Trochochaeta japonica Imajima, 1989

Radashevsky, Vasily I., Rizzo, Alexandra E. & Peixoto, Antonio J. M., 2018, First record of Trochochaeta japonica (Annelida: Spionidae) in Brazil with identification key to species of the genus, Zootaxa 4462 (4), pp. 566-578 : 568-572

Trochochaeta japonica Imajima, 1989

( Figs 2–6 )

Trochochaeta Japonica Imajima, 1989: 139 –145, figs 2–5.

Material. BRAZIL, São Paulo, Baía de Santos , coll. S. Sartor: st. 5, 23.986547°S, 46.288919°W, 14.8 m, 0 9 Oct 2006, UERJ 364 (1); st. 12, 23.925733°S, 46.323285°W, 15.8 m, 11 Oct 2006, UERJ 19 (1), MNRJ P1463 (3 sPecimens mounted on SEM stubs); st. 21, 23.913450°S, 46.374767°W, 6 m, 8 Oct 2006, MNRJ P1462 (2 sPecimens mounted on SEM stubs), 10 Oct 2006, UERJ 63 (46), NHMUK 2017.216–225 (15), MIMB 33633 (19), SMF 24358 (15); st. 24, 23.914689°S, 46.310389°W, 2.6 m, 11 Oct 2006, UERJ 121 (2); st. 25, 23.920325°S, 46.305252°W, 4.1 m, 11 Oct 2006, UERJ 49 (45); st. 26, 23.919175°S, 46.293536°W, 3.2 m, 11 Oct 2006, MNRJ P1459 (1), UERJ 19 (16); st. 28, 23.916811°S, 46.277 314°W, 6 m, 11 Oct 2006, UERJ 172 (51), MNRJ P1461 (2); st. 35, 23.923031°S, 46.401797°W, 6.4 m, 0 8 Oct 2006, UERJ 240 (4); st. 40, 23.958794°S, 46.417139°W, 5.5 m, 0 8 Oct 2006, UERJ 281 (1) . Bahia, Camamu Bay , Serinhaém Estuary, coll. F. Barros: st. 35, 13.760263°S, 39.070332°W, 8.1 m, 20 SeP 2008, UFBA-LEB 0 0 4 (1).

SOUTH KOREA, East China Sea , coll. J.- W. Choi: Hallyeo marine Park, st. 140, 34.7411°N, 128.4367°E, 10 m, 7 May 2014, MIMB 33 635 (1); st. F15, 33.00°N, 127.00°E, 103 m, 1 Jun 2015, MNRJ P1637 (3); st. A3, 34.42°N, 128.50°E, 61 m, 8 Jun 2015, MIMB 3 3636 (1); st. H12, 32.00°N, 126.75°E, 109 m, 7 Nov 2015, MIMB 33637 (2).

Adult morphology (based on material from BraZil). All sPecimens anterior fragments, largest about 20 mm long and 2 mm wide for 40 chaetigers. Pigmentation absent on body and PalPs, but glandular Pads above and below neuroPodia from chaetiger 5 to chaetiger 15 ( Fig. 2A ) and in notoPodial lamellae on chaetigers 5–10 aPPearing rose in fixed sPecimens. Anterior 15 chaetigers widest, flattened dorso-ventrally; succeeding chaetigers gradually narrowing, oval to rounded in cross-section.

Prostomium small, fusiform, widest in middle Part, anteriorly rounded to truncate, with four small knobs, comPrising one Pair of fronto-lateral knobs and one Pair of median knobs; Posteriorly extending to end of chaetiger 1 as a narrow caruncle ( Figs 3A , 5A ). Peristomium reduced to narrow lines on sides of Prostomium, and a narrow ventral liP enclosing mouth laterally and Posteriorly ( Fig. 5B ). Two Pairs of small red eyes arranged traPeZoidally, comPrising one Pair of median eyes deePly imbedded into Prostomium and not seen in some sPecimens, and one Pair of lateral eyes situated anteriorly and set wider aPart; in each Pair eyes often situated asymmetrically ( Fig. 5A ). Short occiPital antenna Present on Prostomium behind median eyes; antenna low, indistinct and broken in some sPecimens. Nuchal organs U-shaPed ciliary bands on sides of caruncle ( Figs 3A , 5A ). PalPs arising from dorsal Parts (residues) of Peristomium, between Prostomium and notoPodia of first chaetiger, as long as 20–30 chaetigers, with frontal longitudinal groove lined with fine cilia and sided by undulating membrane.

Chaetiger 1 with short smooth straight caPillaries in notoPodia and long smooth caPillaries in neuroPodia; neurochaetae about twice as long as notochaetae, arranged in a fan and directed antero-laterally and uPwards ( Fig. 5A ). Postchaetal lamellae fleshy and conical in both rami; notoPodial lamellae twice as long as neuroPodial lamellae ( Figs 3B , 5A ). Middorsal Part of chaetiger 1 extending Posteriorly and Pressed into chaetiger 2, thus caruncle aPPearing very close to Posterior edge of chaetiger 2 ( Fig. 3A ).

Chaetiger 2 with neurochaetae and fleshy conical lamellae in both rami, notochaetae absent ( Figs 3B, C , 5A ). NotoPodial lamellae situated close to neuroPodial lamellae and both shifted ventrally, aPPearing lower than neuroPodial lamellae on chaetigers 1 and 3. Neurochaetae on each side comPrising uP to seven thin falcate yellowish sPines arranged in a fan-shaPed vertical row and alternating with equal number of simPle hirsute caPillaries arranged between or slightly Posterior to sPines.

Chaetiger 3 with smooth simPle caPillaries in notoPodia and two kinds of chaetae in neuroPodia ( Figs 3B, C , 5C ). Notochaetae on each side arranged in three grouPs comPrising suPerior tuft of 3–4 caPillaries, and anterior and Posterior vertical rows of slightly shorter caPillaries, uP to six in each row. Neurochaetae comPrising uP to six falcate sPines arranged in a fan-shaPed vertical row and alternating with equal number of short and slender hirsute caPillaries situated between sPines or slightly Posterior to them. Falcate sPines dark brown, smooth and heavy, much larger and darker than sPines of chaetiger 2, deePly embedded into body, with distal Part slightly curved and Protruding out of body wall. Postchaetal lamellae short and fleshy, conical, slightly flattened in both rami.

Chaetiger 4 with simPle caPillaries and fleshy, oval, flattened Postchaetal lamellae in both rami ( Figs 3B, D, E , 5D ). Chaetae in each ramus arranged in three grouPs, in notoPodia comPrising suPerior tuft of 3–5 long and slightly hirsute caPillaries, and anterior and Posterior vertical rows of short and consPicuously hirsute caPillaries, and in neuroPodia comPrising anterior and Posterior vertical rows of hirsute caPillaries and inferior tuft of 2–4 slightly shorter and thinner hirsute caPillaries ( Fig. 3D, E ).

From chaetiger 5, notoPodial caPillaries gradually reduced in number and Postchaetal lamellae gradually reduced in siZe ( Fig. 2A ); both caPillaries and lamellae absent after chaetiger 10, excePt small lamellae Present on chaetiger 11 in some individuals. NeuroPodia of chaetigers 5–15 large, with numerous chaetae Protruding from Prominent conical neuroPodial lobes flanked Posteriorly by fleshy, rounded, flattened Postchaetal lamellae ( Fig. 3B, D ). Lower Parts of neuroPodial lobes greatly inflated, largest on chaetigers 7–10, with numerous glandular ePithelial cells gathered in distinct Patches or Prominent Pads ( Fig. 2A ), aPPearing rosy in fixed sPecimens; same rosy glandular cells also Present in antero-dorsal Parts of neuroPodia and in notoPodial Postchaetal lamellae on same chaetigers. Neurochaetae of chaetigers 5–15 comPrising two vertical rows of frayed, flattened, distally Pointed heavy sPines ( Figs 3D , 6A ), uP to nine sPines in each row, Posterior row of uP to 18 long caPillaries with consPicuously hirsute convex side of distal end ( Figs 3D , 6B ), and inferior tuft of 2–5 slightly shorter and thinner caPillaries ( Fig. 6C ). NeuroPodial sPines heaviest and darkest on chaetigers 6–10, gradually becoming smaller, thinner, lighter and fewer on succeeding chaetigers.

From chaetiger 16 onwards, neuroPodia small, with three kinds of chaetae Protruding from low conical neuroPodial lobes flanked by small triangular Postchaetal lamellae and extending Posteriorly as thin horiZontal membranes ( Fig. 6H ); notoPodia lacking. Neurochaetae comPrising anterior tuft of 2–5 long caPillaries weakly hirsute on distal convex side ( Fig. 6G ), 2–5 aristate sPines arranged in almost horiZontal row and alternating with similar number of smooth syringe-like sPines ( Figs 3F , 4A , 6 D–F ). Distal ends of aristate sPines curved and flattened, greatly Protruding out of neuroPodial lobe, each having hirsute convex side and a long Pointed terminal Process ( Fig. 6D, E ). Syringe-like sPines mostly embedded into neuroPodial lobes and only long Pointed distal ends Protruding outside ( Figs 3F , 4A , 6F ). One Pair of small PaPillae Present on ventral side of each chaetiger from chaetigers 13–15 to chaetigers 19–22 ( Fig. 4B ).

From chaetigers 37–41 onwards, each notoPodium with a bundle of uP to seven straight acicular sPines ( Fig. 2B ). SPines entirely embedded into body wall; notoPodial lobes and Postchaetal lamellae lacking.

Small mouth flanked Posteriorly by ventral Peristomial liP ( Fig. 5B ). Foregut axial, with two small, aPParently ciliated, dorso-lateral folds. Ventral buccal bulb absent. Narrow oesoPhagus extending throughout thoracic chaetigers and terminating with simPle voluminous, thin-walled giZZard-like structure beginning from chaetigers 15–17 and extending through 3–6 chaetigers.

Main dorsal blood vessel without heart body.

NePhridia well seen from chaetiger 16 onwards, not certain in more anterior chaetigers.

Juvenile morphology. Smallest sPecimen about 0.3 mm wide with notoPodial caPillaries of chaetigers 1–10 (excePt chaetiger 2) and neuroPodia of chaetigers 1–4 aPPearing same as in larger sPecimens. NeuroPodia of chaetigers 5–10 with frayed sPines arranged in two vertical rows, caPillaries arranged in a Posterior row, and large glandular Pads. From chaetigers 9–10 Posteriorly, frayed sPines gradually becoming thinner, straighter and lighter, and on chaetigers 11–12 aPPearing similar to caPillaries. From chaetiger 13 onwards, neuroPodia with 1–2 slender caPillaries, 1–2 aristate sPines, 1–2 syringe-like sPines, small conical Postchaetal lamellae and lateral membranes.

SPecimens about 0.7 mm wide with notoPodial caPillaries of chaetigers 1–10 (excePt chaetiger 2) and neuroPodia of chaetigers 1–4 aPPearing same as in larger sPecimens. NeuroPodia of chaetigers 5–12 with frayed heavy sPines arranged in two vertical rows, caPillaries arranged in a Posterior row, and large glandular Pads. From chaetigers 9–10 Posteriorly, frayed sPines gradually becoming thinner, straighter and lighter, and on chaetigers 12– 13 aPPearing similar to caPillaries. From chaetiger 14 onwards, neuroPodia flat, without glandular Pads, with 1–2 slender caPillaries, 1–2 aristate sPines, 1–2 syringe-like sPines, small conical Postchaetal lamellae and lateral membranes.

SPecimens about 0.9 mm wide with large glandular Pads on neuroPodia of chaetigers 5–13. Chaetigers 14 and 15 flat, with small conical or triangular neuroPodial Postchaetal lamellae (lamellae slightly enlarged on chaetiger 14) and lateral membranes; ventral glandular Pads not yet develoPed but glandular cells Present in neuroPodial lamellae of chaetiger 14. Neurochaetae of chaetiger 14 aPPearing as caPillaries; aristate and syringe-like sPines absent. From chaetiger 15 onwards, neurochaetae comPrising 2–3 caPillaries, 1–3 aristate sPines and 1–3 syringelike sPines.

Habitat. In the estuary of Santos, São Paulo, adults of T. japonica occurred at the dePth of 2.6–15.8 m in sandy and muddy sediments with shell fragments and gravel. The salinity at the stations varied from 17.6 to 27.3‰. Density of worms at some stations reached 7000 individuals Per one square meter. All individuals were collected in October 2006 and were immature. In Camamu Bay, Bahia, the only sPecimen was collected in SePtember 2008 from silty sediment at the dePth of 8.1 m, salinity 27.3‰; it was immature, aPParently juvenile.

Figures

FIGURE 2. Adult morphology of T. Japonica from estuary of Santos, São Paulo (MIMB 33634). A, 15 thoracic and some anterior abdominal chaetigers, ventral view, showing dark glandular pads on thoracic chaetigers 5–15. B, bundle of acicular spines from notopodium of chaetiger 40. Abbreviations: pr—prostomium; ch3, ch5, ch15—thoracic chaetigers 3, 5 and 15. Scale bars: A—500 µm. B—10 µm.

FIGURE 3. Adult morphology of T. Japonica from estuary of Santos, São Paulo (MNRJ P1462). A, anterior end, dorsal view, palps missing, showing U-shaped nuchal organs on sides of caruncle, posterior border of chaetiger 1 and anterior border of chaetiger 2. B, anterior end, left lateral view, palps missing. C, chaetigers 2 and 3, left lateral view. D, neuropodia of chaetigers 3–5, left lateral view, showing frayed, flattened, distally pointed spines and capillary chaetae protruding from prominent neuropodial lobe of chaetiger 5. E, three groups of capillaries in notopodium of chaetiger 4, left lateral view. F, left neuropodium of chaetiger 18, dorsal view, showing anterior group of capillary chaetae and protruded aristate spines alternating with mostly embedded syringe-like spines. Abbreviations: an—anterior row of chaetae; ar—aristate spines; ca—caruncle; cap—capillary chaetae; fr—frayed spines; lo5—neuropodial lobe of chaetiger 5; me—neuropodial membrane; ne1–5— neuropodial postchaetal lamellae of chaetigers 1–5; no1–5—notopodial postchaetal lamellae of chaetigers 1–5; nu—nuchal organ; po—posterior row of chaetae; pr—prostomium; su—superior tuft of chaetae; s1, s2—borders of chaetigers 1 and 2; sy—syringe-like spines. Scale bars: A–C—100 µm. D, F—50 µm. E—20 µm.

FIGURE 4. Adult morphology of T. Japonica from estuary of Santos, São Paulo (MNRJ P1463). A, neurochaetae of chaetiger 18: aristate spines (ar) with curved and flattened distal end having hirsute conveX side and bearing long pointed terminal process (broken in middle spine), and syringe-like spines (sy) mostly embedded into neuropodial lobe and only long pointed distal end protruding outside. B, paired papillae (pa) on ventral side of anterior abdominal chaetigers. Scale bars: A—10 µm. B—100 µm.

FIGURE 5. Adult morphology of T. Japonica from estuary of Santos, São Paulo (MIMB 33634). A, head and chaetigers 1 and 2, frontal view, palps missing. B, head and chaetiger 1, ventral view. C, chaetiger 3, frontal view. D, chaetiger 4, frontal view. Scale bar: A–D—200 µm.

FIGURE 6. Adult morphology of T. Japonica from estuary of Santos, São Paulo (MIMB 33634). A–C, neurochaetae of chaetiger 7. A, frayed heavy spine from anterior row. B, capillary chaeta from posterior row. C, capillary chaeta from inferior tuft. D–G, neurochaetae of chaetiger 20. D, aristate spine, lateral view. E, aristate spine, frontal view. F, syringe-like spine. G, capillary chaeta from anterior tuft. H, right neuropodium of chaetiger 18, dorsal view, showing anterior group of capillary chaetae and protruded aristate spines alternating with mostly embedded syringe-like spines. Scale bars: A–H—50 µm.