Pontella spinipes Giesbrecht, 1889

Francis, Sanu Vengasseril, Nishida, Shuhei & Nandan, Sivasankaran Bijoy, 2018, Psammoecus simonis Grouvelle 1892, Zoological Studies 57 (16), pp. 1-11 : 2-7

Pontella spinipes Giesbrecht, 1889

Synonymy: Female: Pontella spinipes Giesbrecht, 1889 , P. 28; 1892, P. 462, 477, 774, Plate 24 (Fig. 30), Plate 40 ( Figs. 2 , 23, 24); Wolfenden, 1905, P. 1020-1021; Silas and Pillai, 1973, P. 826-827, Fig. 21a, b, Fig. 22a.

Not female Pontella spinipes, Mulyadi, 2011 , P. 1523, Fig. 6.

Male: Pontella spinipes, Wolfenden, 1905 , P. 1020-1021. Pontella diagonalis, Silas and Pillai, 1973 , P. 824-826, Fig. 21g, h, l, Fig. 22e (mislabeled as P. securifer ); Pillai, 1975, P. 131- 132, Fig. 1h, i; Mulyadi, 2000, P. 185-186, Fig. 4 af, Mulyadi, 2011, P. 1515-1519, Fig.3 .

Not male Pontella spinipes, Sewell, 1912 , P. 373-374, plate 24 ( Figs. 1-4); Silas and Pillai, 1973, P. 826-827, Fig. 21c, d, k, Fig. 22b; Pillai, 1975, P. 133-134, Fig. 2a, b ; Mulyadi, 2000, P. 193-194, Fig. 13a-d, 2011, P. 1523-1525, Fig. 7.

Material examined

A total of 150 females and 97 male P. spinipes specimens were collected ( Table 1), of which 10 females and 10 males were used for genetic analysis. The other specimens were incorporated into the copepod collection at the Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology (Catalog entry numbers MBM /DBT/13/16 for female MBM /DBT/14/16 for male specimens). Of these, 15 specimens, each of females and males, were examined for the following description.

Female: Total length 3.75-4.17 mm (mean: 3.97 mm, n = 15). Body robust ( Fig. 2A ). Antennule of 23 segments, reaching posterior margin of last pedigerous somite ( Fig. 2B ). Rostrum bifurcate; upper frontal lens absent; anterior and posterior lower frontal lenses present; diameter of posterior lens 1.3 times that of anterior lens ( Figs. 2C, D ). Three blue and rounded processes present mid-dorsally on first three pedigerous somites. Fourth and fifth pedigerous somites separate. Posterolateral corners of fifth pedigerous somite produced posteriorly into large pointed lobes, of which left one larger than right and reaching near posterior margin of genital somite. Crescent shaped lobular process present on either side between the pointed lobes of fifth pedigerous somite and insertion of urosome. Urosome two segmented; second segment invisible in dorsal view. Genital somite bulged on its right lateral margin, extending dorso-posteriorly and completely covering second urosomal somite, with small process on right dorsal surface appearing as conical projection in right lateral view. Irregular ridges and raised areas present on dorsal surface of genital somite ( Fig. 2G ). Caudal rami asymmetrical, right ramus larger ( Figs. 2E and F ). Fifth leg asymmetrical, right leg slightly larger than left; exopod of each leg acuminate and curved with four lateral spinules; endopod about half length of exopod and bifid apically ( Fig. 2H ).

Male: Total length 3.31-3.73 mm (mean: 3.57 mm, n = 15). Fourth and fifth pedigerous somites separate. Posterolateral ends of fifth pedigerous somite produced into symmetrical, acuminate lobes ( Fig. 3A ). Rostrum well developed with upper frontal lens and anterior and posterior lower frontal lenses ( Figs. 3B, C ); diameter of anterior lower frontal lens 1.4 times those of upper- and posterior lower frontal lenses. Urosome composed of five somites; genital somite asymmetrical with lobe-like projection on left side. Caudal rami nearly symmetrical, each with five long plumose and one small setae. Right antennule ( Fig. 3D ) geniculate; ancestral segment XIV with stout, elongated spine terminating in bent tapering apex. Fused segments XIX-XX with proximally-oriented scalene-triangular ridge with anterior row of denticles. Fused segments XXI-XXIII with anterior process on proximal 1/3, with 3 stout and 2 minute teeth, of which middle one longest ( Fig. 3E ); distal 2/3 of anterior margin with denticulate plate; segment ends distally in falcate spur. Segments XXIV-XXVIII completely fused. Fifth leg with one seta on each basis. Chela on right leg well developed; outer margin of first exopodal segment with three unequal thumb-like processes basally, of which medial one longest and slightly curved and distal one with basal seta, and semicircular process at mid- to slightly distal part. Second exopodal segment slender, curved and pointed with two setae near base and seta at distal third. Left leg first exopodal segment with inner medial seta and outer distal spine; second exopodal segment with inner seta near distal third, outer seta near distal third, outer distal seta, two unequal distal spines, of which inner one 1.5 time longer than medial, and two rows of setules along inner margin ( Fig. 3F ).

Remarks: The present female specimens agree with Pontella spinipes Giesbrecht, 1889 as redescribed by Giesbrecht (1982), Wolfenden (1905), and Silas and Pillai (1973), and distinguished from the two closely similar species - P. securifer Brady, 1883 and P. diagonalis Wilson, 1950 - in the following characters: (1) the left pointed lobe of the fifth pedigerous somite is much larger than the right one (the lobes are subequal in P. diagonalis ; left one slightly larger than the right one in P. securifer ); (2) genital somite bulged on its right lateral margin, extending dorso-posteriorly and completely covering second urosomal somite with a small process on right dorsal surface (on the lateral side of genital somite a conspicuous digitiform process is present in P. securifer , while a sharply pointed, curved process is present in P. diagonalis ; see also Tanaka, 1964; Silas and Pillai, 1973; Jeong et al. 2008 for re-descriptions). There have been slight differences between these authors in the number of lateral spinules on the exopod of leg 5: 4 in Giesbrecht (1982) and the present specimens, 3-4 in Silas and Pillai (1973), and 2 in Wolfenden (1905); this may be assumed as intraspecific variation. The female described as P. spinipes by Mulyadi (2011) differs from the present specimens and those described by Giesbrecht (1982) and Silas and Pillai (1973) in (1) the shape of genital somite (much more swollen laterally on the right side than the latters) and (2) the length of the endopod relative to the exopod of the fifth leg (less than 1/4 compared to about 1/ 2 in the latters. Note that the former length ratio is based on Fig. 6d of Mulyadi (2011) while his text (p. 1523) describes this ratio as about 1/2).

As shown in the list of synonymies, male P. spinipes had been described under the name P. diagonalis ( Silas and Pillai 1973; Pillai 1975; Mulyadi 2000), except Wolfenden (1905) whose description of male P. spinipes accords with the present specimens, although morphological details of the specimen are unknown since the author did not present any illustrations [note that the figures of male P. diagonalis as described by Mulyadi (2011: Fig. 3 ) appear to have been copied from Mulyadi (2000: Fig. 4 )]. Accordingly, the males described as P. spinipes by Sewell (1912), Silas and Pillai (1973), Pillai (1975), and Mulyadi (2000) are considered to belong to another species and distinguished from true male P. spinipes (= male P. diagonalis sensu Silas and Pillai, 1973 ) by (1) differences in the shape and size of the processes on the claw of right fifth leg and (2) the size and number of teeth on the elevated process of the fused segments XXI-XXIII of the right antennule (3 conspicuous teeth in P. spinipes ); note that Silas and Pillai (1973) mislabeled the right antennule of their “male P. diagonalis ” as P. securifer ( Silas and Pillai 1973: Fig. 22e), as evidenced from their text sentence stating presence of 3 stout subequal teeth on the 19th segment ( Silas and Pillai 1973: 825) which accords with their fig. 22e.

Molecular analysis

The mtCOI sequences were successfully generated using the primer pair, reaction mix, and the thermal regime described above. The developed sequences of female P. spinipes and male P. diagonalis sensu Silas and Pillai (1973) were submitted to the NCBI database and assigned the following accession numbers: KT186887 to KT186891and KT267166 to KT267170 for female P. spinipes, KT 282363 to KT282372 for male P. diagonalis sensu Silas and Pillai (1973) . The base pair length for the developed sequences was 639 bp for the male P. diagonalis sensu Silas and Pillai (1973) , and 660 bp for the female P. spinipes . In order to confirm the phylogenetic relationship of these specimens, an ML analysis was performed and pairwise sequence distances were generated and analyzed using the developed sequences as well as the mtCOI sequences of their congeneric species acquired from NCBI database ( Table 2). Acartia bispinosa Carl, 1907 was selected as the out-group. The ML tree clearly exhibited the differential assemblage of congeneric species of the genus Pontella ( Fig. 4 ). The female P. spinipes and male P. diagonalis sensu Silas and Pillai (1973) got arrayed within a single clade with the 100% bootstrap value which is distinct from the sequence of P. rostraticauda Ohtsuka, Fleminger and Onbe, 1987 (AB206446). In addition, P. fera Dana, 1849 (KT186882, KT186883) sequences got assembled next to the latter. The clade containing P. sinica Chen and Zhang, 1965 (KT336558, KT336559) and P. chierchiae Giesbrecht, 1889 (JQ714071) is sister to P. fera . As expected, the out-group A. bispinosa (KP068672) exhibited a diverged array. In order to justify the results of the phylogenetic tree, genetic distance persisting within the selected individuals was analyzed. The level of intra- and interspecific divergence persisting within the genus Pontella was evident from distance matrix data ( Table 3). Specifically, female P. spinipes and male P. diagonalis sensu Silas and Pillai (1973) exhibited 0 - 0.2% intraspecific sequence divergence while all the other selected species showed considerable genetic divergence, justifying the findings of ML tree.

Figures

Fig. 2. Pontella spinipes, female. (A) Habitus, dorsal view; (B) right antennule; (C) head, right lateral view; (D) rostrum, anterior view, showing anterior and posterior frontal lenses in solid and dotted lines, respectively; (E) urosome, dorsal view; (F) urosome, ventral view; (G) urosome, right lateral view; (H) 5th leg, posterior view. Arrow indicates crescent shaped lobular process present on either side between the pointed lobes of fifth pedigerous somite and insertion of urosome.

Fig. 4. Maximum likelihood tree for Pontella spinipes and other Pontella species (taken from GenBank with their accession numbers) based on 1000 bootstrap pseudoreplicas. © 2018 Academia Sinica, Taiwan

Fig. 3. Pontella spinipes, male. (A) habitus, dorsal view; (B) head, right lateral view; (C) rostrum, anterior view, showing anterior and posterior lower frontal lenses in solid and dotted lines, respectively; (D) right antennule, number of ancestral segments indicated with Roman numerals; (E) teeth on fused segments XXI-XXIII of right antennule; (F) 5th leg, posterior view.