Halectinosoma gothiceps

HALECTINOSOMA GOTHICEPS (GIESBRECHT, 1881)

Ectinosoma gothiceps Giesbrecht, 1881: 255

Ektinosoma gothiceps Giesbrecht, 1882: 106, pl. I figs 3, 12, pl. IV fig. 17, 35, pl. V fig. 3, pl. VII fig. 8, pl. VIII figs 10–11, pl. IX fig. 17, pl. X figs 10, 21, pl. XI fig. 13, pl. XII fig. 6, 10

Halectinosoma gothiceps Mielke, 1975: 23, fig. 9

? Ectinosoma (Halectinosoma) gothiceps Lang, 1948: 216–217, figs 112.10, 117.2

? Halectinosoma gothiceps Lang, 1965: 38

Not Ectinosoma gothiceps Sars, 1904: 37, pl. XX fig. 2

Material examined: Alaska: 2♀ from Island Flats, Port Valdez, collected by H. M. Feder, 6.ii.1973 (in R. Hamond’s personal collection). Scotland: S17 (4♀ dissected on six slides NHM1990.378–381, 1♂ dissected on two slides NHM1990.383, 9♀ in tubes NHM1990.1169–1177); S18 (20♀, 2♂ in tubes NHM1990.1180–1189 and NHM1990.1190–1191); S21 (1♂); S70 (29♀, 4♂ in authors’ personal collection); S71 (2♀, NHM1990.1178–1179); S91 (2♀ NHM1990.1192–1193); S95 (28♀, 3♂ NHM1990.1194–1203 and NHM1990.1204–1206); 10♀ from Limekilns, Forth Estuary, muddy sand, lower shore (in authors’ personal collection); 24♀, 6♂ from South Queensferry, Forth Estuary, soft mud, lower shore (in authors’ personal collection). England: 1♀ from Blakeney Harbour, Norfolk and 1♀ from Wells Rocks, among Bowerbankia imbricata, collected by R. Hamond (in R. Hamond’s personal collection). Ireland: the following material from the National Museum of Ireland: 1♀ from Dunlaoghaine, Dublin Bay, collected by C. E. O’Riordan, 31.viii.1966 (NMI17. 1975); 1♀ from Dalkey I., Co. Dublin, collected by K. M. Roe netsweeping in flat pool, 3.xi.1952 (NMI66. 1982); 1♀ from Loch Hyne, Co. Cork, collected by J. M. C. Holmes from gravel under stones, 8.vii.1982. Germany: 1♀ from List, Island of Sylt, collected by W. Mielke (in W. Mielke’s personal collection).

Description of female

Length (n = 10): Habitus 460–550 µm; sum of all somites 530–575 µm; cephalothorax 165–180 µm; genital double-somite 60–70 µm. Cephalothorax with light brown pigment spot near base of antennule and with spinules at anterior distal edge (Fig. 7E). Rostrum broadly rounded and partially fused at base with cephalothorax, with two small sensilla subapically (not visible at magnifications <1250×). Labrum terminating in a spinous projection. Genital double-somite subdivided ventrally by a short transverse chitinous stripe (Fig. 9C). Penultimate somite with rounded pseudoperculum (Fig. 9D).

Caudal ramus (Fig. 9C, D). Slightly longer than broad. Principal setation and general form as in H. pseudosarsi.

Somitic ornamentation (Fig. 9C, D). Genital double-somite with six rows of fine spinules dorsally and a row of hair-like spinules near posterior margin. Urosomite 4 with three rows of fine spinules dorsally and a row of hair-like spinules near distal margin. Penultimate somite with two spinular rows and a dorsal row of hair-like spinules near distal edge.

Antennule (Fig. 7E). Six-segmented. Setation as in H. pseudosarsi. Other cephalosomic appendages are as in H. paragothiceps sp. nov.

P1-P4. Exopod and endopod three-segmented with setal formula as follows:

Exopod Endopod

P1 0: 1: 123 1: 1: 221

P2 1: 1: 223 1: 1: 221

P3 1: 1: 222 1: 1: 221

P4 1: 1: 322 1: 1: 221

P5 (Fig. 7D). Exopod about as long as broad and separated from baseoendopod by a suture on posterior surface only. Anterior surface of baseoendopod with one row of strong spinules near base and on inner expansion and three rows of fine spinules. Inner expansion of baseoendopod reaching almost halfway along inner margin of exopod, with spinules along inner margin (not illustrated) and furnished distally with two spinulose setae, 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, shorter than outer seta of inner expansion of baseoendopod; middle seta more than twice as long as innermost seta; outer seta twice as long as innermost seta. Surfaceseta reaching beyond exopod, articulating on a small lobe accompanied by a row of spinules and issuing from within the proximal half of the surface-seta insertion line.

Description of male

Length (n = 11): Habitus 340–400 µm; sum of all somites 385–430 µm; cephalothorax 125–145 µm. Urosomites 2 and 3 distinct. Otherwise as in female apart from the following features.

Antennule (not illustrated). Seven-segmented with fifth segment enlarged and furnished with an aesthetasc.

Previous description of the male P5 has been given by Mielke (1975). The male P6 (Fig. 7F) consists of a plate with a denticulate posterior edge and one seta at outer distal corner.

Remarks

Of the previously recognized species of the genus, H. gothiceps has a unique setation formula for the pereiopods P1–P4. Also, the male P5 is unusual in having the exopod confluent with the baseoendopod and the male P6 is unusual in possessing only a single seta. We have, however, discovered during our study that a closely related species which shares these features, which we have named H. paragothiceps sp. nov., has been mistakenly assigned to H. gothiceps by some workers. A full description of H. paragothiceps sp. nov. and a further discussion on the morphological differences between these two species are given below. We are, however, certain that the material examined corresponds to the original description given by Giesbrecht (1881). Giesbrecht omitted to mention the pigmented patch on the cephalothorax, but this feature can be easily missed and has not been reported before. We were able to examine a specimen collected by Mielke (1975) and confirm it as H. gothiceps. Following examination of material from Sars’ collection we can confirm that his description of H. gothiceps (Sars, 1904) is based on H. paragothiceps sp. nov. Other records, such as those of Lang (1948) and Chislenko (1967), lack too many important details and must be taken with great caution. Halectinosoma gothiceps is often found intertidally in muddy sediments but can also be found occasionally in coarser sediments.