Hyperietta parviceps Bowman 1973

Hyperietta parviceps

DERIVATION OF NAME.–From the Latin “parvi-” [=small] + “-ceps” [=head], referring to the small head compared to other species of Hyperietta.

TYPES.–Holotype ♀, USNM 137505, allotype ♂, USNM 137506, both from CalCOFI Cruise 9, station 1011, west of Punta Eugenia, Baja California, 27°56′N, 122°59′W. 3 paratypes (2♀, 1♂) from the same sample have been deposited in the Scripps Institution of Oceanography.

DIAGNOSIS.–Length of ♀ 2–2.5 mm, of ♂ 3–3.5 mm. Head and pereon broader than in other species of Hyperietta; head about 1.6 times as broad as long, about twice as high as long, in profile rather flat below insertion of A1. Pereon quite convex dorsally, highest in pereonite 5. Gland cone bluntly rounded, clearly visible in lateral view, separated from epistome by distinct gap. Mxp outer lobe about 1.4 times as long as wide, with many fine setae on anterior surface and a few heavier setae on posterior surface; lateral margin with single long seta. P1 subchelate; s2 slightly more than twice as long as wide; s5 with small carpal process bearing 3 spines and 1 spine on posterior margin; s6 with long spine on anterior margin. P2 with carpal process about ¼ as long as s6, bearing about 6 spines on its margins. P3–7 with rather robust distal segments. P5–7 with strong spine on anterodistal corner of s4–5 of ♀ and s5 of ♂. Telson about as long as wide; in ♀ 4/5, in ♂ half as long as Up3 protopod.

DISTRIBUTION.–Thus far H. parviceps has been found only at two stations of CalCOFI Cruise 5 and five stations of CalCOFI Cruise 9, all well offshore in the southern part of the area (Figure 50).

VI. Themistella Bovallius, 1887b

DIAGNOSIS.–Small species with rather broad pereon. Head rather broad; eyes occupying most of its surface. Pereonites 1–5 fused in both sexes. Coxae fused with pereonites. Telson very short. ♀ A1 2–merous, rather long. ♀ A2 1–merous, rudimentary; gland cone small. Md with serrate incisor; palp absent in ♀. Mx1 outer lobe with 4 terminal spines plus 2 lateral and 1 medial subterminal spines. Mxp outer lobes narrow, tapering distally; inner lobe almost completely absent, apparently represented by slight unarmed bulge on basal segment. P1–7 with rather broad segments. P1–2 chelate; gauge-shaped carpal process bearing marginal spines. P5 much longer than P6–7. Dactyls of P6–7 with flexure slightly distal to midlength.

DERIVATION OF GENERIC NAME.–Diminutive of Themisto (a Greek nymph, daughter of Neptune and Doris); gender, feminine.

TYPE-SPECIES.–By monotypy, Themistella steenstrupi Bovallius, 1887b.

REMARKS.–Themistella was originally a monotypic genus, but in 1889 Bovallius added to it Lestrigonus fuscus Dana (1853). The differences cited by Bovallius for considering the two species distinct are not convincing, since the descriptions and illustrations of both authors lack detail, and neither Dana nor Bovallius can be depended upon for a high degree of accuracy. Hence I am treating the two nominal species as synonyms.

In assigning the amphipod described below to Themistella I have assumed two major inaccuracies in the accounts of Dana and Bovallius. The first assumption concerns the number of fused anterior pereonites: for L. fuscus “thorax seven-jointed, first segment nearly concealed” (Dana, 1853); for T. steenstrupi “The first two peraeonal segments are coalesced, the following are free” (Bovallius, 1889). Bovallius’ pl. 13: fig. 47, a lateral view of the male, shows faint sutures separating pereonites 2–5 from one another and heavier sutures on the margins of pereonites 6–7. I suggest that Bovallius misinterpreted muscle bands or other structures as the faint sutures and that his specimens actually had pereonites 1–5 fused.

My second assumption is that Dana and Bovallius did not notice the angular bend in the dactyls of P6–7. It is difficult to believe that this feature, so conspicuous to me, could have been overlooked, but a character that attracts the attention of one author may escape the notice of another.

If the above assumptions are accepted, there is no difficulty in equating the species described below as T. fusca with those proposed by Dana and Bovallius. The assumptions may appear overly bold and are to some degree intuitive, but they are based on considerable experience and much frustration in attempting to reconcile the accounts of hyperiid species by the above authors with the characters of specimens thought to belong to their nominal species.