Halectinosoma paragothiceps, SP. NOV.

HALECTINOSOMA PARAGOTHICEPS SP. NOV. Ectinosoma gothiceps Sars, 1904: 37, pl. XX fig. 2 Type material: 1♀ holotype dissected on two slides (NHM1990.385), 4♀ paratypes dissected on eight slides (NHM1990.386 – 389), 14♀ paratypes in tube (NHM1990.1142 – 1148) from the Forth Estuary (site S17); 2♂ paratypes dissected on two slides (NHM2005.2639 – 2640) from Loch Creran (site S96). Other material examined: Canada: 1♀ (S97); 2♀ (S98), 1♀ (S99) (in authors’ personal collection). Norway: 8♀ and 1♂ (labelled E. gothiceps) from G. O. Sars collection, tube F20027, Zoology Museum, Oslo. Scotland: S18 (1♀ in authors’ personal collection, 1♀ in tube NHM1990.1149); S21 (61♀ in tube NHM1990.1150–1159); S68 (1♀); S70 (9♀ in tube NHM1990.1160–1168); S73 (1♀); S95 (3♀ in tube in authors’ collection, 1♀ dissected on two slides NHM1990.389); 2♀ from shallow muddy sand, Forth Estuary (in authors’ personal collection). Description of female holotype Length: Habitus 430 µm; sum of all somites 490 µm; cephalothorax 145 µm; genital double-somite 60 µm. Habitus fusiform (Fig. 7A). Cephalothorax gradually attenuating anteriorly and without a light brown pigment spot near base of antennule but furnished with spinules on anterior distal edge. Rostrum broadly rounded, partially fused at base with cephalothorax and furnished with two small sensilla subapically. Labrum terminating in a spinous projection (Fig. 7B). Genital double-somite subdivided ventrally by a short transverse chitinous stripe (Fig. 9A). Penultimate somite with rounded pseudoperculum (Fig. 9B). Caudal ramus (Fig. 9A, B). Slightly longer than broad. Principal setation and general form as in H. gothiceps. Somitic ornamentation (Fig. 9A, B). Body somites, apart from penultimate, sparsely furnished with sensilla and pores. Posterior margin of cephalothorax, first and second free thoracic somites unadorned. Posterior margin of third free thoracic somite and first urosomite finely spinulose. Genital double-somite with semi-incised subulate hyaline frill and with four rows of fine spinules dorsally, ventrally with a complex arrangement of spinule rows. Urosomite 4 with a similar hyaline frill to preceeding somite and with two rows of fine spinules in anterior half and a ventral row of spinules near distal margin. Penultimate somite dorsally with one fine spinule row in anterior half and ventrally with two fine rows in anterior half and a row of stronger spinules along distal margin. Antennule (not illustrated). Short and sixsegmented. Principal setation and form as in H. gothiceps. Antenna (Fig. 8A). Coxa short. Basis with a short row of fine spinules along outer margin and a set of long setules near inner distal corner. Endopodite twosegmented; segment 1 unadorned, segment 2 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 a short seta, segment 2 short with a strong, spinulose seta, distal segment slightly longer than basal one and armed with two spinulose apical setae. Mandible (Fig. 8B). Coxal gnathobase furnished with two setae, a spiniform seta and a slender seta, at ventral base of bidentate pars incisiva and quadridentate lacinia. Basis with two rows of fine spinules on surface and three slender setae issuing from distal inner corner. Endopodite one-segmented with ten setae. Exopodite one-segmented with slender hairs along outer margin and armed with three setae (1 dwarfed). Maxillula (Fig. 8C). Praecoxal arthrite broad and armed along distal edge with three unguiform spines and subdistally with three small setae. Coxa represented by bare seta. Basis with six setae along inner margin. Exopodite small, one-segmented, with two plumose setae. Endopodite one-segmented, with no apparent suture with basis, and furnished with six setae. Maxilla (Fig. 8D). Syncoxa broad, with two transverse spinule rows around outer margin, a small group of spinules near outer distal corner, with three endites along its inner margin. Proximal endite armed with three spiniform setae and a slender seta. Middle endite with two slender setae. Distal endite with three slender setae. Basis as broad as syncoxa, with three small setae along inner margin and two long and slender setae at distal inner margin. Endopodite threesegmented, segments 1 and 2 each armed with a thick, long, geniculate seta, distal segment represented by a broad base from which one lateral and three distal confluent setae arise. Maxilliped (Fig. 8E). Syncoxa short, armed with one seta and with a row of fine hairs on posterior face. Basis segment long, with slender hairs along outer margin and strong transverse spinule row around inner margin. Endopodite segment short, armed with two spinulose setae and two closely set, bare, apical setae. P1–P4 (Fig. 10A–D). Coxa with one row of spinules along distal edge. Exopod and endopod threesegmented with setal formula as in H. gothiceps. P5 (Fig. 7C). Exopod as long as broad and separated from baseoendopod by a suture on posterior surface only. Anterior surface of baseoendopod with two rows of strong spinules near base and one row on inner expansion. Inner expansion of baseoendopod reaching less than halfway along inner margin of exopod, with spinules along inner margin and two spinulose setae distally, the inner seta longer than outer seta. Outer expansion of baseoendopod furnished with a slender seta. Exopod with three spinulose lobes at distal edge, each armed with a spinulose seta: innermost seta short and shorter than outer seta of inner expansion of baseoendopod; middle seta twice as long as innermost seta; outer seta longer than innermost seta. Surface-seta reaching beyond exopod, inserted on a small lobe just within the proximal half of surface-seta insertion line and accompanied by a row of fine spinules. Variability: The following variation in length was observed among paratypes: habitus 405–460 µm; sum of all somites 485–530 µm; cephalothorax 145– 160 µm; genital double-somite 60–70 µm. Description of male paratype Length: Sum of all somites 406 µm; cephalothorax 142 µm. Urosomites 2 and 3 distinct. Otherwise as in female apart from the following features. Antennule (not illustrated). Seven-segmented, segment 5 enlarged and with an aesthetasc. P5 (Fig. 7G). As in H. gothiceps except terminal setae slightly broader towards the distal end. P6 (Fig. 7H). As in H. gothiceps. Etymology: The species name, paragothiceps, reflects the similarity of this species with H. gothiceps. Remarks This species can be distinguished from its close relative H. gothiceps by the following characteristics. The pigmented patch on the cephalothorax is absent in H. paragothiceps. The setae of the female P5 exopod are distinctly shorter relative to the length of the exopod in H. paragothiceps. There are also differences in the ornamentation of the female P5 baseoendopod and also in the spinulation of the urosomites in both female and male. H. paragothiceps is also smaller in size than H. gothiceps when the sum of all somites is taken into consideration. Examination of material from Sars’ collection has confirmed that his description of H. gothiceps (Sars, 1904) is in fact based on material of H. paragothiceps sp. nov. It is likely that some other records of H. gothiceps are also erroneous. Both species have been found to coexist at three sites around Britain.

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