Themistella fusca (Dana 1853)

Themistella fusca (Dana)

Lestrigonus fuscus Dana, 1853:983, pl. 67: figs. 8a–c.–Bate, 1862:291–292, pl. 48: fig. 8 [copied from Dana].

Hyperiella fusca (Dana).–Bovallius, 1887b:20.

Themistella steenstrupi Bovallius, 1887b:23; 1889:313–316, pl. 13: figs. 47–60.

Themistella fusca (Dana).–Bovallius, 1889:316–317, figs. 1–3 [copied from Dana].

Hyperia thoracica Bovallius.–Vosseler, 1901:73–74, pl. 6: figs. 1–4.–Stephensen, 1924:91.

DERIVATION OF NAME.–From the Latin “fuscus” [=dusky, dark], referring to the color of this species.

TYPE-LOCALITY.–Tropical Atlantic, 1°S, 17°–18°W.

DIAGNOSIS.–Since the genus is monotypic the generic diagnosis serves as a specific diagnosis also.

RELATIONSHIPS.–The short telson of Dana’s L. fusca is characteristic of Hyperioides as well as of Themistella, and the possibility that Dana’s L. fuscus was actually Hyperioides sibaginis must be considered. In Dana’s fig. 8a, P7 is nearly as long as P6, whereas in H. sibaginis P7 is much shorter than P6. The uropods of L. fuscus in Dana’s fig. 8c are slender as in Themistella, and the rami are much shorter than the protopods. In H. sibaginis the uropods are broader and the rami are much longer in proportion to the protopod lengths, especially in Up1–2.

The short telson and the structure of the uropods in Vosseler’s (1901) pl. 6: fig. 4 are characteristic of Themistella and quite different from Bovallius’ illustrations of these structures in Hyperia thoracica, hence I have listed Vosseler’s reference to H. thoracica in the synonymy of Themistella. Stephensen (1924) also identified specimens of Themistella as H. thoracica. I have examined his specimen from the Thor Expeditions and found it to be a typical Themistella. The specimen in the Copenhagen Museum called H. Reinhardi by Bovallius (on the label) and H. thoracica by Stephensen (1924) is also a Themistella.

DISTRIBUTION.–I have examined specimens from the tropical Atlantic (off Barbados; Gulf of Guinea), the eastern Pacific (off the southern end of Baja California, Mexico; off Guatemala; off Nicaragua), and the Indian Ocean (Arabian Sea) and have found them all very similar. Previous records are from the tropical mid-Atlantic (Dana: 1°S, 17–18°W; Bovallius: 3°N, 25°W), North and South Atlantic (Vosseler), and near Madeira (Stephensen). The very limited records suggest a pantropical distribution for T. fusca.

VII. Hyperionyx, new genus

DIAGNOSIS.–Small species. Head globular, with eyes occupying most of its surface. Pereonites 1–3 fused in both sexes. Coxae fused with pereonites. Telson very short. ♀ A1 2–merous. ♀ A2 1–merous, slender, moderately long; gland cone small, triangular. Md reduced [?]; palp absent in ♀. Mx1 outer lobe with 1 terminal spine; palp with very few marginal setae. Mx2 with few setae; outer lobe with 2 terminal spines; inner lobe very short. Mxp with very few setae; inner lobe slender; outer lobes obovate. P1 subchelate. P2 chelate, with spinose spoon-shaped carpal process. P3–7 with strong, curved, unarmed dactyls; P3–7 and P6 subequal, P5 much shorter, P7 somewhat longer.

DERIVATION OF NAME.–Hyperia + the Greek “onyx” [=claw], referring to the strongly developed dactyls of P3–7; gender masculine.

TYPE-SPECIES.–Hyperia macrodactyla Stephensen, 1924.

REMARKS.–The distinctive characters of H. macrodactyla warrant the establishment of a new genus for it. The species is well described and illustrated by Stephensen (1924) and Yang (1960) except for the omission of descriptions of any of the mouthparts. The small size of H. macrodactylus (2–3 mm) together with the reduced mouthparts makes dissection of the latter difficult. After removing the posterior mouthparts it was apparent that I would not be able to remove the Md without excessively damaging the only Smithsonian specimen (1 of Yang’s 2 ♀) and I did not attempt to do so. Even when the specimen was cleared I could not see the incisor or molar and I believe they are quite reduced.

Hyperionyx is the only genus of Hyperiidae in which pereonites 1–3 are fused in both sexes. It resembles Themistella in having a short telson and a small gland cone and shares with Hyperioides a well developed female A2, but in other respects it is quite distinct from the latter two genera.