Pseudodiaptomus ardjuna   Brehm,  1953 (Copepod)
Organism information awaits expert curation
Class: Maxillopoda

Image copyrights: Walter Chad

Size: The length of the male is 1.1 mm. It is smaller than the female but has the same general appearance.
The male shows sexual dimorphism in the antennule, the fifth pair of legs and in the urosome. The spines on the posterior prosomal segments are, however, much less pronounced, although their slight asymmetry is maintained. The urosome is 5-segmented, of uniform width and more cylindrical than in the female. The right antennule is geniculate while the left resembles that of the female in all structural details, including the specialized seta of the twenty-first segment. The geniculate antennule consists of 21 segments. The segments from 1st to 16th each bears an aesthetask, except the fifth, seventh and eleventh to thirteenth segments; the latter 3 segments, however, each bears a stout spine. Fifth legs are rather strongly built, asymmetrical and close together; the right leg is slightly longer than the left; right basal one is, of moderate size with no accessory process ; basal two is very large and slightly longer than wide ; it carries on its inner margin a ' y '-shaped spinous process with the arms of unequal length ; this process represents the vestigeal endopod ; it also carries at its distal outer corner a small spine on the anterior face. Exopod is displaced into medial line and consists of 3 segments ; the first segment is fairly large and much wider than long ; three features are notable in this segment: (a) at the distal outer angle there is a spinous process which is quite long and which, in its turn, bears a smaller spine at one-sixth of its proximal length, thus giving a forked appearance to that region ; (b) a small, almost conical spine, also borne on the distal outer corner, is present just below the preceding larger spine ; and (c) a serrated edge is seen along the line of separation of the first and second segments ; this edge curves down after the mid-width of the segment. The second exopod segment is much longer than the first segment, but distinctly less wide ; it carries a fairly long spine on its distal outer angle and a smaller spine at about the centre of the segment on the anterior face. Exopod segment 3 is modified into a stout spine ; its base is bulbous, bearing a few spinules on either side. Left basal one is smaller than its right counterpart and with no accessory spines or processes. Left basal two is quite large with its breadth larger than the length. It bears at its inner distal angleadigitiform process which is fairly long almost equivalent to the length of the entire protopod. This process probably represents the endopod. In the left side, too, the exopod is displaced to a medial line and consists of only two segments ; the first segment is quite short, the greatest length and breadth being almost equal; it bears a sharp spine at its latero-distal angle ; the second segment consists of a thin plate, more or less rectangular in shape ; on its outer margin it bears a spine at two-third of its length and a few minute spinules after that; on the left side the distal margin is provided with three spinules borne on small projections.
In the structure of other appendages and legs the male is identical with the female except in the smaller proportionate sizes.

Size: Length of the female is 1.31 mm.
Body is rather narrow, smoothly rounded anteriorly. The prosome consists of five segments. The first segment is the cephalothorax, formed by the fusion of the cephalosome and the first leg-bearing segment; it is the longest of prosomal segments and is widest at its posterior margin. The second segment is rectangular with the long axis being the width of the copepod body. The third and fourth segments are rather short and subequal; the latter is the widest part of the prosome. The fifth prosomal segment is armed on each of its postero-lateral corners with a sharp spine, directed backwards and slightly outwards; the right spine is slightly larger than the left one. The urosome consists of four joints, the genital segment and three abdominal segments. The genital segment is barrel-like and exceeds other urosomal segments both in length and width ; it has a well-marked ventral swelling on which is borne the genital operculum. The abdominal segments are subequal, each segment being about half as long as the genital segment. The caudal rami are narrow, cylindrical and more or less parallel. It bears numerous setules on its inner margin. Each ramus bears five setae, four of which are apical and one subapical on the outer side. The antennule is moderately long reaching the posterior margin of the prosome. The antenna has a 2-articled protopod, a 2-segmented endopod and a 4-segmented exopod ; it posses two rows of small spinules on the distal inner margin of the last segment of the endopod. The maxilla is apparently 3-segmented but consists of 7 endites. The maxilliped is 7-segmented. The four pairs of swimming legs are borne by the first 4 prosomal segments. All the legs are biramous and constructed on identical plans. The terminal exopod segment of each leg is provided with two outer spines and that the other exopod segments each bears a single outer spine except the second segment of the first pair of legs which has no spine at all. There is a single inner seta on the first and second segments of each exopod. The terminal exopod segment of first legs bears 3 setae while the second, third and fourth legs bear each 5 setae on this segment. The first endopod segment in all the four pairs of legs each carries a single seta while the second segment in these legs carries 1 seta in the first leg and 2 setae each in the next three legs. The terminal endopod segment in the first legs bears 6 setae, in the second and third legs 8 setae each arid in the fourth leg 7 setae. The basal protopod segment carries a single seta in all the four legs, while the second protopod segment does not bear any seta or spine except in the fourth leg where a small spine is present. The fifth legs are uniramous, symmetrical and small. On each side it consists of 4 articles ; the first segment is devoid of any seta or spine ; second and third segments each bears a single setule ; the last segment bears 2 setae of unequal length and 2 flattened spinelike structures, bearing minute teeth on the inner margin. In this genus the basal two segments of the fifth leg represent the protopod and the distal two segments the exopod ; the endopod is entirely lacking.
The female carries a single ovisac, rather irregular in shape and containing about 25 eggs.

Synonym (s)

Common Name (s)
Economic Importance and Threats

Habitat:  Estuarine


• Maharashtra, Mumbai (Lat: 18.98) (Long: 72.83) INDIA
• Goa, Mandovi and Zuari Estuary INDIA
• Maharashtra, Versova INDIA (Record: 05/1991-07/1992)
• Tamil Nadu INDIA
• Orissa, Burhabalanga Estuary (Lat: 21.45) (Long: 87.06) INDIA (Record: 10/1991 - 08/1992)

Literature Source(s)
  • (2001) Sanctuary Asia natural history species: Species checklist: Birds Sanctuary Asia Sanctuary Magazine Available at -
  • Stephen, R; Jayalakshmy, KV and Nair, VR (2003) Intermittent swarming of copepods in Versova mangrove, Mumbai Seshaiyana ENVIS newsletter 2(1) 5-7 Available at -
  • Society for the Management of European Biodiversity Data (2009) World Register of Marine Species (WoRMS) Available at -
  • Ummerkutty, ANP (1960) Studies on Indian copepods 4. description of the female and redescription of the male of Pseudodiaptomus ardjuna Brem (copepoda, calanoida) with notes on the distribution and affinities of the species Journal of the Marine Biological Association of India Cochin, India 2(2) 179-185 Available at -
  • Goswami, SC (1982) Distribution and diversity of copepods in the Mandovi-Zuari estuarine system, Goa Indian journal of marine sciences Scientific Publishers 11 292-295 Available at - NIO, Goa
  • Ramaiah, N; Chatterji, A and Madhupratap, M (1996) A study on the zooplankton of the Burhabalanga Estuary, Orissa Coast Proceedings of the Indian National Science Academy (B. Biological Sciences) Indian National Science Academy 62 1-4 Available at -

Page last updated on:2011-02-07

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