Halectinosoma MANDIBULARIS 2007, SP. NOV.
Creators: name: Clément, Michel
name: Moore, Colin G.
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Maxillopoda
Harpacticoida
Ectinosomatidae
Halectinosoma

description: HALECTINOSOMA MANDIBULARIS SP. NOV.
Type material: 1♀ holotype dissected on three slides (NHM1990.425), 1♀ paratype dissected on slide (NHM1990.426), collected by grab from the North Sea (site S58). 1♂ paratype dissected on two slides (NHM1990.427), 1♂ paratype in tube (NHM1990.1219), collected by C. G. Moore by grab from off Banyuls, France (site S65).
Other material examined: England: S85 (1♀ in tube NHM1990.1218). France: S65 (1♂ in tube NHM1990.1220).
Description of female holotype
Length: Habitus 1195 µm; sum of all somites 1380 µm; cephalothorax 400 µm; genital doublesomite 185 µm. Habitus fusiform (Fig. 1A). Colour of preserved specimen dark brown. Surface of cuticle densely covered with small pores. Cephalothorax gradually attenuating anteriorly. Rostrum broadly rounded and partially fused at base with cephalothorax and furnished with two small sensilla subapically. Genital double-somite with a short, transverse chitinous stripe ventrally and divided dorsally by a suture reaching ventro-laterally. Penultimate somite with rounded pseudoperculum.
Caudal ramus (Fig. 1B, C). Nearly 1.5 times as long as broadest width. Principal setation and general form as in H. pseudosarsi Clément & Moore, 1995.
Somitic ornamentation (Fig. 1A–C). Body somites, except penultimate, sparsely furnished with sensilla and pores. Posterior margin of cephalothorax, first and second free thoracic somites unadorned. Surface of first and second free thoracic somites with one and two rows of fine spinules, respectively. Posterior margin of third free thoracic somite and first urosomite finely crenulated. The surface of third free thoracic somite with two rows of fine spinules, first urosomite with two rows of lappet-like spinules and one row of fine spinules anteriorly. Genital double-somite with a complex arrangement of rows of fine spinules and posteriorly with two rows of lappet-like spinules and a semi-incised subulate hyaline frill. Fourth urosomite with a similar hyaline frill to preceeding somite and furnished with one row of fine spinules and three rows of lappet-like spinules, one of which is only present mid-ventrally. Penultimate somite with one row of fine spinules and two rows of lappet-like spinules; very fine fully incised subulate hyaline frill interrupted dorsally by unadorned pseudoperculum.
Antennule (Fig. 2A). Short, robust and sixsegmented. Principal setation and form as in H. pseudosarsi except for small differences in relative length and spinulation of some setae.
Antenna (Fig. 2B). Coxa short. Basis with a short row of spinules along outer margin and a set of setules at inner distal corner. Endopodite two-segmented; segment 1 unadorned, segment two furnished with two adjacent setae mid-way along inner margin and seven terminal setae (three spinulose geniculate and one dwarfed plumose). Exopodite three-segmented; basal segment well developed and armed with one short seta, segment 2 short, with a strong, spinulose seta, distal segment slightly longer than basal one and armed with two apical setae, which are spinulose and subequal in length.
Mandible (Fig. 2C). Coxal gnathobase extremely well developed and furnished with a short, spiniform seta at ventral base of bidentate pars incisiva and tridentate lacinia. Basis with a row of fine spinules on surface and one spinulose seta issuing from distal inner corner. Endopodite one-segmented and furnished with two juxtaposed setae mid-way along inner margin and five terminal setae. Exopodite onesegmented and armed with three setae.
Maxillula (Fig. 2D). Praecoxal arthrite broad and armed along distal edge with three unguiform spines and three small setae. Coxa absent. Basis small and armed with two strongly spinulose setae and a few spinules along inner margin. Exopodite consisting of a small lobe fused with basis and fringed with few spinules along inner margin, and furnished with two slender setae, the outer seta being spinulose. Endopodite one-segmented and consisting of two lobes each furnished with a pair of setae; the inner lobe with a short, thick spinulose seta adjacent to a much more slender seta, the outer lobe with two slender setae, the innermost seta being more coarsely spinulose.
Maxilla (Fig. 2E). Syncoxa short, broad, with spinule rows on anterior surface and at outer distal corner, and with one short spinulose seta and one endite armed with three setae along its inner margin (two short and spinulose, one bare and slender). Basis approximately twice as long as syncoxa, with short, spinulose seta approximately midway along inner margin. Endopodite three-segmented, segments 1 and 2 armed with one thick, long geniculate seta, distal segment represented by a broad base from which one lateral and three distal confluent setae arise.
Maxilliped (Fig. 2F). Syncoxa short, with a row of fine spinules. Basis segment long, slightly tapering distally and with strong spinules along inner and outer margin. Endopodite segment short, armed with two spinulose setae and two closely set bare apical setae.
P1–P4 (Fig. 3A–D). Coxa with transverse row of spinules on anterior surface and two rows along distal edge (but only one on P1). Exopod and endopod threesegmented with setal formula as follows:
P5 (Fig. 1D). Exopod almost twice as long as broad, separated from baseoendopod by suture on posterior surface only. Inner expansion of baseoendopod reaching almost to inner distal lobe of exopod, with spinules along inner margin and with two setae distally, the inner seta twice as long as outer seta. Outer expansion of baseoendopod with one long slender seta and a small pore on anterior surface. Inconspicuous pore present on anterior surface of baseoendopod at base of outer margin of inner expansion. Exopod with spinules along inner distal margin, one small pore on anterior surface, and three bare lobes at distal edge, each armed with a seta: innermost seta twice as long as outer seta of baseoendopod; middle seta slightly longer than innermost seta; outer seta short and about half as long as inner seta. Surface-seta not reaching beyond exopod, articulating on a small lobe accompanied by two spinules and issuing from a point distal to the exopod–baseoendopod suture (representing a distance of about one-eighth of exopod length).
Description of male paratypes
Length: Habitus 900–1080 µm; sum of all somites 1170–1185 µm; cephalothorax 310–330 µm. Urosomites two and three distinct. Otherwise as in female, except the following features.
Antennule (Fig. 1E). Seven-segmented. Principal segmentation and setation (setae on anterior side not illustrated) as in male of H. neglectum (see Clément & Moore, 1995) except posterior margin of fifth segment with a broader and longer aesthetasc and without grasping processes.
P5 (Fig. 1F). Baseoendopod confluent with first urosomite: inner expansion armed with two setae, innermost almost three times as long as outermost seta. Exopod clearly demarcated from baseoendopod and armed with three setae: the innermost seta subequal in length to middle seta and longer than outermost seta. Surface of exopod with a small pore located near the insertion point of the surface seta.
P6 (Fig. 1G). Plate-like with two setae at outer distal corner, the outer seta twice as long as inner one. Distal edge of plate finely denticulate.
Variability: The following length variations were observed in female specimens from the Celtic Sea and Banyuls: habitus 990–1170 µm; sum of all somites 1325–1405 µm; cephalothorax 420–450 µm; genital double-somite 160 µm.
Etymology: The species name, mandibularis, alludes to the well-developed nature of the mandibular coxal gnathobase.
Remarks
Halectinosoma mandibularis has some distinctive features in the form of reduction in the mouthparts, which place it apart from all other species in the genus. The basis of the mandible has only one seta at the distal inner corner, whereas other Halectinosoma species typically have three, but sometimes two. The endopodite has only seven setae, a reduction from the typical ten setae. The coxal gnathobase is also extremely well developed, being larger than the basis, exo- and endopodite combined. The syncoxa of the maxilla also possesses only one of the three endites, although one of the missing two endites is represented by a seta. The maxillula also shows reduction in the number of setae, with the coxa wanting and the absence of a suture between the exopod and the basis. The syncoxa of the maxilliped also has no seta, which is unique within the genus Halectinosoma. The size and shape of the habitus, as well as the P5 of the female, resemble those of H. pseudosarsi but the two species can be easily distinguished by the characters mentioned above and the rows of lappet-like spinules on the urosome of H. mandibularis.
description: Published as part of Clément, Michel & Moore, Colin G., 2007, Towards a revision of the genus Halectinosoma (Copepoda, Harpacticoida, Ectinosomatidae): new species from the North Atlantic and Arctic regions, pp. 453-475 in Zoological Journal of the Linnean Society 149 (3) on pages 454-459, DOI: 10.1111/j.1096-3642.2007.00267.x, http://zenodo.org/record/4687519