Perinereis khambhatiensis Prajapat, Villalobos-Guerrero & Vachhrajani, 2023

Prajapat, Vaishali, Villalobos-Guerrero, Tulio F. & Vachhrajani, Kauresh D., 2023, A new species of Perinereis Kinberg, 1865 (Annelida: Nereididae) and invalidation of two congeners from Western India, Zootaxa 5330 (3), pp. 398-412 : 402-406

Perinereis khambhatiensis Prajapat, Villalobos-Guerrero & Vachhrajani , sp. n.

Figure 3A–N urn:lsid:zoobank.org:pub:2ABEA8CC-094A-4895-ACD1-39A78B455184

Type material. India, Gulf of Khambhat. Holotype: MSUB-ZL-AN-PCh-01 , Kamboi (22°12’55.67’’N, 72°36’25.42’’E), Gujarat, 04 March 2022, hard mud substratum, coll. V. Prajapat & K. Vachhrajani. Paratypes: Five specimens( ZSI-WRCANN/25 ), Kamboi (22°13’1.10’’N,72°36’57.17’’E), Nahar (22°11’33.21’’N, 72°41’23.75’’E), Gujarat , 27 April 2022, hard mud substratum, coll. V. Prajapat & K. Vachhrajani .

Additional material. India, Gulf of Khambhat. Twenty specimens ( MSUB-ZL-AN-PCh-03 ), Kamboi (22°12’53.61’’N, 72°36’14.63’’E), Gujarat , 12 June 2022, hard mud substratum, coll. V. Prajapat .

Diagnosis. Species of subgroup 2A belonging to ‘ P. aibuhitensis ’ species group. Specimens with broad-petite and smooth bars on area VI; areas VI-V-VI ridge pattern λ-shaped; area III with laterally isolated paragnaths; areas VII–VIII with anterior band consisting of one row; distal dorsal ligule anteriorly conical, subequal in size throughout; falcigers with camerated shaft divided into two partitions; postero-dorsal tentacular cirri extending to chaetiger 4–6.

Description of holotype (MSUB-ZL-AN-PCh-01). Atoke, complete, in good condition, 52 (40–76) mm TL, 5.8 (3−6) mm L10, 1 (1.5−2) mm W10, and 98 (80−91) chaetigers. Overall body color brownish ( Figure 3A ), chaetigers mid-dorsally greenish, laterally creamy white, ventrally creamy or white (anterior region with irregular black spots in one specimen).

Prostomium campanulate ( Figure 3B ); anterior region distally entire, sub-quadrangular, slightly longer than posterior region; anterolateral gap between antenna and palpophore narrow, as wide as basal diameter of antennae.

Palpophores sub-conical, thick, slightly longer than wide, as long as prostomium( Figure3B );sub-distal transverse groove distinct, deeply embedded. Palpostyles oval in paratypes, one-half as wide as diameter of palpophore.

Antennae tapered, conical, short, as long as prostomial posterior region; antennae separated by gap as wide as basal diameter of antennae.

Paired eyes in rectangular arrangement, purplish ( Figure 3B ); gap between both pairs three-quarters as wide as diameter of posterior pair of eyes. Anterior pair of eyes oval, with eye diameter slightly wider than that of antennae, with gap between eyes 3.5 times as wide as eye diameter; lenses visible, whitish, oval, placed anterolaterally, covering 40% of eye. Posterior pair of eyes oval, with diameter as wide as that of antennae, not covered by tentacular belt; lenses visible, purplish, oval, placed centrally, covering 60% of eye.

Tentacular belt 1.3 times as long as chaetiger 1 ( Figure 3B ), with straight anterior margin; dorsum without transverse wrinkle.

Tentacular cirri smooth ( Figure 3B ). Antero-dorsal cirri extending posteriorly to chaetiger 1 (1–2). Antero-ventral cirri as long as palpophore, slightly thicker than and as long as postero-ventral cirri. Postero-dorsal cirri longest, extending posteriorly to chaetiger 4 (4−6). Postero-ventral cirri slenderest, extended over first quarter of prostomial posterior region. Dorsal cirrophores of tentacular cirri cylindrical; postero-dorsal cirrophores as long as wide, subequal to antero-dorsal cirrophores. Ventral cirrophores ring-shaped; postero-ventral cirrophores shortest and narrowest, three-quarters as wide as antero-ventral cirrophores.

Proboscis everted ( Figure 3B–D ), with maxillary and oral rings cylindrical, wider than long. Jaws denticulate, dark brown amber, 6 (5−7) short, with blunt tips ( Figure 3E, F ); inner margin of fang nearly straight; 2 canals emerging from pulp cavity ( Figure 3E, F ). Paragnaths present on both maxillary and oral rings of proboscis, all brown ( Figure 3B–D ); consisting of uniform-base cones, except broad-petite bars on area VI; paragnaths on maxillary ring shorter than those on oral ring; plate-like basements absent. Area I: 4 (1−3), small (longitudinal row when 2, triangular patch when 3) ( Figure 3B ). Areas IIa: 18 (12−19), IIb: 19 (14−18), three irregular rows of uneven cones in ovoid transverse patch, medial cones slightly larger ( Figure 3B ). Area III: 25 (22−34), four irregular transverse rows of uneven cones in oval patch, distal cones larger, with distinct isolated lateral groups of 3 and 5 (2−4) paragnaths ( Figure 3C, D ). Areas IVa: 32 (24−35), IVb: 33 (26−35), 6−7 irregular rows of uneven cones in triangular patch ( Figure 3C, D ), distal cones larger; without merged paragnaths.Area V: 3, triangular patch of coarse cones of similar size, two proximal cones in transverse row and single distal cone on same level as distal-most paragnath on area VI ( Figure 3B ). Areas VIa: 2 and VIb: 2, one oblique row of uneven, coarse bars with round tip, well separated from each other, inner as smooth bar, bigger than outer broad-petite bar ( Figure 3B ). Areas VII–VIII: 37 (28–31), paragnaths in two well-separated bands of similar-sized cones, with anterior band consisting of one furrow row (one paragnath on each region), and posterior band with two transverse rows displaced from each other (furrow row proximal with one cone on each region, ridge row distal with 1–3 cones on each region). Ridges of areas VI-V-VI with λ-shaped pattern ( Figure 3B ). Gap between area VI and areas VII–VIII broad, as wide as half of palpophore width. Paired oesophageal caeca present ( Figure 3G ).

Notopodia consisting of dorsal cirrus, dorsal ligule (distal and proximal regions), and median ligule in biramous parapodia; notopodial prechaetal lobe or notoacicular process not developed throughout.

Dorsal cirrus conical, thick, short ( Figure 3H–L ), longer than proximal region of dorsal ligule and extending up to three-quarters of distal region of dorsal ligule in anterior and middle chaetigers ( Figure 3H–J ), as long as proximal and distal regions of dorsal ligule in following chaetigers ( Figure 3K, L ); attached to one-third of dorsal ligule in anterior chaetigers, medially in following chaetigers.

Dorsal ligule with distal region as long as proximal region in anterior and middle chaetigers ( Figure 3H–L ), becoming shorter than that in following chaetigers ( Figure 3K, L ). Proximal region of dorsal ligule compressed in most chaetigers ( Figure 3H–K ), except distended and sub-oval in most-posterior chaetigers ( Figure 3L ); 2 prominent ovoid patches of dark brown glands present from posterior chaetigers, covering three-quarters of ligule area. Distal region of dorsal ligule becoming gradually shorter and slightly narrower towards posterior end; bluntly conical in most anterior and most posterior chaetigers ( Figure 3H, L ), conical with pointed tip in remaining chaetigers ( Figure 3I–K ); slightly shorter than median ligule in anterior and middle chaetigers, slightly longer than that in following chaetigers; projecting distinctly beyond notoacicula throughout; without glandular patches throughout.

Median ligule similar-sized throughout; bluntly conical in anterior chaetigers, conical and becoming slightly shorter and narrower in following parapodia.

Neuropodia consisting of neuroacicular ligule with superior and inferior lobes, ventral ligule, and ventral cirrus; neuropodial postchaetal lobe reduced throughout.

Neuroacicular ligule sub-rectangular throughout; longer than ventral ligule in anterior and middle chaetigers ( Figure 3H–J ), as long as that in following chaetigers ( Figure 3K, L ); neuroacicular ligule 1.5 times as wide as ventral ligule in anterior and middle parapodia, twice as wide as that in following chaetigers.

Superior lobe rounded ( Figure 3H–J ), subequal to inferior lobe throughout.

Inferior lobe rounded, slightly longer than neuroacicular ligule throughout ( Figure 3H–K ), becoming shorter in posterior chaetigers ( Figure 3L ).

Ventral ligule well developed throughout; digitiform, thick, as long as (or slightly shorter than) median ligule in anteriormost chaetigers, bluntly conical, one-half to one-third as long as median ligule in following chaetigers ( Figure 3I–L ).

Ventral cirri conical, slender; three-quarters to two-thirds as long as ventral ligule in anteriormost and anterior chaetigers ( Figure 3H, I ), half as long as that in following chaetigers ( Figure 3J–L ).

Aciculae mostly dark brown throughout. Notoaciculae absent in first 2 chaetigers ( Figure 3H ). Notoaciculae markedly shorter than neuroaciculae in anterior and middle chaetigers ( Figure 3H–J ), subequal to those in following chaetigers ( Figure 3K, L ). Neuroaciculae as long as median ligule in anteriormost and anterior chaetigers, shorter than median ligule in following chaetigers.

Notochaetae all homogomph spinigers throughout; 7–8 spinigers present in anterior chaetigers, 5–6 in middle chaetigers, and 4–5 in posterior chaetigers.

Upper neurochaetae consisting of homogomph spinigers and heterogomph falcigers throughout; 3–4 spinigers present in anteriormost, anterior and middle chaetigers, 4–5 spinigers in following chaetigers; 3–4 falcigers present in anteriormost and anterior chaetigers, 5–7 falcigers in following chaetigers.

Lower neurochaetae consisting of heterogomph spinigers and heterogomph falcigers throughout; 1–2 spinigers present in anteriormost chaetigers, 3–4 spinigers in anterior chaetigers, 1–2 spinigers in following chaetigers; 6–7 falcigers present in anteriormost and anterior chaetigers, 5–6 falcigers in middle chaetigers and 6–7 falcigers in following chaetigers.

Blade of both homogomph and heterogomph spinigers long, finely serrated, with teeth evenly spaced ( Figure 3M ). Blade of heterogomph falcigers long, slender, straight, partially serrated ( Figure 3N ). Shaft of falcigers camerated, with cavity divided sub-distally into two distinct longitudinal partitions ( Figure 3N ).

Pygidium with long anal cirri, as long as last 4 (3–7) chaetigers.

Variation. Total body length: 39–96 mm. Length to chaetiger 10: 3–6 mm. Body width at chaetiger 10: 1–2 mm. Number of total chaetigers: 76–102. Longest tentacular cirri extending to chaetiger 3–6. Jaws with 9–11 denticles. Number and pattern of paragnaths: area I: 1–5, mostly 1 to 3 and rarely 4–5, two in line, three in triangle, four in rhomboid, or five in circle; area II: 11–24; area III: 22–34 in central patch, 2–4 cones isolated laterally; area IV: 24–42; area V: 1–4, three in most of the specimens and rarely 1, 2 or 4; area VII–VIII: 28–37. Anal cirri as long as last 3–7 chaetigers.

Habitat. Tube dwelling species burrowing in calcrete mud flats. Burrows are found abundantly in the substratum from surface to about 15 cm depth, and are separated from each other by thin muddy walls.

We observed several macrobenthic organisms (amphipods, isopods, brachyurans, burrowing sea anemones, rove beetles and other small fauna) in the hard substratum present studies (unpublished data).

Type locality. Kamboi (22°12’55.67’’N, 72°36’25.42’’E), Gulf of Khambhat, Gujarat, India .

Distribution. Only known from Kamboi and Nahar in the Gulf of Khambhat, Gujarat, northwestern India.

Etymology. The specific epithet makes reference to the Gulf of Khambhat, derived from the region where the type locality is located and all the specimens were collected.

Remarks. Perinereis khambhatiensis sp. n. is a member of the ‘ P. aibuhitensis ’ species group following the definition given by Villalobos-Guerrero et al. (2021b). Out of nineteen Perinereis species recorded from India, only three species have been regarded as belonging to ‘ P. aibuhitensis ’ species group: Perinereis aibuhitensis , P. singaporiensis and P. vancaurica ( Fauvel 1932; Bhatt & Bal 1966; Parulekar 1972; Sivadas & Carvalho 2020).

Based on the presence of isolated conical paragnaths on area III, P. khambhatiensis sp. n. is morphologically similar to P. aibuhitensis and P. singaporiensis , both described from far and distinct biogeographic realms (Eastern and Central Indo-Pacific, respectively, according to Spalding et al. 2007), but reported in Indian waters. However, P. khambhatiensis sp. n. differs from them by the conical shape of the distal region of dorsal ligules in anterior chaetigers (bluntly conical in P. aibuhitensis , bluntly rounded in P. singaporiensis ). In addition, P. khambhatiensis sp. n. differs from P. aibuhitensis by the ridge pattern of areas VI-V-VI, the range number of paragnaths present on area IV, and length of the bar-shaped paragnaths on area VI. In P. khambhatiensis sp. n., the ridge pattern of areas VI-V-VI is λ-shaped, contrary to that π-shaped present in P. aibuhitensis . In P. khambhatiensis sp. n., area IV has 24−42 paragnaths, in contrast to 8−23 present in P. aibuhitensis . In P. khambhatiensis sp. n., the inner bar of area VI is longer than the outer one, contrary to those of similar size in P. aibuhitensis .

P. khambhatiensis sp. n. can be distinguished from P. singaporiensis by the pattern of paragnaths on areas VII– VIII, number of teeth in jaws, and number of paragnaths on areas II, V, and VII–VIII. Perinereis khambhatiensis sp. n. is also different from P. singaporiensis by having the anterior band of areas VII–VIII with one transverse row present on furrows, in contrast to two rows (furrows and ridges) in the latter species. In P. khambhatiensis sp. n., area II has 11–24 paragnaths, area V has typically three paragnaths, and areas VII–VIII have 28–37 paragnaths, whereas in P. singaporiensis area II has 9–10 paragnaths, area V has a single paragnath, and areas VII–VIII have 34–48 paragnaths. In P. khambhatiensis sp. n., the jaws have 9–11 denticles, contrary to 6–7 in P. singaporiensis .

P. khambhatiensis sp. n. differs from P. vancaurica by several features. In P. khambhatiensis sp. n., the ridge pattern of areas VI–V–VI is λ-shaped, contrary to π-shaped in P. vancaurica . In P. khambhatiensis sp. n., the anterior band of areas VII–VIII has one transverse row present on furrows, in contrast to two rows (furrows and ridges) in P. vancaurica . In P. khambhatiensis , area III has laterally isolated paragnaths, in contrast to their absence in P. vancaurica . In P. khambhatiensis sp. n., the number of paragnaths on areas III (22–34), IV (24–42) and VII–VIII (28–37) is fewer than in P. vancaurica (areas III: 32–84; IV: 40–88; VII–VIII: 58–129).

Bhatt & Bal (1966) described two varieties of Perinereis from India (both from Bombay): P. vancaurica var. indica and P. nuntia var. bombayensis . However, several taxonomic characters were not mentioned and properly defined for the specimens, and these taxa are not valid according to the article 45.6.3 (ICZN 1999), which states that varieties described after 1960 are considered of an infrasubspecific rank. Therefore, these are not available names and they are herein considered invalid. The records likely represent species similar to the complexes P. vancaurica and P. nuntia ; however, this requires reexamination of Bhatt & Bal’s (1966) material, or newly collected specimens from the region, since they are known only by the pharyngeal arrangement.

Figures

FIGURE 3. Perinereis khambhatiensis sp. nov. from Kamboi, Gujarat, India. A, H–N, atoke holotype (MSUB-ZL-AN-PCh- 01); B–G, atoke paratype (ZSI-WRC ANN/25).A. Whole body in dorsolateral view. B. Anterior region and everted proboscis in dorsal view. C. Everted proboscis in ventral view. D. Paragnaths of areas III and IV, arrows pointing at lateral isolated paragnaths on area III. E. Left jaw in ventral view and right jaw in dorsal view, respectively. F. Close-up of jaw in ventral view, arrow pointing inner canals. G. Paired oesophageal caeca (arrows) in ventral view. H–L. Parapodia in anterior view, numbers refer to the chaetiger. M. Homogomph spiniger from notopodia (chaetiger 45). N. Heterogomph falciger from neuropodial subacicular fascicle (chaetiger 48). Scale bars: A, 7 mm; B, 0.8 mm; C, E, 0.4 mm; D, 0.5 mm; F, 0.2 mm; G, 1 mm; H–L, 200 μm; M, 40 μm; N, 25 μm.