Scolelepis (Scolelepis) inversa, Götting, Miriam, 2015

Götting, Miriam, 2015, Spionidae (Annelida: ‘ Polychaeta’: Canalipalpata) from Lizard Island, Great Barrier Reef, Australia: the genera Malacoceros, Scolelepis, Spio, Microspio, and Spiophanes, Zootaxa 4019 (1), pp. 378-413 : 386-390

Scolelepis (Scolelepis) inversa n. sp.

(Figs 2, 3)

Type material. Holotype: AM W.44474, MI QLD 2396, formalin.

Diagnosis. Prostomium narrow, anteriorly pointed, and with slight constriction at the level of chaetiger one, posteriorly extended into pointed, erect caruncle which is not attached to dorsum. Low transversal ciliated bands (tcb) present throughout body and as dorsal crests in posteriormost chaetigers. Chaetiger 1 well developed, with small slender notopodial lamellae, in prechaetal instead of postchaetal position; notochaetae and neurochaetae present. Branchiae present throughout body; anterior branchiae long, cirriform and longer than notopodial postchaetal lamellae, with tips almost touching one another above dorsal midline, branchiae from middle chaetigers even longer. Notopodial postchaetal lamellae foliate and folded, with rounded tip, completely fused to branchiae until chaetiger 16; from chaetiger 17 foliate and folded with pointed tip becoming free from branchiae distally. Anterior body region with stout capillaries in both rami; in notopodia in two rows, in neuropodia of about chaetigers 6–16 in three rows. Hooded hooks bidentate with upright apical tooth in neuropodia from chaetiger 23 numbering up to nine hooks per fascicle; in notopodia hooks of the same appearance from about chaetiger 35, 1–5 hooks per fascicle. Pygidium with ventral, entire cushion.

Description. Holotype complete but fragmented specimen: one anterior fragment with 25 chaetigers, one middle fragment with seven chaetigers, one posterior fragment with 28 chaetigers (altogether 60 chaetigers); body width 2.2 mm (measured at anterior middle body region, chaetae and postchaetal lobes omitted), total length of all fragments 21.9 mm. Prostomium anteriorly pointed, projecting over peristomium, narrow with slight constriction at level of chaetiger one, posteriorly extended into pointed, erect caruncle not attached to dorsum (Fig. 2A); two pairs of black eyes arranged in trapezoid, anterior pair crescent-shaped, wider apart than posterior pair, eyes of posterior pair round, pairs very close to each other, almost forming one row and positioned at the prostomial constriction. Peristomium moderately developed, forming low lateral wings partially encompassing prostomium posteriorly. Palps rather thin, short, reaching back to about chaetiger 12–15; with thickened base (sheath, Fig. 3 D) with irregular groups of cilia; palps with two weakly separated rows of mucus secreting cells and accompanying cilia ( Fig. 3 E, F), long rows approximately 46 µm long, short rows approximately 18 µm long. Low but distinct tcb´s present in anterior and middle body region, well developed dorsal crests present in about last 20 chaetigers (Fig. 2G).

Chaetiger 1 well developed, with subulate postchaetal lamellae in both rami, notopodial lamellae small and slender, in prechaetal instead of postchaetal position, neuropodial lamellae larger and in postchaetal position; notochaetae and neurochaetae present (Fig. 2A). Branchiae from chaetiger 2, present throughout body; anterior branchiae long cirriform, longer than notopodial postchaetal lamellae (Fig. 2A), with tips almost touching one another above dorsum; from middle chaetigers branchiae even longer and distinctly longer than notopodial lamellae (Fig. 2B–D); in posterior chaetigers again almost touching above dorsum, only slightly longer than notopodial lamellae or of about same length (Fig. 2E–G). Notopodial postchaetal lamellae foliate, folded, completely fused to branchiae until chaetiger 16 (Fig. 2A, B); from chaetiger 17 foliate and folded with pointed tip becoming free from branchiae distally (Fig. 2C–E); posterior chaetigers with foliate but less folded notopodial postchaetal lamellae, pointed tips free from branchiae, lower portion of notopodial lamellae broadly rounded (Fig. 2F). Neuropodial postchaetal lamellae broadly rounded, from chaetiger 18 slightly notched, from chaetiger 21 divided into large rounded neuropodial lamellae and inferior conical lobe with rounded tip; in posterior chaetigers neuropodial postchaetal lamellae foliate with well developed superior part and in almost interramal position, inferior lobe conical to subtriangular with rounded tip (Fig. 2B–F). Prechaetal lobes absent.

Capillary chaetae and bidentate hooded hooks in neuropodia and notopodia; first chaetiger with bundle of thin capillaries in notopodia, neuropodia with two rows of stouter capillaries with sheaths, capillaries of both rows of about same length; neuropodia of chaetigers 2–5 with slightly granulated capillaries in two rows, in chaetigers 6– 16 in three rows ( Fig. 3 A), capillaries of anterior row with broad sheaths (Fig. 2I) and in second and third row with narrower sheaths (Fig. 2H); after chaetiger 16 until about chaetigers 20/21 stout capillaries, in succedent chaetigers thinner, arranged in two rows; in notopodia of chaetigers 2–21 stout, broadly sheathed capillaries with granulations near the tips, arranged in two rows of about same length; in following chaetigers notochaetae thinner and longer with very narrow sheaths and without granulations; superior fascicle of thin long capillaries with narrow sheaths present in notopodia up to about chaetiger 30, with slight granulations in anterior third of the body; inferior fascicle of thin, long capillaries with narrow sheaths in position of sabre setae in neuropodia present throughout body (Fig. 2J), with slight granulations until anterior middle body region, sabre chaetae absent. Neuropodial hooks from chaetiger 23, numbering 4 per fascicle first, then increasing to 9 hooks per fascicle more posteriorly, notopodial hooks from about chaetiger 35, 1–5 hooks per fascicle but usually 4, all hooks hooded, bidentate with upright apical tooth (Figs 2K, 3B); hooks accompanied by few thin, long, smooth capillaries with very narrow sheaths or more posteriorly without sheaths in neuropodia, capillaries in superior position in the neuropodial ramus; in notopodia hooks accompanying smooth capillaries of normal thickness with narrow sheaths arranged in irregular rows.

Pygidium with ventral, entire cushion and dorsal anus (Fig. 2G).

Pigmentation. Formalin fixed specimen of whitish colour, with tiny spot of brownish pigment at the constriction of the prostomium next to the eyes.

Methyl green staining pattern. Inconspicuous; prostomium, peristomium, pygidium, branchiae and parapodial lobes most intensely stained.

Remarks. Scolelepis inversa n. sp. is most similar to S. precirriseta Blake & Kudenov, 1978 . The two species are the only known species of Scolelepis in which the dorsal lamella of chaetiger 1 is in prechaetal instead of postchaetal position (Fig. 2A). In both species the shape of the prostomium is also very similar. However, there are also several differences: S. inversa n. sp. has bidentate hooded hooks with an upright apical tooth from chaetiger 23 in neuropodia and from about chaetiger 35 in notopodia whereas in S. precirriseta hooks with three pairs of small apical teeth are present in neuropodia from chaetigers 15–20, and notopodial hooks are unknown. In S. inversa n. sp. the postchaetal notopodial lamellae are completely fused to the branchiae in chaetigers 2–16 whereas branchiae and notopodial lamellae are fused only at the base in anterior chaetigers of S. precirriseta . In addition, S. inversa n. sp. has stout capillaries with broad sheaths arranged in up to three rows present in parapodia of the anterior body region ( Fig. 3 A).

FIGURE 2. Scolelepis inversa n. sp., holotype, AM W.44474, MI QLD 2396. A. Anterior end, dorsal-oblique view, palps removed; B. Parapodium from chaetiger 10, anterior view; C. Same from chaetiger 25; D. Same from chaetiger 33; E. Same from 13th last chaetiger; F. Same from 9th last chaetiger; G. Posterior end with pygidium with ventral, entire cushion, dorsaloblique view; H. Capillary from 10th neuropodium; I. Stout, broadly sheathed capillary from 10th neuropodium; J. Inferior capillary from 10th neuropodium; K. Bidentate hooded hook with upright apical tooth from 33rd neuropodium. Scale bars: A = 1 mm, B–G = 0.5 mm, H–J = 5 µm, K = 10 µm.

The general arrangement of mucus secreting cells and cilia on palps of S. inversa n. sp. is in good agreement with the palp ciliary pattern of Scolelepis alisonae Williams, 2007 and Scolelepis magnicornuta Williams, 2007 . All three species exhibit long and short rows of cilia (and mucus secreting cells in S. inversa n. sp.) that are indistinctly separated, with the long rows 41–46 µm in length and the short rows 18–26 µm in length. In S. inversa n. sp. the number of mucus secreting cells is very high (compared to the number of cilia).

Etymology. “ inversa ” - Latin for reversed (turned backward) in order. The name refers to the prechaetal postion of the notopodial lamellae in the first chaetiger.

Habitat / Ecology. The species was found in sand underneath stones at extreme low tide not far from the beach. Eggs are present in segments of the middle and posterior body region; eggs with an ornamented egg envelope resembling honeycombs ( Fig. 3 C), dimensions 203 x 164 µm.

Distribution. So far only known from the type locality at Lizard Island, Australia, Queensland.

Figures

FIGURE 3. Scolelepis inversa n. sp., holotype, AM W. 44474, MI QLD 2396. A. Chaetigers 11 – 13, lateral view (note stout capillaries arranged in three rows in neuropodia); B. Neuropodial bidentate hooded hooks from chaetiger 33 (note upright apical tooth), accompanying capillaries not shown; C. Egg with ornamented egg envelope resembling honeycombs; D. Palp, thickened base (sheath) indicated by arrow, note irregular groups of cilia on the left side of the palp base; E. Palp ciliation and mucus secreting cells at the distal part (near tip), arrow indicates indistinct division between long and short transverse rows of cilia and mucus secreting cells; F. Detail of palp ciliation and arrangement of mucus secreting cells at the distal part. Scale bars: A, D = 100 µm, B, C = 20 µm, E 10 µm, F = 5 µm.