Laonice (Sarsiana) apicelamella, 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 : 496-499

Laonice (Sarsiana) apicelamella sp. nov.

Figs 3A–L , 6 .

LSID: urn:lsid:zoobank.org:act:B915D3EA-1285-49FD-BFD4-A08E7941F968

Holotype. MNCN16.01 /19129, Gulf of Siam, off Thailand, st. 14, 07°49.818′N, 102°45.162′E, 73 m, 97.8% of silt and clay (<63 µm) and 2.2% of fine sand (63–250 µm) with shell fragments, 28 July 1998.

Paratypes. MNCN16.01 /19130, 1 specimen, Andaman Sea , off Myanmar /Burma, st. E7, 15°07.997′N, 94°46.838′E, 46 m depth, 76.3% of silt and clay (<63 µm), 03 December 2003 ; MNCN16.01 /19131, 1 specimen, Andaman Sea , off Myanmar /Burma, st. S4, 15°03.137′N, 94°46.050′E, 51 m depth, 90% of silt and clay (<63 µm), 03 December 2003 ; MNCN16.01 /19132, 1 specimen, Gulf of Siam, off Thailand, st. 8, 07°35.990′N, 102°44.202′E, 66 m depth, 92.7% of silt and clay (<63 µm) and 7.0% of fine sand (63–250 µm) with shell fragments, 27 July 1998 ; MNCN16.01 /19133, 1 specimen, Gulf of Siam, off Thailand, st. 4, 07°32.190′N, 102°47.742′E, 61 m depth, 89.6% of silt and clay (<63 µm) and 10.0% of fine sand (63–250 µm) with shell fragments, 27 July 1998 ; MNCN16.01 /19134, 1 specimen, Gulf of Siam, off Thailand, st. 1, 07°21.293′N, 102°37.073′E, 58 m depth, 81.8% of silt and clay (<63 µm) and 17.8% of fine sand (63–250 µm) with shell fragments, 25 July 1998 .

Description. Body 0.6–0.7 mm wide. Holotype in four fragments of 19 (anterior), 5+2 (middle), and 24 (posterior) chaetigers.

Prostomium short, as a nearly equilateral triangle with truncated, slightly concave anterior margin, fused with peristomial ventral surface by a thin fold deeply hidden in prostomium/peristomium groove ( Fig. 3A, D ). Nuchal organs U-shaped, with two wide loops following caruncle, reaching chaetiger 9–10 (8 in holotype, with a pair of nearly triangular expansions reaching middle of chaetiger 9); distance between loops nearly equivalent to loop width ( Fig. 3A, D ). Occipital antenna moderately developed. One pair of tear drop-shaped eyespots, with frontal and outer borders more strongly colored, just in front of occipital antenna.

Branchiae from chaetiger 2, probably up to chaetiger 24–29 (uncertainty due to types fragmentary condition); as long as notopodial postchaetal lamellae on chaetigers 2–3 (holotype), 1.2 times longer on chaetiger 4, 1.5 times longer on chaetigers 5–6, twice longer on chaetiger 9 (only after chaetiger 14 in holotype), 2.3 times longer on chaetiger 10 and 2.5 times longer on chaetiger 13 (only up to twice longer in paratypes) ( Fig. 3A, C–F ); branchiae shortening on the six posteriormost branchiate chaetigers ( Fig. 3B ), being four and five times longer in last 6–4 chaetigers than in last 3–2 and last one, respectively ( Fig. 3G ). Branchial margins usually bearing long cilia.

Anterior notopodial postchaetal lamellae leaf-like, with acute pointed tips ( Fig. 3E ); from chaetiger 6, tips gradually shifting downwards along lateral lamellar margin ( Fig. 3F ); tips progressively narrowing, becoming elongated upward on posteriormost branchiate chaetigers, and being reduced to small tips (upper one peak-like, lateral one as large, sharply acute peak) on last few branchiate chaetigers ( Fig. 3G ). Posteriormost notopodial postchaetal lamellae oval, leaf-like ( Fig. 3H ). Large, sharply acute lateral peaks quite pronounced on several lamellae of postbranchiate chaetigers. Small, tongue-shaped prechaetal notopodial lamellae from chaetiger 2, gradually shortening along branchiate chaetigers, non-visible on postbranchial chaetigers. Neuropodial postchaetal lamellae ear-like, with an acute peak on upper part of lateral margin ( Fig. 3E–H ).

Dorsal transverse crests connecting notopodial postchaetal lamellae absent, but very pronounced transverse ciliation (nototrochs— Fig. 3B ) present in about last four branchiate chaetigers and, at least, on the following 20 postbranchiate chaetigers.

Lateral inter-neuropodial pouches from chaetiger5–6,up to last chaetiger present in all available anterior fragments.

Capillaries of anterior chaetigers arranged in two vertical rows. Neuropodial hooks probably from chaetiger 28– 32 (uncertainty due to types fragmentary condition), up to 10 per fascicle. Notopodial hooks in posterior notopodia ( Gulf of Siam, st. 1, MNCN16.01 /19134). Neuropodial and notopodial hooks bidentate in lateral view ( Fig. 3I, K ), tridentate in frontal view, with one pair of small apical teeth side by side above main fang ( Fig. 3J, L ). Distal region of notopodial hooks smaller than in neuropodial ones, sometimes small, knob-like, with teeth difficult to distinguish. Sabre chaetae from chaetiger 11–20, 1–2 per fascicle .

Pygidium in poor condition, showing a single remaining anal cirrus in only one specimen ( Gulf of Siam, st. 1, MNCN16.01 /19134) .

Pigmentation absent.

Methyl Green staining. Strong on tips and along outer edges of notopodial postchaetal lamellae on chaetigers 2–7 ( Fig. 3D ) and on upper edges of neuropodial postchaetal lamellae on chaetigers 2–17.

Type locality. Gulf of Siam, off Thailand (07°49.818′N, 102°45.162′E), 73 m depth .

Etymology. The specific epithet apicelamella refers to the very pronounced, large, pointed peak on the lateral edge of the notopodial postchaetal lamellae of nearly all branchiate and several postbranchial chaetigers ( Fig. 3A–B, D, F–G ).

Distribution. Gulf of Siam (Pacific Ocean) and Andaman Sea (Indian Ocean) ( Fig. 6 ).

Remarks. The holotype was assumed as being composed by the four fragments found in st. 14 (Gulf of Siam), but as this may not be the case, the numerical characters of the species must be considered an estimate. All paratypes are short anterior fragments. Also, the single posterior fragment having pygidium was in poor condition, showing only one anal cirrus. However, most likely the species has two short ventral cirri and several paired dorsal cirri surrounding the anus.

Laonice apicelamella sp. nov. belongs to L. ( Sarsiana ) as defined by Sikorski et al. (2017), as it has comparatively short nuchal organs, always similar in length in all studied specimens, capillaries of anterior chaetigers arranged in two rows only, prostomium fused to ventral peristomial surface by a thin fold deeply sunken in the prostomium/peristomium groove, and hooks in the posteriormost notopodia.

Dorsal transverse crests connecting notopodial postchaetal lamellae are absent in this species. As in L. ( Laonice ), this character allows the recognition of various morphological subgroups within L. ( Sarsiana ), which may or may not have a phylogenetic significance. In particular, the absence of dorsal transverse crests in L. ( Sarsiana ) is usually combined with the presence of (1) a minute membrane connecting the anterior angles of prostomium and peristomium, usually sunken in the groove between them, and (2) hooded hooks in the most posterior notopodia. This combination of characters is also present in L. sarsi Söderström, 1920 , L. antarcticae Hartman, 1953 , L. dayianum Sikorski, 1997 , L. rossica Sikorski, 2003 , L. olgae Sikorski & Pavlova, 2016 , and L. alberti Sikorski et al., 2021 . Moreover, L. praecirrata Hartmann-Schröder, 1965 , L. nuchala Blake, 1996 , L. junoyi Aguirrezabalaga & Ceberio, 2005 , L. parvabranchiata Radashevsky & Lana, 2009 , and L. whittardensis Sikorski et al., 2017 also resemble morphologically L. apicelamella sp. nov.

In L. apicelamella sp. nov. the lateral inter-neuropodial pouches appear from chaetiger 5–6, while in L. sarsi they start from 4–33, with only the specimens measuring less than 0.4 mm wide having lateral pouches starting before chaetiger 8 ( Sikorski 2003a). In L. rossica they range from 2–50, and only specimens less than 0.4 mm wide may have lateral inter-neuropodial pouches starting before chaetiger 8 ( Sikorski 2003b). Laonice antarcticae has lateral inter-neuropodial pouches from chaetiger 3–4 and nuchal organs extending to chaetiger 12–13 ( Sikorski, 2011) (9–10 in L. apicelamella sp. nov.); L. olgae has lateral inter-neuropodial pouches starting at chaetigers 32–33 and L. alberti at chaetiger 21–34, but also nuchal organs reaching chaetiger 5–7 and neuropodial hooks starting at chaetiger 35–38 (28–32 in L. apicelamella sp. nov.), and branchiae absent from chaetiger 31–39 (24–29 in L. apicelamella sp. nov.). Laonice dayianum has longer nuchal organs reaching chaetiger 12–14, lateral inter-neuropodial pouches starting from chaetiger 18–28, and sabre chaetae from chaetiger 26 (11–20 in L. apicelamella sp. nov.) ( Sikorski 2011). Laonice parvabranchiata has lateral inter-neuropodial pouches starting from chaetiger 14–16, sabre chaetae from chaetiger 27–29, neuropodial hooks after chaetiger 42, and branchiae absent from chaetiger 35 onwards. Laonice junoyi has shorter nuchal organs extending for 6–7 chaetigers and lateral inter-neuropodial pouches starting at chaetiger 8–9. Laonice nuchala and L. praecirrata have longer nuchal organs reaching chaetiger 13 and 15–21, respectively, lateral inter-neuropodial pouches starting at chaetigers 7–8 and 9–24, and more numerous branchiae (>47 and 59, respectively). The deep-sea species L. whittardensis measures less than 0.4 mm wide and can be distinguished from L. apicelamella sp. nov. by the majority of morphological characters discussed above ( Sikorski et al. 2017). Finally, the characteristic presence of nototrochs on several postbranchiate chaetigers in L. apicelamella sp. nov. is rarely present in the other morphologically similar species.

Figures

FIGURE 3. Laonice apicelamella sp. nov. A: anterior region (12 chaetigers), dorsal view. B: end of branchiate region (chaetigers 44–48), dorsal view. C: anterior region (7 chaetigers), lateral view. D: staining pattern with Methyl Green, anterior region (12 chaetigers), dorsal view. E–H: parapodia of chaetigers 4, 13, 29? (last branchiate chaetiger) and 19 before pygidium, frontal view. I: neuropodial hooded hook, chaetiger 19 before pygidium, lateral view. J: neuropodial hooded hook, chaetiger 19 before pygidium, frontal view (scheme). K, notopodial hooded hook, chaetiger 19 before pygidium, lateral view. L: notopodial hooded hook, chaetiger 19 before pygidium, frontal view (scheme). Scale, mm: A–C, 1; D, 1.4; E–H, 2.1; I–L, 0.05. Material: A–C, E–G, paratype, Andaman Sea, st. E7 (MNCN16.01/19130); D, paratype, Gulf of Siam, st. 8 (MNCN16.01/19132); H–L, paratype, Gulf of Siam, st. 1 (MNCN16.01/19134).

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).