Smacigastes barti Gollner, Ivanenko & Arbizu, 2008
The body is laterally compressed and weakly chitinised, with short sensilla and few pores. The rostrum is rounded and prominent. The prosome has 4 segments, comprising of the cephalothorax and 3 somites that bear legs 2 to 4. The urosome has 5 segments: the first urosomite (bearing leg 5), a genital double somite (with a ventral depression and one gonoporus that is covered by a flap of the minute leg 6), and 2 postgenital somites plus the telson with furca. The length of the furca is 3 times its width, with 7 setae of different length.
The antennule has 7 segments. The formula of setation is 1, 10, 9, 3 + aesthetasc, 6, 4, 6 + aesthetasc.
The antenna has a small coxa and an elongate basis with 1 seta and a field of cuticular spinules. The exopod has 2 segments. The proximal segment has 1 inner setae, whilst the distal segment has 3 apical setae. The endopod also has 2 segments, with the proximal segment having 1 median seta. The ditsal segment has 4 inner setae, 6 terminal setae and a hyaline frill is found subdistally on the outer margin.
The labrum projects over the shield of the cephalothorax in a lateral view.
The mandible possesses a gnathobase. The palp is 2-segmented, with 2 distal setae present on the basis and a 1-segmented endopod, which bears 1 outer and 3 terminal setae.
The maxillule has a praecoxal arthrite that bears 8 spines, and a coxal endite with 1 seta. The exopod bears 2 setae, whilst the basis is elongate with 1 median and 4 terminal setae.
The maxilla has a syncoxa with 2 endites, a proximal endite with 1 spine, and a distal endite with 3 spines. The allobasis has 3 lateral setae, 2 subdistal spines and 1 apical spine.
The maxilliped has 3 segments and is subchelate. The syncoxa is elongated with 1 distal seta. The basis has 2 rows of spinules. The endopod has 1 segment, which is produced into a strong claw that has 2 proximal setae and an inner row of short spinules.
Swimming legs 1-4 are biramous. The armature formula for each leg is as follows:
Leg 1 - Coxa 0-0 Basis 1-0 Exopod 2,I,1 Endopod 1, II, II1
Leg 2 - Coxa 0-0 Basis 1-0 Exopod II-2; II, I, 3 Endopod 0-1; 0-2; I, II, 2
Leg 3 - Coxa 0-0 Basis 1-0 Exopod II-2; II, I, 4 Endopod 0-1; 0-2; 1, II, 3
Leg 4 - Coxa 0-0 Basis 1-0 Exopod I-0; I-1; II, I1, 1I1 Endopod 0-1; 0-2; I, II, 2
Leg 1 has a 1-segmented rami. Legs 2 and 3 have 3-segmented endopods and 2-segmented exopods. The proximal segments of the exopods are elongated, derived by a fusion of the former proximal and middle segments. Leg 4 has 3-segmented rami. The distal exopod segment has an inner seta slightly modified into a spine. Leg 5 has a baseoendopod and an exopod. The baseoendopod has 1 basal outer seta, 3 inner setae, 1 terminal spine and 1 small terminal outer seta. The exopod has 3 outer elements (of which the proximal one is seta-like, whilst the middle and distal ones are spine-like), and 2 terminal spines. Leg 6 has a small flap with 1 minute seta.
The male differs from the female in several ways. In the male the antennule has 10 segments, with a setation formula of 1, 10, 6 + aesthetasc, 1, 7 + aesthetasc, 1, 2, 1, 4, 7 + aesthetasc. Leg 5 is 2-segmented, with a basis bearing 1 outer seta and an exopod bearing 1 outer proximal seta, 1 outer subdistal spine and 2 terminal spines. Leg 6 has a membranous genital flap on the left side.
Size of types:
Female total length 420 um; greatest width 180 um.
Male total length 325 um; greatest width 150 um.
(Gollner et al., 2008)
Ecology and Distribution
Found among artificial substrates deployed in the vacinity of Riftia aggregations at hydrothermal vents from 2,500 m at Tica (9°50.447`N, 104°17.493`W) on the Northern East Pacific Rise (Gollner et al., 2008).
Despite being found at hydrothermal vents, the distribution of Smacigastes micheli shows that the species does not tolerate elevated temperatures and/or the presence of hydrogen sulfide or oxygen fluctuations (Gollner et al., 2008)