INTRODUCTION
Paracalanids are dominant components amongst the subclass Copepoda and comprise about 20 species worldwide, sometimes consisting of 80% of marine copepod abundance. Most of the species are neritic and are abundant in coastal (Yoo & Lee, Reference Yoo and Lee1994) and oceanic surface waters throughout the tropical and temperate regions (Sewell, Reference Sewell1947). They are generally very small-sized copepods, mainly herbivorous (Arashkevich, Reference Arashkevich1969; Itoh, Reference Itoh1970; Paffenhöfer, Reference Paffenhöfer1984) belonging to the order Calanoida and vary in size from 0.5–1.5 mm. They play an important role as primary consumers in marine ecosystems (Yoo & Lee, Reference Yoo and Lee1994). There are six genera in this family: Acrocalanus, Bestiolina, Calocalanus (= Leptocalanus, Ischnocalanus), Delius, Paracalanus and Parvocalanus (Bradford-Grieve, Reference Bradford-Grieve1994). The species of the genus Paracalanus Boeck, 1864 recorded from Indian waters include P. aculeatus Giesbrecht, 1888, P. parvus (Claus, 1863), P. crassirostris Dahl, 1894, P. nanus Sars, 1907, P. denudatus Sewell, Reference Sewell1929, P. nudus Sewell, Reference Sewell1929, P. serratipes Sewell, 1912, P. dubia Sewell, 1912, P. indicus Wolfenden, 1905 and P. clevei Carl, 1907. Paracalanus indicus was also recorded from New Zealand waters (Bradford-Grieve, Reference Bradford-Grieve1994). Paracalanus intermedius Shen & Bai, Reference Shen and Bai1956, P. serrulus Shen & Lee, Reference Shen and Lee1963 and P. brevispinatus Shen & Lee, Reference Shen and Lee1966 were reported from the Yellow Sea, China (Shen & Bai, Reference Shen and Bai1956; Shen & Lee, Reference Shen and Lee1963, Reference Shen and Lee1966). Paracalanus gracilis Chen & Zhang, 1965 was recorded from Korean waters (Yoo & Lee, Reference Yoo and Lee1994). Paracalanus tropicus Andronov, Reference Andronov1977 was recorded from the south-east Atlantic Ocean (Andronov, Reference Andronov1977). Paracalanus scotti Fruchtl, 1923 was recorded from the Gulf of Guinea (Vervoort, Reference Vervoort1963). Paracalanus hibernicus Brady & Robertson, Reference Brady and Robertson1873 was recorded from open seas off Ireland (Brady & Robertson, Reference Brady and Robertson1873). Paracalanus mariae Brady, Reference Brady1918 was recorded as a new species during the Australasian Antarctic Expedition in 1918 (Brady, Reference Brady1918). Paracalanus quasimodo Bowman, Reference Bowman1971 was recorded off the southern coast of Florida (Bowman, Reference Bowman1971). Paracalanus campaneri Bjornberg, Reference Bjornberg1980 was recorded off the coast of Brazil (Bjornberg, Reference Bjornberg1980).
In this paper, a new species of Paracalanus collected from the Mandovi and Zuari estuaries, Goa, west coast of India is described.
MATERIALS AND METHODS
Zooplankton samples were collected by horizontal hauls with a Heron–Tranter (HT) plankton net (100 µm mesh with a digital flow meter (Hydro-Bios, No. 438110)) from the Mandovi and Zuari estuaries (including Marmugao Port Trust (MPT) area), (15°25′N 73°48′E) during May 2005, December 2005 and September 2006. The same species was also observed in the samples collected from Jawaharlal Nehru Port Trust, Mumbai in the year 2001–2002 (Figure 1). The samples were fixed immediately after collection in 5% formaldehyde solution. Specimens of the new species were sorted, dissected and examined with the Olympus CX40 microscope. All drawings were made with the aid of camera lucida and the measurements with an ocular micrometer. The descriptive terminology employed follows Huys & Boxshall (Reference Huys and Boxshall1991).
Location of study area.
TYPE MATERIAL
Holotype: adult female, 0.60 mm, Mandovi and Zuari estuary, Goa, specimen deposited in the National Institute of Oceanography (NIO), Goa, (GOMPC-1).
Paratypes: ten adult females, TL. 0.55–0.60 mm, mean 0.57 mm, SD±0.02, same locality, deposited in the NIO, Goa, (GOMPC-2).
DESCRIPTION OF ADULT FEMALE
Total body length 0.60 mm, broad and short. Forehead uniformly rounded, rostrum short, solid, rounded at tip (Figure 2C & D). Cephalosome incorporating first pedigerous somite, slight demarcation between fourth and fifth pedigerous somites (Figure 2A & B). Urosome 4-segmented. Genital somite broad, rounded. Anal somite longer than second and third urosomites.
Paracalanus arabiensis sp. nov. female (holotype). (A) Habitus, dorsal view; (B) habitus, lateral view; (C) rostrum, lateral view; (D) rostrum, dorsal view.
Antennule (Figure 3A): 25-segmented, extending to posterior margin of genital somite. Segments 1 (I) and 2 (II–IV) partially fused. Segments 3 (V) to 24 (XXVI) separate. Apical segment 25 (XXVII–XXVIII) double. Armature pattern as follows: segments 1 and 2 (I–IV)–4+1 aesthetasc, 3 (V)–1+1 aesthetasc, 4 (VI)–1, 5 (VII)–1+1 aesthetasc, 6 (VIII)–1, 7 (XI)–1, 8 (X)–1, 9 (XI)–1+aesthetasc, 10 (XII)–1, 11 (XIII)–1, 12 (XIV)–1, 13 (XV)–1+aesthetasc, 14 (XVI)–1, 15 (XVII)–1, 16 (XVIII)–1, 17 (XIX)–1+aesthetasc, 18 (XX)–1, 19 (XXI)–1+aesthetasc, 20 (XXII)–1, 21 (XXIII)–1, 22 (XXIV)–2, 23 (XXV)–1, 24 (XXVI)–2, 25 (XXVII–XXVIII)–3+1 aesthetasc. Segments 13–24 bear small spines. Number of spines 4, 2, 4, 4, 5, 5, 9, 10, 11, 10, 19 and 12 respectively.
Paracalanus arabiensis sp. nov., female (holotype). (A) Antennule; (B) antenna; (C) mandible; (D) maxillule; (E) maxilla; (F) maxilliped.
Antenna (Figure 3B): biramous; coxa and basis clearly separate, bearing 1 and 2 setae respectively. Exopod 7-segmented, slightly longer than endopod, segment 1 with 2 setae, segments 2–6 with 1 seta each, segment 7 bearing 3 setae apically. Endopod 2-segmented, first segment with 2 setae, second segment bilobed, with proximal and distal lobes bearing 8 and 6 setae respectively.
Mandible (Figure 3C): with cutting edge of gnathobase bearing 9 cuspidate teeth and 1 seta. Palp biramous; basis with 4 setae; exopod 5-segmented, segments 1–4 each with 1 seta, segment 5 bearing 2 apical setae. Endopod 2-segmented, bearing 4 setae on proximal segment and 11 setae on distal segment.
Maxillule (Figure 3D): praecoxal arthrite with 13 setae. Coxa with 3 setae on endite; epipodite with 8 setae. Basis with 4 setae on proximal endite and 5 setae on distal endite; basal exite with 2 setae. Exopod bearing 11 lateral setae. Endopod 3-segmented, first to third segments with 3, 4 and 7 setae respectively.
Maxilla (Figure 3E): praecoxa bearing 2 endites; proximal endite with 6 setae, distal with 3 setae; coxa with 2 endites each armed with 3 setae; basis with a single endite bearing 4 setae and 1 seta laterally. Endopod 3-segmented with setal formula of 1, 1, 2.
Maxilliped (Figure 3F): praecoxa and coxa apparently separate; praecoxa with 1 seta; coxa bearing 2, 3 and 4 setae representing endites; basis bearing 3 setae. Endopod 6-segmented; first to sixth segments bearing 2, 4, 4, 3, 3 + 1 and 4 setae respectively.
Swimming legs with 3-segmented exopods; endopod 2-segmented in leg 1, 3-segmented in legs 2, 3 and 4 (Figure 4A–D). Spine and seta formula of swimming legs shown in Table 1. Leg 1 basis with inner edged seta, third exopodal segment of legs 3 and 4 with serrate distal margin.
Paracalanus arabiensis sp. nov., female. (holotype). (A) Leg 1; (B) leg 2; (C) leg 3; (D) leg 4; (E) leg 5.
Spine and setal formula of legs 1–4 of Paracalanus arabiensis sp. nov.
Leg 5 (Figure 4E) 2-segmented, symmetrical. First segment slightly robust; second segment bearing 2 terminal spines of unequal length, inner spine twice the length of outer one with a row of six small teeth along its edge. Two small, stiff spines of equal length protrude in between the terminal spines.
MALE
Unknown.
ETYMOLOGY
The species name refers to the locality ‘Arabian sea’ where the specimens of the new species were collected.
REMARKS
The new species is readily distinguished from other Paracalanus species by the following characteristics: size, appearance of rostrum, antennule extension, and total number of spines present on the dorsal surface of exopodal and endopodal segments 1–3 (Table 2). This comparison is mainly based on the structure of leg 5. The new species has a row of six teeth along the edge of inner terminal spine and two small, stiff spines of equal length protrude in between the terminal spines. Inner terminal spine of P. brevispinatus is serrated with four teeth (Figure 5A) and it is armed with seven or eight teeth in P. scotti (Figure 5C). Paracalanus crassirostris bears a row of two or three teeth along its inner terminal spine (Figure 5M). In P. aculeatus, P. nudus, P. serratipes, P. dubia and P. quasimodo the edge of inner terminal spine is armed with small spinules (Figure 5B, K, N, L and Q, respectively). A comparison of total number of spines present in between the terminal spines is also made from the available literature. Paracalanus scotti has four to five stiff spines (Figure 5C), P. serrulus has only one spine protruding in between terminal spines (Figure 5D). Paracalanus serratipes (Figure 5N) has three spines near its terminal spines and in P. dubia five spines are present (Figure 5L). The structure of leg 5 in P. hibernicus (Figure 5O) is different from the other species, it is cylindrical, one branched, three jointed of nearly equal length terminated by two or three fine short setae (Brady & Robertson, Reference Brady and Robertson1873).
Comparative morphology of female leg 5 among the genera Paracalanus and Parvocalanus. (A) Paracalanus brevispinatus; (B) P. aculeatus; (C) P. scotti; (D) P. serrulus; (E) P. indicus; (F) P. intermedius; (G) P. nanus; (H) P. gracilis; (I) P. parvus; (J) P. denudatus; (K) P. nudus; (L) P. dubia; (M) P. crassirostris; (N) P. serratipes; (O) P. hibernicus; (P) P. mariae; (Q) P. quasimodo; (R) Parvocalanus latus; (S) P. elegans.
Comparison of the genera Paracalanus and Parvocalanus (female specimens).
–, data not available; X, figure not available; #, different genus.
Morphologically, the genera Paracalanus and Parvocalanus Andronov, Reference Andronov1970 show a considerable resemblance especially in the structure of leg 5 (Figure 5). Andronov (Reference Andronov1970) revised some species of Paracalanus and placed them in the genus Parvocalanus. These were P. crassirostris, P. scotti, P. serratipes and P. dubia. In addition to this, two new species, Parvocalanus latus Andronov Reference Andronov1972 and Parvocalanus elegans Andronov Reference Andronov1972 were described by Andronov (Reference Andronov1972). In these two species, edge of the inner terminal spine of leg 5 is smooth and no spines observed in between the terminal spines (Figure 5R & S).
A comparison is also made on the basis of leg 1 between the two genera Paracalanus and Parvocalanus and the following are the differences:
Paracalanus clevei Carl, 1907 has not been included in the comparison because Sewell (Reference Sewell1914) in his description of the male P. aculeatus, showed that P. clevei is a developmental stage of this male. Paracalanus campaneri Bjornberg, Reference Bjornberg1980 and P. pygmaeus (Claus, 1863) are also not included in the description as they could possibly be synonyms of P. aculeatus Bjornberg, 1963 and P. denudatus respectively.
Our comparative table based on distribution, morphology (Table 2), differences in leg 5 (Figure 5) among the female Paracalanus species and differentiating characters with respect to leg 1 among the genera Paracalanus and Parvocalanus gives credence for the newly reported species to be a new inclusion in the genus Paracalanus.
ACKNOWLEDGEMENTS
The authors wish to thank Dr S.R. Shetye, Director of the National Institute of Oceanography (NIO), for his support and encouragement. The authors gratefully acknowledge the encouragement by Shri Ajoy Chatterjee, country focal point for ballast water management in India. This work was facilitated by the generous support by Dr Janet M. Bradford-Grieve (Emeritus Scientist, National Institute of Water and Atmospheric Research Limited, New Zealand), Ms Marie Hitchcock (Assistant Librarian, Zoological Society of London), Mr Louis Gibb (Product specialist, Thomson Scientific, UK) and Dr M.P. Tapaswi for compiling the necessary references for the genus Paracalanus. We are thankful for the help and advice from Dr David V.P. Conway regarding the taxonomy of Paracalanus species. We are indebted to the anonymous referees for their valuable advice. We are grateful to Dr S.S. Sawant and Mr K. Venkat and other colleagues of the project team for their support. This work was funded by the Ministry of Shipping and the Directorate General of Shipping, India under the Ballast water management initiative and is a NIO contribution 4550.
