at prostomium base, 1/3 as long as antennae ( Fig 1B and 1C ).

Jaw apparatus not dissected. Mandibles butterfly-shaped medially fused, anterior region enlarged with smooth margins without free or fused teeth, posterior region slender and curved. Basal plates of maxillae with smooth inner margin; two rows of 12–15 pairs of denticulate maxillary plates [ 17].

Two peristomial rings, posterior wider and longer than anterior, covering it dorsally. Chaetigers wide and short, anterior narrower than median and posterior ( Fig 1A ).

Cylindrical parapodia, first pair smaller than the following ones, gradually tapering towards posterior region ( Fig 1A, 1D and 1E ). Small and rounded dorsal cirrus on chaetigers 2 to 9 ( Fig 1D ), inserted slightly distally on the parapodium, absent thereafter. Small papilliform ventral cirrus in all parapodia, absent in the first one ( Fig 1E ), inserted medially in the parapodium; ventral cirrus larger than dorsal on same parapodium.

Supra-acicular chaetae: (1) one long and serrated capillary ( Fig 1F ), with a small limb anteriorly, longer and thinner in median and posterior regions; (2) one thick furcate with short triangular prongs, asymmetrical in size and shape and serrated base ( Fig 1G ), thinner and longer in median and posterior regions. From chaetiger 9, two capillaries and one furcate. Sub-acicular chaetae: (3) three compound heterogomphs ( Fig 1H ), distal end of shafts serrated and blades unidentate with serrated cutting edge; dorsalmost longest with falcigerous or spinigerous blade, median falcigerous, ventralmost falcigerous and shortest. Cultriform chaeta absent. Chaetae from median and posterior regions longer and slender. One internal thick acicula.

Pygidium rounded and smaller than previous chaetigers. Two pairs of clavate pygidial cirri ( Fig 1A ), dorsal pair with 1.5 times as long as pygidium, ventral pair as long as the pygidium.

Variation. Complete specimens with 31–52 chaetigers, some of them with posterior moniliform chaetigers. ZUEC-POL complete specimens 1.7–4 mm long, maximum 0.23 mm wide.

Antennae 1/3–2/3 the length of the prostomium. Some specimens with posterior peristomial ring covering the anterior dorsally. Dorsal cirri from chaetigers 2 to 5–9. Two capillary chaetae in median and posterior regions in most specimens and presence of serrated cultriform chaetae in paratypes and Brazilian specimens, replacing the ventralmost compound

( Fig 5F ).

Anterior region, antennae, palps ( Figs 2A, 2B , 3A and 3B ), peristomial rings, and organization of parapodia and pygidium ( Figs 2D , 3C and 3D ) of ZUEC-POL specimens are in accordance with the above description, except for a ciliary band, viewed under SEM, between prostomium halves ( Fig 3A ), base of peristomial rings and anterior chaetigers ( Figs 2B , 3A and 3B ). Chaetae and both organization on parapodia and form agree with description ( Fig 5 ).

Jaw apparatus of ZUEC-POL specimens with ventrally and medially fused mandibles, anterior region enlarged with smooth margins without free or fused teeth, posterior region slender and curved ( Fig 6A ). Basal plates of maxillae with smooth inner margin, two subsymmetrical rows with 10–12 pairs of free rectangular and denticulate maxillary plates, each one with one posterior main fang and usually four anterior teeth; anterior and posteriormost plates larger and rounded, with small and more numerous teeth ( Fig 6B ).

Remarks. Hartman [ 13] described the parapodial cirri as being obscure and reduced to slight projections in all parapodia, which differs from the analysis performed on the type series and non-type material. The LACM-AHF Poly specimens did not have cirri in parapodium 1, but rather a small papilliform ventral cirrus from the 2, in addition to a small and rounded dorsal cirrus from the parapodia 2 to 7–9. The length of antennae in the original description is not accurate, being actually 2/3 the length of prostomium. The furcate chaetae become slender and longer with asymmetrical prongs in median and posterior regions, character not mentioned by Hartman [ 13].

The jaw apparatus of the type series was not analyzed, but the morphology of the ZUEC-POL specimens agrees with Jumars’s [ 17] description.

Geographic distribution and bathymetric range. Off New England ( USA), 97–508.7 m, very fine sand [ 13]; continental slope off North Carolina ( USA), 850–1,019 m [ 29, 30]; Southwestern Atlantic Ocean, States of Espírito Santo and Rio de Janeiro ( Brazil), 383.8–1,050 m, mud.

Figures

Fig 1. Meiodorvillea minuta (Hartman, 1965), neotype (LACM-AHF Poly 12561). (A) complete specimen, dorsal view; (B,C) anterior region, dorsal view; (D) parapodium 4, anterior view; (E) parapodium 12, anterior view; (F) capillary chaeta; (G) furcate chaeta; (H) compound chaetae.Dash lines represent broken chaeta. Abbreviations: an = antenna; dc = dorsal cirrus; pa = palp; vc = ventral cirrus. Scale bars: (A) = 0.5 mm; (B) = 80 μm; (C) = 50 μm; (D) = 20 μm; (E) = 40 μm; (F,G,H) = 12.5 μm. https://doi.org/10.1371/journal.pone.0264081.g001

Fig 2. Meiodorvillea minuta (Hartman, 1965), ZUEC-POL. (A) complete specimen, dorsal view; (B) anterior region, dorsal view; (C) parapodia from anterior region, dorsal view; (D) pygidium, ventral view. Abbreviations: an = antenna; dc = dorsal cirrus; dpc = dorsal pygidial cirrus; fc = furcate chaeta; pa = palp; vpc = ventral pygidial cirrus. Scales: (A) = 200 μm; (B,C) = 62.5 μm; (D) = 31.25 μm. https://doi.org/10.1371/journal.pone.0264081.g002

Fig 3. Meiodorvillea minuta (Hartman, 1965), ZUEL-POL. (A,B) anterior region, dorsal view; (C,D) pygidium, lateral view. Abbreviations: an = antenna; dpc = dorsal pygidial cirrus; pa = palp; vpc = ventral pygidial cirrus. Scales: (A) = 20 μm; (B) = 25 μm; (C) = 10 μm; (D) = 15.6 μm. https://doi.org/10.1371/journal.pone.0264081.g003

Fig 4. Meiodorvillea minuta (Hartman, 1965), ZUEC-POL. (A,B) parapodia from anterior region; (C,D) parapodia from posterior region; all anterior view. Abbreviations: dc = dorsal cirrus; vc = ventral cirrus. Scales: (A,B) = 10 μm; (C, D) = 15.6 μm. https://doi.org/10.1371/journal.pone.0264081.g004

Fig 5. Meiodorvillea minuta (Hartman, 1965), ZUEC-POL. (A) furcate chaeta from anterior region; (B) furcate chaeta from posterior region; (C,E) compound chaetae; (D) morphology of furcate chaeta, from chaetigers 2, 5, and 10; (F) cultriform chaeta. Scales:(A,B) = 5 μm; (C) = 10 μm; (D,E,F) = 6.25 μm. https://doi.org/10.1371/journal.pone.0264081.g005

Fig 6. Meiodorvillea minuta (Hartman, 1965), ZUEC-POL. (A) mandibles, dorsal view; (B) maxillae, dorsal view. Abbreviations: md = mandibles; mp = maxillary plates; mf = main fang; cls = carrier-like structure.Scales: (A,B) = 10 μm. https://doi.org/10.1371/journal.pone.0264081.g006

Fig 9. Meiodorvillea penhae sp. nov. (A,C) anterior region, dorsal view; (B) anterior region, ventral view; (D) anterior region, ventrolateral view; (E,F) pygidium, ventral view. Abbreviations: an = antenna; dpc = dorsal pygidial cirrus; pa = palp; vpc = ventral pygidial cirrus. Scale bars: (A,B,E) = 25 μm; (C) = 50 μm; (D) = 20 μm; (F) = 10 μm. https://doi.org/10.1371/journal.pone.0264081.g009

Tables

Table 1. Main morphological differences and distribution of Meiodorvillea species.

SPECIES	PALPS	PRESENCE OF	FURCATE CHAETAE		GENICULATE	Y-SHAPED	DISTRIBUTION
		DORSAL CIRRUS	PRESENCE/ ABSENCE	SYMMETRY OF PRONGS	CHAETAE	SHAFT OF DORSAL COMPOUND
Meiodorvilleaminuta			present on all		absent		New England and North
			chaetigers				Carolina, USA; Espírito
						absent	Santo and Rio de Janeiro States, Brazil
		chaetigers 2 to 5–9,					(97–1,050 m)
	small clavate	smaller than ventral		asymmetrical
Meiodorvilleaapalpata			absent		present on all		east coast of California,
					chaetigers		San Diego Trough
							(1,223–1,224 m)
						absent
		absent
absent

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