Perinereis malabarensis, Prajapat, Villalobos-Guerrero & Vachhrajani, 2024

Prajapat, Vaishali, Villalobos-Guerrero, Tulio F. & Vachhrajani, Kauresh D., 2024, Two new species of Perinereis Kinberg, 1865 (Annelida: Nereididae) from the rocky shore of Maharashtra, India, including notes and an identification key to Group 1, European Journal of Taxonomy 935, pp. 256-282 : 264-269

Perinereis malabarensis sp. nov.

urn:lsid:zoobank.org:act:BBF25B43-76D5-46F8-A761-A8F523C4975D

Fig. 2 , Table 1

Diagnosis

Species of subgroup 1B. Specimens with crescent-shaped bars on area VI; areas VI–V–VI ridge pattern π-shaped; area III with laterally isolated paragnaths; areas VII–VIII with anterior band of paragnaths consisting of two rows; distal region of dorsal ligule anteriorly bluntly conical, more elongated in middle parapodia; dorsal cirri extending anteriorly beyond distal region of dorsal ligule, subequal in following chaetigers; falcigers with camerated shaft divided into two partitions; postero-dorsal tentacular cirri extending to chaetiger 3–5.

Etymology

The specific epithet refers to the Malabar Hill ( Mumbai, India), derived from the type locality where all the specimens were collected.

Material examined

Holotype INDIA • Mumbai , Malabar Hill; 18°57′18.0″ N, 72°47′43.0″ E; 29 Jan 2023; V. Prajapat and K. Vachhrajani leg.; rocky shore; MSUB-ZL-AN-PCh-04 .

Paratypes INDIA • 5 specs; same collection data as for holotype; 18°57′21.5″ N, 72°47′44.9″ E; ZSI-WRC ANN/26 .

Additional material

INDIA • 25 specs; Mumbai , Malabar Hill; 18°57′′9.4″ N, 72°47′43.9″ E; 11 May 2023; V. Prajapat and S. Gosavi leg.; rocky shore; MSUB-ZL-AN-PCh-05 .

Description (holotype (MSUB-ZL-AN-PCh-04))

COLOURATION AND MEASUREMENTS. Atoke, complete, in good condition, 37 (28−38) mm TL, 7.8 (4.9−7) mm L10, 1.6 (1.5−2) mm W10, and 74 (67−79) chaetigers. Body colour brownish; dorsum of prostomium, palps, cirrophores of tentacular cirri, and first 12 anterior segments with dark brown pigmentation, reducing intensity towards posterior end, with dark brown line on anterior margin; dorsum of chaetigers 13−44 with dark brown, mid-central, cross-shaped pattern ( Fig. 2A ), remaining chaetigers replaced with triangular shape pointing posteriorly.

PROSTOMIUM. Campanulate ( Fig. 2B ); anterior region distally entire, sub-rectangular, slightly longer than posterior region; anterolateral gap between antenna and palpophore wide, nearly 2 × as wide as basal diameter of antennae. Nuchal organs deeply embedded, slightly oblique, 1.5 × as wide as posterior pair of eyes.

PALPOPHORES. Sub-conical, thick, 1.5 × as long as wide, as long as ¾ × of entire prostomium; sub-distal transverse groove distinct ( Fig. 2B ). Palpostyles oval, 2 / 5 × as wide as diameter of palpophore.

ANTENNAE. Tapered, conical, long, 1.3 × as long as prostomial posterior region ( Fig. 2B ); antennae separated by gap as wide as basal diameter of antennae.

EYES. Paired, in trapezoid arrangement, blackish ( Fig. 2B ); gap between both pairs ¾ × as wide as diameter of posterior pair. Anterior pair sub-rounded, with eye diameter slightly wider than that of antennae, with gap between eyes 4 × as wide as eye diameter; lenses visible, whitish, oval, placed anterolaterally, covering about 40% of eye. Posterior pair oval, with diameter as wide as that of antennae, not covered by tentacular belt; lenses visible, whitish, rounded, placed centrally, covering about 40% of eye.

TENTACULAR BELT. Nearly 2 × as long as chaetiger 1, with straight anterior margin; dorsum without transverse wrinkle.

TENTACULAR CIRRI. Smooth ( Fig. 2B ). Antero-dorsal cirri extending posteriorly to chaetiger 3 (2–3). Anteroventral cirri as long as palpophore, slightly thicker than and as long as posteroventral cirri. Posterodorsal cirri longest, extending posteriorly to chaetiger 5 (3−5). Posteroventral cirri slenderest, extended over first quarter of prostomial posterior region.Dorsal cirrophores of tentacular cirri cylindrical; posterodorsal cirrophores 1.5 × as long as wide, slightly longer than anterodorsal cirrophores. Ventral cirrophores ring-shaped; posteroventral cirrophores shortest and narrowest, three-quarters as wide as anteroventral cirrophores.

PROBOSCIS. Everted ( Fig. 2 B−E), with maxillary and oral rings cylindrical, wider than long. Jaws denticulate, dark brown amber, 6 (6−7) short, with blunt tips ( Fig. 2F ); inner margin of fang curved; 2 canals emerging from pulp cavity ( Fig. 2F ). Paragnaths brownish on maxillary ring ( Fig. 2 B−C), dark brown and much coarser on oral ring ( Fig. 2B, D–E ); consisting of uniform-base cones, except crescent-shaped bars on area VI and some p-bars on areas VII−VIII; plate-like basements absent. Area I: 5 (3−7), cones of similar size in sub-rhomboidal patch, except proximal cone sometimes slightly longer ( Fig. 2B ). Areas II (left): 11 (10−12), II (right): 10 (10−13), three irregular rows of uneven cones in oblique ovoid patch, inner cones thicker and longer ( Fig. 2C ). Area III: 16 (13−19), three slightly regular transverse rows of uneven cones in trapezoid patch, distal cones smaller, with 1−2 (0−2) distinct isolated lateral paragnaths ( Fig. 2C ). Areas IV (left): 22 (14−20), IV (right): 17 (16−23), three irregular rows of uneven cones in slightly crescent patch ( Fig. 2C ), cones of middle row larger; without merged paragnaths. Area V: 3, triangular patch of even cones, two proximal cones in transverse row and single distal cone placed slightly more distally to paragnaths on area VI ( Fig. 2E ). Areas VI (left): 1, VI (right): 1, transverse crescent-shaped bar ( Fig. 2E ). Areas VII – VIII: 38 (33–41), paragnaths in two well-separated anterior and posterior bands; anterior band consisting of two (furrow and ridge) transverse aligned rows, furrow row with one coarse p-bar and ridge row with one cone on each region; posterior band with two (furrow and ridge) transverse rows slightly displaced from each other consisting of even cones, furrow row proximal with one cone slightly displaced from each region, ridge row distal with two cones on region A and one cone in remaining regions ( Fig. 2D ). Ridges of areas VI – V – VI with π-shaped pattern ( Fig. 2B, E ). Gap between area VI and areas VII – VIII broad, as wide as three-quarters of palpophore width. Paired oesophageal caeca present ( Fig. 2G ).

NOTOPODIA. Consisting of dorsal cirrus, dorsal ligule (distal and proximal regions), prechaetal lobe, and median ligule in biramous parapodia.

DORSAL CIRRI. Cirriform ( Fig. 2H–L ), longer than proximal region of dorsal ligule and extending beyond distal region of dorsal ligule in anterior chaetigers ( Fig. 2 H−I), nearly as long as distal and proximal region of dorsal ligule in following chaetigers ( Fig. 2J–L ); attached to one-third of dorsal ligule in anterior chaetigers, medially in following chaetigers.

DORSAL LIGULES. Distal region as long as proximal region in anterior and middle chaetigers ( Fig. 2H–J ), distal becoming slightly longer than proximal in following chaetigers ( Fig. 2 K−L). Proximal region compressed in anterior and middle chaetigers ( Fig. 2 I−J), distended and sub-oval in posterior chaetigers ( Fig. 2K ), enlarged and sub-rectangular in posteriormost chaetigers ( Fig. 2L ); one prominent ovoid patch of dark brown glands in anterior and middle chaetigers, two main patches in following chaetigers, covering ⅔ of ligule area. Distal region subequal in length throughout ( Figs 2I, K ), except longer in middle chaetigers ( Fig. 2J ); digitiform in anteriormost and posteriormost chaetigers ( Fig. 2H, L ), bluntly conical in anterior chaetigers, narrowly fusiform in middle chaetigers ( Fig. 2J ), subulate in posterior chaetigers ( Fig. 2K ); slightly shorter than median ligule throughout, except slightly longer in posteriormost chaetigers; projecting beyond notoacicula throughout; one basal oval patch of dark brown gland in anterior chaetigers, one elongate mid-lower patch in following chaetigers, covering half of ligule area ( Fig. 2 J−K).

NOTOPODIAL PRECHAETAL LOBES. Present in anterior chaetigers ( Fig. 2I ), digitiform, ½ × as long as median ligule, reduced to notoacicular process in middle and posterior chaetigers ( Figs 2 J−K), absent in posteriormost chaetigers ( Fig. 2L ).

MEDIAN LIGULES. Well developed throughout, short and digitiform in anterior chaetigers ( Fig. 2I ), becoming longer, narrower and bluntly conical in following chaetigers ( Fig. 2J–L ).

NEUROPODIA. Consisting of neuroacicular ligule with superior and inferior lobes, ventral ligule, and ventral cirrus; postchaetal lobe reduced throughout ( Fig. 2H–L ).

NEUROACICULAR LIGULES. Sub-rectangular throughout, truncate in anterior and middle chaetigers, becoming acute in following chaetigers; subequal to ventral ligule in anteriormost chaetigers ( Fig. 2H ), longer than ligule in following chaetigers, more distinct in anterior ones ( Fig. 2I ); neuroacicular ligule as wide as ventral ligule in anterior chaetigers, slightly wider than ligule in following chaetigers.

SUPERIOR LOBES. Rounded ( Fig. 2H ), subequal to inferior lobe throughout.

INFERIOR LOBES. Rounded ( Fig. 2H ), slightly shorter than neuroacicular ligule throughout, becoming narrower in posterior chaetigers.

VENTRAL LIGULES. Well developed throughout, distinctly shorter than median ligule in all chaetigers ( Fig. 2I–L ); digitiform and thick in anteriormost chaetigers, becoming narrower in following chaetigers.

VENTRAL CIRRI. Cirriform in anteriormost, anterior and middle chaetigers ( Fig. 2H –J ), conical and slender in following chaetigers; slightly longer than ventral ligule in anteriormost chaetigers, three-quarters as long as ventral ligule in anterior chaetigers, one-quarter to one-third as long as ligule in following chaetigers.

ACICULAE. Mostly dark brown to black throughout. Notoaciculae absent in first 2 chaetigers ( Fig. 2H ). Notoaciculae distinctly shorter than neuroaciculae in most chaetigers ( Fig. 2I–K ), except as long as neuroaciculae in posteriormost chaetigers ( Fig. 2L ). Neuroaciculae as long as median ligule in anteriormost and anterior chaetigers, shorter than median ligule in following chaetigers, two-thirds as long as ligule.

NOTOCHAETAE. All homogomph spinigers throughout; 8–10 spinigers present in anterior chaetigers, 5–6 in middle chaetigers, and 3–4 in posterior chaetigers.

UPPER NEUROCHAETAE. Consisting of homogomph spinigers and heterogomph falcigers throughout; 6–7 spinigers present in anteriormost, anterior and middle chaetigers, 4–5 spinigers in following chaetigers; 2–3 falcigers present in anteriormost and anterior chaetigers, 1–2 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; 8–10 falcigers present in anteriormost and anterior chaetigers, 6–8 falcigers in middle chaetigers, and 5–6 falcigers in following chaetigers.

BLADES OF CHAETAE. Both homogomph ( Fig. 2M ) and heterogomph spinigers long, finely serrated, with teeth evenly spaced. Heterogomph falcigers tapering with pointed tip and even teeth; slender and of medium length, straight, entirely serrated ( Fig. 2 N−O). Shaft of falcigers camerated, with cavity divided sub-distally into two distinct longitudinal partitions.

PYGIDIUM. With short anal cirri, as long as last 3–4 chaetigers.

Variation

Total body length: 31–86 mm. Length to chaetiger 10: 7–11 mm. Body width at chaetiger 10: 1–2.7 mm. Number of total chaetigers: 67–141. Longest tentacular cirri extending to chaetiger 3–6. Jaws with 6–7 teeth. Number and pattern of paragnaths: area I: 3–7 (mean 4–5); area II: 9–18 (mean 11–12); area III: 12–20 in central patch (mean 15–16), 1–2 cones isolated laterally (rarely one side without cones); area IV: 13–27 (mean 19–20); area V: 3 (rarely 2); area VII–VIII: 34–41 (mean 37–38). Total number of paragnaths: 104–141 (mean 123). Anal cirri as long as last 3–4 chaetigers.

Remarks

Perinereis malabarensis sp. nov. is the first species of the subgroup 1B originally described from the Western Indo-Pacific realm (sensu Spalding et al. 2007). Among all the 1B members of Perinereis , P. malabarensis resembles P. euiini Park & Kim, 2017 by having dorsal cirri barely or not projecting beyond the distal region of dorsal ligule in mid-body parapodia, notopodial prechaetal and neuropodial superior lobes, and areas VI–V–VI ridge pattern π-shaped. However, P. malabarensis is distinguished from P. euiini by the paragnath count in area I, the laterally isolated groups of paragnaths in area III, and the length of the dorsal cirrus and dorsal ligule. In P. malabarensis , the area I has 3−7 paragnaths, contrary to 1−3 in P. euiini . In P. malabarensis , the area III has laterally isolated paragnaths, in contrast to their absence in P. euiini . In P. malabarensis ., the dorsal cirrus is slightly longer or as long as the distal region of dorsal ligule throughout, contrary to slightly shorter than that in all chaetigers of P. euiini . In P. malabarensis , the dorsal ligule is 2 × as long as the median ligule in posterior chaetigers, contrary to 3 × longer than that in P. euiini .

Habitat

Worms are found burrowing in the sea bed, formed by oysters, dead shells, algae, and sand clumping on the rocks. This soft sponge-like sea bed provides a habitat for many small invertebrates like crabs, amphipods, isopods, sea anemones, sipunculids, and polychaetes.

Distribution

Species is known only from the type locality.

Figures

Fig. 2. Perinereis malabarensis sp. nov. from Mumbai, Maharashtra, India. A–E, H–O. Holotype (MSUB-ZL-AN-PCh-04), atoke. F–G. Paratype (ZSI-WRC ANN/26), atoke. A. Whole body in dorsal view. B. Anterior end and everted proboscis in dorsal view. C. Maxillary ring of proboscis in ventral view. D. Oral ring of proboscis in ventral view. E. Oral ring of proboscis in dorsal view. F. Left jaw in ventral view, arrow pointing to inner canals. G. Paired oesophageal caeca (arrows) in dorsal view. H–L. Parapodia in anterior view (except I and K, in posterior view), numbers refer to the chaetiger. M. Homogomph spiniger from notopodia (chaetiger 50). N. Heterogomph falciger from neuropodial supracicular fascicle (chaetiger 50). O. Heterogomph falciger from neuropodial subacicular fascicle (chaetiger 50). Scale bars: A = 6 mm; B = 0.7 mm; C–D, F = 0.5 mm; E = 0.4 mm; G = 0.8 mm; H = 0.22 mm; I–L = 0.23 mm; M = 12 μm; N–O = 16 μm.