PROC. BIOL. SOC. WASH. 
97(1), 1984, pp. 71-77 
CLARIFICATION OF THE MONOTYPIC GENERA 
CHIRISCUS AND SYMMIUS 
(CRUSTACEA: ISOPODA: IDOTEIDAE) 
Gary C. B. Poore 
Abstract. — Chiriscus australis Richardson, 1911, has been re-examined and 
placed in the older genus Macrochiridothea Ohlin of which Chiriscus becomes a 
junior synonym. Symmius caudatus Richardson, 1904, is redescribed. Both Sym- 
mius and Macrochiridothea are diagnosed and a list of non-idoteine genera of the 
Idoteidae is given. 
In the early part of this century Harriet Richardson described two monotypic 
genera in the isopod family Idoteidae: Symmius (1904) and Chiriscus (1911). As 
part of an examination of non-idoteine genera present in southern Australia it 
was thought desirable to re-examine the type and only species of the two genera 
in order to establish their continued validity. 
Brusca (1984) has revised in detail the genera of the Idoteinae. The remaining 
genera of the family, a group which Brusca referred to as the "glyptonotine-group," 
are listed in Table 1. They comprise four subfamilies the relationships of which 
are far from clear and receive more attention by Poore (in press). 
Richardson's description of Chiriscus australis was in part incorrect. It may 
now be safely placed in the older genus Macrochiridothea Ohlin, 1 90 1 . The genus 
Chiriscus becomes a junior synonym of the larger genus for which an amended 
generic diagnosis is given. 
Symmius caudatus clearly does not belong to any other genus and is here 
redescribed in more detail and the genus diagnosed. Richardson's (1904) descrip- 
tion contained numerous errors and omissions. 
Family Idoteidae 
Macrochiridothea Ohlin 
Macrochiridothea Ohlin, 1901:286.-Nordenstam, 1933: 105. -Sheppard, 1957: 
168-173. -Menzies, 1 962:98.- Hurley & Murray, 1 968:244. -Moreira, 1973: 
12.-Jones&Fenwick, 1978:619. 
Chiriscus Richardson, 191 1:169-1 70. -Sheppard, 1957:168-169. 
Diagnosis. — Head immersed partly in pereonite 1, laterally expanded, margins 
incised or entire. Eyes dorsal if present. Pereonites 5-7 only with coxal plates 
distinct dorsally. Pereonite 7 much narrower than pereonite 6. Pleonites 1-3 
completely free; pleonite 1 much narrower than following pleonites; no partial 
sutures on the remaining pleotelson. Pereopod 1 subchelate, propodus grossly 
expanded. Pereopods 2 and 3 subchelate; elongate-ovate propodus cupped by 
triangular or lobed fifth article; dactyl well developed, minute or absent. Pereopods 
4-7 ambulatory, pereopod 6 the longest; all pereopods with dactyl, usually minute. 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Table 1. — Non-idoteine genera of the Idoteidae (see Brusca, 1984, for genera of Idoteinae and 
Poore, in press, for one additional genus). 
Austridotea Nicholls, 1937 
Austrochaetilia Poore, 1978 
Chaetilia Dana, 1853 
Chindotea Harger, 1878 
Chiriscus Richardson, 1911 (junior synonym of Macrochiridothea) 
Glyptonotus Eights, 1852 
Macrochiridothea Ohlin, 1901 
Maoridotea Jones & Fenwick, 1978 
Mesidotea Richardson, 1905 (junior synonym of Saduna) 
Notidotea Nicholls, 1937 (may be a synonym of Euidotea (Idoteinae) — Hurley, 1961) 
Parachiridotea Daguerre de Hureaux & Elkaim, 1972 
Proidotea Racovitza & Sevastos, 1910 (Oligocene fossil) 
Saduria Adams, 1852 
Sadunella Holthuis, 1 964 
Symmius Richardson, 1 904 
Mandible with toothed incisor, large lacinia mobilis and substantial setal row, 
molar absent (except for single seta). Maxillipedal palp of 4 articles, about 3 times 
as long as endite, penultimate article proximally broad. Pereopods and antennae 
ornamented with numerous clubbed setae. Uropods overlapping in midline, en- 
closing pleopods except anteriorly; rami unequal. 
Remarks. — This diagnosis modifies those of Menzies ( 1 962) and Moreira (1973) 
to include Macrochiridothea australis which differs from species previously known 
in two respects. Pereopods 2 and 3 of M. australis do not possess dactyls although 
in all other respects they are similar. The state in M. australis is the final step in 
a trend shown in the genus toward loss of dactyls; in at least two species the 
dactyls are minute (Moreira 1973). Only M. australis lacks a lateral incision on 
head. The incision ranges from well developed (e.g., M. stebhingi) to only slight 
(M. robusta) (Moreira 1973). In all other respects Richardson's species conforms 
with Macrochiridothea which must therefore be broadened to include it. 
The figures of M. australis enable it to be distinguished from other species in 
the genus. Moreira (1973), Hurley & Murray (1968), and Bastida & Torti (1969) 
have figured several species in more detail. This enables an assessment of the 
mouthparts and pleopods, which may all be important in generic relationships 
within the family. 
Macrochiridothea australis (Richardson), new combination 
Figs, la, 2 
Chiriscus australis Richardson, 1911:170-171, figs. 1-5. 
Diagnosis. — Body smooth except for broad dorsolateral bosses on pereonites 
1-4. Body 2.3 x as long as wide. Head laterally expanded but without lateral 
incisions. Eyes present, minute. Antenna 2, peduncle article 4 lobed to shield 
article 5. Pereopods 2 and 3 without dactyls, article 5 strongly lobed. Pereopods 
4 and 7 each with an extremely minute dactyl. 
VOLUME 97, NUMBER 1 
Fig. 1 . a, Macrochiridothea australis, holotype; b, Symmius caudatus, 9 syntype; u, uropod of S. 
caudatus (scales 1 mm). 
Material. — Holotype, USNM 42092, ovigerous 9, 7.9 mm; Argentina, off Rio 
de la Plata, 21 m, 12 Jan 1888 (U.S. Fisheries Commission Steamer Albatross 
station 2764). 
Remarks. — Only the holotype, an adult female, is known. The diagnosis given 
enables the species to be distinguished from the eight listed by Moreira (1973). 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Fig. 2. Macrochiridothea australis, holotype: PI, P2, P4, P5, P7, pereopods 1, 2, 4, 5 and 7; Al, 
A2, antennae 1 and 2. 
VOLUME 97, NUMBER 
Fig. 3. Symmius caudatus V syntype: PI, P2, P6, P7, pereopods 1, 2, 6 and 7; Al, A2, antennae 
and 2; MD, mandibles (left & right); MX1, MX2, maxillae 1 and 2; MP, maxilliped. 
76 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Macrochiridothea australis is most similar to M. lilianae in body shape and form 
of the pereopods. 
Symmius Richardson 
Symmius Richardson, 1 904:39-40. -Nordenstam, 1933:103. 
Diagnosis. — Head partly immersed in pereonite 1, laterally expanded slightly, 
margins entire. Eyes dorsal. Pereonites 5-7 only with coxal plates distinct dorsally. 
Pereonite 7 little narrower than pereonite 6. Pleonites 1 and 2 completely free, 
of similar width and laterally acute; no partial sutures on the remaining pleotelson. 
Pereopods 1-6 prehensile; propodus of pereopod 1 swollen, those of pereopods 
2-6 cylindrical, decreasing in size posteriorly and cupped by a triangular lobed 
fifth article. Pereopod 7 ambulatory, of similar size to pereopod 6; dactyl without 
an unguis. Mandible with toothed incisor, large lacinia mobilis and substantial 
setal row, molar absent (except for 3 distal long setae). Maxillipedal palp of 4 
articles, about 3 times as long as endite, articles 2 and 3 mesially lobed. Pereopods 
and antennae ornamented with simple or plumose setae. Uropods overlapping in 
midline, enclosing pleopods except anteriorly; rami equal and narrow. 
Remarks. — The format of this and the previous diagnosis enables the genus to 
be distinguished from others in the non-idoteine group (Poore, in press). Rich- 
ardson ( 1 904) did not illustrate the mouthparts of S. caudatus which are shown 
here in some detail. The relationships of Symmius to other non-idoteines are not 
clear. The genus is unique in that pereonite 7 reaches full width of the body, in 
having only two free pleonites, and in possessing six pairs of prehensile limbs. 
Symmius caudatus Richardson 
Figs, lb, 3 
Symmius caudatus Richardson, 1904:40-41, figs. 11-15. 
Diagnosis. — As given for genus. 
Material. — 3 syntypes (of 9 reported by Richardson): USNM 29081; ovigerous 
2, 12.6 mm; juveniles, 8.8 mm and 12.2 mm. Oxe Zaki, Japan, 109-127 m (U.S. 
Fisheries Commission Steamer Albatross station 3715). 
Acknowledgments 
I thank Brian Kensley, Smithsonian Institution, for arranging the loan of this 
material and for his critical review of the manuscript. 
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