Suggested Common Name: Seapills and Trisobites
Number of subordinate taxa: 806 species in 2 superfamilies, 101 species in both superfamilies in our area.
Etymology: after Sphaeroma Bosc, 1802, see that genus for explanation. Common name refers to the two superfamilies in the suborder, see those for explanations
Taxonomic History: one of the many former members of Flabellifera, which was divided into seperate suborders over the course of the late 1980s to early 2000s.
Description: (modified from Bruce & Poore, 2003) Antenna 1 without scale. Mandible lacinia present on the left, absent or reduced and fused with the spine row on the right; molar cylindrical with a triturative flat end. Maxilla 2 triramous (exopod with 2 endites). Maxilliped endite usually distally truncate and setose, reaching at least the tip of palp segment 2. Pereopods 1-7 coxae fused to tergites into coxal plates. Pleonites 1-5 variously fused (rarely with all free). Pleonite 1 narrower than others (similar in length in the extralimital Plakarthrium). Pleopod 3 endopod roughly triangular, at least with medial angle sharper than the outer. Telson underside vaulted with lateral ridges, defining a branchial chamber. Uropod rami lateral to margin of telson, articulating along longitudinal axis and folding down alongside branchial space.
Type taxon: Sphaeromatoidea Latreille, 1825
Notes: This is one of the smaller "large" suborders in Isopoda, having a similar diversity to Valvifera and Epicaridea but much less than the truely massive orders (Oniscidea, Asellota and Cymothoida) and much more than the very small orders (in our area Microcerberidea and Limnoriidea). The two subfamiles are extremely distinctive from each other and from all other isopods, both having unique morphologies and ecologies. Interestingly, this suborder seems to have a discrete center of diversity around Australasia and the Southern Ocean, with a lower diversity the further away from these regions until a low in the Arctic, where there is only one species (Tecticeps marginalis) barely crossing over the Bering Strait.
Valvifera seems to be Sphaeromatidea's closest relative, with both sharing a fairly unique telson morpholgy.
Key to superfamilies
1 a. Dorsal coxal plates 2-7 distinct from tergites by a suture; pereonite 7 ventral coxal plates either meeting at middle or joined by paired plates; uropods biramous; body very flat --> Seroloidea
b. Dorsal coxal plates 2-7 not distinct from tergites; pereonite 7 coxal plates not meeting in the middle or conjoined by paired plates; uropod endopod fused with protopod, making them functionally uniramous; body flat or domed, many species able to conglobulate --> Sphaeromatidea
Brandt, A., & Poore, G. C. (2003). Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships. Invertebrate Systematics, 17(6):893-923.
Published: Jan 1, 2023
Updated: Mar 1, 2023