Laonice (Sarsiana) andamanica, Sikorski & Pavlova & Martin & Gil, 2023

Sikorski, Andrey, Pavlova, Lyudmila, Martin, Daniel & Gil, João, 2023, New sublittoral species of Laonice (Annelida: Spionidae) from southern Asian coasts, Zootaxa 5277 (3), pp. 490-508 : 499-501

Laonice (Sarsiana) andamanica sp. nov.

Figs 4A–L , 6 .

LSID: urn:lsid:zoobank.org:act:FBB97F5C-9A68-44F9-8D6A-02FC0407ED83

Holotype. MNCN16.01 /19135, Andaman Sea , off Myanmar /Burma, st. E14, 15°07.334′N, 94°46.852′E, 47.4 m depth, 77% of silt and clay (<63 µm), 03 December 2003.

Paratype. MNCN16.01 /19136, Andaman Sea , off Myanmar /Burma, st. E13B, 15°07.537′N, 94°46.854′E, 47 m depth, 85% of silt and clay (<63 µm), 03 December 2003 .

Description. Holotype incomplete, 0.7 mm wide, in three fragments with 37 (anterior) and 6 plus 2 (middle) chaetigers. Paratype incomplete, 0.7 mm wide, with 22 anterior chaetigers.

Prostomium T-shaped, with rounded anterior margin, joined to peristomium, with junction clearly outlined, but completely lacking a space between prostomium and peristomium ( Fig. 4A ). Caruncle visible, extending to posterior border of chaetiger 7–9. Nuchal organs extending to end of chaetiger 9–11, as U-shaped ciliary bands on sides of caruncle. Palps not seen.

Long, acute occipital antenna on posterior prostomial region, as long as notopodial postchaetal lamellae of chaetiger 1. One pair of eyespots in front of occipital antenna ( Fig. 4A ).

Branchiae from chaetiger 2 ( Fig. 4A, C ), narrowing into thread-like tips ( Fig. 4F–G ), shorter than notopodial postchaetal lamellae until chaetiger 4 (those on chaetigers 2–3 being half long), as long as on chaetigers 5–8, and slightly longer (approx. 1.2 times— Fig. 4A, G ) until chaetiger 27–28; last pair visible on chaetiger 35 ( Fig. 4B, H ).

Notopodial postchaetal lamellae much longer than branchiae on posteriormost branchiate region ( Fig. 4B, H ), up to four times longer than last pair of branchiae. Notopodial postchaetal lamellae narrowing to acute tips until chaetiger 42 ( Fig. 4I ), gradually lengthening to end of branchiate region ( Fig. 4B ), then considerably longer from chaetiger 29–35, being twice as long on chaetiger 35 than on chaetigers 5–8 ( Fig. 4F, H ) and three times longer than on chaetiger 2, and sharply decreasing on the postbranchiate chaetigers ( Fig. 4J ). Tips of lamellae acute, gradually extending to increasingly narrow, long, sharply pointed processes from chaetigers 18–29 ( Fig. 4H ), lacking acute tips backwards ( Fig. 4J ). Tips of lamellae reaching opposite chaetal tuft ( Fig. 4B ). Notopodial postchaetal lamellae ear-like, with rounded upper edges from chaetiger 42 ( Fig. 4J ). Inferior regions of notopodial postchaetal lamellae (below neuropodial chaetal tuft) becoming visible from chaetiger 31 ( Fig. 4H–J ). Neuropodial postchaetal lamellae axe-shaped, with upper lateral angle forming an acute tip anteriorly, progressively becoming more rounded on posterior chaetigers ( Fig. 4F–J ). Noto- and neuropodial prechaetal lamellae short, not easily distinguishable.

Continuous dorsal transverse crests connecting notopodial postchaetal lamellae first appearing three chaetigers before last branchiate one; maximum height at chaetigers 35–37 ( Fig. 4B ); present up to the last chaetiger of holotype. Transverse nototrochs quite pronounced anteriorly on several branchiate chaetigers.

Lateral inter-neuropodial pouches from chaetiger 26, up to at least chaetiger 37 in holotype anterior fragment.

Capillaries of anterior chaetigers arranged in two vertical rows. Neuropodial hooks from chaetiger 34, up to eight per fascicle, tridentate in lateral view ( Fig. 4K ), quadridentate in frontal view, with one pair of small apical teeth side by side and a single superior median tooth above main fang ( Fig. 4L ). Notopodial hooks absent in holotype. Sabre chaetae from chaetiger 27.

Pygidium not seen, missing.

Pigmentation absent.

Methyl Green staining. Strong on inner upper parts of notopodial postchaetal lamellae from chaetiger 5–10, on dorsal and ventral side of peristomium, on prostomium below eyespots and behind occipital antenna, and ventrally in front of mouth ( Fig. 4C–D ). Very weak, diffuse staining ventrally and on neuropodial postchaetal lamellae of chaetigers 25–32 ( Fig. 4E ), fading remarkably sooner than on notopodial postchaetal lamellae, prostomium and peristomium.

Type locality. Andaman Sea , off Myanmar /Burma (15°07.334′N, 94°46.852′E), 47.4 m depth .

Etymology. The specific epithet andamanica derives from the toponymic name of the sea where the types were collected, the Andaman Sea.

Distribution. Andaman Sea (Indian Ocean) ( Fig. 6 ).

Remarks. The holotype was the single specimen having enough chaetigers to determine the main numerical characters. Laonice andamanica sp. nov. belongs to L. ( Sarsiana ) as defined by Sikorski et al. (2017), as it has comparatively short nuchal organs (similar in length in all studied specimens) and capillaries of the anterior chaetigers arranged in two vertical rows only. Moreover, it has dorsal transverse crests, but apparently lacks the membrane connecting the anterior angles of prostomium and peristomium, as well as hooks in most posterior notopodia. Thus, it most closely resembles L. japonica ( Moore, 1907) , L. sinica Sikorski & Wu, 1998 , L. praecirrata , L. branchiata Nonato, Bolívar & Lana, 1986 and L. magnacristata . Laonice andamanica sp. nov. can be easily distinguished from these species in having several notopodial postchaetal lamellae of posterior branchiate chaetigers with pointed tips elongated into narrow long lanceolate processes with length equal to the body width on the last branchiate chaetigers ( Fig. 4B, H ). Besides, L. japonica has nuchal organs reaching chaetiger 18 (9–11 in L. andamanica sp. nov.) and lateral inter-neuropodial pouches appearing from chaetiger 4 (26 in L. andamanica sp. nov.); L. sinica has lateral inter-neuropodial pouches from chaetiger 5–9 and a different shape of dorsal transverse crests; L. magnacristata is 0.4 mm wide, has nuchal organs reaching chaetiger 2, 4–7 pairs of branchiae (34 pairs in L. andamanica sp. nov.), sabre chaetae from chaetiger 6 (27 in L. andamanica sp. nov.), and lateral inter-neuropodial pouches from chaetiger 7–8; and L. praecirrata has nuchal organs extending until chaetiger 15–21 and the membrane connecting prostomium with peristomium at the anterior angles is sunken in the groove between them. Finally, the lateral inter-neuropodial pouches in L. branchiata [species mistakenly placed in L. ( Laonice ) by Sikorski et al. (2017)] start from chaetiger 4–10 (instead of 26 in L. andamanica sp. nov.).

Laonice andamanica sp. nov. has the prostomium joined to the peristomium, but the junction still clearly outlined. This unique feature is shared with L. branchiata (see Sikorski 2011) and, probably, is also present in L. japonica (see Sikorski 2003b), which allows us to suggest that these species form a distinctive morphological group within the genus. However, the relevance of this group requires further confirmation.

Figures

FIGURE 4. Laonice andamanica sp. nov. A: anterior region (8 chaetigers), dorsal view. B: end of branchiate region (chaetigers 31–37), dorsal view. C: staining pattern with Methyl Green, anterior region (12 chaetigers), dorsal view. D: staining pattern with Methyl Green, prostomium and peristomium, ventral view. E: staining pattern with Methyl Green, middle region (chaetigers 26–33), ventral view. F–J: parapodia of chaetigers 8, 21, 35 (last branchiate chaetiger), 38 and 46, frontal view. K: neuropodial hooded hook, chaetiger 46, lateral view. L: neuropodial hooded hook, chaetiger 46, frontal view (scheme). Scale, mm: A–B, 1; C–E, 2; F–J, 0.7; K–L, 0.025. Material: holotype, Andaman Sea, st. E14 (MNCN16.01/19135).

FIGURE 6. Location of the different species of Laonice discussed in the study: Persian Gulf (dot), Andaman Sea (square), Gulf of Siam (star), and Yellow Sea (triangle).