Aricidea (Acmira) chilikensis, Choudhury & Dutta & Patro & Rastogi, 2025

Aricidea (Acmira) chilikensis sp. n. Choudhury, Dutta & Patro

Figures 1–3 View Figure 1 View Figure 2 View Figure 3

Material examined

Holotype: Length 8.79 mm, Width 0.31 mm ( ZSI / EBRC /An-15937), Chilika Lagoon , southern sector (19°36ʹ14.16”N, 85°11ʹ33.14”E), Odisha, India, 30/06/2023, Coll. Amita Kumari Choudhury. GoogleMaps

Paratypes (02 numbers): ZSI / EBRC /An-15938, Length- 14.76 mm, Width- 0.64 mm, incomplete specimen, ZSI / EBRC /An-15939, Length- 10.12 mm, Width- 0.35 mm, incomplete specimen .

Other materials: 03 individuals, length (8.01–17 mm), width (0.28–0.59 mm) (004. MSR / BoL-24); same data as holotype GoogleMaps .

Etymology

The species is named after the site of its collection which is the Chilika Lagoon.

Habitat

In soft mud sand, depth 2.6 m, water temperature 30°C, salinity 20 PSU.

Diagnosis

Median antenna cylindrical, widest at the base with a tapered blunt end, branchiae anteriorly short, gradually increasing in size and elongated in last 4–5 chaetigers, modified neurochaetae distally strongly curved with a single long arista.

Description

Based on holotype, length: 8.79 mm, width: 0.31 mm.

Holotype complete with 101 chaetigers, body length 8.79 mm, width 0.31 mm; paratypes incomplete with 78–88 chaetigers, 10.12–14.76 mm long and 0.35–0.64 mm wide. Body wide, dorsoventrally flattened in branchial region, cylindrical in post-branchial region ( Figure 3A View Figure 3 ). Prostomium triangular, width 2× times the length, distally rounded, with reddish pigment spots present along the anterior and lateral prostomial margin. Eye absent. Nuchal organs are a pair of oblique, deep slits. Median antennae are well-developed with central insertion, cylindrical, elongated, widest at the base and tapering to a blunt end, extending up to chaetiger 2 ( Fig 1A View Figure 1 , 3B View Figure 3 ).

Twenty-three pairs of branchiae are present on chaetiger 4–26. Branchiae arranged on dorsum, basally inflated without a ciliary band. Anterior branchiae are foliaceous, blunt-tipped, gradually increase in size and overlap along the midline of the body. Posterior-most (in last 4–5 chaetigers) are elongated, cirriform, blunt-tipped and longer than the anterior ones ( Fig 1A View Figure 1 , 3B View Figure 3 ). The first two notopodial postchaetal lobes are short and round ( Figure 1B View Figure 1 ). Notopodial postchaetal lobes gradually increase from chaetiger 3, progressively longer in the branchial region to long, thin, filiform in the posterior region ( Figure 1C View Figure 1 ). Neuropodial postchaetal lobes are absent. Inter-ramal papilla present till branchial region. Chaetae well-developed. Notochaetae all slender capillaries ( Figure 2A View Figure 2 ). Notochaetae of the anterior region are comparatively thicker and longer than the postbranchial region. Neurochaetae includes slender capillary and modified chaetae starting from chaetiger 33. Modified neurochaetae distally strongly curved with a terminal long arista. Up to 6–8 modified chaetae per neuropodium ( Fig. 2b View Figure 2 , 3c View Figure 3 ). Mid-dorsal transversal line of prebranchial and branchial chaetigers without ciliary band. Pygidium, rounded with four reddish pigment spots and two anal cirri of similar size ( Figure 2C View Figure 2 ).

Remarks

According to WoRMS database, a total of 26 species belong to the genus Aricidea (Acmira) (Read and Fauchald 2024) . Further, Aricidea elongata Imajima 1973 and Aricidea rosea ; Reish, 1968 which are not included under the subgenus Acmira , also possess hook and terminal distal arista in the posterior modified neuropodial region. Including these two species, the total species number under the subgenus leads to 28. A comparative table of the morphological characteristics of the species of the genus Aricidea (Acmira) is provided in Table 1 View Table 1 .

Aricidea (Acmira) chilikensis sp. n. can be distinguished from other members of the subgenus by the shape of the median antenna, structure and pattern of the branchia, and modified neurochaetae. Among the 28 species, 18 species possess single or multiple terminal distal aristae in the modified posterior neuropodial region. Fifteen species, Aricidea (Acmira) bbkingi Barroso, Paiva & Ranauro, 2020 , A. (A.) catherinae , Aricidea (Acmira) elongata Imajima, 1973 , Aricidea (Acmira) filamentosa Barroso, Paiva & Ranauro, 2020 , Aricidea (Acmira) finitima Strelzov, 1973 , Aricidea (Acmira) katzmanni Erdoğan-Dereli & Çinar, 2020 , Aricidea (Acmira) laubieri Hartley, 1981 , A. (A.) lopezi , Aricidea (Acmira) meridionalis Laubier & Ramos, 1974 , Aricidea (Acmira) mirifica Strelzov, 1973 , Aricidea (Acmira) philbinae Brown, 1976 , Aricidea (Acmira) pseudoassimilis Erdoğan-Dereli & Çinar, 2020 , Aricidea (Acmira) rosea Reish, 1968 , Aricidea (Acmira) rubra Hartman, 1963 and Aricidea (Acmira) taylori Pettibone, 1965 have single terminal distal arista similar to A. (A.) chilikensis sp. n.

Amongst the above 15 species, majority have posterior branchiae that are relatively longer than anterior branchiae, however, the last few pairs are equal or short in most species, whereas in A. (A.) chilikensis sp. n., the last pairs are the longest. Aricidea (Acmira) chilikensis sp. n. is characterised by branchiae that are shorter on anterior chaetigers and that gradually increase in size posteriorly, with posterior-most branchiae relatively elongated and narrow. In A. (A.) bbkingi , A. (A.) catherinae , A. (A.) elongata , and A. (A.) pseudoassimilis , the branchiae located at the posterior end are not elongated, indicating a more uniform length throughout. In contrast, A. (A.) philbinae exhibits elongated branchiae in the anterior region, making it distinctive. In species such as A. (A.) laubieri , the posterior pair of branchiae are smaller, while in A. (A.) filamentosa , A. (A.) finitima , and A. (A.) katzmanni , only the last two pairs of branchiae are shorter than the others, giving these species a characteristic appearance. In A. (A.) lopezi , branchiae are present from chaetiger 4 to 53 (while in A. (A.) chilikensis sp. n., they are present from chaetiger 4 to 26). (Continued) Similarly, A. (A.) mirifica and A. (A.) rosea possess only a single short pair of branchiae located at the very end of the body. A. (A.) rubra has antennae that end in a sharply pointed tip ( A. (A.) chilikensis sp. n., has cylindrical, elongated antennae that are widest at the base and taper to a blunt end) and possesses up to 30 pairs of branchiae (23 pairs in A. (A.) chilikensis sp. n., In A. (A.) taylori , the branchiae are ciliated except at the distal tip, while cilia are absent in A. (A.) chilikensis sp. n.

In addition, the median antenna of A. (A.) chilikensis sp. n. is widest at the base tapering to a blunt end. Among the above 15 species, A. (A.) meridionalis shows antenna and branchial characters similar to A. (A.) chilikensis sp. n. Aricidea (Acmira) chilikensis sp. n. differs from A. (A.) meridionalis by lacking a ciliary band on both sides of the branchia and on the mid-dorsal transversal line of branchial and prebranchial chaetigers (vs. present in A. (A.) meridionalis ). Further, the terminal and subterminal region of modified neurochaetae display small hairs which are absent in A. (A.) chilikensis sp. n.