Sphaeromatidea
Wägele, 1989

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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: Body generally compact, ovate to suborbicular (rarely somewhat elongate); sexual dimorphism absent to extremely obvious, especially in telson and uropods, pleopod dimorphism restricted to presence or absence of appendix masculina. Antenna 1 usually well-developed; scale absent. Antenna 2 without scale. Mandible incisor present; lacinia different between sides, present and well-developed on left, reduced to absent and fused with spine row on right (sometimes flipped); spine row present; molar cylindrical, truncate (rarely absent); palp present (rarely absent). Maxilla 1 biramous (rarely uniramous). Maxilla 2 exopod with 2 endites (rarely entirely absent). Maxilliped epipod present, apparently large; basis body not dominating maxilliped structure; endite large, usually truncate. Pereopods 2-7 coxae formed into coxal plates, variously free to fused with tergites. Penes various, flat to elongate, separate to fused. Pleonites 1-5 generally variously fused, often forming a fused segment or multiple free to partially fused segments free from the telson, very rarely with all 5 segments free. Pleonite 1 (when free) narrower than other pleonites. Pleopod 1 not modified, not sexually dimorphic. Pleopod 2 slightly modified, slightly dimorphic mainly in the presence or absence of the appendix masculina. Pleopod 3 endopod vaguely subtriangular to subrectangular, with at least the distomedial corner sharper than the distolateral corner, tip subacute to round-truncate. Telson usually large with large domed branchial chamber flanked by lateral ridges. Uropod set proximolaterally on telson; rami articulating longitudinally to form tail fan with telson; rami well-developed, often with endopod fused with telson (Sphaeromatoidea).
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 truly 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 morphology. A unique feature of Sphaeromatidea is the fusion of the frontal lamina and the clypeus to form the epistome, a stucture that is often very taxonomically important in some groups, especially in Sphaeromatidae. It apparently only occurs in this suborder and does not appear in the standardized diagnosis above only since the total extent of variability in this region of the body across suborders and their constituent taxa is not fully known as of this time.

Subordinate Taxa: Seroloidea, Sphaeromatoidea

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 

Sources

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.

Bruce, N. L. (1985). Biremia ambocerca n. gen., n. sp., the first record of the marine isopod crustacean family Bathynataliidae from Australian waters. Records of the Australian Museum, 37:295-299.

Bruce, N. L. (1997). A new genus of marine isopod (Crustacea: Flabellifera: Sphaeromatidae) from Australia and the Indo-Pacific region. Memoirs of the Museum of Victoria, 56:145-234.

Poore, G. C. (1987). Serolina, a new genus for Serolis minuta Beddard (Crustacea: Isopoda: Serolidae) with descriptions of eight new species from Australia. Memoirs of the National Museum of Victoria, 48:141-189.

Poore, G. C. (1990). Two new species of isopod crustaceans belonging to Australian endemic genera (Serolidae and Chaetiliidae). Memoirs of the Museum of Victoria, 51:99-107.

Poore, G. C., & Brandt, A. (2001). Plakarthrium australiense, a third species of Plakarthriidae (Crustacea: Isopoda). Memoirs of Museum Victoria, 58(2):373-382.

Published: Jan 1, 2023
Updated: Nov 1, 2023