Stellatoniscidae Oanh & Boyko 2020, fam. nov.

Stellatoniscidae fam. nov. Type genus: Stellatoniscus gen. nov.

LSID urn:lsid:zoobank.org:act: A58D4133-2299-427B-894F-BA7055626985

Diagnosis. Immature female developing from 4 lobed stage to 4 lobes with short thin mediodistal extensions to reduced body with 8 short tentacular extensions; mature female with 10 tentacular thin extensions radiating out from central body. Epicaridium larva antenna approximately 3/4 as long as body, composed of 7 articles (4 peduncular + 3 flagellar); 6 pairs of gnathopodal pereopods subequal in size and shape; pleon with 5 pairs of biramous pleopods; uropods biramous. Cryptoniscus larvae antennular plate with mesial demarcated area and distal teeth; coxal plates 1–6 entire, rounded, 1–4 covered with scales, pereomere 7 lacking coxal plate; pereopod 1 carpus and merus with unique ridged surface; pereopods 1 and 2 dissimilar, second pair larger; pereopods 3–7 subequal with mediodorsal expansion of ischium and basis; pleotelson margin entire; uropods with endopod and exopod subequal in size.

Distribution. Nha Trang bay, Khanh Hoa province, Vietnam.

Remarks. The shape of the female of Stellatoniscus tentaculus gen. nov., sp. nov. , with its thin tentacular extensions, is unlike any other female cryptonicoid. Likewise, the cryptoniscus larva possesses several unique characters not seen in any other cryptoniscoid: antennular plate with mesial demarcated area (unique); coxal plates 1–6 rounded, 1–4 covered with scales, pereomere 7 lacking coxal plate (unique); pereopod 1 carpus and merus with ridged surface (unique); pereopods 1 and 2 dissimilar (unique). Given the number of distinct characters shown by the new genus and species, it is as morphologically different from species of the other cryptoniscoid families as those families are from each other and warrants its own family; none of the Cryptoniscoidea incertae sedis genera (Boyko et al. 2008 onwards), mostly known only from cryptoniscus larvae, show any close affinity to the new genus and species. The new genus contains the only cryptoniscoids known to parasitize entoniscid hosts.