Marphysa sessilobranchiata Hartmann-Schröder, 1984

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 : 421-423

Marphysa sessilobranchiata Hartmann-Schröder, 1984

( Fig. 5 )

Marphysa sessilobranchiata Hartmann-Schröder, 1984: 32 , 39.

Material examined. PARATYPES: Australia, Western Australia, Princess Royal Harbor, Little Grove, 35° 04'S, 117° 52'E, 22 Nov 1975, AM W.198420 (2 specimens) . NON-TYPE: Western Australia, Albany , Princess Royal Harbor, Quaranup Jetty, 35° 03' S, 117° 55' E, Jan 1988, AM W.20292 (1 specimen) .

Measurements. Paratypes incomplete with 48 and 58 mm of total length, 147 and 157 chaetigers, 5 and 5.25 mm long to chaetiger 10, 3 mm with parapodia (1.6 mm without parapodia) and 3.5 mm with parapodia (1.76 mm without parapodia) wide at this chaetiger. Non-type, incomplete with 38 mm of total length, 123 chaetigers, 5.3 mm long to chaetiger 10 and 3 mm with parapodia (1.96 mm without parapodia) wide at this chaetiger.

Description. Fixed specimens brown, lacking any color pattern.

Body long, slender, median region widest; cross-section dorsally or dorsoventrally flattened at anterior region and rounded at remaining of body. Chaetigers around 5 times wider than long at widest region of body.

Prostomium as long as or longer, narrower or as wide as and less than half as deep as peristomium ( Fig. 5 A, B). Prostomium dorsally completely flat or with anterior end higher; anteriorly rounded to triangular; not bilobed; median sulcus absent at anterior and dorsal sides, conspicuously present at ventral side.

Median and lateral antennae in straight line, palps slightly more anteriorly ( Fig. 5 A). Median antenna isolated by gap from lateral antennae and palps; longest prostomial appendage, almost as long as to little longer than prostomium, folding back to first chaetiger. Lateral antennae around two thirds length of prostomium, folding back to mid or posterior margin of second peristomium ring. Palps shortest, little longer than half of prostomium, fold back to mid or posterior edge of first peristomial ring. Antennal styles tapering, palpostyle digitiform, all irregularly articulated, appearing wrinkled. Antennophores and palpophores ring shaped. Eyes absent.

Separation between peristomial rings distinct all around. Second peristomial ring about as long as 1/3–1/2 of complete peristomium ( Fig. 5 A, B). Peristomial ventro-lateral lips distinct laterally as elevated surface or by groove. Peristomial ventro-anterior margin straight or shallow arc, ventral side longer than dorsal.

Posterior end of muscularized pharynx at chaetiger 4–5. Mandibles with small delicate calcareous cutting plates more than twice as long as sclerotized matrix; almost diamond shape with curved anterior inner edge, two anterior teeth. MxI about twice as long as carriers ( Fig. 5 C) and six times longer than locking system. MxIII at least in part located ventral to MxII; attachment lamella oval at anterior end of median margin of MxIII ( Fig. 5 D). Left MxIV plate semi-ellipse; attachment lamella shorter than plate, as wide as plate, along complete anterior and lateral edges of plate ( Fig. 5 D). Right MxIV attachment lamella starting between lateralmost teeth 1–2, along around ¾ of plate, longest at lateral side ( Fig. 5 E). Maxillary formula: I= 1+1, II= 5+6, III= 6+0, IV= 4+9, 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 to shorter than neurochaetal lobe in median and posterior chaetigers. Anterior post-neurochaetal lobe wide, distally truncate with longer dorsal edge ( Fig. 5 A, F). Neurochaetal lobe round at anterior region ( Fig. 5 G, I), tapering in remaining of body ( Fig. 5 J). Anterior notopodial cirri tapering, longer than neurochaetal lobe ( Fig. 5 G, I); median and posterior cirri slender and shorter than neurochaetal lobes ( Fig. 5 H). Lateral sense organ slightly elevated to conspicuously ciliated bump. Ventral cirri thumb shaped to tapering with round wide tips at chaetigers 1 to 4, around 2/3 to as long as notopodial cirri ( Fig. 5 F); basally inflated from chaetiger 5, inflated base of round to fusiform shape with round tip ( Fig. 5 G, I), gradually decreasing in size at median region of body.

Branchiae palmate, with 1–2 filaments from chaetiger 25, reaching maximum of 4 filaments at chaetiger 70– 99. Best developed branchial filaments around 3–5 times longer than notopodial cirri and 3 times longer than branchial stems. Branchial stems completely attached to body wall ( Fig. 5 H, J).

Notopodial aciculae yellow, present in notopodial cirri along whole body. Neurochaetae distributed in two distinct bundles, supra-acicular with limbate chaetae and pectinate chaetae, subacicular with bidentate compound falciger chaetae and subacicular hooks. Neuroaciculae blunt, brown; three at anteriormost parapodia, distributed in oblique row, anteriormost neuroaciculae also dorsalmost in parapodium ( Fig. 5 G, K). Towards posterior end, number of neuroaciculae decreasing, mostly one present, as well as of limbate chaetae and compound falciger chaetae. Limbate chaetae longer than all other chaetae, serrated, spike-like serrations may surround middle of its length and tips. Shaft and appendage of compound falciger chaetae serrated; appendage bidentate with guards symmetrically blunt, without mucros; both teeth directed laterally; distal tooth curved; proximal tooth straight, perpendicular to length of chaetae, as long as to longer than distal tooth ( Fig. 5 L–N). One–three curved thin pectinate chaetae present at anterior edge of supra-acicular bundle at anterior and median regions, around 9–13 long teeth present; inner teeth equal in length; both outer teeth longer than inner teeth, equal or unequal in length ( Fig. 5 O). One–two slightly curved thick pectinate chaetae in postero-median region with around 11–13 coarse teeth, one outer tooth longer, inner teeth about same length at distal end but with increasingly deeper proximal ends from margins to center, teeth with deepest proximal end off center ( Fig. 5 P). Pseudocompound chaetae and compound spiniger chaetae absent. Subacicular hook first present from chaetiger 35–38, present in all chaetigers thereafter, always single; yellow, unidentate to bidentate, thinner than aciculae. Bidentate subacicular hooks with small rounded to tapering teeth, both teeth erect ( Fig. 5 Q, R).

Pygidium missing.

Variation. In all examined specimens, jaws are semi-everted, which usually make prostomium seem less deep than when jaws are fully withdrawn. Maxillae are described based on non-type specimen. Both paratypes have symmetric maxillae, the left side is copy of the right side (MxI 1+1, II= 7+7, III absent, IV= 10+10, V= 1+1, VI absent), which may be a malformation. Mandible calcareous cutting plates are missing, probably dissolved due to formalin fixation. Spike-like serration present in some chaetae may be artifact of preparation. Unidentate subacicular hooks are, probably, result of wear.

Remarks. General features are similar to the original description ( Hartmann-Schröder 1984). The main divergences are the shape of the branchiae, number of teeth on MxIV and of pectinate chaetae. Branchiae are palmate with stem attached to the body wall. Branchial filaments are connected to the stems and not individually to the body wall as originally described. In the original description, number of teeth on left and right MxIV appears to be reversed. As in many Marphysa species, M. sessilobranchiata has thin pectinate at the anterior region and thick pectinate at median and posterior regions. In the original description only the thin pectinate were described. Attempts to recollect from the type locality for molecular studies were unsuccessful.

Habitat. Fine sand close to Avicenia mangroves, covered with shell pieces or in seagrass bed of Posidonia sinuosa , intertidal to 3 m deep.

Distribution. Southern Western Australia: Princess Royal Harbor.

Figures

FIGURE 5. Marphysa sessilobranchiata. A. Anterior end of paratype, dorsal view. B. Anterior end of paratype, lateral view. C. Maxillary apparatus of non-type specimen, dorsal view. D. Left MxI, II, III, IV and V, dorsal view. E. Right MxI, II, IV and V, dorsal view. F. Right parapodium 4 of non-type specimen, anterior view. G. Right parapodium 7 of paratype, anterior view. H. Median parapodia, dorsolateral view. I. Right parapodium 21 of non-type specimen, anterior view. J. Right parapodium 116 of non-type specimen, anterior view, branchial stems attached to body wall. K. Left parapodium 5 – 6 of paratype, lateral view, neuroaciculae distributed in an oblique row. L. Compound falciger chaetae, right parapodium 7 of paratype. M. Compound falciger chaetae of paratype. N. Compound falciger chaetae serrated, parapodium 4. O. Curved thin pectinate chaetae, right parapodium 21. P. Curved thick pectinate chaeta, left parapodium 152. Q. Bidentate subacicular hook, right parapodium 76 R. R. Subacicular hook bidentate, left parapodium 152. A, B, G, H, K – M, P, R. AM W. 198420. C – F, I, J, N, O, Q. AM W. 20292. Scale bars: A – G, I, J. 100 µm. H, K. 500 µm. L, N – R. 10 µm.