Heterodina Schotte & Kensley, 2005

Khalaji-Pirbalouty, Valiallah & Bruce, Niel L., 2014, A review of the genus Heterodina Kensley & Schotte, 2005 (Crustacea: Isopoda: Sphaeromatidae) with description of a new species from Iran, Zootaxa 3887 (3), pp. 494-500 : 495-496

Genus Heterodina Schotte & Kensley, 2005

Heterodina Schotte & Kensley, 2005: 1258 .

Type species: Heterodina mccaini Schotte & Kensley, 2005 ; by original designation.

Species included: Heterodina mccaini Schotte & Kensley, 2005 , Persian Gulf; Heterodina mosaica ( Kensley & Schotte, 1987) , Belize; Heterodina qeshmensis sp. nov., eastern Persian Gulf.

Diagnosis. Head laterally overlapped by anterolateral margins of pereonite 1; with median rostral process, separating antennular bases, visible in dorsal view. Pleon consisting of 1 segment. Pleotelson triangular, posterior margin produced to narrowly rounded apex. Pleopod 1 endopod reduced, about half length and half width of exopod. Appendix masculina short and broad, arising sub-basally. Pleopod 3 exopod without suture; pleopods 4 and 5 without plumose marginal setae, with very weak folds; pleopod 5 exopod with 2 scale patches. Penial processes elongate, basally fused. Uropod extending to distal margin of pleotelson; both rami lamellar, exopod endopod much longer than.

Description. Body oval, length more or less twice maximum width, dorsal surface smooth, or finely tuberculate; not or weakly sexually dimorphic. Head with rostral point present; lateral margins concave, extending antero-laterally to edge of pereonite 1; anterior margin of head without paired incisions in front of eyes. Eyes dorso-lateral, surface convex embossed, without posterior lobe. Pereonites 2–7 posterior margins not raised; coxae distally wide, truncate, with sutures clearly visible dorsally; pereonites 2 and 3 sub-equal in length, shorter than pereonite 1; pereonites 5 and 6 of about equal in length, longest; pereonite 7 extending laterally to body margin; pereonites 2–7 overlapping the one behind. Pereonites 6, 7 and pleon simple, without processes. Pleon of 1 segment, as wide as pereonite 7. Pleotelson as wide a pleon, triangular, wider than long, forming a dorsal arch, posterior margin entire, with narrowly rounded apex, lateral margins folded ventrally.

Antennula bases not in contact, peduncular articles 1 and 2 robust, not flattened; peduncular articles 2 and 3 colinear; articles 2 and 3 sub-equal in length, combined lengths approximately 0.5 as long as article 1; flagellum shorter than peduncle, with 4–7 articles, not extending to posterior of pereonite 1.

Antenna peduncular articles all collinear, of sub-similar thickness; article 5 longest. Epistome long, visible in dorsal view, anteriorly wide, lateral margins concave.

Left mandible incisor wide, multicuspid; lacinia mobilis present, tri-cuspid; spine row normal with 2–4 serrate spines; molar process rounded. Maxillula lateral endite with 6 RS, 2 or 3 of which are serrate; mesial endite with 4 major circum-plumose robust setae. Maxilla with curved pectinate RS setae on middle and lateral endites. Maxilliped endite distal margin rounded, with CP robust setae; mesial margin with 1 coupling hook; palp articles 2–4 not lobate, article 2 not expanded.

Pereopod 1 ambulatory; dactylus secondary unguis short, robust, simple. Pereopods 2 and 3, 4 and 5, 6 and 7 are similar in proportion.

Penial processes elongate, basally fused, tapering smoothly from midlength, apeices bluntly rounded.

Pleopod 1 not operculate, rami lamellar, colinear; endopod about half length and half width of exopod; sympod mesial margin with 2 coupling hooks. Pleopod 2 endopod about as long as exopod; appendix masculina stout, with straight margins ( H. mccaini and H. queshmensis sp. nov.) or basally swollen ( H. mosaica ) inserted sub-basally; extending to or beyond distal margin of endopod. Pleopod 3 exopod transverse suture absent, exopod about as long as endopod. Pleopods 4 and 5 rami without PMS, with very weak folds; pleopod 5 exopod with 2 scale patches.

Uropod rami flattened, forming part of body outline; exopod reduced, mobile, inserted near anterior third of endopod margin, about 0.2 length of endopod; endopod lamellar, distally narrowly rounded, not in contact posteriorly.

Female. Similar to male except in sexual characters. Marsupium formed from 2 pairs of opposing pockets opening at sternite 4. Mouthparts not metamorphosed.

Remarks. Heterodina Schotte & Kensley, 2005 can be identified by the head not having the lateral marginal extended (i.e. is laterally overlapped by pereonite 1), the pleon has a single segment, uropodal rami are lamellar with a reduced exopod set mid-margin, the penial processes are basally fused and pleopod 1 rami are collinear with the endopod markedly smaller than the exopod.

Heterodina Schotte & Kensley, 2005 , Cassidinidea Hansen, 1905 and Syncassidina Baker, 1929 form a group of similar genera characterised by their small size (2 to 3 mm), a generally flattened body shape, the epistome visible in dorsal view, simple pereopods (i.e. lacking lobes or processes) with a simple secondary unguis, the penial processes are elongate and basally fused; the uropods are lamellar, with the endopod forming part of the general body outline while the exopod is reduced in size and inserted mid-length along the lateral margin. These genera occupy inshore and sometimes high silt habitats. All three genera have the antennular bases separated by the epistome. Bruce (1994) gave the defining characters for this group. Pleonal sutures and morphology of the appendix masculina are generally consistent within genera of the Sphaeromatidae (e.g. Bruce 1994). Heterodina qeshmensis and also H. mccaini (on examination of paratype material) have short sutures on the pleon posterior margin, whereas H. mosaica is illustrated without pleonite sutures. The shape and size of the appendix masculina is similarly different between the species. At this point we draw no further inferences from these differences.

Heterodina differs from the others of this group of genera by the lateral margins of the head not being extended; Cassidinidea has fully fused penial processes and an elongate appendix masculina, while Syncassidina has antennular peduncle article 1 flattened and expanded and entirely lacks a uropodal exopod.

Apemosphaera Bruce, 1994 is superficially similar, but has short, separate penial processes, the uropodal exopod is relatively large and positioned anteriorly on the endopod, and there are four visible pleonites.