Marphysa pseudosessiloa, Zanol, Joana, Da Silva, Thauane Dos S. C. & Hutchings, Pat, 2017

Zanol, Joana, Da Silva, Thauane Dos S. C. & Hutchings, Pat, 2017, One new species and two redescriptions of Marphysa (Eunicidae, Annelida) species of the Aenea-group from Australia, Zootaxa 4268 (3), pp. 411-426 : 417-420

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Marphysa pseudosessiloa

n. sp.

Marphysa pseudosessiloa n. sp.

( Figs 3 View FIGURE 3 , 4 View FIGURE 4 )

Material examined. HOLOTYPE: Australia, New South Wales, Pittwater, Careel Bay , 33° 36' 54"S, 151° 19' 24"E, 17 Feb 2011 (AM W.37249) GoogleMaps . PARATYPES: same locality as for holotype, AM W.37089, AM W.37088, AM W.37246, AM W.37250 (4 specimens) GoogleMaps .

Measurements. Holotype, complete female with regenerating pygidium, 164 mm in total length, 379 chaetigers, in four fragments, 132 anteriormost chaetigers, 53 median and 174 posteriormost chaetigers fixed in 8% formalin, 20 median chaetigers fixed in 95% ethanol, 6.5 mm length through chaetiger 10 and about 3.5 mm with parapodia (2 mm without parapodia) in width at chaetiger 10 (maximal width). One paratype complete specimen, with 100 mm in total length, 239 chaetigers, 5.2 mm in length through chaetiger 10 and 2 mm with parapodia (1 mm without parapodia) in width at chaetiger 10. Three paratypes incomplete specimens or regenerating posterior end ranging from 50–55 mm in total length, 85–249 chaetigers, 6.5–7 mm in length through chaetiger 10, 2.5–3 mm with parapodia (1.6 mm without parapodia) in width at chaetiger 10.

Description. (Of holotype, values in parentheses for paratypes).

Live specimens whitish translucent with pink to red hues due to red blood. Fixed specimens white, lacking color pattern.

Body long, slender, abruptly tapering towards anterior end from around chaetiger 5, evenly tapering towards posterior end; cross section dorsoventrally flattened at anterior region and rounded at median and posterior regions. Chaetigers around 3–5 times wider than long at widest region of body.

Prostomium as long and wide as peristomium, two-thirds (half) as deep as peristomium; dorsally flat with anterior end higher (completely flat), anteriorly triangular (round); not bilobed; median sulcus absent at anterior and dorsal sides, conspicuously present at ventral side ( Fig. 3 View FIGURE 3 A–D).

Median and lateral antennae in straight line, palps inserted slightly more anteriorly ( Fig. 3 View FIGURE 3 A, B). Median antenna isolated by gap from lateral antennae and palps; longest prostomial appendage, as long as prostomium, folding back to posterior margin of second peristomium ring (mid second peristomial ring). Lateral antennae around two thirds length of prostomium, folding back to mid of second peristomium ring (posterior margin of first to anterior margin of second peristomium ring). Palps shortest, around as long as half of prostomium, folding back to mid of first peristomial ring. Antennal styles and palpostyle tapering (palpostyle digitiform), all irregularly articulated and sensory papillae distributed in rings, last visible only under SEM, under stereomicroscope prostomial appendages appearing wrinkled ( Fig. 3 View FIGURE 3 C, E). Antennophores and palpophores ring shaped. One pair of inconspicuous eyes present, in shape of dark line at base of palpophores (lateral antennae antennophores) ( Fig. 3 View FIGURE 3 D).

Separation between peristomial rings distinct all around. Second peristomial ring about as long as 1/3–1/2 of complete peristomium. Peristomial ventro-lateral lips distinct laterally just as elevated surface. Peristomial anterior margin of dorsal and ventral sides in shallow arc, lateral margins longer; shortest on dorsal side ( Fig. 3 View FIGURE 3 D).

Posterior end of muscularized pharynx at chaetiger 4. Mandibles missing calcareous cutting plates. MxI twice as long as carriers and six times longer than locking system. MxIII at least in part located ventral to MxII; attachment lamella upside down drop-shaped at anterior end of median margin of MxIII ( Fig. 3 View FIGURE 3 F). Left MxIV plate semi-circular; attachment lamella shorter than plate, almost as wide as plate, along most of anterior edge, missing on lateral edge of plate ( Fig. 3 View FIGURE 3 F). Right MxIV attachment lamella starting between lateralmost teeth 2–3, along around 2/3 of plate, longest at lateral side and evenly shorter towards opposite side ( Fig. 3 View FIGURE 3 F). Maxillary formula: I= 1+1, II= 5(6)+6, III= 6(5)+0, IV= 6(7)+9(8), V= 1+1, VI absent.

Pre-neurochaetal lobe shorter than neurochaetal lobe along whole body. Post-neurochaetal lobe longer than neurochaetal lobe in anterior chaetigers, decreasing in length along body, becoming as long as or shorter than neurochaetal lobe in median and posterior chaetigers. Anterior post-neurochaetal lobe wide, distally truncate with longer dorsal edge ( Fig. 3 View FIGURE 3 G, H). Neurochaetal lobe round in anteriormost region (P1) ( Fig. 3 View FIGURE 3 I), tapering from parapodia P2–P6 ( Fig. 3 View FIGURE 3 H, J). Anterior notopodial cirri fusiform (tapering), longer than neurochaetal lobe ( Fig. 3 View FIGURE 3 I); median and posterior cirri slender and slightly shorter than anterior ones, but still longer than neurochaetal lobes ( Fig. 3 View FIGURE 3 J) (shorter than neurochaetal lobe in branchiated region). Lateral sense organs slightly elevated in P1, as conspicuously ciliated bump in remaining of body ( Fig. 3 View FIGURE 3 H). Ventral cirri tapering with round wide tips at chaetigers 1 to 4, around 2/3 as long as notopodial cirri ( Fig. 3 View FIGURE 3 I); basally inflated from chaetiger 5, inflated base of round shape with round tip ( Fig. 3 View FIGURE 3 J), gradually decreasing from chaetiger 61 (35, 43) to 152 (85); round (triangular) tapering with distinct tip from chaetiger 153 (86).

Branchiae palmate ( Fig. 3 View FIGURE 3 J, K), with 2 (1) filaments from chaetiger 28 (21–26), reaching maximum of 6 (4, 5) filaments at chaetiger 129 (71–106; first 1/3 of body), terminating at last chaetiger (21 chaetigers before pygidium). Best developed branchial filaments around 4 times longer than notopodial cirri and 8 times longer than branchial stems, length of filaments decreasing at median region of body. Branchial stems distally loose, basally attached to notopodial cirri and body ( Fig. 3 View FIGURE 3 K).

Notopodial aciculae yellow, present in notopodial cirri along whole body. Neurochaetae in two distinct bundles; supra-acicular with limbate chaetae and pectinate chaetae, subacicular with bidentate compound falciger chaetae and subacicular hooks. Neuroaciculae blunt to tapering, brown in anterior chaetigers, becoming yellow at posterior most chaetigers, dorsal to midline in P1 and in midline thereafter; distributed in oblique row, anteriormost neuroaciculae also dorsalmost in parapodium ( Fig. 3 View FIGURE 3 L). Number of neuroaciculae, limbate chaetae and compound falciger chaetae decreasing towards posterior end. Three neuroaciculae present in P1 and P2, in posterior chaetiger mostly one present. Around 15 limbate chaetae at anteriormost region (P1), 10 in P2 and more posterior chaetigers with as few as 6. Limbate chaetae longer than all other chaetae, strongly serrated, serration increases towards flat distal end (spike like serration surround middle of its length). Compound falciger chaetae numerous in P1, around 40 (30) present, 15 (10) by P2 and 4–6 in more posterior parapodia; shaft and appendage of compound falciger chaetae strongly serrated (shaft serration spike like toward proximal end of chaetae); appendage bidentate with guards symmetrically blunt, marginally serrated, without mucros; both teeth directed laterally, distal tooth curved, proximal tooth straight, perpendicular to length of chaetae, about twice as long as distal tooth ( Fig. 3 View FIGURE 3 M–O). One– two curved thin pectinate chaetae present at anterior edge of supra-acicular bundle from P1–P3; around 11–16 teeth present ( Fig. 3 View FIGURE 3 H, Q, R); inner teeth equal in length; outer teeth not equal in length and longer than inner teeth. Curved thick pectinate chaetae in median to posterior regions with around 12–14 coarse teeth with about same length at distal end but with increasingly deeper proximal ends from margins to center, teeth with deepest proximal end off center ( Fig. 3 View FIGURE 3 M, S); 2–3 present in P4, 2– 4 in P5 and 1–2 in P6. Pseudocompound chaetae and compound spiniger chaetae absent. Subacicular hook first present from chaetiger 37 (27–36), present in all chaetigers thereafter, always single; yellow, clearly bidentate, thinner than aciculae; distal tooth erect tapering directed distally and much smaller than proximal tooth; proximal tooth perpendicular to length of hook, directed laterally to distally, tip tapering to round; guards truncate present on both sides of teeth ( Fig. 3 View FIGURE 3 M, Q, T).

Pygidium longer on ventral side, with two pairs of pygidial cirri attached to ventral margin; pygidial cirri triangular, about as long as pygidium, dorsal cirri as long as ventral (tapering, longer than pygidium, dorsal 3 times longer than ventral cirri in paratype AM W.37089).

Variation. Calcareous cutting plates of mandibles are probably dissolved due to formalin fixation. Thin pectinate is inconspicuous in P1 under light microscopy. It was only clearly observed in the holotype, largest specimen. Spike-like serration present in some chaetae may be artifact of preparation. The appearance of pygidial cirri in the holotype is probably due to recent regeneration.

Remarks. Among the species of the Aenea-group, M. mortenseni , M. bifurcata , M. sessilobranchiata and Marphysa galluccii Orensanz, 1990 are the most similar to this new species in having a tapering non-bilobed prostomium. Marphysa mortenseni , M. bifurcata and M. galluccii are clearly distinct from M. pseudosessiloa n. sp. in having prostomial appendages shorter than half the length of the prostomium; the first two species may also have bifurcated notopodial cirri, which is simple in the current species. Marphysa galluccii also differs from the current species in lacking thin pectinate chaetae, having only single filament branchiae and unidentate subacicular hooks. General features are similar among the specimens examined here, paratypes and non-types of M. sessilobranchiata . The main divergences among them are the shape of the left MxIV plate, left and right MxIV attachment lamellae, teeth of subacicular hooks and position of branchial stem. In the current species branchiae are attached to a loose stem connected only basally to notopodial cirri and body wall, while in M. sessilobranchiata , as well as M. bifurcata , branchial stems are completely attached to the body wall, giving the appearance that branchial filaments are individually connected to the body wall as previously described.

Molecular identification clearly distinguishes this species from other species of the genus (K2P= 18–25%) and from M. bifurcata (K2P= 17%), the only species of the Aenea-group included in the analyses ( Fig. 4 View FIGURE 4 ).

Etymology. It is very similar to M. sessilobranchiata in general morphology but it lacks the sessile branchiae and hence the specific name of M. pseudosessiloa .

Type locality. Australia, New South Wales, Pittwater, Careel Bay .

Habitat. Intertidal mud in seagrass beds of Zostera capricorni .

Distribution. Only known from the type locality.